1

CHAPTER ONE

General Introduction

Increasing numbers of people travel to cold and mountainous regions for work, recreation and

physical activities (e.g. soldiers, mountaineers and skiers) (Young et al. 1998; Oliver et al. 2012). In

such cold and hypoxic climates, accidental hypothermia is a perpetual hazard for casualties of

mountain incidents (Kornberger and Mair, 1996) and is a significant contributor to fatalities (Sallis

and Chassay, 1999; Sharp, 2007). The likelihood of developing a peripheral cold injury (e.g. frost

nip and frost bite) or upper respiratory tract infection (URTI) has been reported to be increased in

mountaineers and individuals exposed to cold and high altitude for prolonged periods (Giesbrecht,

1995; Felicijan et al. 2008; Oliver et al. 2012), however whether acclimatisation to altitude reduces

these risks is unknown. Anecdotal evidence suggests a relationship exists between exertional

fatigue, often experienced during outdoor pursuit activities, and susceptibility to hypothermia

(Thompson and Hayward, 1996; Pugh, 1966; Young et al. 1998). Ultimately, ill health and cold

injury are likely to reduce cognitive function and motor performance (Patil et al. 1995), causing

confusion and lethargy so that the casualty is forced to remain sedentary. Furthermore, loss of

motor control makes it difficult to execute survival procedures (Vanggaard, 1975).

Factors found to alter human thermoregulation and immunity in a cold environment include, but are

not limited to: prolonged exposure to cold-wet conditions (Thompson and Hayward, 1996), hypoxia

(Golja et al. 2004), prolonged fatiguing exercise, sleep deprivation and negative energy balance

(Castellani et al. 1998; Young et al. 1998). Nevertheless, the effect of prolonged (> 2 h) exposure to

cold and hypoxia on thermoregulatory and immune responses remains equivocal (Cipriano and

Goldman, 1975; Blatteis and Lutherer, 1976; Giesbrecht, 1995; Savourey et al. 1997; Gleeson,

2000). Since URTIs are associated with a reduction in the concentration of salivary

2

immunoglobulin A (s-IgA) (Gleeson, 2000) and research surrounding the typical mucosal immune

response to cold, with and without hypoxia, is sparse, further investigation in this area is required.

Although mortality rates are relatively low with severe non-trauma related hypothermia (<28°C),

they rise alarmingly with traumatic injury where mortality is 100% at 32°C (Moss, 1986; Jurkovich

et al. 1987). Rescue times for casualties depend on global location and weather conditions. Yet even

where distances are relatively short between emergency services and a casualty (e.g. Scottish

Highlands) the reported times for evacuation are 2.25 h by helicopter and approximately 3.5 h when

individuals are evacuated by others means (e.g. on foot) (Crocket, 1995; Hindsholm et al. 1992).

While superior re-warming methods are available (i.e. forced air warmer, inhalation re-warming)

these require medically trained personnel and a power supply. Therefore, simple methods that

prevent heat loss and promote re-warming that casualties or first-responders can administer

instantly whilst they wait for evacuation will likely reduce hypothermia related fatalities. Current

water and wind-proof survival bags aim to reduce core cooling by decreasing heat loss through

convection and radiation (Light and Norman, 1990), yet accidental hypothermia still affects

approximately 10% of casualties reported in mountainous environments. It is pertinent therefore to

establish an optimal lightweight device to increase the rate of core re-warming compared to

shivering alone (Giesbrecht et al. 1987; Williams et al. 2005).

Given prolonged exposure to cold and/or hypoxia poses detrimental effects to themoregulation and

immune function, it is of benefit for those individuals travelling to high altitudes and low

temperatures to know which self-administering survival product will offer optimal protection

against peripheral and central cold injury if a situation occurred where they were forced to remain

sedentary.

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Thesis objectives

With this information in mind, the objectives of this thesis were to:

I. Determine the effects of acute and prolonged (18 days) exposure to a simulated high altitude

of 4000 m on physiological and behavioural thermoregulation during mild cold exposure.

II. Examine the mucosal immunity responses to acute and prolonged (18 days) exposure to a

simulated high altitude of 4000 m

III. Compare the effectiveness of four field re-warming methods for the treatment of cold

casualties upon thermoregulation and metabolism during a three hour ‘awaiting rescue’

scenario in 0°C following cold water immersion to reduce core temperature to 36°C.

IV. Examine the mucosal immunity response to prolonged cold exposure (0°C) in pre-cooled

casualties.

V. Investigate the efficacy of three field protection methods for the treatment of non-shivering

cold casualties using an in vitro torso model exposed to -18.5°C, 0°C and 18.5°C for four

hours.

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CHAPTER TWO

Literature review

2.1 Ill health in cold and hypoxic environments

2.1.1 Hypothermia

Hypothermia occurs through a combination of increased heat loss and decreased heat production.

Heat loss is often increased in cold air when wet and windy conditions are also present (Thompson

and Hayward, 1996). The majority of accidental hypothermia cases are reported to result from cold-

water immersion or cold-water submersion (Golden et al. 1997), cold-air exposure (Pugh, 1966) or

traumatic injury with haemorrhage (Moss, 1986; Jurkovich et al. 1987). Hypothermia is strongly

related to coagulopathy and shock (Beilman et al. 2009) and it is this ‘triad’ that significantly

contributes to the mortality of trauma patients (Arthurs et al. 2006). Since the term ‘hypothermic’ is

often misleading regarding severity, systems exist to classify the different stages of hypothermia

(Table 2.2).

5

Table 2.1. Signs, symptoms and physiological changes associated with progressive hypothermia.

Adapted from Danzl and Pozos, (1994).

Stage of

Hypothermia

Rectal

Temperature (°C) Signs and symptoms

37 Normal rectal temperature

Mild

36 Increased metabolic rate due to shivering

35 Maximum shivering thermogenesis

34 Amnesia and judgement problems

33 Ataxia and apathy

Moderate

31 Shivering stops

30 Possible cardiac arrhythmias

29 Decreasing consciousness

28 Increased sensitvity to ventricular fibrillation

27 Loss of voluntary motion

26 No response to pain

Severe

25 Cerebral blood flow decreased to 30%

of normal

22 Maximum risk of ventricular fibrillation

18 Asystole

2.1.2 Peripheral cold injury

In the instance of peripheral cold injury, manual dexterity is impaired and work capacity

deteriorates (Holmer, 1994). For example, military operations in cold, snowy environments increase

the chances for minor cold injuries that limit military unit effectiveness due to lost man-hours. Cold

weather also increases the difficulty of performing tasks related to eating, drinking, and normal

hygiene. This subsequent inability to protect oneself or practise basic survival skills while awaiting

rescue in a cold environment may increase the likelihood of hypothermia related fatalities.

Peripheral ‘freezing’ cold injuries resulting from acute cold exposure include frostbite and frost-nip.

The milder of the two, frost-nip, is a precursor to frostbite and occurs via skin contact with cold

surfaces. With frost-nip, only superficial skin is frozen and tissues are not permanently damaged.

6

Frostbite, on the other hand, develops as a function of the body’s protective mechanisms to

maintain core temperature. Warm blood is shunted from cold peripheral tissues to the core by

vasoconstriction of arterioles that supply capillary beds and venules to the extremities and face,

especially the nose and ears. Frostbite progresses from distal to proximal and from superficial to

deep. As the temperature of these areas continues to decrease, cells begin to freeze. Damage to the

frostbitten tissue is due to electrolyte concentration changes within the cells, resulting in water

crystallization within the tissue (Conway et al. 1998).

Frequent or prolonged exposure to moderate cold has been demonstrated to precipitate or

exacerbate shoulder and extremity pain, respiratory infections (Griefahn, 1995) and the ‘non-

freezing’ cold injuries of chilblains (perniosis) and trench (immersion) foot (Herrington, 1996;

Conway et al. 1998). Muscle and tendon tears may also be more likely in cold environments.

Raynaud’s syndrome and the related white finger syndrome cause severe arterial vasoconstriction

with digital blanching, and severe cases may lead to ulceration and tissue loss (Lloyd, 1994). Any

form of peripheral cold injury may have the potential to inhibit individuals from carrying out simple

behavioural thermoregulatory activities.

2.1.3 Upper respiratory tract infections (URTI)

Upper respiratory tract infection (URTI) is a nonspecific term used to describe acute infections

involving the nose, paranasal sinuses, pharynx, larynx, trachea, and bronchi. Therefore URTI

include, but are not limited to: nasopharyngitis, pharyngitis, laryngitis, tonsillitis, sinusitis and

bronchitis. Upper respiratory tract infections represent the most common acute illnesses evaluated

in the outpatient setting. Viruses cause the vast majority of acute upper respiratory tract infections

(Neemisha et al. 2001; Monto, 2002; Fendrick et al. 2003). The common cold is a viral illness with

7

the most associated cause being rhinovirus; others are parainfluenza, respiratory syncytial, corona

virus, adenovirus, echovirus, coxsackievirus and parainfluenza virus (Turner, 1995). Rhinovirus

accounts for up to 60% of infections but generally resolves spontaneously without antimicrobial

therapy (Ashes, 1999). Symptoms include nasal discharge, nasal obstruction, and throat irritation.

The National Institute of Allergy and Infectious Diseases reports that people in the USA suffer 1

billion colds each year, with an incidence of two to four for the average adult, and six to ten for

children (Nieman et al. 2011). URTIs impose an estimated $40 billion cost on the US economy

(Fendrick et al. 2003). Lifestyle habits and demographic factors such as mental stress (Cohen,

2005), lack of sleep (Cohen et al. 2009), poor nutrition (Wolvers et al. 2006), and old age (Aw et al.

2007) have all been associated with impaired immune function and elevated risk of infection.

Infections and acute mountain sickness (AMS) are common at high altitude, yet their precise

etiologies remain elusive and the potential for misdiagnosis is considerable (Bailey et al. 2003). The

misdiagnosis of altitude illness is likely due to the similarity of nonspecific constitutional symptoms

(e.g. fatigue, fever, shortness of breath on exertion, decreased appetite and headache) associated

with infection and AMS (Bailey et al. 2003). Both conditions are characterised by changes in

peripheral biomarkers related to free radical, skeletal muscle damage and amino acid metabolism

(Bailey et al. 2003). While not establishing cause and effect, free radical-mediated changes in

peripheral amino acid metabolism, known to influence immune and cerebral serotoninergic

function, may enhance susceptibility to and delay recovery from altitude illness (Bailey et al. 2003).

While AMS is not dangerous, at altitudes over 4000 m it can progress unpredictably to one of two

potentially fatal forms (high altitude pulmonary edema (HAPE) and high altitude cerebral edema

(HACE)) that may co-exist with each other and be misdiagnosed (Wright and Fletcher, 1987).

Symptoms of HAPE include a cough, frothy sputum and lung crackles but without definite

abnormal cardiac signs. These features may be misdiagnosed as pneumonia, which sometimes

8

present as an aggravating factor (Wright and Fletcher, 1987). Further, upper respiratory symptoms

(URS) may present in the absence of illness and infection (Giesbrecht, 1995)

2.2 Thermoregulation in cold

During thermoregulatory homeostasis human core temperature (Tc) is maintained close to 37°C

(Widmaier et al. 2004). The central control mechanism in the hypothalamus determines mean body

temperature (Tb) and compares this to a pre-determined set-point temperature by integrating thermal

signals from peripheral and core receptors (Sessler, 1994; Guyton, 1996). Changes in ambient

temperature generate thermo-receptor impulses that are propagated to the anterior hypothalamus via

afferent pathways in the spinal cord (Pocock and Richards, 2006). Efferent responses are mediated

via the posterior hypothalamus to initiate heat loss and heat production mechanisms.

2.2.1 Behavioural responses

Behavioural responses to an increased perception of cold include wearing extra clothing, closing an

open window and turning up the heating. During outdoor pursuits in cold, mountain regions

individuals will often seek cold and wind-proof shelters to make a hot drink or meal. If shelter is

unavailable or stopping is not an option, increasing the intensity of any physical activity or exercise

will help to increase heat production.

2.2.2 Physiological responses – Heat balance

The mechanisms of heat transfer include evaporation, radiation, convection and conduction. Each

mechanism contributes proportionally to heat transfer and fluctuates depending on the air/water

9

temperature and humidity. For a healthy human of normal body core temperature in a temperate

environment considered comfortable however, evaporation, the conversion of water to its gaseous

phase, accounts for 20-30% of total body heat loss; radiation, a loss of heat to the environment via

infra-red radiation, accounts for 55-65% of total body heat loss; convection, the transfer of heat to

the external environment by air or water in contact with the body, is accountable for ~12% of total

body heat loss and conduction, the transfer of heat to another object via direct contact accounts for

only 3% of total body heat loss (Kanzenbach and Dexter, 1999).

An involuntary heat transfer response to maintain core temperature in the cold involves the control

of cutaneous vascular smooth muscle tone (e.g. vasoconstriction) combined with a rapid fall in Tsk

(Wagner et al. 1974). This reduced blood flow to peripheral vessels decreases convective heat loss

and conserves Tc. Peripheral vasoconstriction is a powerful mechanism to reduce the heat loss, but

results in strong cooling of the extremities (Daanen, 2003). However, the extremities (i.e. fingers,

hands, ear lobes and toes) possess the ability to prevent the occurrence of local cold extremes with a

specialised pattern of circulation known as arteriovenous anastomoses. These have smooth muscle

in their walls and are deep to the tips of the capillary loops, close to the surface of the skin. The

arteriovenous anastomoses open up when Tb is above normal during reflexively induced

vasodilation and during cold induced vasodilation (CIVD) when Tb is reduced. Upon opening, a

large flow of blood passes through the shunts increasing heat transfer (Abramson, 1967). Since

blood flow increases substantially in the fingers during CIVD, and this increases muscle

temperature and blood circulation in the large vessels of the forearm (Lewis, 1930; Ducharme et al.

1991), it is likely that CIVD reduces the risk of local cold injuries (Iida, 1949; Wilson and

Goldman, 1970), improves manual dexterity and enhances tactile sensitivity during work in the cold

by improving muscle function (Daanen, 2003). Individuals with a higher CIVD response are

considered to be less susceptible to local cold injuries due to the maintenance of a higher rate of

extremity blood flow during cold exposure (Daanen and van Ruiten, 2000).Beyond the specialised

10

circulation at the extremities further heat transfer systems exist in the human forearm. Veins

running alongside the ulnar and radial arteries, called venae comitantes (Bazett et al. 1948), create a

counter-current heat exchange system between arteries going to the periphery of a limb and venous

blood returning from the periphery.

2.2.3 Physiological responses – Heat production

In addition to a complex vascular system helping to maintain heat balance in the cold, an increase in

metabolic rate (MR) via shivering thermogenesis (ST) or non-shivering thermogenesis (NST)

evokes heat production and attenuates further decrements in Tc (Lindahl, 1997; Potkanowicz et al.

2003). Consequently, the two main physiological adjustments that occur during cold exposure are

insulative and metabolic (van Ooijen et al. 2004). Nonetheless, such physiological adjustments are

particularly reliant upon individual characteristics given that they may be modified by cold

acclimatisation (Scholander et al. 1958), amount of body fat (Wade et al. 1979), relative humidity

(RH) (Burton et al. 1955), wind speed, physical fitness (Adams and Heberling, 1958; Bittel et al.

1988) and age (Horvath et al. 1955; Wagner et al. 1974).

The level of thermogenesis that humans can achieve and maintain is important for survival during

severely cold weather (Vallerand and Jacobs, 1989). During mild hypothermia (Tc = 35°C) it has

been suggested that ST remains the only physiological process available for maintaining Tc in a

non-exercising casualty void of a re-warming device (Folk, 1974; Neufer et al. 1988; Haman et al.

2002). Metabolic rate, as measured by oxygen consumption (VO2), increases proportionally to

shivering intensity of the whole body or specific muscle groups (Horvath et al. 1956; Tikuisis et al.

1991). Peak shivering intensity can increase heat production up to five times the basal metabolic

rate (BMR) (Eyolfson et al. 2001). The intensity of shivering is determined by the severity of cold

11

exposure, the amount of fat-free mass (FFM), the subject’s fitness (Eyolfson et al. 2001) and the

rate of change of the skin temperature (Fiala et al. 2001).

Non-shivering thermogenesis is a heat-production mechanism that involves no muscular

contractions. Heat production under the conditions of basal metabolism is mostly obligatory NST.

Obligatory NST serves to maintain the basic energy demands of the homoeothermic organism

(Jansky, 1973). During cold exposure NST is defined as an increase in heat production in the

absence of shivering (van Ooijen et al. 2005). This additional heat production that occurs is called

regulatory NST (Jansky, 1973).

Non-shivering thermogenesis has been found to occur in the newborn of some species (e.g. humans

and sheep), hibernating animals, and in other animals such as the rat (Horovitz, 1971). Brown fat is

the primary energy source for NST, separating itself from ordinary fat by having much smaller cells

that contain greater amounts of mitochondria (Saito et al. 2009). Studies in animals indicate that

brown adipose tissue (BAT) is important in the regulation of body weight, and it is possible that

individual variation in adaptive thermogenesis can be attributed to variations in the amount or

activity of BAT (van Marken Lichtenbelt et al. 2009). Until recently, the presence of BAT was

thought to be relevant only in small mammals and infants, with negligible physiologic relevance in

adult humans (Astrup et al. 1985; Himms-Hagen, 2001). On the contrary, new evidence has

observed a high rate of occurrence of BAT in healthy young males that is mainly activated during

cold exposure (van Marken Lichtenbelt et al. 2009). The activity of BAT is reported to be greater in

lean males in comparison to those who are overweight or obese (van Marken Lichtenbelt et al.

2009).

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2.3 Thermoregulation in hypoxia

2.3.1 Behavioural responses

Hypoxia has been shown to alter thermal sensation during cold exposure (Golja et al. 2004) which

has been related to a lowered neural activity and delayed signal conduction (Astrup, 1982). This

blunted thermal sensation may cause inappropriate behavioural thermoregulation (e.g. neglecting to

add extra layers of clothing) and therefore be a major implication in cold injury. Anecdotal reports

have also suggested hypoxia alters thermal comfort. However these early reports describe the pain

to single limb, cold water immersion (Mathew, 1979) and thermal discomfort to whole body mild

cold air exposure (Blatteis and Lutherer, 1976) to be greater at altitude than at sea level which did

not abate with altitude acclimatisation (Mathew, 1979; Blatteis and Lutherer, 1976). Further

investigation into the effect of whole body cooling on perception of thermal comfort during acute

hypoxia and following acclimatisation may help provide clarity.

2.3.2 Physiological responses – Heat balance

The effect of hypoxia on typical thermoregulatory responses to the cold remains equivocal. Whilst

some research suggests hypoxia causes greater heat loss and lower core temperatures during cold

exposure compared to normoxia (Cipriano and Goldman, 1975; Kottke et al. 1948, Table 2.2),

other research has reported that hypoxia does not affect thermoregulation (Blatteis and Lutherer,

1976; Robinson and Haymes, 1990, Table 2.2). Those studies that show greater reductions in core

temperature have reported greater increases in skin temperature (Cipriano and Goldman, 1975;

Kottke et al. 1948). Nonetheless, at altitude a significant reduction in CIVD is found where cold co-

exists with systemic hypoxia (Mathew et al. 1977; Daanen and van Ruiten, 2000). Consequently,

the risk for local cold injuries may be enhanced at altitude (Daanen and van Ruiten, 2000).

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2.3.3 Physiological responses – Heat production

It is well established that heat production via the cold-induced increase in VO2 is suppressed during

hypoxia (Blatteis and Lutherer, 1976; Kottke et al. 1948; Savourey et al. 1997) and is coupled with

a reduced time to shivering onset as well as an overall increased shivering intensity (Blatteis and

Lutherer, 1976; Bullard, 1961; Robinson and Haymes, 1990). The occurrence at altitude of a

reduction in the cold-induced increase in VO2 without a diminution of shivering activity suggests

hypoxia depresses NST (Blatteis and Lutherer, 1976) which is related to an inhibition of the aerobic

catabolism of FFA (Robinson and Haymes, 1990). Nonetheless, given the cold-induced increase in

VO2 of high altitude residents has been reported as significantly greater than un-acclimatised

lowlanders, indicates that recovery from the hypoxic depression of the metabolic response to cold

occurs following prolonged exposure to altitude (Blatteis and Lutherer, 1976). However,

acclimatised lowlanders, following a 6 week residence at altitude, showed no reversal in the

hypoxia-induced reduction of the metabolic response to cold. On the contrary, shivering intensity

decreased as altitude exposure continued, yet total VO2 in the cold was not further decreased. This

suggests therefore that some NST recovery may have occurred during the 6-week altitude stay and

helped to replace the reduced ST (Blatteis and Lutherer, 1976).

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15

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2.4 The immune system

2.4.1 Innate immunity - External barriers against infection

The main line of defence from infection is the skin which, when intact, is impermeable to most

infectious agents; when there is skin loss (e.g. burns) infection becomes a major problem (Davies et

al. 2006). Most bacteria fail to survive on the skin because of the direct inhibitory effects of lactic

and fatty acids in sweat and sebaceous secretions and the low pH which they generate.

Mucus secreted by membranes lining the inner surfaces of the body, acts as a protective barrier to

block the adherence of bacteria to epithelial cells. Microbial and other foreign particles trapped

within the adhesive mucus are removed by mechanical stratagems such as ciliary movement and

coughing and sneezing. If microorganisms do penetrate the body, two main avenues of defence

exist to destruct the problem. These are the destructive effect of soluble chemical factors such as

bactericidal enzymes and the mechanism of phagocytosis.

2.4.2 Innate immunity - Phagocytosis

After inoculation, viruses and bacteria encounter several barriers, including physical, mechanical,

humoral and cellular immune defenses. Adenoids and tonsils contain immune cells that respond to

pathogens. Humoral (Immunoglobulin-A) and cellular immunity reduce infections throughout the

entire respiratory tract. Resident and recruited macrophages, monocytes, neutrophils, and

eosinophils coordinate to engulf and destroy the virus or bacteria in the process known as

phagocytosis. A host of inflammatory cytokines mediates the immune response to invading

pathogens. Phagocytic cells have a system of receptors that recognise molecular patterns expressed

by pathogens. Normal nasopharyngeal flora, including various staphylococcal and streptococcal

17

species, help defend against potential pathogens. After adherence of the microbe to the surface of

the neutrophil or macrophage the resulting signal initiates the ingestion phase.

2.4.3 Innate immunity - Soluble chemical factors

The spread of infection may be limited by enzymes released through tissue injury which activate the

clotting system. Of the soluble bactericidal substances elaborated by the body, the most abundant

and widespread is the enzyme lysozyme. Like the α-defensins of the neutrophil granules, the human

β-defensins are peptides derived by proteolytic cleavage from larger precursors. The main human β-

defensin (hDB-1) is produced mostly in the kidney, female reproductive tract, oral gingiva and

particularly the lung airways. Another airway antimicrobial active against Gram-negative and

positive bacteria is LL-37.

A number of plasma proteins collectively termed acute phase proteins show a dramatic increase in

concentration in response to early ‘alarm’ mediators such as macrophage derived interleukin-1 (IL-

1) released as a result of infection or injury. It is likely that the acute phase response enhances host

resistance, minimising tissue injury and promoting repair.

2.4.4 Specific acquired immunity – Antibody

Antibodies are an adaptor molecule capable of stimulating the phagocytic cells and sticking to an

invading microbe. Antibodies have three main regions, two concerned with communicating with

phagocytes and one devoted to binding to a microorganism. Each antibody has a recognition portion

complementary in shape to some microorganism to which it can then bind firmly to. The molecules

in the microorganisms which evoke and react with antibodies are called antigens. Each lymphocyte

18

of a subset from B-lymphocytes, is programmed to make one antibody on its outer surface to act as

a receptor. When an antigen enters the body it binds to the receptor that it fits best. Lymphocytes,

whose receptors have bound to an antigen receive a triggering signal and develop antibody-forming

plasma cells.

When the body makes an antibody response to a given infectious agent, that microorganism must

exist in the environment and is likely to come into contact again. On first contact with an antigen

the information received imparts some memory so that the body is prepared to repel any later

invasion by that same organism. Upon secondary contact with the antigen the response is

characterised by a more rapid and more abundant production of antibody resulting from the priming

of the antibody-forming system.

2.5 Mucosal immunity

The mucous membranes covering the aerodigestive and urogenital tracts as well as the eye

conjunctiva, the inner ear and the ducts of all exocrine glands are endowed with powerful

mechanisms that degrade and repel most foreign matter (Holmgren and Czerkinsky, 2005). In

addition, a large and specialised innate and adaptive mucosal immune system protects these

surfaces, and thereby also the body interior, against potential insults from the environment. In a

healthy human adult this local immune system contributes to almost 80% of all immunocytes

(Holmgren and Czerkinsky, 2005). The adaptive immune defense at muscosal surfaces is to a large

extent mediated by secretory IgA antibodies, the predominant immunoglobulin in human external

secretions. The resistance of secretory IgA to proteases makes these antibodies uniquely suited for

functioning in mucosal secretions (Holmgren and Czerkinsky, 2005). Although secretory IgA is the

19

predominant mucosal defense mechanism, locally produced IgM and IgG can also contribute

significantly to immune defense (Holmgren and Czerkinsky, 2005).

The production of natural antimicrobial peptides (AMP) has emerged as an important mechanism of

innate immunity in plants and animals. Antimicrobial peptides are polypeptides of fewer than 100

amino acids that are found in host defense settings (Ganz, 2003). Cationic antimicrobial peptides,

such as defensins, cathelicidins and thrombocidins, are an important human defense mechanism,

protecting skin and epithelia against invading microorganisms and assisting neutrophils and

platelets (Peschel, 2002). Individual members of these AMP families have been implicated in AMP

activity of phagocytes, inflammatory body fluids and epithelial body secretions. Defensins are

diverse members of a large family of AMPs, contributing to the antimicrobial action of

granulocytes, mucosal host defense in the small intestine and epithelial host defense in the skin and

elsewhere (Ganz et al. 1985; Selsted et al. 1985; Ganz, 2003). Cathelicidins are structurally and

evolutionarily distinct AMPs, similar to defensins in abundance and distribution (Zanetti et al.

1995; Lehrer and Ganz, 2002). Defensins however, are particularly prominent in humans, as

evidenced by the large number of expressed human genes, the various forms that are present in

human tissues, and the ubiquitous occurrence of defensins in inflamed or infected human tissues

(Ganz, 2003).

Saliva is essential for the maintenance of oral health (Mandel, 1989). Saliva flow and composition

function in lubrication, remineralisation, buffering and digestion, while also possessing anti-viral

and anti-bacterial properties (Tenovuo, 1998; West et al. 2006). Saliva is the first line of defense

against pathogens invading the oral cavity (Gleeson, 2000, Table 2.3). The importance of mucosal

secretions cannot be underestimated given that 95% of all infections are initiated at mucosal

surfaces (Bosch et al. 2002). Saliva provides a mechanical washing effect to protect the oral mucosa

whilst mucosal secretions (e.g. immunoglobulins, mucins, amylase, lactoferrin) prevent viral

20

replication and bacterial attachment to the mucosal surfaces (McNabb et al. 1981; Mackinnon and

Hooper, 1994; Dowd, 1999).

2.6 Immune system in cold and hypoxia

2.6.1 Cold and immune system

Folklore suggests that exposure to cold ambient temperatures causes humans to contract colds

(rhinoviruses) or other URTI (Dowling et al. 1958; Biggar et al. 1984; Castellani et al. 2002).

