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Lecture

BPK 142 Lecture Notes - Altitude Training, Acclimatization, Cardiac Output


Department
Biomedical Physio & Kines
Course Code
BPK 142
Professor
Craig Asmundson

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Altitude and Performance 1
Thought
Questions
1. How does it seem that exercise is more tiring at altitude than at sea level?
2. How is the physical environment changed at altitude?
3. How does the body respond to reduced oxygen pressures (hypoxia)?
4. Why is maximal exercise reduced at altitude?
5. Will a person adapt to altitude after a period of time?
6. Will training at altitude be beneficial to performance on returning to sea level?
Definitions
PO2 = partial pressure of oxygen; measures how well your lungs bring oxygen into your bloodstream
Ambient air = untreated air
Oxyhemoglobin dissociation curve = a mathematical relationship, that is viewed as a graph, showing the amount
of oxygen that combines with hemoglobin as a function of the partial pressure of oxygen
Acclimatized = adaptation to a new climate (such as temperature, altitude, etc)
Hypoxia = deficiency in the amount of oxygen reaching the tissues
2,3 DPG = present in RBC; binds with greater affinity to deoxygenated hemoglobin than it does to oxygenated
hemoglobin
Physics of
Altitude
Medium = 5000 - 10,000 feet = we are concerned with this altitude in relation to athletics
High = >10,000 feet = over 40 million people live/work between 10,000-18,000 feet (3048m – 5486m)
Barometric (air) pressure decreases when altitude increases. (i.e., as the weight of the column of air above the
point of measurement decreases).
The chemical composition is the same up to 20,000m
PO2 in dry ambient air @ sea level = .209 x 760 mm Hg = 160 mm Hg
PO2 in dry ambient air @ 10,000 feet = .209 x 510 mm Hg = 107 mm Hg
PO2 in dry ambient air @ summit of Mt Everest (29,028 ft) = .209 x 250 mm Hg = 52 mm Hg
Oxyhemoglobin dissociation curve – minimal change in percent saturation of hemoglobin is observed with
decreasing PO2 until 10,000 ft. Measurable negative effects on VO2MAX have been seen as low as 4000 ft.
Critical alveolar PO2 when an unacclimatized person loses consciousness within a few minutes during acute
exposure to hypoxia occurs at 23,000 ft.
Decreased air density decreased external air resistance external work decreased at altitude in
sprint-type activities (high velocities) + less air resistance.
Temperature decreases linearly by 6.5OC per 1000m or 2OC per 1000ft.
Increasing altitude = increasingly dry air water loss via respiratory tract higher at high altitudes

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Altitude and Performance 2
Solar radiation = UV radiation more intense at higher altitudes sunburn and snow blindness
Force of gravity decreased with distance from earth’s center
Immediate and Longer Adjustments to Altitude Hypoxia
Cardiovascular System
At rest, the Fick equation states that O2 uptake equals cardiac output times the arterial-mixed venous O2 content
difference. This is expressed as: VO2 = (HR x SV) x (CaO2 CVO2)
VO2 = oxygen uptake, SV = stroke volume, HR = heart rate, CaO2 = arterial O2 content, CVO2 = venous O2 content
Increase altitude decrease CaO2
o To compensate, cardiac output initially increases for rest + submaximum exercise due to increase in HR
o During the 1st week at the higher altitude, cardiac output falls to or below sea level values for the
same VO2 but there is a progressive increase in O2 extraction
More efficient O2 delivery
Most important long-term (~2 weeks) adaptation to altitude = increase in the blood’s O2 carrying capacity
[Hemoglobin] starts increasing during the first 2 days at altitude due to a decrease in plasma volume and
an increase in RBC production by bone marrow.
o These haematological changes are dependent on adequate iron intake.
Women need more than men due to menstruation.
High altitude natives and well-acclimatized individuals, [hemoglobin] may be up to 50% above normal!
Left shift (high affinity for O
2
Right shift (low affinity for O
2
)
Temperature
Decrease Increase
2,3
-
DPG
Decrease Increase
p(CO
2
)
Decrease Increase
p
(CO)
Increase Decrease
pH (Bohr effect)
Increase (alkalosis) Decrease (acidosis)
Concentration of 2,3 DPG within RBC increases shift O2 dissociation curve to right unload more O2 at tissues
for a given capillary PO2.
Even after several months of acclimatization, VO2MAX still remains remarkably below sea-level values.
Pulmonary System
Decreased alveolar PO2 decreased arterial PO2 stimulation of aortic & carotid chemoreceptors increase
in ventilation increase in PAO2 and PaO2 hyperventilation decreased PACO2 and PaCO2 increase in blood
pH (respiratory alkalosis) plasma bicarbonate levels decrease during first 2 days because kidneys excrete excess
HCO3 to compensate pH
After the acid-base balance is corrected, hyperventilation persists during acclimatization.
Within a week at high altitude, a new level or VE is attained (40-100% above sea level values).
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