Mountain Lab: Studying the effects of stress and extreme conditions on human physiology
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Transcript of Mountain Lab: Studying the effects of stress and extreme conditions on human physiology
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Mountain Lab: Studying the effects of stress and extreme conditions on human physiology
A webinar discussing the effects of tilt, exercise and high altitude on human cardiorespiratory and autonomic nervous systems, as studied in traditional laboratory settings and on location at Everest Base Camp.
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Mountain Lab: Studying the effects of stress and extreme
conditions on human physiology
Dr. Trevor DayAssociate Professor of Physiology Department of BiologyFaculty of Science and TechnologyMount Royal University
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AcknowledgementsTrainees:
Jeff Baden B.Sc. M.Sc. Maria Abrosimova B.Sc. Gary Saran B.Sc. Lauren Lavoie B.Sc. Jamie Pfoh B.Sc. Christina Bruce B.Sc. Kennedy Borle B.Sc. Andrea LinaresRachelle Brandt B.Sc. Kartika Tjandra Ph.D.Michael Tymko M.Sc. Rachel Skow M.Sc. Lindsey Boulet B.Sc.
A special thank you to our research participants, MRU Human Research Ethics Board and Nepal Health Research Council
Collaborators:
Funding & Support:
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Calgary, Alberta, Canada
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Mount Royal University
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Chemoreflex Control of Breathing• Central respiratory chemoreflex• Peripheral respiratory chemoreflex• Central-peripheral chemoreceptor interaction• Intermittent hypoxia • High altitude hypoxia and acclimatization
Cerebral Blood Flow Regulation• Cerebral autoregulation• Cerebrovascular CO2 reactivity• Neurovascular coupling
Hypovolemia and Tilt• Cerebrovascular regulation• Baroreflex responses • Respiratory sinus arrhythmia (RSA)
MRU INTEGRATIVE Physiology labDepartment of Biology, Faculty of Science and Technology
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Kidneys
Heart
Lungs
Brain
Stress Stress
Stress Stress
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List of Acronyms
• ECG: Electrocardiogram
• HR: Heart rate
• BPM: beats per minute
• RSA: Respiratory sinus arrhythmia
• VTI: Inspired tidal volume (L)
• FVC: Forced vital capacity (L)
• MAP: Mean Arterial Pressure (i.e., blood pressure; mm Hg)
• TCD: Transcranial Doppler ultrasound (for brain blood flow)
• MCAv: Middle cerebral artery velocity (using ultrasound; cm/s)
• Q: Cardiac output (L/min)
• V/Q: Ratio relating alveolar ventilation and perfusion of the lung
• PETCO2: pressure of end-tidal CO2 (Torr)
• HUT and HDT: Head-up and head-down tilt
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Novel Integrated Tilt Table-Lower Body Negative Pressure Box (LBNP)
• Built by Michael Tymko (M.Sc.; now PhD student UBC)
• Superimposes tilt and LBNP stressors
• Tilt table allows HUT and HDT• LBNP chamber creates a
negative pressure to translocate blood volume toward the lower body
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2014 Alberta Science and Technology (ASTech) Young Innovator Award
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Michael Tymko recently published an “instruction manual” on constructing LBNP chambers (Nov 2016, In press).
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“The effects of superimposed tilt and lower body negative pressure on anterior and posterior cerebral circulations” Tymko et al., 2016
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2015 American Physiological Society ADInstruments MacknightEarly Career Innovative Educator Award
APS President David Pollock and Anthony Macknightof ADI present the ADInstruments Macknight Early Career Innovative Educator Award to Trevor A. Day
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Respiratory Sinus Arrhythmia (RSA)
• RSA is the normal fluctuation of heart rate in phase with the respiratory cycle
• Inspiration = increase in HR• Expiration = decrease in HR• HR quantified from the
ECG• The “peak-valley” of the
HR tracing quantifies RSA magnitude
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• These signals are processed in ADI LabChartPro from analog inputs
• IHR from ECG• MAP from a raw
finometer input• MCAv mean from TCD• VTI from respiratory flow• PETCO2 from breath by
breath expired gas analyzer
• Note that MAP and MCAvfluctuate in phase with RSA
RSA affects blood pressure and brain blood flow
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Possible mechanisms underlying Respiratory sinus arrhythmia (RSA)
RSA magnitude is thought to represent the dominance of parasympathetic nervous system tone at rest.
Possible mechanisms include:
1. Firing of respiratory neurons impacting the firing of cardiac motor neurons in the brainstem.
2. Stretch receptors in the lungs and chest wall.
3. Changes in blood pressure with breathing acting on arterial baroreceptors (carotid and aortic sinus).
4. Changes in venous return and cardiac loading with breathing stimulating low pressure receptors in the right atrium (Bainbridge reflex).