However, data to support a link between cold ambient temperatures, reduced immune function and

increased susceptibility to infections in humans is not well delineated (Castellani et al. 2002; Lavoy

et al. 2011). On the contrary, URTI are the most common infections worldwide with peaks often

observed in cold winter months (Mourtzoukou and Falagas, 2007). Furthermore, URTI substantially

increase wintertime morbidity (Hajat et al. 2004) and account for at least 20% of the excess winter

mortality (The Eurowinter Group, 1997; Diaz et al. 2005; Nayha, 2005). Inhalation of cold air and

cooling of the body surface have both been shown to cause pathophysiological responses that may

contribute to increased susceptibility to URTI (Moutzoukou and Falagas, 2007; Giesbrecht, 1995;

Eccles, 2002; Cruz et al. 2006). Albeit, the interaction of exercise and cold exposure on immune

function has not been widely studied (Castellani et al. 2002), data have shown cross country skiers

commonly contract URTIs during outdoor training periods (Bergland and Hemmingsson, 1990).

Secondly, soldiers completing sustained military operations in the Canadian Arctic have displayed

an increased incidence and severity of URTI (Sabiston and Livingstone, 1973). It remains unclear

however, if increased reports of URTI during prolonged cold exposure are due to high levels of

energy expenditure, negative energy balance, cold exposure per se or to a combination (Walsh and

Whitham, 2006).

21

Cold exposure has been found to increase plasma nor-adrenaline concentration, a marker of

sympathetic nervous system (SNS) activity (Castellani et al. 2001; Castellani et al. 1999; Castellani

et al. 1998). Since the SNS mediates immune function, exposure to cold may indirectly evoke an

immune response (Castellani et al. 2001). A change in plasma cortisol has demonstrated

modulations in immune function (Shephard, 1997) but at present the effects of cold exposure on

plasma cortisol concentrations remain unclear (Frank et al. 1997; Wilkerson et al. 1974; Wittert et

al. 1992). Nor-adrenaline and natural killer (NK) cell activity have been shown to increase in men

following 30 minutes exposure to 4°C (Lackovic et al. 1988, Table 2.3). However, cell

proliferation decreased after mitogen stimulation in almost identical conditions (Jurankova et al.

1995, Table 2.3). Acute cold water immersion (14°C) demonstrated increased white blood cell

counts (Jansky et al. 1996) and a cold acclimation period with six weeks of cold water immersion,

three times per week increased the percentage of CD14+

and CD25+ cells. Given cold exposure

activates various cellular immune markers, a direct causal relationship to illness or infection

remains unclear. Furthermore, since URS (i.e. persistent dry cough and nasal drying), with the

absence of infection, have been reported following increased ventilation in cold dry air (Giesbrecht,

1995), further studies investigating mucosal immunity during cold exposure may provide some

clarity.

In clinical environments, patients undergoing general anesthetic often experience mild hypothermia

occurring from a reduced ability to produce heat via shivering. This perioperative model of

hypothermia can also be related to a hypothermic casualty in the field who, through additional

trauma, may also be unable to shiver. Perioperative hypothermia is associated with disturbances in

the cardiovascular and respiratory systems, abnormalities in blood coagulation and platelet function,

increased protein catabolism and urinary nitrogen loss following surgery (Forstot, 1995).

Consequently, investigators have reported that hypothermia may delay wound healing and

predispose patients to wound infections (Kurz et al. 1996).

22

In laboratory animals, exposure to hypothermia has been found to enhance the sensitivity of animals

to bacterial infections as compared with normothermic animals (Sheffield et al. 1994). Similarly, in

patients undergoing surgery, mild hypothermia impaired neutrophil oxidative killing during the

intraoperative period (Wenisch et al. 1996). Suppression of immune defense mechanisms occurs in

the postoperative period as a result of surgery stress and anesthesia (Salo, 1992). Such immune

compromise could affect the postoperative infection rate, healing reaction, and the rate and size of

tumor metastases disseminated during surgery (Salo, 1992).

2.6.2 Hypoxia and immune system

Ascent to high altitude is associated with alterations in physiological and metabolic functions

(Mazzeo et al. 1994; Mazzeo et al. 1995; Mazzeo et al. 2001). These adjustments to high altitude

are a necessary attempt to maintain homeostasis in the presence of hypoxemia (Mazzeo, 2005).

However, the sympathoadrenal responses associated with acute and chronic high altitude exposure

can influence immune function which may increase the risk of illness and infection while

individuals are a far distance from appropriate medical resources (Mazzeo et al. 1994; Mazzeo et al.

1995; Mazzeo et al. 2001; Pedersen et al. 1994).). Short term hypoxia has been reported to induce

similar immunosuppression upon the mobilisation of T-cells and natural killer cells (Klokker et al.

1993; Klokker et al. 1995) as that demonstrated during surgery (Lennard et al. 1985) and exercise

(Pedersen et al. 1990). Neutrophil concentration and function changes and the regulation of

cytokine production and release have also been shown to be reduced in hypoxia (Pyne et al. 2000;

Pedersen and Steensburg, 2002).

On the contrary, research remains equivocal regarding the effect of hypoxia on the immune system.

For example, a study examining plasma concentrations of IgG, IgA and IgM were found either

23

unchanged or increased following 40 days between 3200m and 3800m and after two years at an

altitude of 3700m (Meehan, 1987). An earlier investigation comparing the effects of chronic

hypoxia on antibody production of natives from three different altitudes (3051, 3700 and 4680m)

and natives from lower land (150m) (Lopez et al. 1975) found no significant differences between

serum concentrations of IgG, IgA and IgM, albeit there was a tendency for greater IgA values in the

natives from the highest altitude.

2.6.3 Hypoxia and cold and immune system

Given the limited research regarding the immune response to hypoxia, even less information is

available highlighting the immune response to hypoxia in the cold. Nonetheless, it has been

reported that AMS and HAPE are notably more common in mountain climbers during seasons of

lowest ambient temperatures (Giesbrecht, 1995). Furthermore, it is believed that travelling to

regions of high altitude and cold temperatures increases susceptibility to URTI (Walsh and

Whitham, 2006). However, the evidence to support this is lacking and the problem is confounded

by possible misdiagnosis due to some overlap in the symptoms of AMS and URTI (Bailey et al.

2003). On the contrary, it was reported that soldiers stationed at an altitude of 3692m had a higher

prevalence of pneumonia compared with troops stationed at low altitude (Singh et al. 1977).

Anecdotal reports and specific case studies also document an increase in URTI symptoms when

ascending to altitudes >4000m (Basnyat et al. 2001; Oliver et al. 2012).

24

2.7 Mucosal immunity in cold and hypoxia

2.7.1 Cold and mucosal immunity

Stress induced immune perturbations have been attributed to the stimulation of the

sympatheticoadrenal-medullary and hypothalamic-pituitary adrenal axis which cause an increase in

circulating stress hormones (catecholamines and cortisol). An influx of these hormones initiates a

subsequent increase in secretory IgA production (Glesson, 2007). Cold stress is associated with an

increased incidence of bronchorrhea, sinusitis, and other URTI (Clothier, 1974; Giesbrecht, 1995).

Increased ventilation in very cold dry air, due to exercise or increased shivering activity, can cause a

persistent dry cough and nasal drying (Giesbrecht, 1995). Human mucociliary clearance is slowed

on exposure to cold air (Proctor, 1982). This is because the decrease in temperature is likely to

reduce both ciliary beat frequency and the rate of mucus secretion (Proctor, 1982). A large decrease

in temperature is also likely to cause an increase in the viscosity of respiratory mucus. Following a

cross country ski race, a decrease in saliva immunoglobulin-A (s-IgA) concentration was associated

with a large inflow of cold air that lowered the temperature of the mucous membranes (Tomasi et

al. 1982). On the contrary, exercise in the cold has also been found to have no effect on s-IgA

concentration (Housh et al. 1991). However, s-IgA was only reported as a concentration and not

secretion rate, thus ignoring the drying effect of heavy breathing during cold exposure and exercise.

Nonetheless, performing prolonged exercise in freezing cold conditions did not influence saliva

flow rate or s-IgA secretion rate responses (Walsh et al. 2002, Table 2.3). Given research has

investigated mucosal immunity during exercise in the cold, surprisingly little is known regarding

the effects of sedentary activity in the cold upon the mucosal immunity of shivering, cold casualties.

This seems pertinent since heat production arising from shivering activity and subsequent

hyperventilation is similar to that during exercise. Furthermore, since heat production during

25

sedentary activity is eventually outweighed by heat loss, corresponding with a reduction in Tc could

evoke an even larger mucosal immune response.

2.7.2 Hypoxia and mucosal immunity

Mucosal immunity is suggested to be unchanged by hypoxia, and any reduced IgA and lysozyme

levels may be caused by the combined stresses of cold, isolation and reduced humidity (Meehan et

al. 1988; Muchmore et al. 1981). Secondly, given physical activity is often undertaken at altitude

may also inadvertently affect mucosal immunity. For example, individuals enrolled in a ‘live high,

train low’ training camp demonstrated a decline in s-IgA levels, which was suggestive of a

cumulative negative effect of physical exercise and hypoxia on s-IgA (Tiollier et al. 2005, Table

2.3). On the contrary, epidemiologic data has provided indirect evidence that hypoxia may indeed

impair immune competence in humans (Meehan et al. 1988). For example, a higher prevalence of

pneumonia has been found among military troops stationed at high altitude (Singh et al. 1977) and

an increase in infant mortality due to respiratory infections among high altitude natives has also

been reported (Chohan et al. 1975, Table 2.3). Exposure to hypobaric hypoxia therefore, may serve

as a stimulus to activate the neuroendocrine system and identify the mechanisms responsible for

immune modulation during environmental stress in humans (Meehan et al. 1988).

2.7.3 Hypoxia and cold and mucosal immunity

Since URTIs are the main cause of illness and missed practise in elite cross country skiers

(Berglund and Hemmingson, 1990) and cases of acute mountain sickness and high-altitude

pulmonary edema (HAPE) are increased in mountaineers during cold seasons (Giesbrecht, 1995),

26

cold-induced decrements in immune-surveillance may be a potential problem for individuals at

altitude. The additional stressor of cold in hypoxia-exposed humans may evoke a similar

suppression on the mucosal immune system as that demonstrated with physical activity in the cold.

At present, little attention has been directed toward the influence of hypoxia upon mucosal

immunity in the cold. Whether the risk of illness or infection is exacerbated in un-acclimatised

expeditioners upon arrival to hypoxic and cold environments remains unknown. Furthermore, it has

not been clarified whether such detriments to mucosal immunity are reduced following a period of

altitude acclimatisation. This information may have significant implications for spaceflight

personnel during long term missions where conditions of low oxygen supply are likely (Cogoli,

1981; Taylor and Dardano, 1983).

27

28

29

30

2.8 Cold casualty re-warming and protection

The treatment of hypothermia should aim to minimise the post-exposure after-drop and promote a

steady continuous rate of re-warming (Giesbrecht et al. 1997). ‘After-drop’ is the term given when

removal from the cold induces a further reduction in Tc (Giesbrecht and Bristow, 1992) as such re-

warming should be continued until thermal, cardiorespiratory, and metabolic homeostasis can be

maintained (Giesbrecht et al. 1997). One explanation for the after-drop phenomenon is proposed by

the circulatory theory, which has two variations. The first states that upon re-warming, Tc decreases

because of the cold blood returning from vasoconstricted peripheral vessels (Hervey, 1973).

However, it is unlikely that vasoconstriction during cooling would preferentially trap blood

peripherally but rather force it back to the core, leaving minimal blood in these tissues (Giesbrecht

and Bristow, 1992). The second variation is that vasodilation, upon re-warming, results in the flow

of cold blood from the core to previously hypoperfused colder superficial and peripheral tissue,

resulting in further cooling of the blood and subsequently the core (Burton and Edholm, 1955;

Golden, 1973).

Since the movement of cold casualties has been demonstrated to increase after-drop following cold

water immersion (Giesbrecht et al. 1987), after-drop rate may be related to the ambulation of

subjects from a cold to warm environment. For example, core cooling has been measured at 1.2 –

1.3°C/h in subjects buried in snow and wearing only lightweight clothing insulation systems

(Grissom et al. 2004). However, subjects extricated from snow burial after 60 minutes and taken to

a warm environment, displayed a core temperature after-drop rate of 3.3°C/h (Grissom et al. 2008).

The after-drop rate was more than double the core cooling rate, suggesting that movement is a

significant factor of hypothermia severity when indivudals are moved from a cold environment to a

warm environment (Grissom et al. 2010).

31

Currently, most technical re-warming methods for the treatment of hypothermia require

hospitalisation. However, immediate field methods for treating hypothermia occurring during

military operations or outdoor recreation activities are essential when evacuation to hospitals may

be difficult (Giesbrecht et al. 1987). Portable central airway re-warming devices have been

developed for field use (Lloyd, 1973); however these can only be administered by fully qualified

rescue teams. A paucity of information is available for simple, economical and practical re-warming

methods that can be administered by a first responder in the field while awaiting evacuation to

superior means (Giesbrecht et al. 1987).

2.8.1 Hospital based methods

The safety of external whole body re-warming by warm water immersion has created controversy

within the literature. While warm water immersion donates large amounts of heat to promote a rapid

rate of re-warming (Romet and Hoskin, 1988), it causes a large initial Tc after-drop (Hayward et al.

1975) and increases the risk of fibrillation (Webb, 1986). This is because direct warming of the

periphery promotes an increased inflow of cold blood to the heart which creates large core cooling.

Thus, whole body re-warming should not be used with severely hypothermic casualties. By heating

core organs first, (e.g. heating blood in an extracorporeal circuit or peritoneal lavage) after-drop can

be avoided (Webb, 1986). In comparison to warm water re-warming, core temperature after-drop

has been demonstrated to decrease by 30% when forced air warming is used to donate heat by the

direct transfer of warm air onto the periphery of the body (Giesbrecht et al. 1994). On the contrary,

studies investigating the re-warming capacity of inhaling warm, humidified air in mildly

hypothermic subjects removed from the cold have found little (Hayward and Steinman, 1975;

Romet and Hoskin, 1988) or no (Collis et al. 1977; Goheen et al. 1997) benefit compared to

shivering thermogenesis alone. Given perioperative hypothermia may contribute to

32

immunosuppression during the postoperative period, the use of non-invasive re-warming devices

with patients during surgery may help to reduce this.

2.8.2 Field methods

It is acknowledged that mildly hypothermic victims can be suitably re-warmed in the field if

adequate insulation is provided (Pugh, 1964; Grissom et al. 2010). In the field, sources of heat are

limited to the ingestion of warm liquid, body-to-body contact (Harnett et al. 1980; Giesbrecht et al.

1994), heating pads (Collis et al. 1977; Giesbrecht et al. 1987) and possibly inhalation of

humidified air or oxygen (Giesbrecht, 2001). The charcoal burning ‘Heat Pac’ (Heat Pac, Oslo,

Norway) provides a thermal advantage when metabolic heat production is minimal (Hultzer et al.

1999) and is probably the most efficient portable warming device available (Giesbrecht, 2001). It is

small, light and produces approximately 250 W for up to 12 –14 h. Although inhalation warming is

often proposed as an effective strategy for body warming, or at least prevention of further body

cooling (Weinberg, 1998), the advantage regarding thermal balance is minimal (Geisbrecht, 2001).

In shivering subjects, no re-warming advantages were found when re-warming trials were

conducted in 20°C (Romet and Hoskin, 1988), 2°C (Sterba, 1991) or –20°C air (Mekjavic and

Eiken, 1995). When using a human model for severe hypothermia (shivering inhibited by pethidine

in hypothermic subjects) (Giesbrecht et al.1997) inhalation rewarming still did not provide any core

rewarming advantage over spontaneous warming over 150 min of recovery (Goheen et al. 1997).

Early reports suggest body-to-body contact with a minimally clothed euthermic heat donor whilst in

an insulated bag may be beneficial for the re-warming of hypothermic victims (Collis, 1976; Mills

et al. 1987; Robinson, 1992). However, it has been demonstrated that heat donors blunt the

recipients’ shivering thermogenesis and re-warming rates remain the same as that of shivering alone

33

(Giesbrecht et al. 1994, Table 2.4). Therefore, mildly hypothermic victims who are otherwise

healthy and shivering normally should simply be removed from the cold stress to a dry insulated

environment (i.e. a sleeping bag). Victims who are not shivering because of severe hypothermia,

impaired thermoregulatory control, or depleted metabolic substrates should be evacuated to a

medical facility immediately (Grissom et al. 2010). The absence of shivering has been reported to

induce a three-fold increase of Tc after-drop and a four-fold increase in the length of the after-drop

period compared to when shivering is not inhibited (Giesbrecht et al. 1997). However, research is

limited as to the effects of hypothermia on non-shivering casualties due to the ethical boundaries of

injecting subjects with shivering depressants.

An alternative way to increase the body’s own heat production is through exercise. However, after-

drop amount and length were found to be greater in cold individuals during an exercise re-warming

protocol compared to shivering only or externally applied heat (Giesbrecht et al. 1987, Table 2.4).

It is likely that before exercise, blood in the muscles is cooler than blood at the core; nonetheless,

given that exercise increases circulation, blood at the core is readily cooled (Hudlicka, 1982;

Giesbrecht et al. 1987). For this reason exercise should be avoided in an individual whose Tc is

unknown or less than 32°C and shows signs of physical and / or metabolic exhaustion, (i.e.

incapable of shivering). Additionally, through injury, individuals may be forced to remain sedentary

while awaiting rescue.

2.8.3 Single and multi-layer survival products

Metalized plastic sheeting (MPS) is a single layered, water and windproof material thought to

benefit the human body by reflecting radiated heat lost from the body surface (Marcus et al. 1977,

Table 2.4). Single-layer MPS products were originally favoured for their small (e.g. 9.5cm x 2.5cm

34

(folded)), light-weight (e.g. 50g) appeal compared to heavier, bulkier casualty bags made of

materials such as goose down (Light et al. 1980, Table 2.4). However, research to date is equivocal

as to the thermal protection provided by MPS. For example, MPS and metal foil have been

associated with a reduced heat loss in cold conditions (Spencer-Smith, 1977). On the other hand,

MPS has been found to be inefficient at preventing heat loss during operative surgery (Radford and

Thurlow, 1979), and was reported to provide no additional thermal protection to the periphery of

cold exposed humans in comparison to polythene and nylon (Marcus et al. 1977).

Anecdotal reports suggest the light-weight structure and weak adhesive of MPS bags makes them

insecure and easily torn. Yet, bulk and weight of a casualty bag is of direct importance to the

individual who must survive in an isolated environment using only what they may have carried with

them in a rucksack (Light et al. 1980). Single layer MPS may be light-weight but appears to offer

little thermal protection in cold environments. However, placing a fibre pile liner inside a casualty

bag incorporating MPS seems to evoke significantly smaller reductions in Trec and Tsk compared

with single layer MPS (Light et al. 1980). In this study, shivering was also noted to be eliminated in

the MPS and fibre pile bag, indicating multi-layer products may offer thermal and metabolic

advantages. Additionally, multi-layer survival products tested during a one hour cold exposure in -

10°C and average wind speed 3.0m∙s-1

, were able to maintain Tsk close to normothermia, while

single layer MPS was not (Grant et al. 2002, Table 2.4). Despite this, participants reported similar

increased perceptions of cold and displayed a rapid fall in Trec. Each multi-layer system had a wind

and water-proof nylon outer; one contained a fibre pile lining and the other incorporated an inner

Duffel bag. Evidently multi-layer systems may better conserve heat via improved insulation in

comparison to single-layer systems. However, while Tc continues to decline rapidly in currently

available survival products, alternative materials should be researched.

35

Albeit, multi-layer devices may provide initial re-warming treatment to a cold casualty, subsequent

peripheral warming has been reported to evoke a secondary decline in Tc (Grant et al. 2002).

Peripheral vasoconstriction therefore, is likely to be limited in casualties wearing thick winter

garments inside a survival bag because of a high heat transfer generated from the body’s core to the

skin (Grant et al. 2002; Vokac and Hjeltnes, 1981). A temperature gradient between the skin and

the air inside the bag may impair peripheral thermoreceptor activity (Grant et al. 2002). To protect

ecological validity most research with survival products includes participants wearing typical

outdoor clothes (Marcus et al. 1977; Light et al. 1980; Light and Norman, 1990; Grant et al. 2002).

However, this could be causing a temperature gradient within the survival bag and thus contributing

to the observed decline in Tc. At present, the maximal capacity to protect Tc in survival bags

remains unknown. Research should therefore examine multi-layer survival products while subjects

are minimally clad.

A recent in vitro study comparing cooling times of pre-heated fluid bags protected with different

field methods reported that a multi-layered survival bag (Blizzard Survival™) was superior at

preventing core heat loss compared with a polythene survival bag, single layer MPS and wool

blanket (Allen et al. 2010). Further, an active heating combination of the multi-layered metalized

sheeting survival bag (Blizzard Reflexcell™) with chemical heat pads was shown to be superior to

all other methods tested. Nonetheless, given that the exposure conditions did not reflect typical cold

temperatures experienced during outdoor winter pursuits, it remains unknown how well these

devices will protect non-shivering, sedentary humans in the cold.

Reflexcell™ has an elasticised and cellular construction to trap warm air and draw the material to

the body. This reduces the number of cold spaces and heat loss by convection. The silvered surfaces

of Reflexcell™ reduce heat loss by radiation and provide a wet and wind proof layer. Minimising

heat loss by convection and radiation during cold exposure reduces the likelihood of hypothermia

36

(Light and Norman, 1990). The Blizzard Survival™ bag, light-weight and easily compressed in to a

video cassette package, is a full sized sleeping bag constructed entirely from Reflexcell™ material.

The Blizzard Survival Heat™ comprises Reflexcell™ technology with self-activating heat pads

which can also be vacuumed to the size of a video cassette. Self-activating heat pads eliminate the

need for a power supply, and Velcro sides allow medical attention to be administered efficiently.

Thermal efficiency of sleeping bag materials is generally expressed as a warmth-to-weight ratio by

dividing the insulating value of the material (Togs) by the weight of a typical sleeping bag made

from that material. The basic unit of insulation coefficient is the RSI (1m2k/watt). One tog is equal to

0.1 RSI. This means the thermal resistance in togs is equal to ten times the temperature difference

(in °C) between the two surfaces of a material, when the flow of heat is equal to one watt per square

metre. University laboratory tests using a Tog rating of 8 Togs and a weight of 330 g for the

Reflexcell™ bag found a value of 24 Togs/kg. This is over twice the value for goose down, which

was previously regarded as having the highest possible warmth-to-weight ratio among insulating

materials. Further investigation of Reflexcell™ with human participants is required to test the

thermal capacity provided by this new technology.

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38

39

CHAPTER THREE

General methods

3.1 Ethical approval

Approval for all studies was obtained from the local Ethics Committee (School of Sport, Health and

Exercise Sciences, Bangor University). The nature and purpose of each study was explained both

verbally and in writing to each volunteer (Appendix A). Each participant was made aware that they

were free to withdraw from the study at any time and completed an informed consent form

(Appendix B). All volunteers were non-smokers and had no significant oral, dental, or systemic

disease and were not taking any medication at the time of participating in the studies. To determine

eligibility for inclusion into a research study, participants completed a medical and health

questionnaire (Appendix C) and reported no incidences of illness in the six weeks prior to

beginning the study.

3.2 Anthropometry and body composition

Height was recorded using a wall stadiometer (Bodycare Ktd, Warickshire, UK) and NBM by

digital platform scales accurate to the nearest 50 g (Model 705, Seca, Hamburg, Germany). Whole

body skeletal muscle mass, appendicular lean mass, and fat free mass were assessed using

segmental multiple frequency bioelectrical impedance (InBody 230, Biospace, Seoul, 3 Korea). For

this procedure participants removed shoes and socks and dressed in t-shirt and shorts only. Validity

and reliability of this technique to assess regional and whole body composition has been shown

previously (Malavolti et al. 2003; Jensky-Squires et al. 2008).

40

3.3 Experimental procedures

The day prior to each experimental trial participants ingested water equal to at least 35 ml·kg-1

body

mass and a prescribed diet. Participants arrived to the laboratory euhydrated. This was verified by

urine specific gravity equal to or less than 1.020 g·ml-1

(Casa et al. 2005) and urine osmolality no

greater than 800 mOsm/kg (Urine Osmolality Meter PAL-mOsm). Hydration was also inspected

against a urine colour chart with hyrdration accepted as a level 3 or less (Armstrong, 2000).

3.4 Thermoregulatory measures

Core temperature (Trec) was recorded using a flexible thermistor inserted 12 cm beyond the anal

sphincter (YSI 4000A, Daytona, FL, Chapter 4 and 5) (2020 series, Squirrel data logger, Grant)

(Chapter 6 and 7). Measurements of core temperature by flexible thermistor was considered the

least invasive yet most accurate method. For example tympanic temperature is not as accurate as

measurements taken from the rectum, yet eosophageal measurements would have caused a degree

of discomfort for participants and they would have been unable to consume fluids (Chapter 6 and

7). Gastrointestinal telemetry pills would have been affected by the ingestion of hot fluids (Chapter

6). Skin temperature was recorded at 8 sites using either iButton® technology (Maxim Integrated

Products, Inc., Sunnyvale, CA, USA) (Chapter 4 and 5) or skin thermistors (2020 series, Squirrel

data logger, Grant) (Chapter 6 and 7). Weighted mean skin temperature was calculated using an

area-weighted formula (ISO-standard 9886, 2004) (eq. 1) (Chapters 4, 5, 6 and 7). Metabolic heat

production (M) was assessed and calculated via indirect calorimetry methods (Servomex 1420B,

Crowborough, UK and Harvard Apparatus, Edenbridge, UK) (eq. 2) (Chapters 4, 5, 6 and 7).

Thermal comfort was measured using the McGinnis Scale of Thermal Comfort (Hollies and

Goldman, 1977) (Chapters 4, 5, 6 and 7).

41

3.5 Sample collection and analysis

Saliva and urine samples were collected at least 15 min after fluid consumption and at least 1 h after

the participants had eaten. In addition, saliva samples were obtained after participants had remained

seated for 10 min.

3.5.1 Saliva

Each participant was asked to thoroughly rinse their mouth with water and swallow residual before

saliva collection of un-stimulated whole saliva samples into a pre-weighed universal container (HR

120-EC, A & D instruments, Tokyo, Japan) (Chapters 5 and 7). All saliva samples were collected

for 5 minutes while the participant sat quietly, leant forward and passively drooled with minimal

orofacial movements. Saliva volume was estimated by weighing the universal container

immediately after collection to the nearest mg and saliva density was assumed to be 1.00 g∙ml-1

(Cole and Eastoe, 1988). From this, saliva flow rate was determined by dividing the volume of

saliva by the collection time. Saliva was then aspirated into eppendorfs and stored at -40°C prior to

analysis.

Saliva IgA concentration was determined by ELISA (Salimetrics Europe Ltd, Suffolk, UK) using an

IgA monomer derived from human serum as standard. During the ELISA a constant amount of goat

anti-human s-IgA conjugated to horseradish peroxidase was added to tubes containing specific

dilutions of standards or saliva. The antibody-conjugate was bound to the s-IgA in the standard or

saliva samples. The amount of free antibody remaining was inversely proportional to the amount of

s-IgA present. After incubation and mixing, an equal solution from each tube was added, in

duplicate, to the microtitre plate coated with human s-IgA. The free or unbound antibody conjugate

bound to the s-IgA on the plate. After further incubation, unbound components were washed away.

42

Bound conjugate was measured by the reaction of the peroxidase enzyme on the substrate

tetramethylbenzidine. This reaction produced a blue colour, followed by yellow once the reaction

had been chemically stopped. Optical density was read on a standard plate reader at 450 nm. The

amount of peroxidase was inversely proportional to the amount of s-IgA present in the sample

(Chard, 1990). The intra-assay CV was 1.4% and 2.6% for chapters 5 and 7 respectively. The s-IgA

secretion rate was calculated by multiplying the saliva flow rate by s-IgA concentration.

