BPK 142 Lecture Notes - Lecture 18: Altitude Sickness, Acclimatization, Vo2 Max

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ERGONOMICS
Physical Altitude:
Medium altitude - 5000 - 10,000 feet - in relation to athletics, we are concerned with
this altitude range
High altitude - greater than 10,000 feet. More than 40 million people live and work
between 10,000 ft. (3048 meters) and 18,000 ft. (5486 meters).
Barometric (air) pressure decreases as altitude increases
Example: As the weight of the column of air above the point of measurement
decreases. However, the chemical composition of the atmosphere is uniform
up to 20,000 meters.
PO2 in dry ambient air at sea level = .209 X 760 mm Hg = 160 mmHg
PO2 in dry ambient air at 3048 meters (10,000 ft.) = .209 X 510 mm Hg = 107 mm
Hg.
PO2 in dry ambient air at summit of Mt Everest - 8848 meters (29,028 ft.) = .209 X
250 mm Hg = 52 mm Hg.
Oxyhemoglobin dissociation curve: Only a small change in percent saturation of
hemoglobin is observed with decreasing PO2 until an altitude of about 10,000 ft.
Measurable negative effects on VO2max. have been noted at altitudes as low
as 4000 ft.
The critical alveolar PO2 at which an unacclimatized person loses consciousness
within a few minutes during acute exposure to hypoxia occurs at an altitude of
23,000 ft.
Decreased density of air --> decreased external air resistance --> external work is
decreased at altitude in sprint type activities where high velocities are involved. There
will also be less air resistance encountered by projectiles.
Air temperature decreases linearly by 6.5 degrees C per 1000 meters of altitude
or 2oC (3o F) per 1000 ft.
Air becomes increasingly dry with increasing altitude --> water loss via
respiratory tract is higher at high altitude.
Solar radiation: UV radiation is more intense at high altitude --> sunburn, snow
blindness
Force of gravity is decreased with distance from the earth's center --> higher
altitudes should have a favourable effect on jumping and throwing events.
Immediate and Longer Adjustments to Altitude Hypoxia
Cardiovascular System
VO2 = (HR X SV) X (CaO2 - CvO2)
With increasing altitude, CaO2 progressively decreases.
To compensate, cardiac output initially increases during rest
and submaximal exercise due to an increase in heart rate.
Over the first week at altitude, cardiac output falls to or below sea
level values for the same
VO2 and there is a progressive increase in O2 extraction -->
more efficient method of delivering O2.
The most important long-term adaptation to altitude is an increase in
the blood's oxygen carrying capacity.
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Hemoglobin concentration starts to increase during the first two days
at altitude due to a decrease in plasma volume and an increase in
RBC production by bone marrow.
These hematological changes during acclimatization are dependent
on an adequate iron intake
In some high altitude natives and well-acclimatized sojourners,
hemoglobin concentration may be increased 40 - 50% above normal.
Concentration of 2,3 DPG within RBC increases --> shift O2
dissociation curve to right --> unload more O2 at the tissues for a
given capillary PO2.
Even after several months of acclimatization, VO2 max. still remains
significantly below sea level values.
Pulmonary System
Decreased alveolar PO2 --> decreased arterial PO2 --> stimulation of aortic
and 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 two days because the 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 for VE is attained - 40 to
100% above sea level values.
Sensory and Mental Function
Research studies have shown the following decrements in performance at
altitude:
At 3048 meters (10,000 ft.) – a 30% decrease in visual acuity, a 25%
decrease in light sensitivity, and a 25% decrease in attention span.
At 4500-5500 meters (14,800-18,000 ft.) – a 15-20% decrease in
cognition and recall. A 25% decrease in pursuit tracking ability
At 6100 meters (20,000 ft.) – a 25% decrease in reaction time.
Responses To Exercise
VO2 max. decreases 3 - 3.5% per 1000 ft. above 5000 ft. At 14,000 ft. VO2
max. is decreased approximately 30%. This is due to
Decreased oxygen content of arterial blood --> decreased a-vO2
difference in maximal exercise
After acclimatization: Decrease in maximal cardiac output due to a
decrease in maximum heart rate and stroke volume.
The decrease in maximal stroke volume is most likely due to
the reduction in venous return which is caused by the
decreased blood volume - Starling mechanism
The percentage reduction in VO2 max. is equal in both trained and untrained
individuals.
Oxygen uptake is the same at altitude as at sea level for the same
submaximal workload.
However, heart rate and minute ventilation will be greater.
During heavy exercise, muscle and blood lactate levels are higher at altitude
for any given workload for two reasons:
Since the VO2 max. is reduced, any given workload now requires a
higher percentage of the VO2 max. to perform
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