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Respiratory Pump
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Inspiration
Increased heart rate
Increased venous return
Increased right atrial pressure
Inhibition of medullary cardiac neurons and vagal withdrawal
Stimulation of stretch receptors in right atria and pulmonary artery
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Expiration
Decreased heart rate
Decreased venous return
Decreased right atrial pressure
No inhibition of medullary cardiac neurons and increased vagal tone
Less stimulation of stretch receptors in right atria
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Factors Modulating RSA Magnitude?
Tidal volume
Nervous system activation
Blood gas levels
Fitness level
Respiratoryfrequency
Age RSA
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Possible Utility of RSA?
RSA may increase
pulmonary gas
exchange efficiency
through improved
V/Q matching
Ventilation
Perfusion
InspirationHR and Q increase
ExpirationHR and Q decrease
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Tilt Exercise Hypoxia
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Tilt and blood volume distribution
• Tilt causes gravity-dependent redistribution of blood volume
• Standing or HUT translocates up to 1L of blood volume toward the lower extremities
• HDT translocates blood into the central cavity, increasing venous return and cardiac loading Trendelenburg position
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• Gelinas et al., 2012 AviatSpace Environ Med
• Skow et al., 2013 Resp PhysiolNeurobiol
• Skow et al., 2014 Prog Brain Res
• Tymko et al., 2015 Exp Physiol
We investigated the effects of steady-state tilt on respiratory and cerebrovascular regulation.
Previous tilt studies in the lab
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Baden et al., 2014 Aviat Space Environ Med
Case Report: 45 Degree Head Down Tilt
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Case Report: 45 Degree Head Down Tilt
• Sinus arrhythmia
• Note the P waves
(red arrows)
• NOT pathological
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Ba
den
et
al.,
20
14
Avi
at
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nvir
on
Med
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Experiment #1: Tilt and RSA
Aim:
To explore the relationship between superimposed gravity-dependent and inspiration-dependent cardiac filling on RSA magnitude.
Hypothesis:
Superimposed gravity- and inspiration-dependent cardiac loading will increase RSA magnitude in a synergistic fashion.
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Methods
10%, 20%, 30%, 40%, and 50% of FVC
RANDOMIZED
RANDOMIZED
40o HDT
40o HUTFVC (x3)
n=19
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Analysis
• Peak-valley method
• Data from 5 of the most accurate, consecutive breaths
• Correlation between VTI
and RSA magnitude
• RSA magnitude plotted against each targeted VTI (% FVC)
• Linear regression of RSA magnitude against VTI
• Slopes calculated to quantify “RSA reactivity”
20% FVC
40% FVC
Abrosimova et al., Manuscript in Preparation
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HUT; r = 0.64; P<0.001 HDT; r = 0.53; P<0.001
RSA magnitude is correlated with VTI
Abrosimova et al., Manuscript in Preparation
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HUT=0.43 HDT=0.33R2=0.99 R2=0.99
P=0.02
“RSA reactivity” in response to increases in VTI is linear
Abrosimova et al., Manuscript in Preparation
Response slopes are tilt-dependent
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Summary
• RSA magnitude increases linearly with increases in VTI (“RSA reactivity”)
• RSA reactivity is not increased with HDT
• RSA reactivity is decreased in HDT, likely do to sympathetic NS modulation
• Question: Can we test RSA reactivity during another stressor where venous return is increased and the sympathetic NS is activated?
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Skeletal Muscle Pump
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Aim:
To explore the relationship between superimposed exercise stress (with skeletal muscle pump activity and sympathetic nervous system activation) and inspiration-dependent cardiac filling on RSA magnitude.
Hypothesis:
Sympathetic activation during exercise will reduce RSA magnitude, despite superimposed inspiratory-dependent and skeletal muscle pump cardiac filling.
Experiment #2: Exercise and RSA
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Methods and Instrumentation
• Participants (n=13) instrumented for respiratory volumes and heart rate
• Seated on a cycle ergomenter
• Participant feedback on respiratory volume via computer screen
• RSA trials repeated at rest and during exercise
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Protocol
Lavoie et al., Manuscript in Preparation
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Results – Raw Traces
Rest Exercise
Lavoie et al., Manuscript in Preparation
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ResultsResults – RSA reactivity is reduced during exercise
Rest Exercise
Lavoie et al., Manuscript in Preparation
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Results
P = 0.001• RSA reactivity is
eliminated during exercise
• This is despite an increase in venous return during exercise
• RSA is likely NOT driven by increases in venous return.
Lavoie et al., Manuscript in Preparation
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• RSA is maintained during exercise.
• However, RSA reactivity is eliminated during exercise, despite increases in venous return, likely because of increased sympathetic activity.