The alpha amylase ELISA method (Salimetrics Europe Ltd, Suffolk, UK) utilized a chromagenic

substrate, 2-chloro-p-nitrophenol linked with maltotriose (Wallenfels et al. 1978). The enzymatic

action of alpha amylase on this substrate yielded 2-chloro-p-nitrophenol were

spectrophotometrically measured at 405 nm. The amount of alpha amylase activity present in the

sample was directly proportional to the increase in absorbance at 405 nm. For ease of use, the

reaction was read in a 96-well microtiter plate with controls provided. The intra-assay CV was 2.5%

and 2.1% for chapters 5 and 7 respectively.

3.5.2 Urine

First morning urine samples were collected in full and determined for volume, urine specific gravity

(Atago Uricon-NE; NSG Precision Cells, Farmingdale, NY, USA) and osmalality. Urine colour was

determined by a urine colour scale (Armstrong et al. 1994). Provided particpants fulfilled the

hydrated criteria they were able to take part in the studies. Urine was aspirated into eppendorfs,

frozen at -40°C and later thawed for analysis of urinary urea nitrogen content (Chapter 6: Randox

Laboratories, Co. Antrim, UK).

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3.6 Calculations

Mean skin temperature (Tsk) area-weighted 8-site equation, adjusted for regional proportions (ISO-

standard 9886, 2004):

Mean Tsk = (0.07 · Tforehead) + (0.175 · Tright scapula) + (0.175 · Tleft upper chest)

+ (0.07 · Tright arm in upper location) + (0.07 · Tleft arm in lower location)

+ (0.05 · Tleft hand) + (0.19 · Tright anterior thigh) + (0.2 · Tleft calf ). (eq. 1)

From expired gas samples, values for the respiratory exchange ratio (RER) and VO2 were obtained

and calculated with body surface area (AD) to estimate metabolic heat production (M) in W·m2

using the following equation (Gagge and Gonzalez, 1996):

M = [0.23(RER) + 0.77] · (5.873) (VO2) · (60/ AD) (eq. 2)

3.7 Statistical analysis

Statistical analyses were completed using Statistical Package for Social Sciences (SPSS Version

14). Data were examined using repeated measures ANOVA. Where assumptions of sphericity and

normality were violated appropriate adjustments to the degrees of freedom were made. Effect sizes

(η2) were determined for main outcome measures and were interpreted as small (0.010), medium

(0.060) and large (0.140) (Cohen, 1988). Significance was accepted at P < 0.05. Where significance

occurred Post Hoc Tukey’s HSD was used. All data are presented as Mean ± standard deviation

(SD). Sample sizes were estimated using similar data from previous investigations

(http://www.dssresearch.com/toolkit/sscalc). Alpha and power levels were set at 0.05 and 80%

respectively.

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CHAPTER FOUR

Thermal Comfort and Thermoregulatory Responses to Cold Exposure in Hypoxia before and

after an Altitude Stay

4.1 Abstract

The purpose of this study was to determine thermal comfort and thermoregulation in relation to

potential cold injury during hypoxic and mild cold exposure before and after an 18-day

mountaineering expedition. In shorts only, ten males completed 2-hour cold air tests (CAT 15°C,

RH 44%) in an environmental chamber in a supine position. Three CATs were performed: 1. Sea

level (SL); 2. Un-acclimatized in normobaric hypoxia (UN: ~4000m); 3. Post expedition in

normobaric hypoxia (PEX: ~4000m). During the CAT core and mean skin temperature were not

different between SL, UN and PEX. However, compared with SL, metabolic heat production was

lower during hypoxic exposures (SL 93 ± 36, UN 68 ± 25, PEX 65 ± 25 W∙m-2

; P < 0.001: mean ±

SD). Observed shivering activity was also lower after the expedition, which suggests a different

contribution of non-shivering and shivering thermogenesis (SL 1.1 ± 0.1, UN 1.0 ± 0.2 and PEX 0.6

± 0.1; P = 0.002). Thermal comfort was increased PEX compared with SL and UN (SL 5.0 ± 1.4,

UN 5.6 ± 1.1, PEX 6.1 ± 0.8; P = 0.004). Following an 18-day mountaineering expedition a lack of

change in core and skin temperature despite a decrease in shivering is consistent with a greater

reliance on non-shivering thermogenesis. The alterations observed post expedition in thermal

comfort suggest a greater thermal tolerance but an increase in susceptibility to cold injury in

hypoxia.

45

4.2 Introduction

High altitude environments may alter perceptual and thermoregulatory responses to the cold that

predispose individuals to greater cold injury (Blatteis and Lutherer, 1976; Cipriano and Goldman,

1975; Golja et al. 2004; Johnston et al. 1996; Savourey et al. 1997). Indeed epidemiological studies

suggest cold injury rates increase at high altitude (Hashmi et al. 1998; Harirchi et al. 2005).

Research studying the effect of hypoxia on thermoregulatory responses to cold is however

equivocal.

Compared with cold alone exposure to cold and hypoxia is associated with a decreased thermal

sensitivity (Golja et al. 2004), lower core temperature and higher skin temperature (Cipriano and

Goldman, 1975; Kottke et al. 1948) which may increase predisposition to cold injury. Nonetheless,

some studies have reported no change in thermal comfort (Golja et al. 2005), core temperature

(Blatteis and Lutherer, 1976; Robinson and Haymes, 1990) or skin temperature (Brown et al. 1952).

An earlier onset of shivering with increased intensity is a common observation in men exposed to

hypoxia and cold (Blatteis and Lutherer, 1976; Bullard, 1961; Robinson and Haymes, 1990). This

may result from reduced non-shivering thermogenesis (NST), demonstrated by a reduced cold-

induced increase in VO2 (Blatteis and Lutherer, 1976). Hypoxic-induced suppression of NST has

been explained by an inhibition of the aerobic catabolism of body fat stores (Robinson and Haymes,

1990). However, patterns of fuel selection during hypoxia in the cold remain to be clarified.

An altered perception of cold sensation has been reported at altitude (Golja et al. 2004) and has

been suggested to be related to a lowered neural activity and delayed signal conduction (Astrup,

1982). A diminished cold sensation is likely to predispose individuals to cold injury because they

neglect basic behavioural thermoregulatory mechanisms (e.g. putting on extra layers and seeking

shelter). However, following acclimation by intermittent exposure to hypoxia, cold and warm

sensitivities of the hand were unchanged compared with baseline measures (Malanda et al. 2008).

46

At present, local and whole body sensations to cold have not been simultaneously measured. In

addition to hypoxic-induced alterations in cold sensation, anecdotal reports suggest hypoxia also

alters thermal comfort. Early reports describe the pain to single limb cold water immersion

(Mathew et al. 1979) and thermal discomfort to whole body mild cold air exposure (Blatteis and

Lutherer, 1976) to be greater at altitude than at sea level. These same anecdotal reports suggest that

the increased pain and discomfort did not abate with altitude acclimatisation (Mathew et al. 1979;

Blatteis and Lutherer, 1976). Greater pain to single limb cold water immersion has recently been

confirmed by a more systematic investigation (Daanen and van Ruiten, 2000). However, the effect

of whole body cold exposure during acute hypoxia and following a high altitude stay on perception

of thermal comfort has yet to be explored.

Demonstrated by the maintenance of a higher mean body temperature and mean skin temperature

during acute cold stress, hypoxic acclimatisation has been shown to induce greater cold tolerance

(Blatties and Lutherer, 1976; Mathew et al. 1979). Studies also suggest altitude acclimatisation may

result in NST recovery (Blatteis and Lutherer, 1976; Mathew et al. 1979). The amount of recovery

however remains unclear and is complicated by the methods of data collection used (Blatteis and

Lutherer, 1976; Cipriano and Goldman, 1975; Mathew et al, 1979). For example, sample sizes in

these studies were small and methods to determine shivering activity were not valid. It is plausible

to suggest that while un-acclimatised exposure to hypoxia may inhibit the catabolism of fat stores

and thus reduce NST, the same might not be true following acclimatisation. Research has examined

thermoregulatory responses after acclimatisation during cold exposure at sea level (Blatteis and

Lutherer, 1976; Savourey et al. 1997), yet no studies have assessed such responses during hypoxia

in the cold following a mountaineering expedition.

The effect of hypoxia in the cold on thermoregulatory mechanisms of un-acclimatised men is

equivocal. It is unknown whether acclimatisation, resulting from mountaineering activity at altitude,

affects thermoregulatory, metabolic and perceptual responses to hypoxia in the cold. The aim of the

47

present study therefore, was to examine these responses in un-acclimatised and acclimatised

individuals after an 18-day Alpine expedition. It was hypothesised that un-acclimatised exposure to

hypoxia and cold would impair thermoregulatory responses compared to those reported in

normoxia. Secondly, it was hypothesised that acclimatisation due to the expedition would restore

the responses toward those observed in normoxic cold exposure.

48

4.3 Method

4.3.1 Participants

Ten healthy males (mean ± SD: age, 21.7 ± 2.4 years; height, 181.7 ± 5.1 cm; body mass, 76.4 ± 9.9

kg and body fat, 11.6 ± 6.6 %), accustomed to multi-day expedition-type activities were recruited

from an 18-day Alpine expedition (Figure 4.1). Participants gave written consent and medical

history before the study that had received local Ethics Committee approval.

4.3.2 Study design

Participants completed three experimental trials in a normobaric, temperature and humidity

controlled chamber (Dry bulb temperature of the chamber remained at 15°C with a relative

humidity (RH) 40% and 0.2 m.s-1

wind velocity; Delta Environmental Systems, Chester, UK) over

a 12 week period. Trials were 1. sea-level (SL: FIO2 = 0.209); 2. Un-acclimatised in normobaric

hypoxia (UN: FIO2 = 0.125, ~4000m); and 3. post expedition acclimatised in normobaric hypoxia

(PEX: FIO2 = 0.125, ~4000m). To avoid an order effect SL and UN were performed before the

expedition in half of the participants and 2 months after the expedition in the remainder. During

PEX the mean altitude gained on a daily basis was 2989 ± 867 m.

4.3.3 Experimental procedures

Having consumed no food within 4 hours, participants arrived to the laboratory euhydrated

(Chapter 3). After voiding bladder and bowels, anthropometric measures of height and body mass

were obtained. Body composition was analysed by segmental multiple-frequency bioelectrical

impedance (InBody 230, Biospace, Seoul, S Korea: Malavolti et al. 2003; Jensky-Squires et al.

2008). Daily energy requirements were determined by body composition and a mean of daily

49

metabolic rate, hourly basal metabolic rate, eight hours sleep, eight hours of occupational activities

(e.g. moving, sitting and standing) and eight hours of residual time (WHO, 2004).

4.3.4 Experimental Trials

Participants completed each trial at the same time of day. Following pre-trial measures, participants

began a 10 minute supine rest in a thermo-neutral environment (ambient temperature: 21.3 ± 1.1°C;

RH: 52 ± 5.4%). Resting values of core (Trec) and skin (Tsk) temperature were recorded. Metabolic

heat production (M), thermal comfort, peripheral and central coldness (Borg CR100) (Borg and

Borg, 2001), heart rate (HR) (Polar, Electro Kempele, Finland), and arterial oxygen saturation

(SaO2%) by finger pulse oximetry (Supermon 7210, Kontron, Watford, UK), were also recorded.

Following baseline measures and wearing shorts only, participants entered the chamber and rested

supine upon roll mats situated on the floor for 150 minutes. Core temperature, M, SaO2%, HR,

whole body thermal comfort and peripheral and central coldness were recorded every 5 minutes.

Skin temperature was recorded every minute. To detect potential CIVD, toenail and fingernail bed

temperatures were measured with i-buttons taped to the large toe and index finger of the right hand

and foot. During the initial 30 minutes, participants were covered with a standard duvet (4.5 togs).

This thermo-neutral condition (van Ooijen et al. 2005) ended and the 120 minute CAT began when

the duvet was removed. Thermo-neutral conditions were necessary in order to establish any change

between non-shivering thermogenesis and shivering thermogenesis.

Electromyograms (AD instruments Powerlab) of the pectoralis major determined shivering activity.

Pilot work demonstrated this muscle to provide accurate traces with little background noise

compared to abdominal or quadriceps muscles. In addition, acetate traces were taken of each

participant’s torso to ensure exact placement of EMG leads during each trial. EMG data was logged

every minute and measured in micro-volts. Shivering was also rated using a 4 point scale by an

50

observer (Appendix F) (Blatteis and Lutherer, 1976). Training was given to a maximum of two

researchers in order to maintain consistant observational practice. Participants remained in the

environmental chamber for 150 minutes unless: 1. Trec decreased to 36°C or fell 1.5°C below

resting, 2. Lake Louise scores went above 1 to highlight the presence of headache (hypoxic trials

only) or 3. participants chose to withdraw. Upon completion participants were re-warmed and

monitored until core temperature was within 0.5°C of resting.

Figure 4.1. Mean daily altitude of participants during an Alpine expedition.

4.3.5 Statistical analyses

A sample size of nine was estimated using rectal temperature data from a previous investigation

(Blatteis and Lutherer, 1976). To allow for incompletion, ten subjects were recruited. A one-way

fully repeated-measures ANOVA was performed on body mass and composition data and urine

osmolality. Two-way fully repeated-measures ANOVA (time x trial) were performed on

thermoregulatory, metabolic and EMG data. Data was normally distributed.

Day

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

51

4.4 Results

4.4.1 Environmental chamber conditions, hydration status, body mass and composition

Chamber temperature (SL: 15.0 ± 0.1; UN: 15.2 ± 0.2; PEX: 15.2 ± 0.2°C, F2, 10 = 1.168, P = 0.350)

and relative humidity (SL: 46 ± 4; UN: 43 ± 8; PEX: 39 ± 4%, F2, 10 = 0.292, P = 0.753) were not

different between trials. Urine osmolality indicated hydration status was similar before each trial

(SL: 364 ± 129, UN: 366 ± 129, PEX: 382 ± 202 mOsm∙Kg-1

, P = 0.670). Body fat and mass were

unchanged before and after the expedition (SL: 11.6 ± 6.6; PEX: 11.5 ± 6.3 %, P = 0.745; SL: 75 ±

10; PEX: 76 ± 10 Kg, P = 0.786 respectively).

4.4.2 Core and skin temperature responses

Cold exposure caused Trec to decline similarly during all CATs (F12, 108 = 4.456, P = 0.000, η2

=

0.326) (Figure 4.2). Cold exposure reduced mean Tsk in all trials (F12, 108 = 170.084, P = 0.000, η2

=

0.942) but was also not influenced by hypoxia (F2, 18 = 1.450, P = 0.261, η2

= 0.136) (Figure 4.3).

Skin temperature at the forehead was lower throughout SL compared to UN and PEX (F2, 18 =

9.875, P = 0.001, η2 = 0.521) (Table 4.1). Skin temperature at the left chest was also lower during

SL compared to PEX following 10 minutes of cold exposure (F1.291, 11.618 = 4.743, P = 0.043, η2 =

0.324). No differences occurred for any other individual skin sites (Table 4.1).

Temperatures at the fingernail bed were the same in each trial (F2, 18 = 0.033, P = 0.967, η2

= 0.004)

(Table 4.2). During the initial exposure, temperatures at the toenail bed were also the same (F2, 18 =

1.324, P = 0.291, η2

= 0.101). However, following 60 minutes, toenail bed temperature was lower

during UN compared to SL (F2, 18 = 3.793, P = 0.042, η2

= 0.288) (Table 4.2). An interaction

established cold exposure evoked a cooler toenail bed temperature in unacclimsatised individuals

(F24, 216 = 6.882, P = 0.000, η2

= 0.356).

52

Figure 4.2. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level ( ♦ ) and at 4000 m before ( ■ ) and after ( △ ) acclimatisation on Trec (°C). Values are mean ±

SD. * significant difference vs. 0 mins (P < 0.05).

Figure 4.3. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level ( ♦ ) and at 4000 m before ( ■ ) and after ( △ ) acclimatisation on mean skin temperature (°C).

Values are mean ± SD. * significant difference vs. 0 mins (P < 0.05).

27

28

29

30

31

32

33

34

0 10 20 30 40 50 60 70 80 90 100 110 120

Skin

Te

mp

era

ture

(°C

)

Time (mins)

36

36.2

36.4

36.6

36.8

37

37.2

37.4

37.6

37.8

38

0 10 20 30 40 50 60 70 80 90 100 110 120

Co

re T

em

pe

ratu

re (

°C)

Time (mins)

53

Table 4.1. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level (SL) and at 4000 m before (UN) and after (PEX) acclimatisation on skin temperature (°C).

Values are mean ± SD. * significant difference vs. 0, † significant difference vs. SL (P < 0.05).

Skin temperature at individual sites (°C)

SL UN PEX

Forehead

0 30.3 32.0† 32.4†

60 28.7* 30.4*† 31.0*†

120 28.6* 30.3*† 30.8*†

Mean (SD) 28.9 ± 2.3 30.7 ± 2.0 31.1 ± 1.1

Right Scapula

0 34.0 34.7 34.0

60 34.5 35.1 34.7

120 34.4 34.4 34.1

Mean (SD) 34.5 ± 2.2 35.1 ± 0.7 34.4 ± 1.0

Left chest

0 32.9 32.6 32.8

60 27.2* 28.2* 29.1*

120 27.5* 28.4* 29.5*

Mean (SD) 27.9 ± 2.8 28.7 ± 3.1 29.7 ± 1.8†

Right upper arm

0 32.7 33.5 32.6

60 27.7* 29.0* 28.5*

120 27.2* 28.1* 27.4*

Mean (SD) 28.4 ± 2.0 29.6 ± 1.9 29.0 ± 1.7

Forearm

0 32.1 32.5 32.5

60 27.3* 27.6* 28.2*

120 26.2* 26.1* 26.9*

Mean (SD) 27.9 ± 2.3 28.1 ± 2.1 28.7 ± 2.0

Left hand

0 27.0 28.0 28.3

60 22.2* 22.6* 23.7*

120 21.3* 20.8* 22.6*

Mean (SD) 22.8 ± 3.2 22.9 ± 2.4 24.2 ± 3.3

Right thigh

0 32.3 33.2 33.0

60 29.9* 30.3* 30.3*

120 29.2* 29.9* 29.8*

Mean (SD) 30.1 ± 1.9 30.6 ± 1.7 30.6 ± 1.9

Left calf

0 32.1 31.9 32.1

60 31.9 30.3* 30.9*

120 30.9* 29.7* 29.8*

Mean (SD) 31.9 ± 1.2 30.6 ± 2.2 31.0 ± 1.9

54

Table 4.2. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level (SL) and at 4000 m before (UN) and after (PEX) acclimatisation on fingernail and toenail

temperature (°C).

Values are mean ± SD. * significant difference vs. 0, † significant difference vs. SL (P < 0.05).

4.4.3 Metabolic responses

Metabolic heat production was similar at rest in all trials during exposure to a thermo-neutral,

normoxic environment (F2, 18 = 0.038, P = 0.963, η2 = 0.004). As expected, M increased in all trials

during the CAT (F12, 108 = 12.071, P = 0.000, η2

= 0.528). However, compared to SL, M was less

after 20 minutes of CAT on UN and PEX (F2, 18 = 7.907, P = 0.003, η2

= 0.431) (Figure 4.4).

During UN, RER was higher than SL and PEX (F2, 18 = 6.501, P = 0.008, η2

= 0.327) (Table 4.3).

This may have been a direct result of the hypoxic ventilatory response during UN, however the

same RER reponse was not observed during PEX yet a similar pattern in ventilator response was.

During CAT, the percentage of kilocalories derived from carbohydrate oxidation, calculated using

RER values, was greater during UN compared to SL and PEX (F2, 18 = 9.025, P = 0.002, η2

= 0.416)

(Figure 4.5).

Fingernail Toenail

SL UN PEX SL UN PEX

0 23.2 ± 3.3 24.2 ± 3.4 24.3 ± 3.8 20.6 ± 1.2 21.0 ± 1.2 21.9 ± 1.0

60

20.3 ± 3.7* 20.3 ± 3.7* 20.7 ± 3.4*

17.8 ± 0.6* 17.5 ± 0.9*† 18.2 ± 1.4*

120 18.3 ± 1.4* 17.5 ± 1.1 * 18.2 ± 1.6* 16.9 ± 1.1* 15.2 ± 1.0*† 16.0 ± 0.8*

Mean (SD) 20.4 ± 3.5 20.5 ± 3.9 20.6 ± 3.6 18.1 ± 0.9 17.7 ± 0.9† 18.2 ± 0.9

55

Figure 4.4. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level ( ♦ ) and at 4000 m before ( ■ ) and after ( △ ) acclimatisation on metabolic heat production

(W∙m-2

). Values are mean ± SD. * significant difference vs 0 mins, † significant difference vs. SL

(P < 0.05).

Table 4.3. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level (SL) and at 4000 m before (UN) and after (PEX) acclimatisation on the respiratory exchange

ratio (RER).

RER (respiratory exchange ratio)

SL UN PEX

0 0.84± 0.14 0.76 ± 0.05 0.74 ± 0.03

60 0.91 ± 0.3 1.04 ± 0.13*# 0.87 ± 0.13

120 0.81 ± 0.11 1.05 ± 0.14*†# 0.85 ± 0.09

Mean 0.9 ± 0.2 1.00 ± 0.1 0.9 ± 0.1

Values are mean ± SD. * significant difference vs.0 mins, † significant difference vs. SL, #

significant difference vs. PEX (P < 0.05).

0

20

40

60

80

100

120

140

160

0 10 20 30 40 50 60 70 80 90 100 110 120

Me

tab

olic

He

at P

rod

uct

ion

(W

·m2)

Time (mins)

♦; *

■, △; *

†

56

Figure 4.5. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level ( ■ ) and at 4000 m before ( ■ ) and after ( ■ ) acclimatisation on carbohydrate and lipid

oxidation (%).Values are mean ± SD. † significant difference vs. SL, # significant difference vs.

PEX (P < 0.05).

4.4.4 Observed shivering activity and EMG

After 80 minutes, observed shivering activity was lower PEX compared to SL and UN (F2, 18 =

6.322, P = 0.008, η2

= 0.322) (Figure 4.6). After 110 minutes, maximum observed shivering

activity was reached in all trials. However, shivering intensity at this time was higher during SL and

UN (2 = Generalised but discontinuous shivering) compared to PEX (1 = Mild shivering bursts).

While not significant, EMG traces displayed lower shivering activity during PEX compared to SL

and UN, particularly toward the end (F2, 18 = 0.908, P = 0.421, η2

= 0.087) (Figure 4.7).

0

20

40

60

80

100

120

Carboyhdrate Oxidation (%) Lipid oxidation (%)

Pe

rce

nta

ge k

Cal

de

rive

d f

rom

car

bo

hyd

rate

an

d

lipid

(%

)

Tneut †#

†#

Carbohydrate Oxidation (%) Lipid Oxidation (%)

57

Figure 4.6. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level ( ■ ) and at 4000 m before (■ ) and after (■ ) acclimatisation on observed shivering activity.

Values are mean ± SD. * significant difference vs. 0 mins, † significant difference vs. SL, ¥

significant difference vs. UN (P < 0.05).

Figure 4.7. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level ( ♦ ) and at 4000 m before ( ■ ) and after ( △ ) acclimatisation on EMG activity of the

pectoralis major (µV). Values are mean ± SD.

0

0.5

1

1.5

2

2.5

3

3.5

0 10 20 30 40 50 60 70 80 90 100 110 120

Ob

serv

ed

Sh

ive

rin

g In

ten

sity

(0

: N

o S

hiv

eri

ng

- 3

: M

arke

d a

nd

Co

nti

nu

ou

s)

Time (mins)

■; †, ¥ *

Tneut

-200

0

200

400

600

800

1000

1200

1400

1600

0 10 20 30 40 50 60 70 80 90 100 110 120

Shiv

eri

ng

acti

vity

(µ

V)

Time (mins)

58

4.4.5 Thermal comfort and pain sensation

Thermal comfort was increased PEX compared with SL and UN (F1.284, 11.558 = 11.779, P = 0.004,

η2

= 0.542) (Figure 4.8). Perceived peripheral coldness was lower during PEX compared to SL and

UN (F2, 18 = 14.407, P = 0.000, η2

= 0.572) (Figure 4.9A). An interaction established that perceived

peripheral coldness depended on hypoxic acclimatisation (F24, 216 = 3.441, P = 0.000, η2

= 0.086).

Perceived central coldness was also lower during PEX compared to SL and UN (F2, 18 = 5.678, P =

0.012, η2

= 0.365) (Figure 4.9B). Similarly, an interaction suggested perceived central coldness was

also dependant on hypoxic acclimatisation (F24, 216 = 2.018, P = 0.005, η2

= 0.084). Perceived

coldness at the periphery was higher than perceived central coldness throughout all trials (P < 0.05).

Figure 4.8. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level ( ♦ ) and at 4000 m before ( ■ ) and after ( △ ) acclimatisation on thermal comfort (McGinnis’

thermal comfort scale). Values are mean ± SD. * significant difference vs. 0 mins, † significant

difference vs. SL (P < 0.05).

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50 60 70 80 90 100 110 120

The

rmal

Co

mfo

rt (

1:

So c

old

I am

he

lple

ss –

8:W

arm

b

ut

fair

ly c

om

fort

able

)

Time (mins)

△; †

59

Figure 4.9. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level ( ♦ ) and at 4000 m before ( ■ ) and after ( △ ) acclimatisation on perceived central coldness

(A) and Perceived peripheral coldness (B). Values are mean ± SD. * significant difference vs. 0

mins; † significant difference vs. SL, ¥ significant difference vs. UN (P < 0.05).

4.4.6 Heart rate and Arterial oxygen saturation

HR was higher UN compared to PEX during the initial 50 minutes (F2, 18 = 7.254, P = 0.005, η2

=

0.385) (Table 4.4). Arterial oxygen saturation was lower during UN compared to SL (F1.082, 9.734 =

23.517, P = 0.001, η2

= 0.694) (Table 4.4). Arterial oxygen saturation during PEX was not different

to SL or UN.

Tneut

-10

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90 100 110 120

Ce

ntr

al C

old

ne

ss (

0:

No

thin

g at

all-

50

: St

ron

g /

He

avy)

Time (mins)

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90 100 110 120

Pe

rip

he

ral C

old

ne

ss (

0:

No

thin

g at

all

- 5

0:

Stro

ng

/ H

eav

y)

Time (mins)

A. B.

#*†

A. Tneut

Time (mins)

Shiv

erin

g A

ctiv

ity

*†

*† *† *†

*† *†

*

△; †, ¥ *

△; ¥

△; †

60

Table 4.4. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level SL) and at 4000 m before (UN) and after (PEX) acclimatisation on heart rate (beats∙min-1

) and

arterial oxygen saturation (SaO2 %).

HR (beats∙min-1

) SaO2(%)

SL UN PEX

SL UN PEX

0 55 ± 9 60 ± 9# 54 ± 6

98 ± 2 85 ± 9# 89 ± 3

60 57 ± 11 56 ± 10 54 ± 9

97 ± 2 85 ± 7† 90 ± 4

120 59 ± 10 65 ± 10 59 ± 9

97 ± 2.6 86 ± 6† 90 ± 4

Mean 57 ± 11 60 ± 10 54 ± 9

97 ± 3 85 ± 9 91 ± 5

Values are mean ± SD. † significant difference vs. SL, # significant difference vs. PEX (P < 0.05).

4.4.7 Results summary

The key findings of these results demonstrate an unaltered core and mean skin temperature during

UN and PEX, compared with SL. However, metabolic heat production was significantly altered

during UN and remained so PEX. RER and substrate oxidation were altered during UN as was

shivering activity, which demonstrated a reduced capacity for non-shivering thermogenesis.

Thermal comfort was increased PEX compared with SL and UN. Heart rate was higher UN

compared with PEX during the initial 50 minutes. Arterial oxygen saturation was lower during UN

compared with SL.

