The Lungs in Special Situations

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Aviation and High Altitude

Physiology


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Composition of AtmosphericGases


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Barometric Pressures

Barometric pressure at sea level is 760mm Hg

As altitude increases, barometric pressuredrops while partial pressure of oxygenremains at 21% PO 2 at sea level is about 159 mm Hg while at

50,000 feet is only 18 mm Hg


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Partial Pressures of O2 andCO2

020

406080

100120140160180

Air Trachea Alveoli Tissues Cells

Oxygen Carbon Dioxide


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Alveolar PO 2 at Different Elevations

CO 2 and water vapor decrease alveolaroxygen Vapor pressure in the alveoli remain at 47 mm

Hg regardless of altitude CO 2 decreases in higher altitudes due to

hyperventilation, more so in the acclimatized

individual


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Alveolar PO 2 at Different Altitudes


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Effect on high altitude on O2saturation

0 10 20 30 40 50

50

60

70

80

90

100

Altitude (thousands of feet)

A r t e r i a

l o x y g e n s a

t u r a

t i o n

( p e r c e n

t )

Pure oxygen

Breathing air


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Acute Effects of Hypoxia

At 12,000 feet drowsiness, lassitude,mental and muscle fatigue, headache,nausea, sometime euphoria

At 18,000 feet twitching or seizures At 23,000 feet coma followed shortly by

death


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Acclimatization

Hypoxia is the primary physiological insulton ascent to high altitude

The response to hypoxia depends on boththe magnitude and the rate of onset ofhypoxia

The process of adjusting to hypoxia,termed acclimatization, is a series ofcompensatory changes in multiple organsystems over differing time courses fromminutes to weeks


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Acclimatization

Most important immediate response of thebody to hypoxia is an increase in minuteventilation Increased ventilation = higher alveolar PO 2 Lowered alveolar PCO 2 = respiratory alkalosis Renal compensation, through excretion of

bicarbonate ion, gradually brings the blood pHback toward normal and allows furtherincrease in ventilation


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Acclimatization

Ventilatory acclimatization requires 4 days Enhanced by acetazolamide


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Acclimatization

Circulatory changes increase delivery ofO2 to tissues Increase HR, CO, BP Pulmonary vasoconstriction to improve VQ Increase in cerebral blood flow Increase in RBC and Hgb concentration Alkalosis causes left shift of O2-Hgb curve


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Natural Acclimatization

Acclimatization begins at infancy Chest size is increased, body size somewhat

decreased, larger right heart Delivery of oxygen is also greatly facilitated


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Work Capacity at High Altitudes

Capacity of all muscles is greatlydepressed in hypoxia, including cardiacmuscle

Acclimatized individuals can perform morework at high altitudes


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Acute Mountain Sickness

Nonspecific symptoms with a broadspectrum of severity

Occurs in non-acclimatized persons in thefirst 48 h after ascent to altitudes above2500 m, especially after rapid ascent (1 dor less)

Exact cause is unknown but cerebraledema may play a role


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Chronic Mountain Sickness

RC mass and hct become very high Blood becomes very viscous

Pulmonary arterial pressure becomeselevated Alveolar hypoxia


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Chronic Mountain Sickness

Right side of the heart becomes greatlyenlarged

Peripheral arterial pressure begins to fall Congestive heart failure Death ensues unless moved to lower

altitude


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Physiology of Deep Sea Diving

and Other Hyperbaric Conditions


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Hyperbarism exposure of blood in thelungs to extremely high alveolar gaspressures


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Sea Depth to Pressure

Depth (feet)

Sea Level3366

100133166200300400500

Atmosphere(s)

1234567

101316


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Effect on Depth on Volume Boyles Law


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Henrys Law

The Henry law states that the solubility ofa gas in a liquid is directly proportional tothe pressure exerted upon the gas andliquid


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Effect on High Partial Pressures onGases on Body

Gases which a diver breathes is nitrogen,oxygen, and carbon dioxide

Nitrogen narcosis at high nitrogenpressures Varying degrees of narcosis at high pressures 1 st symptoms of mild narcosis appear at 120

feet for 1 hour exhibits joviality At 150 to 200 feet, diver becomes drowsy At 200 to 250 feet, too clumsy


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Effect on High Partial Pressureson Gases on Body

Nitrogen narcosis at high nitrogenpressures Characteristics similar to alcohol intoxication Narcotic effect is same as gas anesthetics Nitrogen dissolves freely in the fats of the

body


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Oxygen Toxicity at High Pressures

Effect of extremely high PO 2 on bloodoxygen transport

Effect of high alveolar PO 2 on tissue PO 2 Acute oxygen poisoning

Brain mostly affected cause seizuresfollowed by coma at 4 atm within 30 to 60minutes

Nausea, muscle twitching, dizziness,disturbance of vision, irritability anddisorientation


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Oxygen Toxicity at High Pressures

Excessive intracellular oxidation as thecause of nervous system oxygen toxicity oxidizing free radicals O 2 has little capability oxidizing other chemical

compounds must be active Oxygen free radicals (superoxide O 2-)

Tissues contain enzymes that remove freeradicals (peroxidases, catalases, superoxidedismutases)


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Decompression After Exposure toHigh Pressures

Amount of nitrogen dissolved in bodybecomes great after a person breathes airunder high pressure Blood flowing thru capillaries becomes

saturated with nitrogen saturate tissues not metabolized

When pressure in the lungs normalizes,nitrogen is removed but slowly


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Decompression After Exposure toHigh Pressures

Volume of nitrogen dissolved in body fluidsat different depths At sea level 1L of nitrogen is dissolved in the

body (half in water, half in fat) At 33 feet 2L of N 2 are dissolved, at 100 feet,

4L are dissolved

Water equilibrates in 1 hour while fat takesseveral hours to equilibrate


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Decompression sickness (Bends,Caisson Disease)

If a diver has been beneath the sea longenough and ascends rapidly,decompression sickness develops

Gas forms bubbles due to suddendecompression of gasses

Symptoms depend on where bubblesdislodge (joints, nervous system,pulmonary capillaries)


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Nitrogen Elimination

Decompression tables Tank decompression


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Treatment

Decompression tank


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Helium Oxygen in Deep Dives

Divers working at deep levels between250 to 1000 feet use helium-oxygenmixtures

Helium used due to: One fifth narcotic effects of nitrogen One half as much volume dissolves in tissues Low density of helium

Use 1 percent oxygen mixtures


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Hyperbaric Oxygen Therapy

Oxidizing free radicals responsible foroxygen toxicity are also responsible fortherapeutic benefits Treatment of gas gangrene leprosy

The Lungs in Special Situations

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