• Questions: Will RSA be affected by acclimatization to high altitude hypoxia? Could RSA reactivity magnitude affect V/Q matching and oxygenation during hypoxic stress?
Summary
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Integrate and analyze all your data streams in one place
Setting the pace for Exercise Research
• Wireless physiological monitoring and EMG
• Metabolic Systems
• Accelerometry
• Goniometers
• Human NIBP
• Stimulators
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Himalayan Mountain Range - Tibet/NepalMount Everest 8848 m (29,028 ft)
Atmospheric Pressure = 253 mm HgAvailable Oxygen ~33% of Sea Level
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0
100
200
300
400
500
600
700
800
0 1 2 3 4 5 6 7 8 9 10
Gas P
ressu
re (
mm
Hg
)
Altitude (kilometres)
Patm(mmHg)
PO2(mmHg)
The Relationship Between Altitude and Relative Gas Pressures
Day TA (2010). Human Adaptation to High Altitude Hypoxia: Getting High.
Biology on the Cutting Edge: Canadian Research and Issues around the Globe. (pp. 117-122) Pearson Education Canada, Toronto, Ontario.
Vancouver
Calgary Airplane Cabin
Everest
Half the available oxygen
of sea level
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Aim:
To explore the relationship between superimposed high altitude hypoxia and inspiration-dependent cardiac filling on RSA.
Hypothesis #1:
Increases in sympathetic nervous system during high altitude hypoxia will reduce RSA magnitude (similar to exercise).
Hypothesis #2:
Larger RSA magnitude will improve oxygenation through improved V/Q matching at altitude.
Experiment #3: High Altitude Hypoxia and RSA
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Everest Base Camp (EBC) Trek
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Why Nepal?
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Altitude Comparisons: Banff and Mt. Rundle = Kathmandu and Lukla
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May 2016
23 participants recruited including nine paid trainees from MRU, collaborators, industry partners (ADI) and community members from across Canada, USA, New Zealand and Ireland.
Ethical Clearance: • Mount Royal University Human Research Ethics Board 2015-26b
• Nepal Health Research Council 96/2016
Objective: • A fast and light approach to high altitude acclimatization on a trek
to Everest Base Camp
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Pelican cases packed outside the Lab April 29, 2016
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Calgary Airport April 30, 2016
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Kathmandu(1400m)
Monjo(2835m)
Namche(3440m)
Tengboche(3860m)
Pheriche(4370m)
Lobuche(4940m)
Gorak Shep(5160m)
Pheriche(4370m)
Pangboche(3985m) Kunde
(3840m)Namche(3440m)
Phakding(2610m)
Lukla(2860m)
Kathmandu(1400m)
0
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1,500
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3,000
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4,000
4,500
5,000
5,500
6,000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Day
Acetazolamide (Diamox)
125mg PO BID
Alt
itu
de (
m)
Asc
ent-
Des
cen
t P
rofi
le –
Nep
al 2
01
6
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Lukla Airport (2800m)
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Daily Measures: Nepal May 2016
• Between 6-8 am, before breakfast, following one night at that altitude.
• Heart rate and peripheral oxygen saturation
• Respiratory rate and pressure of end-tidal CO2
• Blood pressure
• Acute Mountain Sickness scores (Lake Louise Scoring system)
• Actigraph accelerometers for daily activity and sleep disturbances
• Collected on ascent and descent
• n=21
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Rest Day Measures: Nepal May 2016
• On rest days during ascent between 10 AM and 5 PM
• Calgary (1045m), Namche (3440m), Tengboche (3860m) and Pheriche(4370m)
• [Hemoglobin] and hematocrit, urine pH and renal reactivity, voluntary breath holding, ventilatoryacclimatization, heart rate variability (RSA reactivity)
• n=12
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Namche (3440m)
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Namche (3440m)
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Tengboche (3860m)
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Pheriche (4370m)
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Pheriche (4370m)
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Poincare Plot – Quantification of heart rate variability
Saran et al., Manuscript in Preparation
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Poin
care
Plo
ts a
nd
Alt
itu
de
Saran et al., Manuscript in Preparation
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RSA during spontaneous breathing via SD1/SD2 ratio
Resting RSA magnitude is not changed with high altitude ascent
Saran et al., Manuscript in Preparation
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• RSA quantified using the peak-valley approach
• Participant targets inspired volume through computer screen feedback
RSA and targeted VTI
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RSA Reactivity Slopes and Altitude
• RSA protocol during ascent
• We plotted RSA magnitude against %FVC
• Slopes quantify “RSA Reactivity”
• Slopes appear unchanged with altitude
Saran et al., Manuscript in Preparation
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Results - RSA reactivity magnitude is not altitude dependent
Saran et al., Manuscript in Preparation
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Gorak Shep (5160m)
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70
75
80
85
90
95
100
Kathmandu (1400m) Monjo (2840m) Namche (3440m) Tengboche (3860m) Pheriche (4370m) Lobuche (4940m) Gorak Shep (5160m)
Peri
ph
eral
Oxy
gen
Sat
ura
tio
n (
%)
Location and Altitude
Oxygen Saturation and Altitude
• SpO2 (%) measured every morning during ascent
• Note the reduction in SpO2 (%) with increases in altitude
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RSA and V/Q matching hypothesis
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The effects of RSA magnitude on oxygen saturation
Saran et al., Manuscript in Preparation
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• Resting RSA magnitude is unchanged with acclimatization to high altitude (Poincare plots)
• RSA reactivity to targeted increases in VTI is also unchanged with acclimatization to high altitude
• RSA magnitude does not improve oxygen saturation in the context of hypoxia, suggesting V/Q matching hypothesis is incorrect.