61

4.5 Discussion

The aim of this study was to examine the acute and chronic effects of hypoxia upon

thermoregulation in mild cold. As anticipated, un-acclimatised men exposed to hypoxia in the cold

demonstrated an impaired thermoregulatory and metabolic response compared with cold exposure

at sea level. This was demonstrated by a reduced contribution of NST via an increased catabolism

of CHO that initiated an earlier onset and increased intensity of shivering activity. Despite this, cold

exposure in hypoxia regardless of acclimatisation did not impair core or mean skin temperature

compared to cold alone. Following prolonged hypoxic exposure however, perceptions of thermal

comfort reflected an improved cold tolerance and impaired thermal sensitivity that might lead to

poor behavioural thermoregulation and greater risk of cold injury.

Contradictory to early reports (Bullard, 1961; Cipriano and Goldman, 1975; Kottke et al. 1948), un-

acclimatised exposure to hypoxia in the cold did not increase the rate of heat loss from the core or

periphery. Core temperature however, has been reported elsewhere as unaltered during both

normobaric and hypobaric hypoxia in the cold (Blatteis and Lutherer, 1976; Brown et al. 1952;

Robinson and Haymes, 1990). On the contrary, when individuals were un-acclimatised, reduced

temperatures at the toenail bed were observed. Exposure to acute hypoxia in the cold has been

associated with a reduction in CIVD at the extremities (Mathew et al. 1977; Takeoka et al. 1993)

and an increased risk of local cold injury at altitude (Golja et al. 2004). Following the 18-day

mountaineering expedition at altitude, core and mean skin temperatures during subsequent cold

exposure in hypoxia were also unaltered compared with cold alone. Local temperature at the

forehead and left chest however, were higher during acclimatised exposure to hypoxia compared to

normoxia. Future studies should look to measure skin blood flow at these local areas to see if

warming is repeated. Potentially, warmer skin temperature at these sites is reflecting an adaptation

to hypoxia following a prolonged stay.

62

Thermal comfort and perception provides the basis for the initiation of behavioural

thermoregulation (Golja et al. 2004). During unacclimatised hypoxic-cold exposure in the present

study, men rated their thermal comfort the same as in cold alone. This has been previously reported

(Golja et al. 2005). Core and skin temperature sensors transform thermal energy into neural coded

information that give a sensation of either cold or warmth and a perception of pleasure or

displeasure (Cabanic, 1969, 1981; Hensel 1976). Given that core and mean skin temperatures were

the same in both trials it is likely the amount of thermal energy was also the same which suggests

why no differences in thermal comfort occurred. This contradicts previous work where an inspired

air content of 10% oxygen decreased cold sensation in humans (Golja et al. 2004). However, since

it has been suggested oxygen limitations may only begin to implement thermoregulatory

impairments when inspired oxygen is less than 11% (Gautier et al. 1997), the modest level of

hypoxia that participants were exposed to in the present study may have induced milder

impairments. It should be noted however, that arterial oxygen saturation levels varied substantially

between participants during unacclimatised hypoxic exposure and conclusions from this study

therefore should be generalised to wider populations with caution. Nonetheless, despite variations

no participant rated themselves to be suffering AMS symptoms as highlighted by the Lake Louise

scale.

Post-expedition, a decrease in cold sensation at the core and periphery was demonstrated. This

suggests prolonged exposure to altitude stressors during mountaineering may affect core and skin

temperature sensors so that neural coded information is impeded and nerve conduction impaired

(Golja et al. 2004; Malanda et al. 2008). When oxygen supply diminishes below the metabolic

demands of the nerve tissue, the energy requiring cell functions are reduced and membrane

depolarisation causes complete loss of neural cell function (Astrup, 1982; Golja et al. 2004). Neural

impairment by prolonged hypoxic exposure may affect both the central and peripheral nervous

system. Acclimatised individuals at altitude may often feel warmer than their core temperature

63

would suggest. As a result, behavioural thermoregulation may be neglected and as altitude

continues to increase and ambient temperatures reduce, impaired thermal sensation may increase

the likelihood of cold injury (e.g. hypothermia and frostbite).

Metabolic heat production was reduced during the initial hypoxia and cold exposure, which was

similar to earlier reports (Blatteis and Lutherer, 1976; Robinson and Haymes, 1990). A reduction in

heat production coupled with an earlier onset and more intense shivering activity supports that

hypoxia may suppress NST (Blatteis and Lutherer, 1976; Bullard, 1961; Gautier, 1996; Robinson

and Haymes, 1990). Given that BAT is the primary energy source for NST and has been observed

to be mainly activated during cold exposure (van Marken Lichtenbelt et al. 2009), suggests that

hypoxia may indeed restrict the activity of BAT in the cold leading to an increased likelihood of a

reduction in body temperature. This is supported by previous work which suggests the hypoxic-

induced suppression of NST by an inhibition of the aerobic catabolism of lipid stores, when un-

acclimatised, may occur through an increased hormonal response to hypoxic stress that decreases

the lipolytic response of adipocytes and thus lowers lipid mobilisation (de Glisezinski et al. 1999;

Masoro, 1966; Robinson and Haymes, 1990).

Carbohydrate oxidation increased by almost 100% when un-acclimatised men were exposed to

hypoxia and cold compared with cold alone. However, this increase was reduced by 50% post-

expedition. Increased carbohydrate oxidation occurs to fuel intense shivering thermogenesis

(Martineau and Jacobs, 1988) which may explain how the body successfully maintained core and

mean skin temperature given the reduction of NST. Increased shivering activity coupled with an

increased rate of carbohydrate oxidation suggests a physiological response similar to moderate

exercise (Roberts et al. 1996a). While muscle glycogen and blood glucose contribute equally to

carbohydrate energy production, sources become depleted quickly compared to fatty acids and

glycerol (Coyle, 1995). Therefore, un-acclimatised men with a diminished ability to oxidise lipids

in hypoxic and cold environments risk muscle glycogen depletion, earlier onset of fatigue and

64

ultimately cold injury. Comparable with un-acclimatised exposure to cold and hypoxia, the

metabolic response remained suppressed post-expedition. Nonetheless, shivering activity was

reduced and was also less than normoxia. This finding supports that NST recovery may occur

following a stay at altitude which may result from a small recovery in fuel selection.

Present results also suggest there may be an increase in thermal comfort following a stay at high

altitude. Reduced cold sensitivity and increased thermal comfort accompanying acclimatisation may

be related to the observed reductions in shivering activity post-expedition. Given peripheral thermo-

receptors at the skin control the onset of shivering it would appear these are not readily stimulated

upon exposure to mild cold in acclimatised individuals. In conclusion, following an 18 day

mountaineering expedition, a decrease in shivering despite no changes in core or mean skin

temperature is consistent with a greater reliance on NST. The alterations observed post-expedition

in thermal comfort may suggest a greater thermal tolerance and poorer thermal sensation that may

increase susceptibility to cold injury.

65

CHAPTER FIVE

Hypoxia and cold effects on Mucosal Immunity before and after an altitude stay

5.1 Abstract

The purpose of this study was to examine the effect of hypoxia and cold on mucosal immunity. Ten

males completed four different trials. Three 2 hour CATs were performed in an environmental

chamber (CAT 15°C, RH 44%): 1. sea-level (n = 15) (SL: FIO2 = 0.209); 2. un-acclimatized in

normobaric hypoxia (n = 15) (UN: FIO2 = 0.125, ~4000m) and 3. post expedition in normobaric

hypoxia (n = 10) (PEX: FIO2 = 0.125, ~4000m). Participants also completed a thermo-neutral

control trial (n = 10) (TC: FIO2 = 0.209, 19.5°C and 45% RH). Un-stimulated whole saliva samples

were collected before, at the end of CAT, immediately after, and one-hour after the CAT. On TC,

saliva was collected at the same time of day as CAT trials. Cold exposure caused a progressive

decline in Trec (~0.4°C) throughout all trials (P = 0.001) which was not further altered by altitude (P

= 0.097). Hypoxia also caused a significant reduction in oxygen saturation during UN (SL: 98 ± 2,

UN: 86 ± 6 PEX: 91 ± 5 %; P = 0.000). Saliva flow rate (µl·min-1

) was decreased by hypoxia in the

cold during UN compared with SL and TC (P = 0.047; P = 0.022) respectively. No differences were

observed in s-IgA concentration (µg·ml-1

) (P = 0.642) or s-IgA secretion rate (µg·min-1

) (P =

0.335). Cold exposure however, increased α-amylase concentration compared with TC (P = 0.003).

In combination, a cold-induced increase in α-amylase concentration and a hypoxic-induced

reduction in saliva flow rate might increase the risk of infection for un-acclimatised individuals at

altitude since saliva is important for oral washing.

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5.2 Introduction

Given unacclimatised exposure to cold and hypoxia denotes changes in thermoregulatory

homeostasis (Chapter 4), it would be beneficial to understand how these correspond to immune

function in the same conditions. This knowledge could better inform individuals regarding health

risks involved when traveling to cold, hypoxic environments. A study investigating

thermoregulation and immune function using controlled methodology has not been reported.

Sympathoadrenal responses associated with acute and chronic high altitude exposure can influence

immune function which may increase the risk of illness and infection while individuals are a far

distance from appropriate medical resources (Meehan et al. 1988; Mazzeo et al. 1994; Mazzeo et al.

1995; Mazzeo et al. 2001). For example, early research has found a higher prevalence of pneumonia

among military troops stationed at high altitude (Singh et al. 1977). However, findings have limited

application to new and un-acclimatised arrivals at altitude. Furthermore, individuals visiting high

altitudes are often exposed to multiple stressors, including cold, dehydration, novel infectious

agents and poor hygiene. It is incorrect to assume an increase in infection is exclusively due to

hypoxia-induced immune suppression. Whether the risk of illness or infection is exacerbated in un-

acclimatised expeditioners upon arrival to hypoxic and cold environments remains unknown.

Furthermore, it has not been clarified whether such potential detriments to mucosal immunity are

reduced following a period of altitude acclimatisation. Given the possibility of low oxygen

conditions during space flight, this information may also have significant implications for

spaceflight personnel during long term missions (Cogoli, 1981; Taylor and Dardano, 1983).

Cold exposure is associated with an increased incidence of bronchorrhea, sinusitis, and upper

respiratory tract infections (URTI) (Clothier, 1974; Giesbrecht, 1995; Castellani et al. 2002; Lavoy

et al. 2011). Much research to date however, has examined individuals undertaking the additional

stress of physical activity which likely exacerbates the immune response to cold (Castellani et al.

2002). Since URTIs are the main cause of illness and missed practise in elite cross country skiers

67

(Berglund and Hemmingson, 1990), cold-induced decrements in immune-surveillance may be a

problem for individuals at altitude. The additional stressor of cold in hypoxia-exposed humans may

evoke a similar suppression on the mucosal immune system as that demonstrated with physical

activity in the cold.

Short term hypoxia is reported to induce similar immunosuppression upon the mobilisation of T-

cells and natural killer cells (Klokker et al. 1993; Klokker et al. 1995) as that demonstrated during

surgery (Lennard et al. 1985) and exercise (Pedersen et al. 1990). The regulation of cytokine

production and release has also been shown to be reduced in hypoxia (Pedersen and Steensberg,

2002). On the contrary, nasal mucosal immunity is suggested to be unchanged by hypoxia and any

reduced secretory IgA and lysozyme levels may be caused by the combined stresses of cold,

isolation and reduced humidity (Meehan et al. 1988; Muchmore et al. 1981). While cold exposure is

often unavoidable at high altitude, the effect of hypoxia itself upon the normal mucosal immune

response to cold has received little attention. Salivary IgA is often the mucosal secretion of choice

for studies of the human mucosal immune system due to the ease and standardisation of collections.

It is well established to characterise the effects of many stressors, for this reason however, it may

not always reflect compencies in other aspects of immune defence and therefore it is of benefit to

assess additional mucosal immune parameters. Secretion of amylase from saliva glands is

controlled by autonomic nervous signals and substantial literature reveals that salivary amylase is

correlated to sympathetic activity under conditions of stress. Specifically, α-amylase increased

under a variety of physically (i.e. exposure to heat or cold) and psychologically (exams) stressful

condtions (Chatterton et al. 1996). Furthermore, s-IgA acts with α-amylase to provide the first line

of defence against pathogens and antigens at the mucosa. A study to determine the effect of acute

and chronic hypoxia on s-IgA and α-amylase responses in the cold compared to cold alone will

likely clarify any increased risk of infection upon and following ascent to high altitude.

68

The aim of the present study was to examine the effect of hypoxia on saliva responses to the cold

before and after an 18 day altitude expedition. This was achieved by comparing saliva responses in

thermo-neutral, mild cold, and mild cold with hypoxia. To determine the effect of prolonged

exposure to a multi-stressor, mountainous environment, typically experienced by mountaineers, the

same saliva responses were compared in the same mild cold with hypoxia. Given fluctuations in

catecholamines and cortisol activate the SNS and effect s-IgA and amylase responses; it was

unnecessary to measure these stress hormones if changes in mucosal immunity occurred. It was

hypothesised that un-acclimatised exposure to hypoxia would evoke greater detrimental effects on

mucosal immunity in the cold compared with normoxia. This might include an increase in α-

amylase concentration and a reduction in s-IgA secretion rate. Following an altitude stay it was

hypothesised that typical s-IgA and α-amylase responses to the cold would be resumed regardless of

hypoxia.

69

5.3 Method

5.3.1 Participants

Fifteen healthy males (mean ± SD: age, 22 ± 3 years; height, 180 ± 6 cm; body mass, 66 ± 12 kg

and body fat, 12 ± 6 %) were recruited from an Alpine expedition. Due to unexpected

circumstances only ten participants were able to complete PEX and TC. Participants gave written

consent and medical history before the study which received local Ethics Committee approval.

5.3.2 Preliminary measurements

Before each experimental trial participants arrived at the laboratory after an overnight fast having

consumed no food, caffeine or alcohol within 10 h. Participants ingested water equal to at least 35

ml·kg-1

body mass the day prior to each trial. After voiding bladder and bowels, nude body mass

and height were measured. Daily energy requirements were determined by body composition and

calculated from a mean of daily metabolic rate, hourly basal metabolic rate, eight hours of sleeping,

eight hours of occupational activities (e.g. moving, sitting and standing) and eight hours of residual

time (WHO, 2004). Energy requirements were provided and given as standardised meals (breakfast,

lunch and dinner) in the 24 h period prior to each experimental trial.

5.3.3 Experimental Trials

Participants completed three experimental trials in a normobaric, temperature and humidity

controlled chamber (Dry bulb temperature of the chamber remained at 15°C with a relative

humidity (RH) 40% and 0.2 m.s-1

wind velocity; Delta Environmental Systems, Chester, UK) over

a 12 week period (Chapter 4). Trials were 1. sea-level (SL: FIO2 = 0.209); 2. un-acclimatised in

normobaric hypoxia (UN: FIO2 = 0.125, ~4000m); and 3. post-expedition (n=10) in normobaric

hypoxia (PEX: FIO2 = 0.125, ~4000m). To avoid an order effect SL and UN were performed before

70

the expedition in half of the participants and 2 months after the expedition in the remainder. Ten of

the fifteen participants also completed a thermo-neutral control trial (TC) fully clothed in ambient

conditions (19.5°C and 45% RH) to account for the diurnal variation in saliva responses.

Participants completed each trial at the same time of day and consumed no food, caffeine or alcohol

within 4 h of each trial. Throughout UN and PEX, inspired oxygen fraction (FIO2) was equal to

0.125 to simulate an altitude of approximately 4000 m. Following pre-trial measures and after 10

minutes supine rest in normothermia (ambient temperature: 21.3 ± 1.1°C; relative humidity: 52 ±

5.4%), baseline measures of Trec and SaO2% were recorded. Wearing shorts only, participants then

entered the chamber and rested in a supine position on roll mats situated upon the floor for 120

minutes. Early removal from the chamber occurred if: 1. core temperature reduced to 36°C or fell

1.5°C below baseline, 2. Lake Louise scores went above 1 (UN and PEX only) or 3. participants

chose to withdraw. Upon completion participants were re-warmed and monitored until core

temperature was within 0.5°C of baseline.

5.3.4 Saliva collection and analysis

Un-stimulated whole saliva samples were collected using pre-weighed universal tubes (Chapter 3).

Saliva samples were collected while the participant sat quietly in the laboratory (1: before CAT, 2:

at the end of CAT – inside chamber conditions, 3: immediately after CAT – outside chamber (21.3

± 1.1°C and rh: 52 ± 5.4%), 4: one-hour after CAT (21.3 ± 1.1°C and rh: 52 ± 5.4%). Saliva volume

was estimated by weighing the universal container immediately after collection to the nearest mg.

From this, saliva flow rate was determined by dividing the volume of saliva by the collection time.

Saliva was aspirated into Eppendorfs and stored at -40°C for further analysis. After thawing s-IgA

concentration was determined by ELISA (Salimetrics Europe Ltd, Suffolk, UK) using IgA

71

monomer from human serum as standard. The intra-assay CV was 1.4%. s-IgA secretion rate was

calculated by multiplying the saliva flow rate by s-IgA concentration.

Alpha amylase concentration was determined by ELISA (Salimetrics Europe Ltd, Suffolk, UK)

using a chromagenic substrate, 2-chloro-p-nitrophenol linked with maltotriose. The intra-assay CV

was 2.5%.

5.3.5 Statistical Analysis

A sample size of ten participants was estimated using previous data examining the effects of

environmental stress on immune indices (Costa et al. 2010; Laing et al. 2008; Oliver et al. 2007).

One way fully repeated measures ANOVA were performed on pre-experimental body composition

measures. Two-way fully repeated measures ANOVA were performed on saliva parameters

(Chapter 3).

72

5.4 Results

5.4.1 Thermoregulatory (Trec and Tsk) and metabolic responses

Core and mean skin temperature values were analysed using mean scores for n = 10 and n = 15 on

SL and UN. Given n = 10 completed all four trials and significance scores were not different for the

two trials completed by n = 15 and n = 10, n = 10 was used in order to be able to compare all trials

(SL, UN, PEX and TC). Core and mean skin temperatures were lower after cold air tests than at

baseline (Trec, F (12, 168) = 8.955, P = 0.000, η2 = 0.610; Tsk, F (12, 168) = 227.041, P = 0.000, η

2 =

0.058) (Chapter 4). At rest M was not different between either trial (SL: 49 ± 7, UN: 49 ± 11;

PEX: 50 ± 10 W·m2; F (1, 14) = 0.033, P = 0.859, η

2 = 0.997). However, compared with SL, the cold-

induced increase in M was reduced with hypoxic exposure (Table 5.1: F (1, 14) = 21.188, P = 0.000,

η2 = 0.398). RER was higher on UN (Table 5.1: F (1, 14) = 19.478, P = 0.001, η

2 = 0.418).

Table 5.1. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level SL) and at 4000 m before (UN) and after (PEX) acclimatisation on rectal temperature, mean

weighted skin temperature, metabolic heat production and respiratory exchange ratio.

SL UN PEX

Trec at 120 min CAT (°C) 36.9 ± 0.3 36.8 ± 0.3 36.7 ± 0.2

Mean weighted Tsk at 120 min CAT (°C) 29.3 ± 1.0 29.5 ± 1.1 29.8 ± 0.9

M at 120 min CAT (W·m2) 118 ± 44 69 ± 13

† 83 ± 20

†

RER at 120 min CAT 0.81 ± 0.11 1.05 ± 0.14† 0.85 ± 0.09

Values are mean ± SD. † significant difference vs. SL (P < 0.05).

5.4.2 Heart rate and arterial oxygen saturation

Heart rate was higher in UN compared to PEX but was not different to SL (SL: 57 ± 11, UN: 60 ±

910, PEX: 54 ± 9 beats·min-1

; F2, 18 = 7.254, P = 0.005, η2

= 0.385). Arterial oxygen saturation

however, was lower during UN compared to SL but was unchanged during PEX, albeit values on

73

PEX were still low (SL: 98 ± 2, UN: 86 ± 6 PEX: 91 ± 5 %; F (1, 14) = 71.704, P = 0.000, η2 =

0.163).

5.4.3 Saliva IgA and amylase responses

A decline in s-IgA concentration was demonstrated following baseline measures (Figure 5.1: F (3,

42) = 9.540, P = 0.000, η2 = 0.595). No interactions were observed for s-IgA concentration (F (3, 42) =

0.564, P = 0.642, η2 = 0.961) or secretion rate (F (3, 42) = 1.164, P = 0.335, η

2 = 0.923). However, an

interaction was found where saliva flow rate increased from baseline throughout cold exposure

during SL but was suppressed with hypoxia in UN (Figure 5.1: F (3, 42) = 2.873, P = 0.047, η2 =

0.118). There were no observed differences in any saliva parameter between UN and PEX or SL

and PEX. Saliva flow rate was less during SL and UN compared with TC but PEX was not (Figure

5.1: F (3, 24) = 3.859, P = 0.022, η2 = 0.325).

Hypoxia and cold exposure conferred no further increases in α-amylase concentration compared

with cold only (Figure 5.2: F (2, 18) = 0.490, P = 0.621, η2 = 0.052). Compared with TC however,

cold exposure, with or without hypoxia, increased amylase concentration almost three-fold by the

end of the CAT (Figure 5.2: F (3, 24) = 5.957, P = 0.003, η2 = 0.427). Nonetheless, α-amylase

secretion rate was not different between trials (Figure 5.2: F (3, 18) = 2.320, P = 0.110, η2 = 0.278).

5.4.4 Results summary

Core and mean skin temperatures were lower after CATs. Compared with SL, the cold-induced

increase in M was reduced with hypoxic exposure. Saliva flow rate increased from baseline

throughout cold exposure during SL but was suppressed in UN. Hypoxia and cold exposure caused

no further increases in α-amylase concentration compared with cold only. Compared with TC

however, cold exposure, with or without hypoxia, increased amylase concentration almost three-

fold by the end of the CAT. For hydration data see chapter 4.

74

Figure 5.1. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level ( ♦ ), at 4000 m before ( ■ ) and after (▲ ) acclimatisation, and a thermo-neutral control

(19.5°C) ( ● ) on saliva flow rate (µl·min-1

) (A), s-IgA concentration (µg·ml-1

) (B) and s-IgA

secretion rate (µg·min-1

) (C). Values are mean ± SD. * significant difference vs Baseline, # vs. TC

(P < 0.05).

♦, ■; *

♦, ■; #

A B C A

B

C

Baseline CAT end Immediately after CAT 1 hour after CAT

75

Figure 5.2. The effect of 120 min cold air test (CAT; 15°C) in un-acclimatised participants at sea

level ( ♦ ), at 4000 m before ( ■ ) and after (▲ ) acclimatisation, and a thermo-neutral control ( ● )

on α-amylase concentration (µg·ml-1

) (A) and secretion rate (µg·min-1

) (B). Values are mean ± SD.

* significant difference vs Baseline, # vs. TC (P < 0.05).

A B C

76

5.5 Discussion

The aim of the present study was to examine the effect of hypoxia on saliva responses to the cold

before and after an 18 day altitude expedition. Due to the potential for greater sympathetic nervous

system activity, vasoconstriction of blood vessels at the salivary glands and reduced saliva secretion

(Bishop, 2006), it was hypothesised that hypoxia in the cold, prior to acclimatisation, would evoke

an increase in α-amylase concentration and reductions in saliva flow rate, s-IgA concentration and

secretion rate of greater magnitude than when individuals were exposed to cold only or post-

expedition. In direct contrast to the hypothesis, s-IgA concentration and secretion rate, regardless of

acclimatisation, were not affected by cold or hypoxia and cold. Nonetheless, α-amylase

concentration was increased during cold exposure but was not exacerbated by hypoxia. When un-

acclimatised however, saliva flow rate was reduced in cold and hypoxia compared with normoxia.

Since the effect of acute hypoxia on leukocytes resembles the same effect as exercise, it has been

suggested that exercise and hypoxia-induced changes in leukocyte subpopulations might be

mediated by similar mechanisms involving neuroendocrinological factors (Pedersen and

Steensberg, 2002). Although physiological mechanisms underlying the decline in s-IgA responses

remain unclear, it is likely that both neural and endocrine factors also influence this mucosal

immune response (Pedersen and Steensberg, 2002). Given arterial oxygen saturation was reduced

during un-acclimatised hypoxic exposure in the present study, and remained low following

acclimatisation, it is not unreasonable to suggest both the neural and endocrine systems were

compensating to maintain homeostasis (Mazzeo, 2005), thus explaining the difference in saliva flow

rate compared with normoxia. Temporal skin temperature was higher during hypoxic exposure

(Chapter 4) suggesting cerebral blood flow may have been increased. This may have been a

subsequent effect of increased neural and endocrine activity in an environment of reduced oxygen.

Future research should look to examine cerebral blood flow in hypoxia to help further understand

mechanisms to maintain homeostasis.

77

The absence of hypoxia-induced s-IgA and α-amylase alterations to cold suggests the mucosal

immune system is robust to a combination of environmental stressors, and as such common URTI

complaints are not likely to be related to the mucosal system upon arrival to high altitude or

following a prolonged stay. Nonetheless, given α-amylase concentration and secretion rate were

affected by cold, regardless of hypoxia, and saliva flow rate was only affected by hypoxia when un-

acclimatised, it is possible there is an increased risk of URTI for new arrivals at altitude if

temperatures are particularly low.

A study to examine the effects of a live high – train low (LHTL) training camp on mucosal

immunity reported similar s-IgA changes from baseline after the first 12 days of training in both the

control (i.e. lived and trained at 1200 m) and LHTL (groups lived at 2500 m or 3000 m and trained

at 1200 m) groups (Tiollier et al. 2005). However, after the last 6-day phase (when living was at an

altitude of 3500 m) s-IgA concentration decreased more in the LHTL group compared with the

2500 and 3000 m phases. It has been suggested that an altitude of 3500 m corresponds to a

threshold that physiological changes intended to tolerate the drop in the partial pressure of oxygen

fail to fully compensate the effect of hypoxia (Colin et al. 1999). Thus, it was speculated that at or

above this altitude the adverse effect of hypoxia on s-IgA responses is more substantial (Tiollier et

al. 2005). In the present study, participants were exposed to an altitude equal to 4000 m while at

rest and displayed no alterations in s-IgA regardless of acclimatisation status. Therefore, it is more

likely the observed changes in s-IgA during the last phase of an 18 day LHTL training camp were

not due to the level of hypoxia per se, or as a result of chronic exposure, but more likely a

cumulative effect of intense physical training at altitude. Had there been an exercise element during

cold air tests of the present study, participants may have demonstrated greater changes in s-IgA and

α-amylase. Further, it might have been clearer to see whether acclimatisation reduced such changes.

Additionally, the normobaric nature of the altitude exposures discussed here does not fully replicate

typical high altitude conditions. It is plausible to suggest that if barometric pressure was also

78

reduced to reflect the real value coinciding with that level of altitude (i.e. 661 mmHg at 4000 m),

the impact on homeostasis and subsequent mucosal immune status may be greater during cold

exposure.

Given that salivary secretion is under neural control (Chicharro et al. 1998) and chronic hypoxia has

been shown to cause marked activation of the sympathetic nervous system (Chicharro et al. 1998;

Calbet, 2003; Zaccaria et al. 2004; Tiollier et al. 2005), this provides the physiological basis for a

potential involvement of neural factors in the s-IgA changes related to hypoxia. Nonetheless, since

mucosal responses to cold were unchanged in hypoxia compared with normoxia it is concluded that

altitude exposure while at rest, before and following an altitude stay, does not cause disruption to

either sympathetic nervous system activity (Mazzeo et al. 2003) or alpha-adrenergic mechanisms

(Ring et al. 2000). Secondly, the reduction in arterial oxygen saturation accompanying exposure to

acute hypoxia unlikely evokes a physiological or metabolic stress great enough to disrupt mucosal

immune responses to cold at rest. On the contrary, in combination, a cold-induced increase in α-

amylase concentration and a hypoxic-induced reduction in saliva flow rate might increase the risk

of infection for illness-prone, un-acclimatised individuals at higher altitudes (e.g. > 4500m) since

saliva is important for oral washing. With regard to the number of mucosal parameters available for

the assessment of potentially stressful situations, future studies would do well to analyse a wider

variety of such parameters in order to provide clarity and help build a framework of likely mucosal

immune responses in extreme environments (i.e. cold and hypoxia).

