mountain lab: studying the effects of stress and extreme conditions on human physiology

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

[email protected]

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:

Calgary, Alberta, Canada

Mount Royal University

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

Kidneys

Heart

Lungs

Brain

Stress Stress

Stress Stress

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

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

2014 Alberta Science and Technology (ASTech) Young Innovator Award

Michael Tymko recently published an “instruction manual” on constructing LBNP chambers (Nov 2016, In press).

“The effects of superimposed tilt and lower body negative pressure on anterior and posterior cerebral circulations” Tymko et al., 2016

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

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

• 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

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).

Respiratory Pump

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

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

Factors Modulating RSA Magnitude?

Tidal volume

Nervous system activation

Blood gas levels

Fitness level

Respiratoryfrequency

Age RSA

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

Tilt Exercise Hypoxia

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

• 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

Baden et al., 2014 Aviat Space Environ Med

Case Report: 45 Degree Head Down Tilt

Case Report: 45 Degree Head Down Tilt

• Sinus arrhythmia

• Note the P waves

(red arrows)

• NOT pathological

Ba

den

et

al.,

20

14

Avi

at

Spa

ce E

nvir

on

Med

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.

Methods

10%, 20%, 30%, 40%, and 50% of FVC

RANDOMIZED

RANDOMIZED

40o HDT

40o HUTFVC (x3)

n=19

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

HUT; r = 0.64; P<0.001 HDT; r = 0.53; P<0.001

RSA magnitude is correlated with VTI


HUT=0.43 HDT=0.33R2=0.99 R2=0.99

P=0.02

“RSA reactivity” in response to increases in VTI is linear


Response slopes are tilt-dependent

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?

Skeletal Muscle Pump

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

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

Protocol

Lavoie et al., Manuscript in Preparation

Results – Raw Traces

Rest Exercise


ResultsResults – RSA reactivity is reduced during exercise

Rest Exercise


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.


• 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

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

http://www.adinstruments.com/

Himalayan Mountain Range - Tibet/NepalMount Everest 8848 m (29,028 ft)

Atmospheric Pressure = 253 mm HgAvailable Oxygen ~33% of Sea Level

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

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

Everest Base Camp (EBC) Trek

Why Nepal?

Altitude Comparisons: Banff and Mt. Rundle = Kathmandu and Lukla

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

Pelican cases packed outside the Lab April 29, 2016

Calgary Airport April 30, 2016

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

500

1,000

1,500

2,000

2,500

3,000

3,500

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

Lukla Airport (2800m)

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

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

Namche (3440m)

Tengboche (3860m)

Pheriche (4370m)

Poincare Plot – Quantification of heart rate variability

Saran et al., Manuscript in Preparation

Poin

care

Plo

ts a

nd

Alt

itu

de


RSA during spontaneous breathing via SD1/SD2 ratio

Resting RSA magnitude is not changed with high altitude ascent


• RSA quantified using the peak-valley approach

• Participant targets inspired volume through computer screen feedback

RSA and targeted VTI

RSA Reactivity Slopes and Altitude

• RSA protocol during ascent

• We plotted RSA magnitude against %FVC

• Slopes quantify “RSA Reactivity”

• Slopes appear unchanged with altitude


Results - RSA reactivity magnitude is not altitude dependent


Gorak Shep (5160m)

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

RSA and V/Q matching hypothesis

The effects of RSA magnitude on oxygen saturation


• 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

Summit of Kala Patthar (~5600m)

Acute Mountain Sickness (AMS)

Lukla (2800m)

Lukla Airport (2800m)

Kathmandu (1400m)

Calgary

Research in Austere Environments…a balance between FEASABILITY and NOVELTY

Research in Austere Environments

• Building the right team

• Organization and safety

• Managing expectations: the needs of the individual/team with needs of the researchers

• Cultural sensitivity

• Personal and interpersonal perspectives

• Staying positive and optimistic

• Keeping your sense of humour


• Creativity

• Improvisation

• Serendipity

• Persistence

• Compromise

• Problem solving

• Responsive to new opportunities

• Expect the unexpected

• Know the limitations of your gear

• Power?


Undergradute Students!

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 =


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 =



Thank You!

Dr. Trevor DayAssociate Professor of Physiology Department of BiologyFaculty of Science and TechnologyMount Royal University

[email protected]

For additional information on the solutions presented in this webinar please visit www.adinstruments.com

http://insidescientific.com/