Summary
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Summit of Kala Patthar (~5600m)
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Acute Mountain Sickness (AMS)
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Lukla (2800m)
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Lukla Airport (2800m)
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Kathmandu (1400m)
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Calgary
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Research in Austere Environments…a balance between FEASABILITY and NOVELTY
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Research in Austere Environments
• Building the right team
• Organization and safety
• Managing expectations: the needs of the individual/team with needs of the researchers
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• Cultural sensitivity
• Personal and interpersonal perspectives
• Staying positive and optimistic
• Keeping your sense of humour
Research in Austere Environments
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• Creativity
• Improvisation
• Serendipity
• Persistence
• Compromise
• Problem solving
• Responsive to new opportunities
• Expect the unexpected
• Know the limitations of your gear
• Power?
Research in Austere Environments
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Undergradute Students!
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Lake Louise AMS Scoring System [Roach et al., 1993]
LAKE LOUISE AMS SCORING SYSTEM
Name:
Date:
Location and Altitude:
Instructions: Please circle the number of each item to correspond to HOW YOU FEEL AT THIS PRESENT MOMENT. PLEASE ANSWER EVERY ITEM. If you do not have the specific symptom, please circle [0].
Self-Assessment Score
1. Headache
[0] None at all
[1] Mild Headache
[2] Moderate Headache
[3] Severe Headache. Incapacitating
Score =
2. Gastrointestinal Symptoms
[0] Good Appetite
[1] Poor Appetite/Nausea
[2] Moderate Nausea/Vomiting
[3] Severe. Incapacitating Nausea and Vomiting
Score =
3. Fatigue and/or weakness
[0] Not Tired or Weak
[1] Mild Fatigue/Weakness
[2] Moderate Fatigue/Weakness
[3] Severe Fatigue/Weakness
Score =
4. Dizziness/light-headedness
[0] None
[1] Mild
[2] Moderate
[3] Severe. Incapacitating
Score =
5. Difficulty sleeping
[0] Slept as well as usual
[1] Did not sleep as well as usual
[2] Woke many times. Poor night’s sleep
[3] Could not sleep at all
Score =
Sum 1-5 Total AMS Score =
Sum 1-4 Total AMS Score =
LAKE LOUISE AMS SCORING SYSTEM
Name:
Date:
Location and Altitude:
Instructions: Please circle the number of each item to correspond to HOW YOU FEEL AT THIS PRESENT MOMENT. PLEASE ANSWER EVERY ITEM. If you do not have the specific symptom, please circle [0].
Self-Assessment Score
1. Headache
[0] None at all
[1] Mild Headache
[2] Moderate Headache
[3] Severe Headache. Incapacitating
Score =
2. Gastrointestinal Symptoms
[0] Good Appetite
[1] Poor Appetite/Nausea
[2] Moderate Nausea/Vomiting
[3] Severe. Incapacitating Nausea and Vomiting
Score =
3. Fatigue and/or weakness
[0] Not Tired or Weak
[1] Mild Fatigue/Weakness
[2] Moderate Fatigue/Weakness
[3] Severe Fatigue/Weakness
Score =
4. Dizziness/light-headedness
[0] None
[1] Mild
[2] Moderate
[3] Severe. Incapacitating
Score =
5. Difficulty sleeping
[0] Slept as well as usual
[1] Did not sleep as well as usual
[2] Woke many times. Poor night’s sleep
[3] Could not sleep at all
Score =
Sum 1-5 Total AMS Score =
Sum 1-4 Total AMS Score =
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Thank You!
Dr. Trevor DayAssociate Professor of Physiology Department of BiologyFaculty of Science and TechnologyMount Royal University
For additional information on the solutions presented in this webinar please visit www.adinstruments.com