79

CHAPTER SIX

Practical Field Methods for the Pre-hospital Management of Hypothermia: Shivering Cold

Casualties

6.1 Abstract

The aim of this study was to examine thermoregulatory responses of shivering men to four re-

warming treatments. Seven males completed five randomised trials. These included a thermo-

neutral control trial (TC) and four cold trials. On each cold trial, participants were cooled to 36°C

core temperature. They then completed a 3-hour cold air test (CAT, 0°C) in one of four field

methods; 1. Single layer polythene survival bag (PB), 2. PB with 70°C hot drink in insulated

contatiner (PB+HD), 3. triple-layered metallised Blizzard survival bag with cells to trap and reflect

heat (BB), and 4. BB with chemical heat pads (BB+HP). Core and mean skin temperature,

metabolic heat production and thermal comfort were assessed. Prior to CAT, time to 36°C was not

different (P = 0.50). Compared with PB and PB+HD, skin temperature was greater (PB 25 ± 1,

PB+HD 25 ± 1, BB 27 ± 2, BB+HP 28 ± 2, TC 32 ± 1 °C, P < 0.01) and metabolic heat production

lower during BB and BB+HP (PB 133 ± 73, PB+HD 149 ± 74, BB 112 ± 73, BB+HP 96 ± 62, TC

57 ± 16 W∙m2, P < 0.01). Thermal comfort was higher in BB+HP (cold) compared with PB+HD

(very cold) (P < 0.05). Despite cold exposure, all methods supported re-warming to resting core

temperatures in shivering casualties. However, less metabolic heat production was required to

promote core temperature in triple-layered metallized survival bags compared with polythene

survival bags. Hot drinks had no thermoregulatory or thermal comfort benefit.

80

6.2 Introduction

It is known that exposure to cold with hypoxia may induce greater health risks with regard to

thermoregulatory homeostasis (Chapter 4). However, hypoxia aside, it is not clear whether these

changes would be more severe with harsher conditions that induce mild hypothermia, and whether

they can be treated appropriately with simple cold protection methods available for use in the field.

Accidental hypothermia affects approximately 10% of casualties reported in mountainous

environments and is a significant contributor to fatalities (Sallis and Chassay, 1999; Sharp, 2007).

Although mortality rates are relatively low with severe non-trauma related hypothermia (<28°C),

they rise alarmingly with traumatic injury where mortality is 40, 69 and 100% at 34, 33 and 32°C,

respectively (Moss, 1986; Jurkovich, 1987). Trauma is a frequent medical problem observed in

mountainous environments, accounting for approximately 40% of all emergency call outs and 80%

of all rescues (Hearns, 2003). Rescue times for casualties depend on global location and weather

conditions. Yet even where distances are relatively short between emergency services and a

casualty (e.g. Scottish Highlands) the reported times for evacuation are 2.25 hours by helicopter and

approximately 3.5 hours when individuals are evacuated by others means (e.g. on foot) (Crocket,

1995; Hindsholm et al. 1992). Simple methods that prevent heat loss and promote re-warming that

casualties or first-responders can administer instantly whilst they wait for evacuation will likely

reduce hypothermia related fatalities.

Vapour proof (e.g. polythene) survival bags and metalized plastic sheeting are produced and carried

for emergency use in cold and mountainous environments. These single layer products are also

associated with lower shivering and higher core temperatures in anesthetized patients undergoing

surgery (Buggy and Hughes, 1994; Allen et al. 2010). Contradictory to investigations with human

subjects, where results showed single-layered devices to provide similar thermal protection as

multi-layered devices (Appendix I), an in vitro study where cooling times of pre-heated fluid bags

were compared between different field methods, a multi-layered survival bag (Blizzard Survival™)

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was shown to be superior at preventing heat loss from fluid filled bags compared with a polythene

survival bag, single layer metalized plastic sheeting or wool blankets (Allen et al. 2010). Further, a

combination of the multi-layered metalized sheeting survival bag (Blizzard Reflexcell™) with

chemical heat pads was shown to be superior to all other methods tested (Allen et al. 2010). Given

the limitations of a fluid filled bag model to simulate the complex thermoregulatory control of

humans, in vivo studies are required to confirm the beneficial effects of a light-weight multi-layer

metalized sheeting survival bag combined with chemical heat pads.

In the field sources of heat are limited to exercise, body-to-body contact, portable warming devices

such as the charcoal burning ‘Heat Pac’, heat pads and the ingestion of warm drinks. Exercise has

been shown to re-warm mildly cold casualties more quickly than shivering alone (Giesbrecht et al.

1987); however, it has obvious limited use for those forced to remain sedentary because of injury,

unconscious state or poor weather. The administration of hot drinks is recommended practice in

shivering cold casualties by the International Commission for Mountain Emergency Medicine

(Durrer et al. 1998); however, to the best of the author’s knowledge, no study has investigated the

efficacy of this practice. Studies investigating the effect of cold beverages indicate core temperature

may be lowered by approximately 0.7°C with the ingestion of one litre of cold fluid (4-7°C) (Imms

& Lighten, 1989; Lee et al. 2008). It is therefore hypothesized that the ingestion of a similar

volume of fluid at 70°C could raise core temperature at least transiently.

Numerous studies have investigated re-warming efficacy of external heat application with results

varying dependent on the amount of heat delivered and the surface area to which the heat is applied

(Daanen et al. 1992; Giesbrecht et al. 1994). In mildly hypothermic casualties capable of normal

shivering, externally applied heat sources (i.e. body-to-body contact and ‘Heat Pac’) have been

shown to be either no better than shivering alone or detrimental to re-warming as they decrease

shivering heat production (Giesbrecht et al. 1987, Giesbrecht et al. 1994). Studies examining these

field methods have completed experiments in thermo-neutral conditions over short periods (<2

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hours) as opposed to longer exposures in the cold which casualties typically experience awaiting

rescue. It is plausible that in colder conditions, with modest heat sources not applied directly to the

skin, a survival bag containing chemical heat pads (e.g. Blizzard HeatTM

) may confer a significant

advantage for thermoregulation compared with polythene survival bags.

The aim of this investigation was to examine the effectiveness of four practical field methods for

the treatment of cold casualties with a normal shivering response. A secondary aim was to examine

the effect of each field method on long-term energy expenditure and thermal comfort.To simulate

real-life awaiting-rescue events these methods were studied in a cold environment (0°C) following

the reduction of core temperature with cold water immersion to 36°C. It was hypothesised that the

core re-warming rate (°C/h) would be greatest in the Blizzard Heat bag with the chemical heat pads,

followed by the Blizzard survival and polythene survival bag with hot drink. Polythene survival bag

alone was hypothesised to be the least effective method of re-warming.

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6.3 Method

6.3.1 Participants

Seven healthy males (mean ± SD: age, 21.4 ± 2.6 years; height, 177.8 ± 5.1 cm; nude body mass,

70.5 ± 5.2 kg; body surface area, 1.87 ± 0.10 m2; body fat, 9.9 ± 3.0 %) volunteered to participate in

this study which received local Ethics Committee approval. Prior to commencing trials participants

completed weekly medical reports (Appendix H) to ensure the absence of illness prior to and

during the experiemental period and informed written consent.

6.3.2 Study design

Separated by 7 days, participants completed five randomised experimental trials (Research

Randomiser; www.randomizer.org). The field re-warming interventions were a polythene bag (PB)

(Giesbrecht et al. 1987), a polythene bag with a hot drink (PB+HD), Blizzard survival bag (BB) and

Blizzard survival heat bag (BB+HP). The fifth trial was a thermo-neutral control (TC) where

participants remained seated in an ambient temperature 20.2 ± 1.7°C.

6.3.3 Experimental procedures

The day prior to each experimental trial participants ingested water equal to 35 ml·kg-1

body mass

and the same meals. After an overnight fast and having consumed no caffeine or alcohol within 10

hours participants arrived to the laboratory, euhydrated at 0800 hours. After voiding bladder and

bowels anthropometric measures of height and body mass were obtained. Body composition was

also assessed (Chapter 3).

Following pre-trial measures, participants began a 30 minute seated rest in a thermo-neutral (TN)

environment (ambient temperature: 19.2 ± 1.1°C; relative humidity (RH): 41 ± 6%). Core

temperature (Trec) was measured continuously and recorded every 5 minutes. Metabolic heat

production (M) was assessed every 10 minutes and calculated via indirect calorimetry methods.

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Thermal comfort (Hollies and Goldman, 1977) and pain sensation (Chen et al. 1998) were also

recorded every 5 minutes. During TC the initial 30 minute rest period was followed by an

additional 30 minute rest period.

After the 30 minute seated rest on cooling trials participants were immersed up to the axilla in 13.0

± 0.1°C stirred water wearing swim shorts until core temperature reduced to 36°C. During cold

water immersion Trec, M, thermal comfort and pain were recorded every 5 minutes. Upon removal

from water participants dressed in dry shorts, socks and gloves prior to entering the environmental

chamber (0°C, RH 40% and wind velocity 0.2 m.s-1

: Delta Environmental Systems, Chester, UK).

Socks and gloves were prescribed based upon results of pilot work which demonstrated pain at the

extremeties may cause necessary withdrawal. After 5 minutes seated, participants were given one of

four interventions which covered whole body and head, then remained seated for the 3 hour CAT or

until core temperature reached 35°C. During Blizzard Heat trials heat pads were placed evenly to

the bag with Velcro adhesive and not placed directly onto skin to avoid contact with skin

thermistors. Unlike supine rest in Chapter 4, a seated position was adopted in order for blood and

saliva samples to be collected most efficiently. During field interventions participants consumed

flavoured water of trace nutritional value in volumes equal to 6 ml∙kg-1

body mass at 0, 60 and 120

minutes. Participants consumed beverages within 15 minutes which were served in insulated drinks

containers to minimise heat loss. During PB+HD beverages were served at 80°C whilst on other

trials were 36°C. No food was provided during CATs. During the CAT Trec, skin temperature (Tsk),

thermal comfort and pain sensation were recorded every 5 minutes. Skin temperature was recorded

at eight sites using skin thermistors. Weighted mean skin temperature was calculated using an area

weighted formula (ISO 9886, 2004). Expired gases were collected every 10 minutes for the

determination of M. Afterdrop period was measured in minutes as the total time taken for an

increase in core temperature following exit of the cold water and entrance to the chamber. Urine

was collected ad libitum from the onset of cold stress until re-warming had commenced. Samples

85

were stored at -40°C and later thawed for analysis of urinary urea nitrogen content (Randox

Laboratories, Co. Antrim, UK). Following CATs participants were immersed up to the axilla in

40°C water until core temperature reached 36°C or 1 hour passed. Participants re-clothed and

consumed a meal (1234 Kcal; CHO 58%, Fat 28%; Protein 14%) (Costa et al. 2010). Following 2

hours seated rest and monitoring, participants left the laboratory. On TC participants sat for the

same time period as in the CATs but freely choose their attire. They were not permitted to eat food

during this period and were required to consume fluids (36°C) equal to 6 ml∙kg-1

body mass at 0, 60

and 120 minutes.

6.3.4 Calculations

The quantity of urinary nitrogen excreted and collected during the entire cold stress period was used

as an index of protein oxidation (Ravussin et al. 1985). The oxidation of carbohydrate and lipid

were assessed by the amount of oxygen consumed per gram of substrate oxidized:

Carbohydrate Oxidation (g·4h-1

) = 4.21 · VCO2 - 2.96 · VO2 - 2.37 · N (eq. 3)

Lipid Oxidation (g·4h-1

) = 1.7 · VO2 - 1.7 · VCO2 - 1.77 · N (eq. 4)

Protein Oxidation (g·4h-1

) = urinary urea nitrogen · 6.25 (eq. 5)

Energy Expenditure (kJ) = 16.18 · VO2 + 5.02 · VCO2 - 5.99 · N (eq. 6)

Nitrogen (N) = urinary nitrogen in grams

6.3.5 Statistical analyses

A sample of six was estimated using rectal temperature data from a previous investigation

(Giesbrecht et al. 1987). To allow for subject incompletion seven participants were recruited. A

one-way fully repeated measures ANOVA was performed on body composition data and on re-

warming parameters. Two-way fully repeated-measures ANOVA (time x trial) were performed on

thermoregulatory and metabolic variables.

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6.4 Results

6.4.1 Preliminary and cold water immersion measures

Throughout the experimental period body mass and composition did not change (Table 6.1: Body

mass: P = 0.496; Body fat: P = 0.631). Participants were always hydrated upon arrival to the

laboratory (Chapter 3). Core temperature prior to cold water immersion was similar in each trial

(Table 6.1: P = 0.881). No trial differences occurred between oxygen consumption or time required

for individuals to reach 36°C (Table 6.1 and Figure 6.3: P = 0.347 and P = 0.496). Oxygen

consumption was greater during cold water immersion compared with seated rest (P = 0.000).

When analysed for order of trial (e.g. trial 1 vs. 4) there were no differences Trec (P = 0.917) or time

to 36°C (P = 0.660) suggesting that a single weekly cold water immersion evokes no cold

acclimatisation.

Table 6.1. Body composition and resting core temperature (Trec) immediately prior to cold water

immersion and time taken to reach 36°C during the cold water immersion.

Trial Body Mass (Kg) Body Fat (%) Mean Trec during

30min rest (°C)

Time to 36°C (mins)

PB 70.4 ± 5.5 9.5 ± 3.3 36.7 ± 0.2 28 ± 11

PB+HD 70.4 ± 5.8 9.6 ± 2.4 36.6 ± 0.2 28 ± 11

BB 70.2 ± 6.0 10.1 ± 3.8 36.7 ± 0.2 35 ± 19

BB+HP 71.0 ± 5.4 10.4 ± 3.0 36.7 ± 0.3 36 ± 18

TC 70.5 ± 5.1 9.8 ± 3.1 36.7 ± 0.2 N/A

Results are means ± SD, n = 7. Abbreviations: PB, polythene survival bag; PP+HD, hot drink plus

polythene survival bag; BB, Blizzard™ Survival bag; BB+HP, Blizzard Heat™ Survival bag; TC,

Thermo-neutral control; N/A, not applicable.

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6.4.2 Cold Air Test Results

Initial re-warming (0-30 mins post cold water immersion)

There were no significant differences in re-warming parameters between the four interventions

(Table 6.2). Skin temperature was however higher during the first hour on BB and BB+HP

compared with PB and PB+HD (Figure 6.2: P = 0.001). Additionally in the first hour, metabolic

heat production was similar in BB and BB+HP compared with TC; whereas it was higher in PB and

PB+HD (Figure 6.3: P = 0.028).

Table 6.2. A summary of re-warming parameters

Trial Afterdrop

magnitude (°C)

Time to afterdrop

nadir (mins)

Afterdrop period

(mins)

Re-warming

rate (°C∙h-1

)

PB 0.55 ± 0.28 20 ± 13 76 ± 61 0.39 ± 0.11

PB+HD 0.61 ± 0.21 21 ± 12 93 ± 63 0.37 ± 0.14

BB 0.51 ± 0.13 24 ± 19 74 ± 41 0.34 ± 0.10

BB+HP 0.62 ± 0.26 19 ± 18 84 ± 58 0.37 ± 0.12

Results are means ± SD, n = 7. Statistics: Afterdrop magnitude, F(3,18) = 0.610, P = 0.617, η2 =

0.092; Time to afterdrop nadir, F(3,18) = 0.311, P = 0.817, η2 = 0.045; Afterdrop period, F(3,18) =

0.439, P = 0.728, η2 = 0.068; Re-warming rate, F(3,18) = 0.522, P = 0.673, η

2 = 0.082. Effect sizes

(η2) interpreted as small (0.01), medium (0.06) and large (0.14) (Cohen, 1988).

6.4.3 Longer Term Cold Protection (30 – 180 mins): Core and skin temperature

Compared with the TC, Trec was lower in all cold trials (F(32,192) = 7.936, P = 0.000, η2

= 0.112).

However there were no Trec differences during cold exposure between the four interventions. All

methods returned Trec to within normal resting core temperature by 180 min. Mean weighted skin

temperature (Tsk) was higher TC compared to re-warming trials (Figure 6.2: F(24,144) = 10.039, P =

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0.000, η2

= 0.044). By 10 minutes into the cold air test all practical field methods had increased Tsk

compared to 0 minutes (P = 0.000). However compared with PB and PB+HD, Tsk was higher from

30 minutes on BB and BB+HP. There were no differences between BB and BB+HP or PB and

PB+HD.

Figure 6.1. The effect of 180 minute cold air test (CAT; 0°C) on core temperature in four field cold

casualty interventions and a thermo-neutral control. TN; thermo-neutral, End CWI; end of cold

water immersion. Values are Means ± SD. * significant difference vs. TC (P < 0.05).

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Figure 6.2. The effect of 180 minute cold air test (CAT; 0°C) on mean weighted skin temperature

in four field cold casualty and a thermo-neutral control. Values are Means ± SD. * significant

difference vs. TC, † significant difference vs. PB, ‡ significant difference vs. PB+HD (P < 0.05).

6.4.4 Metabolic Responses

Metabolic heat production was higher than TC on all cold trials at the end of the cold water

immersion and at 0 min of the cold air test (Figure 6.3: F(32,192) = 10.599, P = 0.000, η2

= 0.158).

Metabolic heat production remained higher than TC in PB (10-30 min) and PB+HD (10-180 min).

In contrast, no differences occurred between TC and BB or BB+HP from 10-180 min. However,

cold exposure increased the oxidation of carbohydrates 3 fold during PB, PB+HD and BB+HP

above TC. Despite this, carbohydrate oxidation during BB was not different to other trials (Figure

6.4: F(4, 24) = 3.809, P = 0.016, η2

= 0.388). Regardless of cold exposure, the oxidation rate of lipids

90

was not different between any trial (Figure 6.4: F(4, 24) = 0.992, P = 0.432, η2

= 0.142). However,

while not statistically significant, protein oxidation in the cold tended to be greater than TC (Figure

6.4: F(4, 24) = 2.690, P = 0.055, η2

= 0.310). Energy expenditure from the onset of cold stress was

greater PB+HD compared to all other trials (Figure 6.5: F(4, 24) = 52.240, P = 0.000, η2

= 0.310).

Energy expenditure during BB and BB+HP were not different (P = 0.079), however values were

less than PB (P = 0.025) yet greater than TC (P = 0.001).

Figure 6.3. The effect of 180 minute cold air test (CAT; 0°C) on metabolic heat production in four

field cold casualty interventions and a thermo-neutral control. TN; thermo-neutral, End CWI; end of

cold water immersion. Values are Means ± SD. * significant difference vs. TC, † significant

difference vs. PB, ‡ significant difference vs. PB+HD (P < 0.05).

91

Figure 6.4. The effect of 180 minute cold air test (CAT; 0°C) on substrate oxidation in four field

cold casualty and thermo-neutral control. Values are Means ± SD. * significant difference vs. TC (P

< 0.05).

*

*

*

PB PB+HD BB BB+HP TC

92

Figure 6.5. The effect of 180 minute cold air test (CAT; 0°C) on energy expenditure in four field

cold casualty interventions and thermo-neutral control. Values are Means ± SD. * significant

difference vs. TC, † significant difference vs. PB, ‡ significant difference vs. PB+HD (P < 0.05).

6.4.5 Thermal comfort and pain sensation

Thermal comfort was higher throughout TC compared to the cold trials (Figure 6.6. F(32,192) =

3.734, P = 0.000, η2

= 0.071). Following 30 minutes of cold exposure thermal comfort was higher

during BB+HP compared with PB+HD (P < 0.05). Pain sensation was lower during TC compared

to all cold trials (Figure 6.5. F(32,192) = 3.880, P = 0.000, η2

= 0.077).

* * ‡

*†‡

*†‡

PB PB+HD BB BB+HP TC

93

Figure 6.6. The effect of 180 minute cold air test (CAT; 0°C) on thermal comfort in four field cold

casualty interventions and a thermo-neutral control. Values are Means ± SD. * significant

difference vs. TC, ‡ significant difference vs. PB+HD (P < 0.05).

94

Figure 6.7. The effect of 180 minute cold air test (CAT; 0°C) on pain sensation in four field cold

casualty interventions and a thermo-neutral control. Values are Means ± SD. * significant

difference vs. TC (P < 0.05).

6.4.6 Results summary

Core temperature returned toward normal following three hours in all field treatments. Mean skin

temperature however increased faster and was maintained at a higher level during both Blizzard

trials. Metabolic heat production, thermal comfort and pain sensation were most similar to TC

during BB+HP. Energy expenditure was less during BB+HP compared with any other treatment.

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6.5 Discussion

The results of this investigation imply that the four interventions supported rewarming to near

normal resting core temperatures of shivering cold casualties within three hours of cold exposure.

Although typical rewarming parameters were not different between either intervention metabolic

heat production was greater in polythene compared with the Blizzard survival bags during the first

hour of cold exposure. Furthermore, re-warming in the Blizzard survival bags was achieved with

lower total energy expenditure which may be beneficial for long term survival (Tikuisis, 1995;

Tikuisis et al. 2002).

As anticipated multi-layer, metalized sheeting survival bags led to thermoregulatory advantages

compared with the polythene survival bag with or without a hot drink. The administration of hourly

hot drinks (~430 ml) seemed to confer no advantage in re-warming or the maintenance of core or

skin temperature during cold exposure when compared with polythene survival bags alone. It has

been reported that provided shivering is not contraindicated, core re-warming rate is not different in

cold individuals using either active or passive rewarming devices (Williams et al. 2005). In

contrast, Blizzard survival bags maintained a higher skin temperature throughout the cold air test

which is indicative of superior cold protection and may be speculated to indicate a lower likelihood

of peripheral cold injury. On the contrary, while vasoconstriction reduces heat loss from the skin,

the reduced peripheral blood flow also increases tissue insulation helping to maintain core

temperature (van Ooijen et al. 2005; Toner and McArdle, 1986). The application of external heat

sources to the skin of an individual in the cold may blunt the vasoconstrictive response forcing heat

to be transferred from the core to the skin (Grant et al. 2002). Furthermore, cutaneous temperatures

greater than 29°C reduce peripheral thermo-receptor activity resulting with inadequate stimuli to

activate shivering (Vokac and Hjeltnes, 1981; Rennie, 1988; Mercer. 1991). When shivering is

blunted through peripheral warming in a severe cold environment, heat loss may exceed heat

production (Giesbrecht et al. 1994; Grant et al. 2002). In the present study however, cutaneous

96

temperatures of participants never exceeded this threshold compared with normothermic individuals

in earlier work (Grant et al. 2002). As a result, vasoconstriction was not blunted and as such, large

amounts of heat were not transferred from the core to the periphery, thus these methods provided a

more efficient heat source by conserving more heat.

Upon initial exposure to the cold, metabolic heat production was increased compared to thermo-

neutral in all rewarming trials. By 90 minutes however, metabolic heat production had decreased on

the Blizzard Heat trial to within thermo-neutral control values that were approximately 40% lower

than those recorded during the polythene survival bag trials. Co-incidentally, heat production during

polythene survival bag trials fluctuated throughout, that may reflect greater shivering thermogenesis

(van Ooijen et al. 2005). Since warming of peripheral thermo-receptors reduces shivering and

blunts metabolic heat production (Giesbrecht et al. 1987), cooler skin temperatures demonstrated

during both polythene survival bag trials may have stimulated a greater thermo-receptor response

and thus, shivering activity. Comparatively, during Blizzard Heat the warmer skin temperatures

provided less stimulation to activate shivering and therefore produced less metabolic heat

production. This has been considered detrimental for maintaining heat balance in a cold casualty

(Giesbrecht et al. 1987; Giesbrecht et al. 1994). However, if cold exposure is not recognised by the

body as severe shivering will not begin (Vybiral et al. 2000). Cold protection provided by the

Blizzard Heat survival bag may therefore reduce the amount of heat an individual needs to produce

through shivering and non-shivering thermogenesis. Given the amount of noise produced by

survival bags in contact with the skin, it was not ecological to measure shivering via

electromyography in this study. Nonetheless, metabolic heat production provides a clear indication

of how much extra the body needed to work in order to maintain core temperature. Addtionally,

participants subjectively rated the amount of cold induced pain they felt in each bag which gave a

representation of their perception of physical output needed to keep warm.

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While survival depends on the capacity to counterbalance the rate of heat loss by increasing

thermogenic rate (Haman, 2006), Blizzard survival bags may have significant benefit in longer term

survival where food sources might be restricted and finite. Specifically, the lower cold-induced

energy expenditure during the Blizzard Heat trial coupled with a continuous increase in core

temperature likely provides a more efficient re-warming effect whereby energy is preserved and

fatigue from excessive shivering is reduced (Martineau and Jacobs, 1988; Vallerand and Jacobs

1989; Vallerand et al. 1993). As a likely consequence of the superior cold protection provided by

Blizzard Heat, perceptual measures (i.e. thermal comfort and pain) tended to be better during the

cold air test compared with when individuals were in the polythene survival bag. In combination

with previous in vitro results (Allen et al. 2010) it is speculated that where cold casualties have

impaired shivering, Blizzard survival bags would also provide superior cold protection including re-

warming capacity compared to polythene survival bags. Future studies where shivering activity is

blunted either medically, or through the use of thermal manikins would help determine this

superiority. An investigation with the superior rewarming interventions compared to no protection

in more severe conditions would also identify any further strengths or weaknesses. To conclude, in

contradiction to the hypothesis, all four of the cold treatment methods tested in 0°C, assisted

shivering cold casualties to increase core temperature to normothermia within the same 3 hour

period. Nonetheless, of the four methods the Blizzard Heat survival bag was the most efficient for

field rewarming given a reduced metabolic heat production was required to increase core

temperature.

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CHAPTER SEVEN

Salivary IgA and Amylase Responses to Mild Hypothermia and Prolonged Cold Exposure

7.1 Abstract

The aim of this study was to examine the effect of mild hypothermia and prolonged cold exposure

upon s-IgA and α-amylase responses. Twelve males completed two experimental trials which

included a thermo-neutral control (TC) and a cold trial (COLD). On COLD, participants wore

shorts only and were cooled to 36°C core temperature (Trec) in 13°C water. They then completed a

3-hour cold air test (CAT, 0°C) with a polythene survival bag to prevent core temperature

decreasing beyond ethical guidelines. Unstimulated whole saliva samples were collected at

baseline, lowest Trec, 1 h CAT, 2 h CAT and immediately after, 1 h and 3 h after CAT. An

interaction was observed for saliva flow rate and s-IgA secretion rate (F(6,66) = 3.379, P = 0.006;

F(3.086, 33.947) = 3.697, P = 0.020, respectively). Saliva s-IgA secretion rate was significantly lower

during COLD compared to TC (P < 0.05). Compared with lowest Trec, saliva s-IgA secretion rate

was higher at 1 and 3 h post CAT (P < 0.05) during COLD, but no differences occurred throughout

TC. Saliva flow rate was significantly lower during the first hour of CAT during COLD compared

with TC (P < 0.05) and remained lower until 3 h post. Saliva s-IgA concentration was significantly

reduced following baseline measures on both cold and thermo-neutral trials (P < 0.01), whereas α-

amylase concentration was greater throughout CAT compared to TC until re-warming had occurred

(P < 0.05). These results suggest a reduction in core temperature (≥ 1.5°C) resulting from cold

water immersion and subsequent cold air exposure alters the usual daily saliva responses which may

increase susceptibility to illness and infection (i.e. URTI, common colds, influenza) if re-warming

is not initiated immediately.

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7.2 Introduction

It is known that exposure to cold with hypoxia may induce greater health risks with regard to

mucosal immunity compared to exposure to cold alone (Chapter 5). However, it is not clear

whether these changes would be more severe in colder conditions that induce mild hypothermia.

Furthermore, current knowledge in this area has not been verified in accordance with diurnal

fluctuations and thermal-neutral control trials for comparison.

It is the popular belief that most common colds occur because the host is exposed to a cold

environment beforehand (Dowling et al. 1958; Biggar et al. 1984). However, a direct causal relation

between getting cold and developing an infection remains to be clarified (Lavoy et al. 2011). Cold

exposure has been associated with an increased incidence of bronchorrhea, sinusitis, and upper

respiratory tract infections (URTI) (Clothier, 1974; Giesbrecht, 1995; Castellani et al. 2002; Lavoy

et al. 2011). However, much of this research has examined individuals undertaking intense physical

activity in the cold (i.e. athletes and military personnel). Cold-induced decrements in immune-

surveillance are a particular problem for physically active individuals (Brenner et al. 1999). For

example, URTIs are the main cause of illness and missed practise in elite cross country skiers

(Berglund and Hemmingson, 1990). Nonetheless, the risk of illness or infection for those forced or

required to remain sedentary in the cold, due to injury or adverse weather, for a prolonged period of

time is unknown.

It has been suggested that a continuum exists for the effects of body core cooling on immune

function whereby mild decreases in body core temperature have little stimulatory effects on

immune function, but more severe decreases have depressive effects (Costa et al. 2010). However,

it remains to be shown whether large (≥ 1.5°C) reductions in body core temperature suppress

mucosal immunity and increase the likelihood of infection (Costa et al. 2010).

100

A decrease in the saliva concentration of s-IgA accompanies an increased susceptibility to URTI

(Gleeson et al. 1999; Hanson et al. 1983; Nieman and Nehlsen-Cannarella, 1991). However,

breathing cold dry air itself can elicit symptoms similar to these infections, such as a persistent dry

cough and nasal mucosal drying (Silvers, 1991; Giesbrecht, 1995). Thus it may be that cold weather

negatively impacts the respiratory system independently of changes in immunity. For example,

performing prolonged exercise in freezing cold conditions did not influence saliva flow rate or s-

IgA secretion rate responses (Walsh et al. 2002). However, modest whole body cooling (Trec

35.9°C) at rest showed reduced s-IgA responses (Costa et al. 2010). Unfortunately, a lack of a

thermo-neutral control trial for comparison means changes may reflect diurnal variation of saliva

concentrations (Walsh et al. 2002). The influence of prolonged cold exposure upon s-IgA and α-

amylase responses in clinically hypothermic individuals (Trec 35°C) has received little attention. In

the field, cold stress may evoke suboptimal host defence that subsequently may increase the risk of

illness and infection (Johnson et al. 1977; Houben et al. 1982; Hiramatsu et al. 1984).

Evidence to date indicates that a mild decrease in core body temperature (Trec decrease ~ 0.5°C)

during short (30 min) (Lackovic et al. 1988) or prolonged (2 h) (Brenner et al. 1999) cold air

exposure can have immuno-stimulatory effects. During short cold air exposures (4°C) natural killer

cell activity was found to increase (Lackovic et al. 1988). The immersion of healthy males in cold

water (14°C) has been shown to induce a leukocytosis (Jansky et al. 1996). However, it is unknown

what core temperature participants presented with during and following these immersions.

Therefore, little information is available from controlled laboratory studies regarding any immuno-

stimulatory effects of a decrease in core temperature ≥1.5°C. Further, it remains unclear how

prolonged (3 h) cold air exposure in combination with such a decline in core temperature effects s-

IgA and α-amylase responses. Previous explanations for the disruption to mucosal immunity

observed with modest whole-body cooling at rest have included: cold air decreasing the temperature

of mucosal membranes, the subsequent drying effect which may reduce mucociliary clearance and

101

phagocytic activity (Eccles, 2002), and a cooling-evoked neuro-endocrine regulation of trans-

epithelial s-IgA translocation (Giesbrecht, 1995; Proctor and Carpenter, 2007).

The aim of the present study, therefore, was to examine the effect of mild hypothermia and

prolonged cold exposure on s-IgA and α-amylase responses. It was hypothesised that mild

hypothermia and cold exposure would lower s-IgA and amylase secretion in comparison with

normal responses in a thermo-neutral environment. Given it would be unethical to expose

participants to cold without some form of thermal protection, the polythene bag was chosen as it

offers minimal warmth to the body inside compared with other devices (Chapter 6) and therefore

would prevent a blinding of the effects of cold on immune function.

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7.3 Method

7.3.1 Participants

Twelve healthy males (mean ± SD: age, 20.7 ± 2.2 years; height, 177.5 ± 6.6 cm; nude body mass,

68.6 ± 6.4 kg; body fat, 10.9 ± 3.7%) participated in this study. Participants gave written consent

and medical history before the study, which received local Ethics Committee approval. Participants

also completed the Wisconsin Upper Respiratory Symptom Survey (Appendix H) two weeks prior

to and during the experimental period.

7.3.2 Preliminary measurements

Before each experimental trial participants arrived at the laboratory after an overnight fast having

consumed no food, caffeine or alcohol within 10 h. Participants ingested water equal to at least 35

ml·kg-1

body mass the day prior to each trial. After voiding bladder and bowels, nude body mass

and height were measured. Using segmental multiple frequency bioelectrical impedance measures

of body fat were obtained.

7.3.3 Experimental Trials

Separated by 7 d, participants completed two randomised experimental trials (Research

Randomiser; www.researchrandomizer.org). The two trials were: cold exposure with a polythene

survival bag (COLD) and a thermo-neutral control trial (TC). A polythene survival bag was

necessary to prevent core temperature falling to below mild hypothermic levels. Following pre-trial

measures participants began each experimental trial at 0800. Following 30 minutes seated rest in a

thermo-neutral environment (ambient temperature: 19.2 ± 1.1°C; relative humidity: 40.9 ± 6.0%),

the first saliva sample was collected.

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For the cold trial participants were immersed in 13.0 ± 0.1°C stirred water up to the axilla wearing

swim shorts only until core temperature reduced 36°C. Upon removal from the water and after

drying, participants entered the chamber where they remained seated for a 3 h cold air test (Dry

bulb temperature (Tdb) of the chamber remained constant at 0°C with a relative humidity (rh) 40%

and 0.2 m.s-1

wind velocity; Delta Environmental Systems, Chester, UK). Once in the chamber,

participants sat wearing dry shorts only for five minutes before being given the survival bag.

Expired gases were collected every 10 minutes for the determination of M. Saliva was collected at

baseline, lowest Trec, 1 h, 2 h and 3 h during cold exposure. The lowest Trec sample was collected in

the chamber once core temperature showed the first sign of increasing following a distinct afterdrop

phase. Early removal from the chamber occurred if core temperature reduced to 35°C. Following

the cold air test participants were immersed in 40°C water to increase core temperature. After 1 h

participants gave another saliva sample, re-clothed and consumed a meal (1234 Kcal; CHO 58%,

Fat 28%; Protein 14%) (Costa et al. 2010). Following a further 2 h recovery, participants gave a

final saliva sample and were free to leave the laboratory.

All participants completed a control trial to account for diurnal fluctuations in s-IgA concentration

(Gleeson et al. 2001; Walsh et al. 2002). During the control trial participants remained seated in an

ambient temperature of 20.2 ± 1.7°C and wore normal clothing (0.8-1.0 clo / 1.24-1.55 togs). Saliva

samples were collected in the same manner as those in the cold trial.

7.3.4 Saliva collection and analysis

Un-stimulated whole saliva samples were collected using pre-weighed universal tubes (Chapter 3).

Saliva samples were collected while the participant sat quietly in the laboratory. Saliva volume was

estimated by weighing the universal container immediately after collection to the nearest mg. From

this, saliva flow rate was determined by dividing the volume of saliva by the collection time. Saliva

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was aspirated into Eppendorf tubes and stored at -40°C for further analysis. After thawing s-IgA

concentration was determined by ELISA (Salimetrics Europe Ltd, Suffolk, UK) using IgA

monomer from human serum as standard. The intra-assay CV was 2.6%. s-IgA secretion rate was

calculated by multiplying the saliva flow rate by s-IgA concentration.

Alpha amylase concentration was determined by ELISA (Salimetrics Europe Ltd, Suffolk, UK)

using a chromagenic substrate, 2-chloro-p-nitrophenol linked with maltotriose. The intra-assay CV

was 2.1%.

7.3.5 Statistical analyses

A sample size of ten participants was estimated (http://www.dssresearch.com/toolkit/sscalc) using

previous data examining the effects of stress on immune indices (Costa et al. 2010; Laing et al.

2008; Oliver et al. 2007). One way fully repeated measures ANOVA were performed on pre-

experimental body composition measures. Two-way fully repeated measures ANOVA were

performed on saliva parameters.

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7.4 Results

7.4.1 Body mass and composition

Throughout the experimental period body mass and composition did not change (Table 7.1: Body

mass: P = 0.733; Body fat: P = 0.097). Core temperature prior to cold water immersion was similar

in each trial (Table 7.1: P = 0.545).

Table 7.1. Resting core temperature (Trec) immediately prior to cold water immersion and time

taken to reach 36°C during the cold water immersion

Trial Body mass (Kg) Body fat (%) Resting Trec (°C) Time to 36°C (mins)

Cold 68.6 ± 6.4 10.9 ± 3.7 36.8 ± 0.3 29 ± 14

TC 68.7 ± 6.2 11.4 ± 3.7 36.8 ± 0.2 N/A

Results are means ± SD, n = 12. Abbreviations: TC, Thermo-neutral control; N/A, not applicable.

7.4.2 Thermoregulatory and metabolic responses

Compared with the thermo-neutral control, Trec and mean weighted skin temperature (Tsk) were

lower during cold exposure (Table 7.2: F(1.877,15.012) = 4.192, P = 0.038, η2

= 0.113 and F(24,144) =

10.039, P = 0.000, η2

= 0.044, respectively). During the first hour of the cold air test, metabolic heat

production was higher in the cold compared with thermo-neutral (Table 7.2: F(1.073,8.583) = 11.531, P

= 0.008, η2

= 0.083).

Table 7.2. Summary of mean thermoregulatory parameters

Trial Lowest Core

Temperature (°C)

Mean Weighted Skin

Temperature (°C)

Metabolic Heat

Production (W·m2)

COLD 35.4 ± 0.3 25.0 ± 1.3 150 ± 64

TC 36.6 ± 0.3 31.6 ± 1.0 49 ± 11

Results are means ± SD, n = 12.

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7.4.3 Salivary secretory IgA and alpha amylase concentration

Saliva s-IgA secretion rate was lower during COLD at baseline and throughout CAT compared to

TC (Figure 7.1C: P = 0.05). Saliva s-IgA secretion rate however, was similar between the trials

following one hour of recovery from cold exposure. Compared with lowest core temperature, saliva

s-IgA secretion rate was higher at one and three hours post CAT during the cold trial, but no

differences occurred throughout the thermo-neutral control. An interaction was observed for both

saliva flow rate and s-IgA secretion rate (Figure 7.1A: F(6,66) = 3.379, P = 0.006, η2 = 0.280; Figure

7.1C: F(3.086, 33.947) = 3.697, P = 0.020, η2

= 0.417 respectively). A main effect of time was observed

for saliva s-IgA concentration (Figure 7.1B: F(2.93, 32.262) = 7.696, P = 0.001, η2

= 0.386). Saliva flow

rate was lower during the first hour of the CAT compared with thermo-neutral and remained lower

until three hours post CAT. Saliva flow rate was higher three hours post-CAT compared with

lowest core temperature. Following the initial morning sample there were no further changes in

saliva flow rate during the thermo-neutral control. Saliva s-IgA concentration was reduced

following baseline measures on both cold and thermo-neutral trials (P = 0.01).

Saliva α-amylase concentration was greater during COLD throughout CAT compared to TC

(Figure 7.2A: F(1, 8) = 8.506, P = 0.019, η2

= 0.5150). When core temperature was at its lowest

during COLD, α-amylase concentration was at its greatest. At 1h post CAT and 3h post CAT α-

amylase concentration in COLD and TC was the same (P = 0.05). Despite a small increase when

core temperature was at its lowest, saliva secretion rate remained unchanged between TC and

COLD (Figure 7.2A: F (1, 8) = 0.547, P = 0.481, η2 = 0.063).

107

Figure 7.1. The effect of 180 min cold air test (CAT; 0°C) on saliva flow rate (µl·min-1

) (A), s-IgA

concentration (µg·ml-1

) (B) and secretion rate (µg·min-1

) (C) in comparison to a thermo-neutral

control. Values are means ± SD. * significant difference vs. thermo-neutral, † significant difference

vs. lowest Trec, ‡ significant difference vs. baseline (P < 0.05).

A

B

C

Baseline

108

Figure 7.2. The effect of 180 min cold air test (CAT; 0°C) on saliva alpha amylase concentration

(µg·ml-1

) (A) and amylase secretion rate (µg·ml-1

) (B) in comparison to a thermo-neutral control.

Values are means ± SD. * significant difference vs. thermo-neutral (P < 0.05).

7.4.4 Results summary

Saliva s-IgA secretion rate was lower during COLD compared to TC. Saliva flow rate was lower

during the first hour of the CAT compared with TC and remained lower until three hours post CAT.

Saliva α-amylase concentration was greater during COLD throughout CAT compared to TC.

B

A

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7.5 Discussion

The aim of the present study was to examine the effect of mild hypothermia and prolonged cold

exposure on mucosal immunity in comparison to a thermo-neutral control trial. This novel design

allowed for the diurnal variation in mucosal parameters to be accounted for. In support of the

hypothesis, mild hypothermia evoked a reduction in saliva flow rate and an increase in α-amylase

concentration which was not due to the time of day samples were collected. Saliva-IgA secretion

rate was lower and α-amylase concentration was higher throughout the cold exposure until re-

warming to within normal resting core temperature values had occurred.

Given the presence of a thermo-neutral control trial, these results extend previous research that

showed whole body cooling (Trec 35.9°C) via cold air exposure (0°C) decreased s-IgA secretion rate

compared to baseline (Costa et al. 2010). Explanations included the effects of cold air reducing the

temperature of the mucosal membranes, a possible drying effect of cold air and whole body

cooling-evoked neuro-endocrine regulation of trans-epithelial s-IgA translocation (Giesbrecht,

1995; Proctor and Carpenter, 2007). The time course of the response suggested that whole body

cooling decreases s-IgA translocation because s-IgA synthesis usually takes many hours to days

(Costa et al. 2010; Hucklebridge et al. 1998). However, such explanations could only have been

speculative owing to an absent control trial. During the present study a more intense cooling

procedure induced mild hypothermia (Trec 35°C) in almost all individuals. The diurnal variation

pattern for s-IgA responses was similar throughout both cold and thermo-neutral conditions.

However, both saliva flow rate and s-IgA secretion rate were markedly suppressed by mild

hypothermia and cold exposure.

Early experiments (Proetz, 1953; Baetjer, 1967) examining beat frequency of cilia in the paranasal

sinuses of rabbits and the trachea of chicks indicated that exposure to cold air decreases the

temperature of the nasal respiratory epithelium and causes a decrease in mucociliary clearance

(Eccles, 2002). A decrease in mucociliary clearance associated with cold exposure has been

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suggested to increase the predisposition to respiratory infection (Diesel et al. 1991). With this in

mind, throughout each trial, temperature controlled fluid (36°C) was consumed hourly in order to

be able to combine findings with chapter 4. It is plausible that this fluid, similar to body

temperature, may have reduced the drying effect of cold air and maintained the temperature of the

mucosal membranes. It is speculated therefore that these earlier explanations for changes in

mucosal immunity are less likely within the present study and an alternative factor is responsible for

changes in saliva flow rate, s-IgA secretion rate and α-amylase concentration.

A body of literature exists, detailing saliva responses during exercise in the cold (Mylona et al.

2002; Walsh et al. 2002; Costa et al. 2010). However, the present study is the first to observe a

reduction in the saliva flow rate and s-IgA secretion rate but an increase in the α-amylase

concentration of mildly hypothermic, sedentary individuals exposed to the cold. Saliva flow rate, s-

IgA secretion rate and α-amylase concentration were only similar to those levels observed during

thermo-neutral control after three hours of re-warming and consumption of a hot meal. Despite this,

that cold exposure and mild hypothermia disrupt mucosal immunity should be suggested with

caution. This is because the s-IgA secretion rate recorded at rest, prior to cold exposure, was lower

than at that same time during thermo-neutral control. It is possible this was due to an anticipatory

effect of the forthcoming cold water immersion. Psychological stress, defined as the experience of

negative events or the perception of distress, has been shown to alter saliva total protein

concentration, α–amylase activity and IgA concentration (Bosch et al. 1996; Cohen et al. 2001).

Such as, an increase in saliva total protein concentration but a decrease in saliva α-amylase activity

was observed in patients awaiting dental treatment compared with a non-stress situation (Morse et

al. 1983). It is possible that participants in the present study were more anxious upon arrival to the

laboratory on the day they were going to be exposed to the cold compared with when they remained

warm. In future, blinding participants to the experimental trial prior to baseline samples may be

beneficial. On the contrary, after re-warming and a meal, s-IgA secretion rate was greater and α-

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amylase concentration lower than when participants displayed their lowest core temperature,

whereas no changes occurred throughout the thermo-neutral trial. This suggests that until re-

warming is initiated, cold, sedentary individuals are at risk from increased mucosal immune

disturbance.

In conclusion, a reduction in core temperature resulting from cold water immersion and cold air

exposure alters the usual daily mucosal response which may increase a person’s susceptibility to

illness and infection (i.e. URTI, common colds, influenza), particularly if they are not rewarmed

immediately. In combination with earlier findings (Chapter 5), exsposure to severe cold

environments with hypoxia create an even greater risk for un-acclimatised individuals travelling to

high altitudes. It is necessary for such individuals to practise a programme of constant monitoring to

ensure health is maintained during exposure to extreme environments.

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CHAPTER EIGHT

Practical Field Methods For Cold Protection of Non-shivering Cold Casualties: An in Vitro

Model

8.1 Abstract

The aim of this investigation was to examine the effectiveness of three field methods for non-

shivering cold casualty protection and re-warming. To achieve this, an in vitro fluid bag model was

used to simulate a non-shivering cold casualty. Three field methods were compared with a control

trial (CON). Trials were a polythene bag (PB), a triple-layered, metalised plastic sheeting survival

bag (Blizzard Survival bag (BB)), a triple-layered, metalised plastic sheeting survival bag with heat

pads (Blizzard Heat survival bag (BB+HP)). Cold protection methods were assessed for four hours

in a range of environmental conditions (-18.5°C, 0°C and 18.5°C). Trials began once fluid bag core

temperature had reached 37°C. The effectiveness of the survival bags was assessed by the amount

of core temperature decline in each environmental condition. After exposure to 18.5°C there were

no differences in final Trec between the cold protection methods (P > 0.05). In 0°C, final Trec during

BB+HP was significantly greater than CON (P = 0.004). After 240 minutes in -18.5°C final Trec in

BB+HP was significantly greater than PB (P = 0.019). At 60 minutes of exposure to 18.5°C the

reduction in Trec was significantly greater in PB compared to BB+HP (P = 0.036). Following 120

minutes, the amount of heat lost was significantly greater in PB and BB compared to BB+HP (P <

0.05). The effectiveness of chemical heat pads in combination with a triple layered, metallised

survival blanket may counteract the decline in thermogenesis accompanying the onset of severe

hypothermia and reduce hypothermia related fatalities.

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8.2 Introduction

When a human is hypothermic but has the ability to shiver, core temperature can recover to normal

provided a protective layer is supplied (Chapter 6). Ethical guidelines surrounding hypothermia

research often limit how cold a human can be made. This creates a grey area with regard to

knowledge about how the human body can cope once shivering has ceased and there is no longer

any form of internal heat production. It is pertinent to understand, even if only by the use of a fluid

model, how well an external heat source that can be easily administered in the field, will treat a

body with a core temperature so low that heat production via shivering has ceased.

During cold exposure vasoconstriction and shivering are the main defence against temperature loss

(Holcomb, 2005). However, as core body temperature decreases the adrenergic, cardiovascular and

metabolic mechanisms begin to fail (Farkash et al. 2002). When core temperature reaches 32°C

shivering is terminated (Giesbrecht et al. 1997). Although mortality rates are relatively low with

severe non-trauma related hypothermia (<28°C), they rise alarmingly with traumatic injury where

mortality is 40, 69 and 100% at 34, 33 and 32°C (Moss, 1986; Jurkovic et al. 1987) (Chapter 6). In

military environments, including wartime countries such as Afghanistan, where temperatures

remain fairly mild in the winter, hypothermia is commonly encountered during combat operations

(Marshall, 2005; Moran et al. 2003). Casualty’s air lifted by helicopter experience ambient

temperature drops up to -15°C per 1000 feet of altitude gain (Johnson et al. 2010). This, in

combination with a four hour evacuation flight will likely accelerate the onset of hypothermia.

Additionally, drugs administered to the casualty such as sedatives and opioids decrease the

thermogenic effect of shivering (Kurz et al. 1995; Giesbrecht and Bristow, 1997). Given a non-

shivering casualty presents a more dangerous condition than one who is shivering (Hamilton and

Paton, 1996), simple methods that prevent further heat loss in non-shivering casualties that can be

administered instantly whilst waiting for evacuation will likely reduce hypothermia related fatalities

(Arthurs et al. 2006).

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Studies examining heat loss and field cold protection methods in non-shivering casualties are

limited because of ethical limitations with cooling humans to a state of non-shivering. A recent in

vitro study where cooling times of fluid bags were compared between different field methods

showed a multi-layered survival bag (Blizzard Survival™) to be superior at preventing heat loss

compared with a polythene survival bag, single layer metalized plastic sheeting and wool blanket

(Allen et al. 2010). Further, a combination of the multi-layered metalized sheeting survival bag

(Blizzard Reflexcell™) with chemical heat pads was shown to be superior to all other methods

tested. Nonetheless, given that the exposure conditions did not reflect typical cold temperatures

experienced during outdoor winter pursuits, it remains unknown how well these devices protect

non-shivering, sedentary humans in the cold. Furthermore, trials were terminated before critical

core temperatures were reached. Potentially, the amount of heat loss may increase as time in the

cold continues. More specifically, when shivering is terminated as a result of severe hypothermia,

body heat loss increases. Chemical pads inside a survival bag have obvious advantages in

comparison to alternative active warming devices, such as durability, lightness and adaptability to

many situations (Hamilton and Paton, 1996). However, rescue teams are unaware of an optimal

field treatment method for non-shivering casualties.

The in depth study of severe hypothermia has been difficult given that the experimental study of

humans has mostly been confined to mild hypothermia (Giesbrecht et al. 1997). However, in

clinical situations, the narcotic drug meperidine is commonly used to inhibit post-operative

shivering (Macintyre et al. 1987). With an immediate onset following intravenous administration

and short duration of action, meperidine is particularly desirable for use in experimental research to

effectively abolish shivering during mild hypothermia. Its use in cold exposed humans has resulted

in a three-fold increase in core temperature after-drop and more than a four-fold increase in length

of the after-drop period (Giesbrecht et al. 1997). However, since participants remained in a thermo-

neutral environment following shivering inhibition, it remains unknown how severe the after-drop

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would be in a cooler environment. The administration of narcotics has helped improve

understanding of severe hypothermia in humans. It is of limited use however, because a medically

trained practitioner must be present at all times. The use of a non-shivering fluid bag model allows

research to be performed in a controlled, safe manner without risk to humans. Albeit, a human body

has a far smaller heat capacity range than that of water in a fluid model, a number of varying

environmental conditions can be applied using this design to gain a better understanding of cooling

rates without requiring human participants.

The aim of this investigation was to examine field cold protection methods for the prevention of

heat loss in a non-shivering casualty model in a range of environmental temperatures (18.5ºC, 0ºC

and -18.5 ºC). To simulate real-life awaiting-rescue events, the field cold protection methods were

studied for a four-hour period with thermo-neutral conditions (18.5°C). It was hypothesised that the

active heating device (Blizzard Heat survival bag) would minimise the reduction in core

temperature in all ambient conditions so that the final core temperature remained higher compared

to the passive devices (Polythene and Blizzard survival bags).

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8.3 Method

8.3.1 Fluid bag model

Two fluid bags were configured to represent a human adult male torso similar to those of human

participants in chapters 4, 5, 6 and 7 (~60% of 70 Kg or 48.6 Kg (Allen et al. 2010)). Each torso

model used one 60 L polyvinyl chloride bag with electrically welded seams and was filled with 48.6

L water pre-heated to 37.5°C. Water was used instead of saline given the ease of access, use and

cost. Models had an indwelling thermistor that represented core temperature and two surface

temperature probes situated on the anterior and posterior.

8.3.2 Study design

Separated by at least 24 hours, each fluid bag completed twelve randomised experimental trials

(Research Randomiser; www.randomizer.org). Four of these trials were performed with three field

cold protection methods that included a polythene bag, a Blizzard Survival bag and a Blizzard

Survival heat bag. The fourth trial was a control where the fluid bag had no protection. Each

method was assessed in -18.5°C, 0°C and 18.5°C.

8.3.3 Experimental procedures

Each fluid bag was filled with heated water to a starting core temperature of 37.5°C. At this

temperature fluid bags were transported into the environmental chamber set to one of the three

experimental temperatures (RH 40% and wind velocity 0.2 m.s-1

: Delta Environmental Systems,

Chester, UK). During each trial, fluid bags were placed on a flexible plastic sheet to prevent direct

contact with the floor. Core temperature was measured continuously and recorded every 5 minutes

using a flexible thermistor inserted to the medial section of the fluid bag. Surface temperature was

also recorded every 5 minutes at two sites using surface thermistors. Water was circulated in the

117

fluid models by manual rotation of the bag every 5 minutes to eliminate temperature gradients

within the bag.

8.3.4 Statistical analyses

A two-way fully repeated-measures ANOVA (time x trial) was performed on thermoregulatory

variables. Significance was accepted at P < 0.05. Where significant main effects and interactions

occurred Post Hoc Tukey’s HSD was used. All data are presented as Mean ± SD.

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8.4 Results

8.4.1 Final Core Temperature

After 240 minutes exposure to 18.5°C there were no differences between the final core temperatures

in any of the trials. However, after 240 minutes in -18.5°C the final core temperature in BB+HP

(26.0°C) was greater than PB (16.5°C) (P = 0.019).

Final core temperatures on CON 0°C and CON -18.5°C were lower than PB 18.5°C (P = 0.03 and P

= 0.048, respectively), BB+HP 18.5°C (P = 0.006 and P = 0.023, respectively) and BB+HP 0°C

(Figure 8.1: P = 0.033). Additionally, final core temperatures in PB -18.5°C and BB -18.5°C were

also lower than PB 18.5°C (P = 0.038 and P = 0.022, respectively). BB+HP in -18.5°C was not

lower than any final core temperature in a warmer ambient condition except BB 18.5°C (P = 0.038)

which was also higher than PB in -18.5°C (P = 0.026).

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Figure 8.1. Final core temperature after 240-minute exposure to 18.5°C, 0°C and -18.5°C in three

field cold casualty interventions and a control. Values are Means ± SD. * significant difference vs.

CON 0°C; † significant difference vs. PB-18.5°C, a significant difference vs. CON 18.5°C, b

significant difference vs. PB 18.5°C, c significant difference vs. BB+HP 18.5°C, d significant

difference vs. BB+HP 0°C, e significant difference vs. BB 18.5°C (P < 0.05).

8.4.2 Hourly change in Core Temperature

At 60 minutes of exposure to thermo-neutral conditions (18.5°C) the reduction in core temperature

was greater in PB compared to BB+HP and continued to increase throughout the remainder, with a

final difference at 240 minutes of 2.9°C (Figure 8.2A: F(3, 3) = 11.890, P = 0.036, η2 = 0.067). The

hourly change in core temperature within each thermo-neutral trial was greater following the initial

core temperature at the onset of exposure (Figure 8.2A: F(4, 4) = 533.447, P = 0.000, η2 = 0.002).

Similarly, a main effect of time in 0°C also established that the hourly change in each trial was

120

greater following the onset of exposure (Figure 8.2B: F(4, 4) = 1638.403, P = 0.000, η2 = 0.001). The

amount of heat loss during CON in 0°C was greater each hour compared to the other trials in that

environment (Figure 8.2B: F(12,12) = 7.584, P = 0.001, η2

= 0.116). No differences occurred between

PB and BB. However, following 120 minutes, the amount of heat lost was greater in PB and BB

compared to BB+HP. The difference continued to increase over each hour so that by 240 minutes

PB and BB had lost 14°C whereas BB+HP had only lost 7.6°C.

Following 60 minutes of exposure to -18°C, core temperature change was greater during CON

compared to all trials (P = 0.05). Exposure to -18°C evoked an interaction whereby BB+HP had the

smallest amount of heat loss at 60 minutes of exposure compared to CON and PB trials (Figure

8.2C: F(12, 12) = 15.364, P = 0.000, η2 = 0.061). The difference in core temperature between these

trials continued to increase at each hour throughout. No difference occurred between BB and

BB+HP until 180 minutes, yet a difference between PB and BB was established an hour earlier and

continued to increase throughout the remainder of the exposure. With each hour following the onset

of cold exposure core temperature heat loss increased in all trials (Figure 8.2C: F(4, 4) = 1314.03, P

= 0.000, η2 = 0.001).

121

Figure 8.2 Hourly change in core temperature during 240 minute exposure to A, 18.5°C, B, 0°C

and C, -18.5°C in three field cold casualty interventions and a control. Values are Means ± SD. #

significant difference vs. 0; * significant difference vs. CON; † significant difference vs. PB, ‡

significant difference vs. BB (P < 0.05).

A

B

C

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8.4.3 Predicted Survival for Non-Shivering Cold Casualty

Time to 32°C from 37°C was calculated as an estimate of time to mortality with traumatic injury

(Moss, 1986; Jurkovic et al. 1987). During CON -18.5°C time to 32°C was lower (30 mins)

compared to any other trial (Table 8.1). PB -18.5°C demonstrated a similar time to 32°C as CON

0°C, but was less than CON 18.5°C, PB 18.5°C and BB+HP 18.5°C. The longest time to 32°C from

37°C was observed during BB+HP 18.5°C (230 mins) which was longer than CON 0°C, PB 18.5°C

and CON -18.5°C (P = 0.05) (Table 8.1). Time to 32°C during BB+HP 0°C was the same as PB

18.5°C. Time to 32°C did not differ between BB 0°C and BB -18.5°C. Time to 32°C during

BB+HP -18.5°C was similar to CON 18.5°C. No differences occurred between PB and BB when

exposed to the different ambient temperatures, yet time to 32°C was slightly longer during BB

exposure to 0°C and -18.5°C (Table 8.1).

Following the reduction of core temperature to 32°C, the time to 24°C for each trial was calculated

as an estimate of time from cessation of shivering (non-trauma related hypothermia) to apparent

death (Durrer et al. 1998). Exposure to thermo-neutral conditions (18.5°C) did not cause a reduction

in core temperature to 24°C in any trial (Table 8.1). However, time to 24°C from 32°C was less

during CON in 0°C compared to PB (P = 0.033) and a trend occurred between CON and BB (P =

0.07) (Table 8.1: F(5, 5) = 25.293, P = 0.001, η2 = 0.038). Core temperature did not reduce to 24°C

in any of the temperature controlled environments for BB+HP.

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Table 8.1. Time to 24°C from 32°C during 240 minute exposure to 0°C and -18.5°C.

Values are mean ± SD. a significant difference vs. CON 18.5°C, * significant difference vs. CON

0°C, b significant difference vs. PB 18.5°C,

c significant difference vs. BB+HP 18.5°C,

d significant

difference vs. BB+HP 0°C, f vs. CON -18.5°C (P < 0.05). Abbreviations: N/A, not applicable.

8.4.4 Results summary

After 240 minutes exposure to 18.5°C there were no differences between the final core temperatures

in any of the trials. However, after 240 minutes in -18.5°C the final core temperature in BB+HP

(26.0°C) was greater than PB (16.5°C). The longest time to 32°C from 37°C was observed during

BB+HP 18.5°C (230 mins) which was longer than CON 0°C, PB 18.5°C and CON -18.5°C. Core

temperature did not reduce to 24°C in any of the temperature controlled environments for BB+HP.

Trial Time from 32°C to 24°C (mins) Time from 37°C to 32°C (mins)

CON 18.5°C N/A 90 ± 1

PB 18.5°C N/A 163 ± 11f

BB 18.5°C N/A 180 ± 57

BB+HP 18.5°C N/A 230 ± 1*bf

CON 0°C 93 ± 4 38 ± 11

PB 0°C 140 ± 1* 75 ± 28

BB 0°C 160 ± 7 68 ± 11cdf

BB+HP 0°C N/A 163 ± 18*f

CON -18.5°C 53 ± 4 30 ± 7

PB -18.5°C 98 ± 18 38 ± 4abc

BB -18.5°C 115 ± 14 68 ± 4c

BB+HP -18.5°C N/A 88 ± 4c

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8.5 Discussion

The aim of the present investigation was to examine field cold protection methods in a non-

shivering casualty model. To simulate real-life rescues these methods were studied over a four-hour

period in a range of environmental temperatures. In support of the hypothesis the Blizzard Heat

survival bag was superior compared to other devices in all environmental temperatures as indicated

by a higher final core temperature. Additionally, the Blizzard Heat survival bag was the only

method that prevented core temperature reaching 24°C, a temperature associated with death (Durrer

et al. 1998). As reported previously, Blizzard survival was superior to polythene (Allen et al, 2010),

yet neither could maintain a core temperature above 24°C during exposure to 0°C. These results

imply that for a non-shivering casualty, lying sedentary and awaiting rescue in a cold environment,

survival time may be increased by the immediate administration of a lightweight active warming

survival device, such as the Blizzard Heat survival bag.

During exposure to 0°C, the hourly reduction in core temperature from the in vitro torso model

protected with a Blizzard Heat survival bag was not only less than the passive devices exposed to

the same conditions, but replicated that of both passive devices in a thermo-neutral environment

(18.5°C). This novel finding supports a previous investigation where an active heating combination

of a multi-layered metalized sheeting survival bag (Blizzard Reflexcell™) with chemical heat pads

was superior to all other methods tested (Allen et al. 2010). Nonetheless, this previous investigation

only exposed fluid models to a thermo-neutral ambient temperature which does not reflect the likely

cold environments experienced by casualties. Exposure to -18.5°C evoked a similar outcome as 0°C

so that the hourly reduction in core temperature from the model protected with a Blizzard Heat

survival bag was again, not only less than both the polythene and Blizzard survival bags in the same

conditions but similar to these passive devices in 0°C. Hourly heat loss was also similar between the

in vitro torso model protected with a Blizzard Heat survival bag in -18.5°C and no protection in

thermo-neutral conditions. These findings have implications for trauma casualties wounded in

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warmer conditions, who, when air lifted by helicopter will experience ambient temperature drops up

to -15°C per 1000 feet of altitude gain (Johnson et al. 2010). It is likely a Blizzard Heat survival bag

will decrease the risk of accelerated heat loss during altitude gain and as such, reduce trauma related

fatalities.

When exposed to 0°C and 18.5°C, the polythene bag and Reflexcell device without chemical heat

pads (Blizzard survival bag) presented similar hourly heat loss and final core temperatures. This

contradicts a recent investigation where the same multi-layered survival bag was found to be

superior in comparison to single-layer polythene in thermo-neutral conditions (Allen et al. 2010).

Nonetheless, when the fluid model was protected with the Blizzard survival bag, hourly heat loss in

-18.5°C with still air (equivalent to -15°C with 6 km∙h-1

wind speed, -10°C with 20 km∙h-1

wind

speed and -5°C with 95 km∙h-1

wind speed) was less compared with polythene. This also meant the

final core temperature was higher with the Blizzard survival bag which in combination suggests as

ambient temperatures decrease, multi-layered devices are better at reducing heat loss which may

increase survival times and reduce the number of hypothermia related fatalities, particularly when

time to 24°C from 32°C was greater in the Blizzard bag compared to polythene in 0°C and -18.5°C.

However, as aforementioned, when protected with an active device, core temperature did not

decrease to a critical level in any ambient condition.

When the fluid models were exposed to any temperature with no protection, a greater reduction in

core temperature was observed compared to when a protective layer was available. This suggests

for cold casualties unable to shiver, any extra layers that can be provided may indeed reduce the

decline in core temperature (Hamilton and Paton, 1996). Active heating devices such as chemical

heat pads are more beneficial for the immediate field treatment of hypothermic casualties prior to

evacuation to superior methods because of the additional heat energy being put into the system,

particularly when core temperature is critically low (i.e. < 32°C) (Durrer et al. 1998; Allen et al.

2010). Furthermore, of the devices tested in the present study, following the evacuation of

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casualties from cold to thermo-neutral temperatures (e.g. 18.5°C), an active warming device may

provide the most superior protection for a non-shivering casualty. This is because only a modest

decline in core temperature occurred in 18.5°C during the four hour exposure in comparison to

when fluid models were covered with passive devices.

Regarding surface temperature among all the devices examined, not one met the threshold

temperature considered to cause thermal injury (Moritz and Henriques, 1947) which has also been

shown with human subjects (Appendix J). Similar to previous research (Allen et al. 2010), given

the fluid model in the present study did not consist of a biological organism and had no basal

metabolic activity, extrapolation of this study to efficacy in humans may be limited. Despite this,

the model was effective in detecting drops in temperature among the devices exposed to different

ambient temperatures. Furthermore, the findings of this study reinforce those of a recent

investigation by our group where the multi-layered metallised sheeting with chemical heat pads was

the most superior device (Chapter 6). As such, re-warming of mildly hypothermic cold casualties

to near resting core temperatures occurred with significantly less energy expenditure.

The present study suggests a continuum exists for the amount of heat lost, whereby the lower the

ambient temperature is the greater the difference between heat lost from a passive device is

compared with active heating. Given an increased risk of accidental hypothermia accompanies

previous conclusions in earlier chapters, findings here have implications for those individuals

climbing to high altitudes in cold conditions (Chapter 4 and 5) and those who by accident, have

been immersed in cold water in cold ambient conditions (Chapter 6 and 7). In conclusion, a non-

shivering fluid model exposed to different ambient environments suggested that the effectiveness of

chemical heat pads in combination with a triple layered, metallised survival blanket may counteract

the decline in thermogenesis accompanying the onset of severe hypothermia or administration of

sedatives thus preventing hypothermia related fatalities including those combined with trauma.

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CHAPTER NINE

General Discussion

9.1 Background

Military personnel, athletes and outdoor enthusiasts frequently travel to cold, mountainous regions

for work, training and recreational activities. It is not uncommon therefore, for such individuals to

be exposed to the extreme environmental conditions of cold and cold with hypoxia for prolonged

periods of time. Additionally, arrival at high altitude predominantly occurs prior to hypoxic

acclimatisation. High altitude environments have been suggested to alter thermoregulatory,

metabolic, perceptual (Blatteis and Lutherer, 1976; Johnston et al. 1996; Golja et al. 2004) and

immune responses (Pedersen and Steensberg, 2002) to the cold which may increase the

susceptibility to cold injury (e.g. frostbite, hypothermia) and infection (e.g. URTI). Accidental

hypothermia affects approximately 10% of casualties reported in mountainous environments and is

a significant contributor to fatalities (Moss, 1986; Sharp, 2007). Cold exposure alone is associated

with an increased incidence of bronchorrhea and URTI (Giesbrecht, 1995; Castellani et al. 2002). It

has been suggested that a continuum exists for the effects of body core cooling on immune function

whereby mild decreases in core temperature have little stimulatory effects, but more severe

decreases have depressive effects (Costa et al. 2010). Given the cold and hypoxic environments that

may be encountered during wilderness or mountainous pursuits and the subsequent risks to

thermoregulation and immune function the main objectives of this thesis were to investigate: 1. the

effects of acute and chronic exposure to high altitude on thermoregulation, metabolism (Chapter 4)

and mucosal immune responses (Chapter 5) during cold exposure; 2. the effectiveness of four field

methods for the treatment of cold casualties on thermoregulation and metabolism during an

‘awaiting rescue’ scenario in 0°C following cold water immersion (Chapter 6); 3. the mucosal

immune response to prolonged cold exposure in cold casualties (Chapter 7); and 4. the efficacy of

128

three field protection methods for the treatment of non-shivering cold casualties using an in vitro

torso model exposed to -18.5°C, 0°C and 18.5°C for four hours (Chapter 8).

Findings from the two threads of experiments in this study (i.e. thermoregulation and mucosal

immunity) can be integrated together to help produce a clear representation of potential health risks

for those individuals performing activities in extreme environments including cold and/or hypoxia.

Such findings could be applied and used in practise by a wide spectrum of associations including,

but not limitied to, the medical industry, the military and outdoor pursuits companies. Knowledge

gained from this thesis may help to reduce hypothermic related casulaties in the field and reduce a

potential increased susceptibility to illness and infection from pursuits in these extreme

environments.

9.2 Summary of Main Findings

Un-acclimatised men exposed to hypoxia in the cold demonstrated a reduced capacity for NST via

an increased catabolism of CHO substrates which may have been responsible for the earlier onset

and increased intensity of shivering activity. Nonetheless, hypoxia, regardless of acclimatisation,

did not impair typical core or mean skin temperature responses to the cold. Following an 18 day

high altitude mountaineering expedition, a decrease in shivering despite no changes in core or mean

skin temperature is consistent with a greater reliance on NST. The alterations observed post-

expedition in thermal comfort may suggest greater thermal tolerance but increased susceptibility to

cold injury (Chapter 4). Saliva flow rate was altered during un-acclimatised exposure to hypoxia in

the cold compared with post-expedition, yet α-amylase concentration was increased in the cold with

and without hypoxia in all conditions. However, since s-IgA concentration and secretion rate were

unchanged regardless of hypoxia or cold, it is unlikely reductions in arterial oxygen saturation

negatively effect the mucosal immune response to cold at the level employed in the study (Chapter

5). All four field re-warming methods supported re-warming of shivering cold casualties to near

129

normal resting core temperatures within three hours of cold exposure. Although typical re-warming

parameters were not different between either intervention, metabolic heat production was greater in

polythene bag trials compared with Blizzard during the first hour of cold exposure. Re-warming in

the Blizzard survival bags was achieved with lower TEE which may be beneficial for long term

survival (Chapter 6). While s-IgA concentration was unchanged during and following prolonged

cold stress, saliva flow rate and s-IgA secretion rate were reduced and α-amylase concentration was

increased until the return to normal resting core temperature. This supports that a reduction in core

temperature (≥ 1.5°C) may increase susceptibility to illness and infection (i.e. URTI, influenza)

(Chapter 7). A non-shivering torso model reinforced suggestions that the Blizzard Heat survival

bag was the most superior of the field treatments investigated by demonstrating a reduced amount

of core temperature heat loss and an increase in predicted survival time (Chapter 8).

9.3 Thermoregulation, metabolism and perception

Core and mean skin temperature were unaffected by exposure to hypoxia in the cold regardless of

hypoxic acclimatisation. Similar decrements in core and mean skin temperature were observed

during 2 hours supine rest in SL (FiO2: 20.9%), UN (FiO2: 12.5%) and PEX (FiO2: 12.5%)

conditions (Chapter 4). These results suggest that underlying homeostatic mechanisms are robust

to unaccustomed environmental conditions in order to maintain primary thermoregulation (i.e. core

and skin temperature). Earlier reports are contradictory however, and compared with cold alone, un-

acclimatised exposure to cold and hypoxic environments has been associated with a reduction in

core temperature and an increase in skin temperature (Bullard, 1961; Cipriano and Goldman, 1975;

Kottke et al. 1948). Nonetheless, core temperature has been reported elsewhere as unaltered during

both normobaric and hypobaric hypoxia in the cold (Blatteis and Lutherer, 1976; Brown et al. 1952;

Robinson and Haymes, 1990). A limitation of chapter 4 is that the exposure temperature was 15°C

which may be considered too mild to evoke such a thermoregulatory stress. However, in

130

combination with a simulated high altitude of 4000m it was regarded as an extreme and

unaccustomed climate for the participants taking part. Additionally, this ambient temperature has

been used previously in studies where differences did occur (Cipriano and Goldman, 1975). Given

that the body of evidence surrounding the effect of hypoxia on thermoregulatory responses in the

cold includes a wide spectrum of methodological differences, it would appear that thermoregulatory

alterations cannot be predicted, and therefore suitable precautions, such as following acclimatisation

protocols ahead of travelling, should be taken upon ascent to high altitude.

The metabolic response to cold was impaired during un-acclimatised exposure to hypoxia (Chapter

4). A reduction in heat production coupled with an earlier onset and more intense shivering activity

supports that acute hypoxia suppresses NST (Blatteis and Lutherer, 1976; Bullard, 1961; Gautier,

1996; Robinson and Haymes, 1990). Additionally, significant alterations in lipid and carbohydrate

oxidation were demonstrated prior to acclimatisation. It is plausible to suggest that the hypoxic-

induced suppression of NST by an inhibition of the aerobic catabolism of lipid stores may occur

through an increased hormonal response to hypoxic stress which decreases the lipolytic response of

adipocytes and thus lowers lipid mobilisation (de Glisezinski et al. 1999; Masoro, 1966; Robinson

and Haymes, 1990). As a result, carbohydrate oxidation is increased to fuel intense shivering

thermogenesis (Martineau and Jacobs, 1988). In turn, this may explain how the body maintains core

and mean skin temperature despite the absence of NST in hypoxia (Chaper 4). The severity of

hypoxia-induced metabolic alterations, as a diagnostic marker of homeostatic disruption at altitude,

appears to provide more information regarding the effects of hypoxia during cold exposure

compared to core and mean skin temperature alone. Given that the metabolic response remained

impaired following acclimatisation but shivering activity was reduced, supports that NST recovery

may occur following a high altitude stay (Blatteis and Lutherer, 1976; Mathew et al. 1979). Since

the work in this thesis (Chapter 4) was the first to quantify shivering using electromyography

provides a particularly novel aspect that previous investigations do not.

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Behavioural thermoregulation is initiated by the perception of thermal comfort (Golja et al. 2004).

In support of a previous report (Golja et al. 2005), acute exposure to a reduced oxygen supply prior

to acclimatisation did not alter sensitivity to the cold. Given core and mean skin temperatures were

similar between trials it is likely the neural information transformed from peripheral sensors giving

rise to the perception of thermal comfort was also similar (Chapter 4). However, following an 18

day altitude expedition the sensation of cold was decreased and thermal comfort was increased

which suggests prolonged hypoxic exposure may impair nerve conduction so that thermal

information is impeded (Golja et al. 2004; Malanda et al. 2008). Consequently, acclimatised

individuals at altitude may often feel warmer than their core temperature would suggest. As a result,

behavioural thermoregulation may be neglected. These alterations observed post-expedition may

suggest a greater thermal tolerance but an increase in susceptibility to cold injury (Chapter 4).

Chapter 6 examined four field re-warming methods for the treatment of cold casualties. Core

temperature re-warming rate was unaffected by the type of re-warming device administered and in

all cases where cold individuals were able to adequately thermoregulate (e.g. shiver) the time taken

to return to normal resting core temperature values was the same. This finding provides further

support to a conclusion of Chapter 4, suggesting that homeostatic mechanisms ensure optimal core

temperature control during exposure to environmental stressors where core temperature is

compromised. Mean weighted skin temperature differed between the field methods however,

whereby the triple-layered metallised sheeting survival bags maintained a higher skin temperature

throughout the cold exposure compared to polythene trials. The administration of hourly hot drinks

(~430 ml) seemed to confer no thermoregulatory advantage compared with polythene survival bags

alone. It is plausible to suggest that these multi-layered devices may reduce the pre-disposition to

peripheral cold injuries (e.g. frostbite) during more prolonged cold exposures (Chapter 6). As a

likely result of the lower mean skin temperature during polythene trials, metabolic heat production

was greater compared with the Blizzard survival bags during the first hour of cold exposure.

132

Furthermore, re-warming in the Blizzard Heat survival bag was achieved with lower TEE which

may be beneficial for long term survival (Tikuisis, 1995; Tikuisis et al. 2002). As hypothesised, a

consequence of the superior protection provided by the Blizzard Heat survival bag improved the

perception of pain and thermal comfort.

That the Blizzard Heat survival bag offered superior thermal protection compared with single layer

polythene (Chapter 6) was also suggested by the results of Chapter 8. An in vitro torso model

exposed to the cold suggested that the Blizzard Heat survival device could maintain a higher core

temperature throughout prolonged exposure to extreme conditions than other methods tested. This

supports previous findings where an active heating combination of a multi-layered metalized

sheeting survival bag (Blizzard Reflexcell™) with chemical heat pads was superior to all other

methods tested (Allen et al. 2010). The findings of Chapter 8 however, offer more information

regarding the depth of thermal protection provided by each device as a result of the number of

different ambient conditions they were exposed to. Consequently, the active heating device was the

only treatment able to prevent core temperature from becoming fatally low in all ambient conditions

when shivering was absent (~24°C; Durrer et al. 1998).This may imply for a non-shivering

casualty, lying sedentary and awaiting rescue in a cold environment, survival time may be increased

by the immediate administration of a lightweight active warming survival device, such as the

Blizzard Heat survival bag. While the results from this in vitro study have obvious limitations, the

model was effective in detecting drops in temperature among the different devices exposed to

different ambient temperatures.

133

9.4 Mucosal Immunity: Saliva flow rate, s-IgA concentration, s-IgA secretion rate, α-

amylase concentration and α-amylase secretion rate

Cold exposure is associated with an increased incidence of bronchorrhea, sinusitis, and URTI

(Clothier, 1974; Giesbrecht, 1995; Castellani et al. 2002; Lavoy et al. 2011). A decrease in s-IgA

has been implicated as a possible causal factor in the increased susceptibility to URTI (Hanson et

al. 1983; Nieman and Nehlsen-Cannarella, 1991; Gleeson et al. 1999; Cairns et al. 2002).

Coincidentally, modest whole body cooling (Trec 35.9°C) via cold air exposure (0°C) has

demonstrated a decrease in s-IgA responses (Costa et al. 2010), nevertheless literature surrounding

the effects of hypoxia on saliva responses are limited (Meehan et al. 1988; Muchmore et al. 1981).

Further, whether the combination of hypoxia and cold exacerbates alterations in mucosal immunity,

until now has not been examined.

Contradictory to the hypotheses in Chapter 5, hypoxia did not alter typical mucosal immune

responses in the cold. However, following cold water immersion to reduce core temperature to

36°C in a normoxic environment, s-IgA secretion rate was reduced and α-amylase concentration

was increased (Chapter 7). This suggests that when cold stress is mild (15°C) and core temperature

remains un-compromised, hypoxia unlikely increases the predisposition to URTI. Nonetheless,

given that s-IgA secretion rate was altered following a more severe cold stress in normoxia

(Chapter 7), it is not unreasonable to suggest that colder conditions in hypoxia may indeed evoke

s-IgA alterations, particularly as saliva flow rate was mildly suppressed in hypoxia in combination

with a cold induced increase in α-amylase concentration (Chapter 5). Although physiological

mechanisms underlying mucosal alterations remain unclear, it is likely that both neural and

endocrine factors influence such responses (Pedersen and Steensberg, 2002). As arterial oxygen

saturation was reduced during un-acclimatised hypoxic exposure in Chapter 5, both the neural and

endocrine systems may have been compensating to maintain homeostasis (Mazzeo, 2005), thus

explaining the difference in saliva flow rate. Nonetheless, the absence of hypoxia-induced s-IgA

134

alterations to cold suggests the mucosal immune system may be robust to a combination of

environmental stressors and as such common URTI complaints may not resonate upon arrival to

high altitude.

Following a prolonged stay at altitude, saliva flow rate, α-amylase and s-IgA responses remained

unaltered during hypoxic exposure in the cold. This may be as a result of the observed recovery in

arterial oxygen saturation to near normal sea level values following the 18 day expedition. Given an

altitude of 3500m has been suggested to correspond to the threshold at which the physiological

changes intended to tolerate the drop in partial pressure of oxygen fail to fully compensate the effect

of hypoxia (Colin et al. 1999), it has been speculated that at or above this altitude the adverse effect

of hypoxia on s-IgA is more substantial (Tiollier et al. 2005). However, in Chapter 5, both un-

acclimatised and acclimatised participants exposed to a simulated altitude of 4000m while at rest

displayed no alterations in s-IgA. Therefore, it is more likely the previously observed s-IgA changes

(Tiollier et al. 2005) were not due to the level of hypoxia per se or as a result of chronic exposure

but more likely a cumulative effect of intense physical training. Additionally, the normobaric nature

of the altitude exposure during Chapter 5 and other work (Tiollier et al. 2005) does not suitably

replicate typical high altitude conditions. If barometric pressure was manipulated to reflect the value

coinciding with that level of altitude (i.e. 661mmHg at 4000m) the impact on homeostasis and

subsequent mucosal immune status may be greater during cold exposure. On the contrary, since s-

IgA concentration and secretion rate were unchanged in both altitude exposures compared to

normoxia (Chapter 5) suggests it is unlikely that altitude exposure while at rest, before and

following an altitude stay, causes disruption to either sympathetic nervous system activity (Mazzeo

et al. 2003) or alpha-adrenergic mechanisms (Ring et al. 2000). In conclusion, exposure of

lowlanders to normobaric hypoxia, whether acute or following a prolonged stay, does not evoke a

physiological or metabolic stress great enough to disrupt the typical mucosal immune response to

cold. Very little resesrch exists with regard to mucosal immunity at altitude so while the experiment

135

here (Chapter 5) does not offer masses of information it does provide the beginnings of what

should be an area of continual investigation.

Chapter 7 identifies that saliva flow rate and s-IgA secretion rate are reduced and α-amylase

concentration increased in mildly hypothermic, sedentary individuals exposed to the cold. These

findings are consistent with previous work (Costa et al. 2010), yet the results of Chapter 7 are

strengthened by the inclusion of a thermo-neutral control trial to account for the diurnal variations

in saliva parameters. However, that cold exposure and mild hypothermia reduce s-IgA secretion rate

should be suggested with caution. This is because s-IgA secretion rate at baseline, prior to cold

exposure, was also lower than at that same time during thermo-neutral control. While psychological

stress has been found to reduce s-IgA concentration in humans (Stone et al.1987; Stone et al. 1994;

Cohen et al. 2001), it is possible that participants were more anxious on the morning of their cold

trial and as a result s-IgA responses were already altered. In the future, blinding participants to the

trial may avoid this potential anticipatory effect. Nonetheless, following re-warming, s-IgA

secretion rate was greater and α-amylase concentration lower than when participants displayed their

lowest core temperature, whereas no significant changes occurred throughout the thermo-neutral

control trial. This suggests that until re-warming is initiated, cold, sedentary individuals are at risk

from increased mucosal immune disturbance which supports the popular belief that most common

colds occur because the host is exposed to a cold environment (Dowling et al. 1958; Biggar et al.

1984). Furthermore, Chapter 7 provides some evidence that there may be a direct causal relation

between an individual getting cold and subsequently developing an infection (Lavoy et al. 2011).

To confirm this however, studies including larger subject numbers would be beneficial. In

conclusion, a reduction in core temperature (≥ 1.5°C) resulting from cold water immersion and

subsequent cold air exposure suppresses the usual daily s-IgA response which may increase

susceptibility to illness and infection (i.e. URTI, common colds, influenza) if re-warming is not

initiated immediately.

136

9.5 Future directions

Work in this area could continue to develop firstly by repeating the experiments outlined in this

thesis in order to gain larger sample sizes and thus, more specific conclusions. Secondly, methods

for each experiment could be performed in conditions that pose a greater strain on the human body

(e.g. colder and more hypoxic) to demonstrate particular thresholds for normal human body

function. It would be beneficial to examine a wider variety of immune parameters in order to

provide a more complete template of the likely effects of exposure to extreme environments.

137

9.6 Conclusions

The major conclusions from this thesis are:

I. Demonstrated by a reduced capacity for NST via an increased catabolism of CHO, exposure

to hypoxia in the cold impairs the thermoregulatory and metabolic response of un-

acclimatised men.

II. Exposure to a simulated high altitude of 4000m in the cold following an 18 day

mountaineering expedition evokes a decrease in shivering activity despite no changes in

core or mean skin temperature which likely represents a greater reliance on NST for heat

production.

III. Alterations observed post-expedition in thermal comfort during exposure to a simulated high

altitude of 4000m in the cold may suggest a greater perception of thermal tolerance but an

increase in susceptibility to cold injury.

IV. Two hours of exposure to a simulated high altitude of 4000m does not disrupt the typical

mucosal immune response to cold regardless of hypoxic acclimatisation status. Common

URS are not likely to be increased upon arrival to high altitude or following a prolonged

stay.

138

V. Of four cold treatment methods tested in 0°C, with minimal wind, all were able to assist

shivering cold casualties to increase core temperature to normothermia within three hours.

VI. Blizzard survival bags are a more efficient field re-warming device than polythene bags

given complete core re-warming was achieved with lower total energy expenditure which

may be beneficial for long term survival.

VII. A reduction in core temperature (≥ 1.5°C) resulting from cold water immersion and

subsequent cold air exposure alters the usual daily mucosal immune responses which may

increase susceptibility to illness and infection (i.e. URTI, common colds, influenza) if re-

warming is not initiated immediately.

VIII. In Vitro torso models protected in various ambient temperatures with different cold

protection field treatments highlighted that the Blizzard Heat survival bag was superior at

reducing heat loss which resulted with higher final core temperatures compared to other

devices. This active heating device was the only treatment able to prevent core temperature

from becoming fatally low in all ambient conditions when shivering was absent

IX. The effectiveness of chemical heat pads in combination with a triple layered, metallised

survival blanket may prevent the decline in thermogenesis accompanying the onset of severe

hypothermia or administration of sedatives, thus preventing hypothermia related fatalities in

the field, including those combined with trauma.

139

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182

Appendix A:

Bangor University

School of Sport, Health and Exercise Sciences

Subject Information Sheet

Project Title: An Experimental Study of Practical Field Methods for Cold Casualty Protection and

Treatment during Prolonged Cold Exposure

Research Co-ordinators: Dr Sam Oliver and Dr Neil Walsh

Tel: 01248 383965 Email:s.j.oliver@bangor.ac.uk

Additional Investigators: Dr Matt Fortes, Dr Gavin Lawrence, Jenny Brierley, Alberto Dolci, Phil

Heritage, Aaron Burdett, Robin Wilson, Beth Palmer and James Firman

Invitation to take part

You are being invited to take part in a research study. Before you decide to take part it is important

for you to understand why the research is being conducted and what will be required of you should

you agree to be involved. Please take time to read the following information carefully and discuss it

with the investigators. Ask us if there is anything that is not clear or if you would like more

information.

Do I have to take part?

This is entirely your decision. If you decide to take part you will be given this information sheet to

keep and be asked to sign a consent form. If you decide to take part you are still free to

withdraw at any time without giving a reason. If you decide not to participate or withdraw during

the study, your decision will not affect your relationship with the School of Sport, Health and

Exercise Sciences, or any of the investigators involved in the study. All information collected

during the study will be treated confidentially and if you choose to withdraw then your data will be

deleted from our records.

Background

Prolonged cold exposure and becoming mildly cold is associated with impaired health and

performance. Accidents in cold and wet environments can lead to hypothermia. This is especially

the case when casualties remain stationary or are suffering from trauma with blood loss (for

example, mountaineering or car accident). In the UK average mountain rescue times are typically at

least 2 hours. It is therefore important that easily administrable and transportable cold protection

methods are developed which can be used whilst casualties wait for emergency services rescue.

Ultimately, mortality rates will be decreased if cold protection methods can be developed and

shown to reduce or maintain a casualty’s core temperature. Current field cold protection methods

have been shown to be relatively ineffective (e.g. polythene survival bag), or their effectiveness is

presently unknown (e.g. hot drinks and Blizzard Survival bags). Therefore the present investigation

aims to determine the effectiveness of polythene survival bags with hot drinks and Blizzard survival

bags with and without heat pads.

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Visit One

Project Briefing

30 minutes

Objective

To assess which field method offers optimal protection for casualties in a cold environment.

What will be expected of you?

If you decide to take part in this study there will be a number of constraints placed upon you.

During the day prior to completing a trial you will be expected:

To avoid drinking alcohol or caffeinated drinks (i.e. coffee, tea, coke and diet coke).

To avoid participating in moderate to high intensity exercise.

Whilst completing the experimental trials in the laboratory you will be expected:

To spend one whole day in the laboratory on four separate occasions.

To eat and drink only what is prescribed to you.

Arrive to the laboratory after an overnight fast (10-12 hours)

To follow the study’s timetable.

To be weighed nude (behind screens to maintain privacy).

To have four blood samples taken during each one day trial (~65 ml) totaling 16 blood

samples during the 4 week study period (~260 ml).

To provide saliva and urine samples.

To perform four cold water immersions (~13°C for a maximum of 60 minutes).

To perform four 3 hour cold air tests in 0°C.

To complete a health log 2 weeks prior, during and 2 weeks following the last trial.

You will be excluded if you are a smoker, asthmatic, diabetic, have a pacemaker or any heart

condition or you are currently taking specific types of medication or supplements.

IN TOTAL, THE STUDY WILL REQUIRE YOU TO GIVE UP 34 HOURS OF YOUR

TIME.

Summary of visits

Visit One: Project briefing and familiarisation (1 hour)

At this meeting you will be fully briefed about the requirements of the project. You will be talked

through the subject information sheet by an investigator and given the opportunity to ask any

questions. You will then leave with the information sheet so as to allow you time to discuss your

possible involvement in the study with significant others. This will also allow you additional time to

think of questions.

Visit Two

Question &

Answer

Session

(Optional)

30 minutes

Visit Three

1st

Experimental

trial

8 h

Visit Four

2nd

Experimental

trial

8 h

Visit Five

3rd

Experimental

trial

8 h

Visit Six

4rd

Experimental

trial

8 h

184

You will be asked to refrain from exercise and alcohol and caffeine consumption for 24 hours prior

to each visit. At this visit you will be familiarised with the procedures for collection of saliva and

venous blood. All blood samples will be collected by a qualified member of staff from a forearm

vein using a small needle (~16 ml of blood at each collection). A saliva sample will be obtained by

asking you to dribble into a plastic container for 5 minutes. You will also be familiarised with the

cognitive function tests and also the health log which you will be asked to complete at the end of

each day.

Visit Two: Question and answer session (optional)

Visit two is provided as an additional opportunity for you to ask questions. Once you are fully

satisfied with the information and on agreement to take part in the study you will be asked to

complete an informed consent form, a medical questionnaire and make arrangements for the

following visits.

Experimental trials:

You will be required to complete four experimental trials in a random order each separated by 7

days. Each experimental trial will consist of an 8 hour period where you will be in the laboratory

under treatment conditions (Visit three, four, five and six). Including the briefing meeting,

familiarisation visit and all four experimental trials you will be required to visit the

laboratory on seven occasions for a total of ~34 hours.

Visit Three, Four, Five and Six: (8 hours)

Prior to arriving at the laboratory

You will be instructed to consume your normal daily food intake and keep a food diary of what you

ate the day before the trial. We will also provide you with your daily water requirements

(approximately 2.5 L for a 70 kg person), which will help to ensure that you are hydrated prior to

each trial. We ask that you arrive at the physiology laboratory with the appropriate clothing (i.e.

swim shorts, a second pair of dry shorts and a towel) following an overnight fast at 07:00 hours.

Experimental procedures

On arrival to the laboratory and after completely emptying your bladder and bowels, your body composition

will be estimated by a non-invasive bio-electrical impedance analysis; which requires you to stand on a set of

weighing scales. On arrival at the laboratory you will be given a rectal probe to fit, and a universal container

with which to collect a urine sample. The rectal probe will be used to monitor core temperature. You will

also be asked to wear a chest strap so that we can monitor your heart rate. You will then sit quietly for 30

minutes in the laboratory (ambient temperature ~20°C) after which blood and saliva samples will be obtained

and you will complete the cognitive function tests. You will then enter the cold water bath (~13°C) and be

immersed up to your shoulders until your core temperature has decreased to 36°C (~40 minutes). At this

point you will be withdrawn from the water. After drying and putting on your dry shorts you will enter the

environmental chamber (0°C) with one of the four survival bags. You will then be asked to sit on a chair

whilst inside the survival bag. You will be randomly assigned at each trial to one of the four practical cold

protection methods: 1. Polythene survival bag; 2. Polythene survival bag with hot drink; 3. Blizzard Survival

bag and 4. Blizzard Survival Heat bag. After getting into the survival bag and at 1 and 2 hours you will be

provided with a flavoured drink. The quantity of this drink will depend on your body weight but will be

185

similar to a large mug of tea. On one trial (trial 2) this drink will be hot, i.e. similar to that temperature of

regular tea or coffee. You will be asked to consume these drinks within 15 min. Regular measurements of

thermoregulation will be made and core temperature will be continually monitored. Cognitive function tests

and saliva samples will be obtained at one hour intervals. The experimental trials will end and you will be

removed from the chamber at 3 hours or if core temperature decreases to 35°C. Following removal from the

environmental chamber (0°C), a blood and saliva sample will be obtained and you will be wrapped in

blankets. You may be immersed in warm water to aid rewarming. One and two hours following the cold

exposure we will obtain further blood and saliva samples during which time you will sit in a comfortable

ambient temperature ~20°C with blankets or dressed in your normal clothes. During this time, your core

temperature will be monitored and you will be supervised by experimenters. In the second hour of this

recovery you will be provided with a large meal and warm drink. Following the final blood and saliva

sample you will be allowed to eat and drink freely and you will be permitted to leave when your core

temperature returns to with 0.5°C of your initial core temperature. Transport home will be provided if

required.

Advantages of taking part

A benefit of taking part in this study is that you will receive comprehensive feedback, with full

explanations, of your body composition (e.g. body fat %) and blood measures (e.g. immune

function). This feedback should help you with planning and monitoring your athletic training

program. The feedback you will receive regarding your body composition is similar to that which

many testing facilities provide as a fee-paying service. Advantages for Undergraduates from within

SSHES are that you will gain a valuable insight into the procedures and work involved in a 3rd

year

project. Additionally participation in this project can be used for skills units of the Undergraduate

portfolio.

Disadvantages of taking part The disadvantages of taking part in this study, which you will probably be most concerned about, are: 1. cold

exposure test 2. blood samples; and 3. time commitment.

1. Cold exposure: Cold tests lasting two to three hours have been safely used to stress the body’s ability to

maintain core body temperature by our research group and many others. During these cold air tests you will

likely experience some peripheral numbness and mild discomfort in your hands and feet. To minimise this

discomfort, we will provide you with thermal gloves and socks.

A number of military studies have exposed individuals to freezing and/or wet conditions following periods of

prolonged physical exercise, inadequate nutrition and sleep loss, and no medical complications were reported

after rewarming in individuals whose core temperature decreased to 35°C). In these investigations no

voluntary ‘drop out’ or medical withdrawal of subjects was reported. Additionally, in contrast to these

previous investigations in which subjects sat uncovered, the provision of survival bags in the proposed study

will provide insulation.

186

In the current investigation you will be removed from the climate chamber if your core temperature

decreases to 35°C. It is important to note that 35°C is considered the upper limit of mild hypothermia (35-

32°C), and following the removal of cold stress your thermoregulatory mechanisms are likely to steadily

recover normal core temperature (~37°C). For example, in a study using cold water immersion to reduce

core temperature to 33°C participants left to shiver post immersion were able to recover core temperature to

36°C within 1 hour.

Following removal from the chamber you will be wrapped in blankets. In addition, if your core temperature

reduces below 35°C you will be immersed up to the axilla in a warm water bath (38-42°C). This technique

has previously been used in a number of studies to rewarm participants in experiments where core

temperature is decreased to between 33-34°C. For your safety your core temperature will be monitored by a

rectal probe every minute throughout the cold exposure protocol and during the first hour of recovery period

or until your core temperature returns to within 0.5°C of their starting core temperature.

The results of this study will ensure people can be better informed as to the most effective method of cold

protection in extreme environmental conditions.

2. Blood samples: The blood samples will be taken using a smaller needle than is typically used by doctors

in your local surgery or hospital. Therefore you will likely experience only very mild discomfort i.e. like a

scratch. The quantity of blood we are taking in each visit is small (i.e. approximately one tenth of that which

would be obtained when you give blood). Additionally, qualified phlebotomists experienced at performing

this procedure will collect blood samples. To ensure you are completely happy with giving blood samples,

we will familiarise you with the blood sampling procedure on your first visit to the laboratory.

3. Time commitment: To complete all aspects of the study we will require you to visit the

laboratory on six occasions for a total of approximately 33 hours. Thus, participation in this project

satisfies the requirement in hours for the Undergraduate portfolio skills unit.

At all times you will be closely supervised by an experimenter trained in First-Aid.

Any further questions will be happily answered by Dr Sam Oliver or any of the additional investigators.

187

Appendix B:

INFORMED CONSENT TO PARTICIPATE

IN A RESEARCH PROJECT OR EXPERIMENT

Title of Research Project: The researcher conducting this project subscribes to the ethics conduct of research and to the

protection at all times of the interests, comfort, and safety of participants. This form and the

information sheet have been given to you for your own protection and full understanding of the

procedures. Your signature on this form will signify that you have received information which

describes the procedures, possible risks, and benefits of this research project, that you have received

an adequate opportunity to consider the information, and that you voluntarily agree to participate in

the project.

Having been asked by Jenny Brierley of the School of Sport, Health and Exercise Sciences at

Bangor University, to participate in a research project titled:

Effect of hypoxia on the thermoregulatory responses to cold

I have received information regarding the procedures of the experiment.

I understand the procedures to be used in this experiment and any possible personal risks to me in

taking part.

I understand that I may withdraw my participation in this experiment at any time.

I also understand that I may register any complaint I might have about this experiment to Professor

Mike Khan, Head of the School of Sport Health and Exercise Sciences, and that I will be offered the

opportunity of providing feedback on the experiment using standard report forms.

I may obtain copies of the results of this study, upon its completion, by contacting:

Jenny Brierley (Tel: 07825841523 or Email: peu474@bangor.ac.uk)

I confirm that I have been given adequate opportunity to ask any questions and that these have been

answered to my satisfaction.

I have been informed that the research material will be held confidential by the researcher.

I agree to participate in the study

NAME (please type or print legibly): __________________ _____________________________

ADDRESS: (Optional)____________ __________________________________________ ____

___________________________________________ ____________________________ _________

PARTICIPANT’S SIGNATURE: __________________________ DATE: ___ ______

RESEARCHER’S SIGNATURE: __________________________ DATE: _ ________

188

Bangor University

SCHOOL OF SPORT, HEALTH AND EXERCISE SCIENCES

1 Title of project An Experimental Study of Practical Field Methods for Cold

Casualty Protection and Treatment during Prolonged Cold

Exposure

2 Name and e-mail

address(es) of all

researcher(s)

Sam Oliver - pes60b@bangor.ac.uk

Neil Walsh – pes804@bangor.ac.uk

Gavin Lawrence - g.p.lawrence.ac.uk

Matt Fortes – pep006@bango.ac.uk

Jenny Brierley – peu474@bangor.ac.uk

Alberto Dolci – dolcialberto@gmail.com

Phil Heritage – p.heritage@bangor.ac.uk

Bethan Palmer – peu86e@bangor.ac.uk

James Firman – peu81c@bangor.ac.uk

Robin Wilson – peu833@bangor.ac.uk

Aaron Burdett – peu632@bangor.ac.uk

Please tick boxes

1 I confirm that I have read and understand the Information Sheet dated …………………. for the above study. I have had the opportunity to consider the information, ask questions and have had these answered satisfactorily.

2 I understand that my participation is voluntary and that I am free to withdraw at any time without giving a reason, without my medical care or legal rights being affected.

3 I understand that my participation is voluntary and that I am free to withdraw at any time without giving a reason. If I do decide to withdraw I understand that it will have no influence on the marks I receive, the outcome of my period of study, or my standing with my supervisor, other staff members of with the School.

4 I understand that I may register any complaint I might have about this experiment with the Head of the School of Sport, Health and Exercise Sciences, and that I will be offered the opportunity of providing feedback on the experiment using the standard report forms.

189

5 I agree to take part in the above study.

Name of Participant ………………………………………………………………….

Signature …………………………………. Date …………………………………..

Name of Person taking consent…………………………………………………….

Signature …………………………………. Date …………………………………..

WHEN COMPLETED – ONE COPY TO PARTICIPANT, ONE COPY TO RESEARCHER FILE

190

Appendix C:

PHYSIOLOGY INFORMED CONSENT

& MEDICAL QUESTIONNAIRE

Name: …………………………….

Age:………………..

Are you in good health? Yes/No

If no, please explain:

How would you describe your present level of activity? Tick intensity level and indicate approx.

duration.

vigorous moderate low intensity

Duration (Min).

How Often: < once per month

once per month

2-3 times per week

4-5 times per week

> 5 times per week

Have you suffered from a serious illness or accident? Yes/No

If yes, please give particulars:

Do you suffer, or have you ever suffered from:

Asthma Yes No

Diabetes Yes No

Bronchitis Yes No

Epilepsy Yes No

High blood pressure Yes No

Are you currently taking medication ? Yes/No

If yes, please give particulars:

Are you currently attending your GP for any condition or have you

consulted your doctor in the last three months? Yes/No

If yes, please give particulars:

Have you, or are you presently taking part in any other laboratory

experiment? Yes/No

191

PLEASE READ THE FOLLOWING CAREFULLY

Persons will be considered unfit to do the experimental exercise task if they:

have a fever, suffer from fainting spells or dizziness;

have suspended training due to a joint or muscle injury;

have a known history of medical disorders, i.e. high blood pressure, heart or lung disease;

have had hyper/hypothermia, heat exhaustion, or any other heat or cold disorder;

have anaphylactic shock symptoms to needles, probes or other medical-type equipment.

have chronic or acute symptoms of gastrointestinal bacterial infections (e.g. Dysentery,

Salmonella)

have a history of infectious diseases (e.g. HIV, Hepatitis B); and if appropriate to the study

design, have a known history of rectal bleeding, anal fissures, hemorrhoids, or any other

condition of the rectum;

DECLARATION

I agree that I have none of the above conditions and I hereby volunteer to be a participant in

experiments/investigations during the period of …………………20___.

My replies to the above questions are correct to the best of my belief and I understand that they will

be treated with the strictest confidence. The experimenter has explained to my satisfaction the

purpose of the experiment and possible risks involved.

I understand that I may withdraw from the experiment at any time and that I am under no obligation

to give reasons for withdrawal or to attend again for experimentation.

Furthermore, if I am a student, I am aware that taking part or not taking part in this experiment, will

neither be detrimental to, or further, my position as a student.

I undertake to obey the laboratory/study regulations and the instructions of the experimenter

regarding safety, subject only to my right to withdraw declared above.

Signature of Participant:………………………………………………………………..

Date:…………………………………………..

Signature of Experimenter:…………………………………………………………

Date: ………………………………………….

192

Bangor University

SCHOOL OF SPORT, HEALTH AND EXERCISE SCIENCES

Name of Participant ……..…………………………………………………………..

Age ………………………

Are you in good health? YES NO

If no, please explain

How would you describe your present level of activity?

Tick intensity level and indicate approximate duration.

Vigorous Moderate Low intensity

Duration (minutes)…………………………………………………………………….

How often?

< once per month 4-5 times per week

once per month > 5 times per week

2-3 times per week

Have you suffered from a serious illness or accident? YES NO

If yes, please give particulars:

193

Do you suffer, or have you ever suffered from:

YES NO YES NO

Asthma Epilepsy

Diabetes High blood pressure

Bronchitis

Are you currently taking medication? YES NO

If yes, please give particulars:

Are you currently attending your GP for any condition or have you consulted your doctor in the last three

months? YES NO

If yes, please give particulars:

Have you, or are you presently taking part in any other laboratory experiment?

YES NO

PLEASE READ THE FOLLOWING CAREFULLY

Persons will be considered unfit to do the experimental exercise task if they:

have a fever, cough or cold, or suffer from fainting spells or dizziness;

have suspended training due to a joint or muscle injury;

have a known history of medical disorders, i.e. high blood pressure, heart or lung disease;

have had hyper/hypothermia, heat exhaustion, or any other heat or cold disorder;

have anaphylactic shock symptoms to needles, probes or other medical-type equipment;

have chronic or acute symptoms of gastrointestinal bacterial infections (e.g. Dysentery, Salmonella);

194

have a history of infectious diseases (e.g. HIV, Hepatitis B); and if appropriate to the study design, have a known history of rectal bleeding, anal fissures, haemorrhoids, or any other condition of the rectum.

DECLARATION

I agree that I have none of the above conditions and I hereby volunteer to be a participant in

experiments/investigations during the period of February – June 2011

My replies to the above questions are correct to the best of my belief and I understand that they will be

treated with the strictest confidence. The experimenter has explained to my satisfaction the purpose of

the experiment and possible risks involved.

I understand that I may withdraw from the experiment at any time and that I am under no obligation to

give reasons for withdrawal or to attend again for experimentation.

Furthermore, if I am a student, I am aware that taking part or not taking part in this experiment, will neither

be detrimental to, or further, my position as a student.

I undertake to obey the laboratory/study regulations and the instructions of the experimenter regarding

safety, subject only to my right to withdraw declared above.

Signature (participant) ……………………………..…………. Date ……………………..

Print name ……………………………………………………..

Signature (experimenter) ………………….…………………. Date ……………………..

Print name ……………………………………………………….

195

Bangor University

SCHOOL OF SPORT, HEALTH AND EXERCISE SCIENCES

Name of Participant ………………………………………………………………..

Researcher ………………………………………………………………………….

Date …………………………………………………

YES NO

1 Have you had any kind of illness or infection in the last two

weeks?

2 Are you taking any form of medication?

3 Do you have any form of injury?

4 Have you eaten in the last hour?

5 Have you consumed any alcohol in the last 24 hours?

6 Have you performed exhaustive exercise in the last 48 hours?

IF THE ANSWER TO ANY OF THE ABOVE IS 'YES', THEN YOU MUST CONSULT A MEMBER OF STAFF BEFORE

UNDERGOING ANY EXERCISE TEST.

Signature (participant) …………………………………………… Date ………………….

Print name …………………………………………………………

196

Appendix D:

McGinnis Thermal Comfort Scale

1.So cold I am helpless

2.Numb with cold

3.Very cold

4.Cold

5.Uncomfortably cold

6.Cool but fairly comfortable

7.Comfortable

8.Warm but fairly comfortable

9.Uncomfortably warm

10. Hot

11. Very hot

12. Almost as hot as I can stand

13. So hot I am sick and nauseated

197

Appendix E:

100

90

80

70

60

50

40

30

95

85

75

65

45

55

35

25

20

10

15

5

3

7

0

21

13

120

110

• Absolute maximum

”Maximal”

Very strong

Strong Heavy

Somewhat strong

Moderate

Weak

Very weak

Extremely weak Minimal

Nothing at all

Light

Extremely strong

198

Appendix F:

Shivering Intensity Scale – Observer rating scale

0 = No shivering activity

1 = Mild shivering in bursts

2 = Generalised but discontinuous

shivering

3 = Very marked and continued shivering

movements.

199

Appendix G:

PAIN SENSATION SCALE

1 = BARELY COOL

2 = COOL, NO PAIN

3 = COLD, NO PAIN

4 = SLIGHT PAIN

5 = MILD PAIN

6 = MODERATE PAIN

7 = MODERATE – STRONG PAIN

8 = STRONG PAIN

9 = SEVERE PAIN

10 = UNBEARABLE PAIN

200

Appendix H:

201

Appendix I:

A cross-sectional study examining human thermoregulation during survival bag treatment in

the cold

Accidental hypothermia affects approximately 10% of casualties reported in mountainous

environments and is a significant contributor to fatalities (Sallis and Chassay, 1999; Sharp, 2007).

Rescue times for casualties depend on global location and weather conditions. Yet even where

distances are relatively short between emergency services and a casualty (e.g. Scottish Highlands)

the reported times for evacuation are 2.25 hours by helicopter and approximately 3.5 hours when

individuals are evacuated by others means (e.g. on foot) (Crocket, 1995; Hindsholm et al. 1992).

Simple methods that prevent heat loss and promote re-warming which casualties or first-responders

can administer instantly whilst they wait for evacuation will likely reduce hypothermia related

fatalities. Polythene survival bags however, have been shown to confer no additional thermal

protection for a shivering individual compared to single layer MPS. However it remains unknown

whether triple layered MPS reduces heat loss in comparison to single polythene. PURPOSE: To

determine whether a multi-layered survival bag offers superior thermal protection compared to

single-layer polythene in the cold. METHOD: 18 individuals (13 m, 5 f) volunteered to participate.

Participants completed a 5 day wilderness expedition before being randomly assigned to one of two

groups. The groups were 1. Polythene Survival bag (PB) or 2. Blizzard Survival bag (BB). During

the trials participants wore shorts only (vests also for females) and completed a 2 h cold air test

(CAT, 0°C) in a seated position. Core temperature was assessed throughout. A two-way ANOVA

was performed on the core temperature data. RESULTS: Core temperature was not different

between the groups prior to cold exposure and no further differences occurred at any time point

throughout the CAT (Figure A.1). CONCLUSION: For normothermic, shivering individuals at

rest, a multi-layered MPS survival bag conferred no advantage in reducing heat loss compared with

a single-layer polythene bag during cold exposure.

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Figure A.1. The effect of a 120 minute cold air test on core temperature in two field cold protection

interventions (i.e. Polythene survival bag (PB, ∎); Blizzard Survival bag (BB, ◆) Values are Means

± SD.

203

Appendix J.

The effect of chemical heat pads on skin temperature in 10°C, 20°C and 30°C

Chemical heat pads self activate upon contact with air and can continue to supply heat for up to 24

hours. Given thermal injury may occur when skin is heated to above 44°C (Moritz and Henriques,

1947) and survival devices incorporating chemical heat pads may be employed in ambient

conditions that are already warm (e.g. military trauma casualties), it is vital that such heat pads

situated inside survival bags do not supply heat great enough for this threshold to be reached.

PURPOSE: The purpose of this investigation was to examine skin temperature during the

application of chemical heat pads in an ambient temperature of 10°C, 20°C and 30°C. METHOD:

Three volunteers participated in the study (2 f, 1 m). Participants completed three experimental

trials in an environmental chamber wearing shorts and vests only. Trials were: 1. Blizzard Heat in

10°C, 2. Blizzard Heat in 20°C and 3. Blizzard Heat in 30°C. During each trial participants

remained seated inside the Blizzard Heat survival bag which incorporated four chemical heat pads.

Skin temperature was recorded throughout at four sites (calf, forearm, chest and thigh). Data are

presented as Means ± SD. RESULTS: The chemical heat pads did not evoke skin temperatures

above the threshold deemed to initiate thermal injury in any of the three ambient exposures (Figure

A.2). CONCLUSION: The chemical heat pads provided in a Blizzard Heat survival bag do not

cause skin temperature to rise above the threshold temperature considered to cause thermal injury

even in warm environments. This has significant benefit for trauma casualties who are predisposed

to hypothermia even in warm temperatures (e.g. military personnel).

204

Appendix A.2. The effect of chemical heat pads in three ambient temperatures (10°C, 20°C and

30°C) upon skin temperature. Values are Means ± SD.