CH. 13 - Exercise at Altitude Flashcards
Pb (at sea level)
Barometric pressure = 760mmHg at sea level
PO2
partial pressure of oxygen
- > reduced PO2 at altitude, limits exercise performance
- > portion of Pb exerted by oxygen (about 21% x Pb = 159mmhg)
- > PO2 at altitude = 132
hypobaria
- > reduced Pb seen at altitude
- > results in hypoxia (low PO2 in air), hypoxemia (low PO2 in blood)
effects of different altitudes on performance
Sea level = < 500m; no effects
Low altitude (500-2000m)
- > no effects on well-being, performance may decrease but can be restored with acclimation
Moderate altitude (2000-3000m)
- > performance and aerobic capacity decreases (on unacclimated ppl)
- > performance may or may not be restored with acclimation
High altitude (3000-5500m)
- > acute mountain sickness
- > performance may or may not be restored with acclimation
Extreme high altitudes (>5500m)
- > severe hypoxic effects
- > highest settlements: 5200-5800m
altitude (in this course)
1500m
(this is considered a low altitude)
sea level Pb vs Mt Everest
SL Pb = 760mmHg
MT E Pb = 250mmHg
there is not less O2 on Everest, Pb is different
Pb vs Air composition at various altitudes
Pb varies, air composition does not
- > PO2 is always 21% of Pb
- > air PO@ affects PO2 in lungs, blood, tissues
air temp at altitude
temp decreases 1C per 150m ascent
- > contributes to risk of cold-related disorders
Humidity at altitude
- > cold air holds very little water
- > air at altitude is very cold and very dry
dry air = quick dehydration via skin and lungs
how do general conditions vary at altitude
- > solar radiation increases at high alts
- > UV rays travel through less atmosphere
- > water normally absorbs suns radiation, but low water vapour at altitude cannot
- > snow reflects/amplifies solar radiation
pulmonary ventilation at altitude
- > it will increase immediately at rest and submax exercise (but not maximal exercise
- > decrease in PO2 stimulates chemoreceptors in aortic arch, carotids
- > increases tidal volume for several hours/days
increase ventilation at altitude = hyperventilation
respiratory alkalosis
high blood pH
- > caused by a decrease in alveolar PCO2 that increases CO2 gradient into the blood “blowing off CO2)
- > oxyhemoglobin will. curve to the left
- > prevents further hypoxia-driven hyperventialtion
why do kidneys excrete more bicarbonate at high altitudes
to offset pulmonary alkalosis
- > bicarbonate ions buffer carbonic acid from CO2, thus reducing bloods buffering capacity will keep more acids in the blood, bringing pH back down
pulmonary diffusion
at rest, does not limit gas exchange with blood
at altitude, alveolar PO2 still = capillary PO2
- > hypoxemia is a direct reflection of low alveolar PO2
gas exchange at muscles at altitude
PO2 gradient at muscle decreases
sea level: 100-40 = 60mmHg
4300m = 42-27 = 15mmHg
- > O2 diffusion into the muscles is significantly reduced
why is the location of the oxygen gradient change critical?
hemoglobin desaturation at the lungs = no/little effect on performance
- > decrease PO2 gradient at muscle = decrease exercise capacity
short term effects of acute altitude exposue
plasma volume will decrease within a few hours
- > respiratory water loss, increase urine production
- > lose up to 25% of plasma volume
- > short term increase in hematocrit, O2 density
how are RBC affected by acute altitude exposure
RBC count increase after weeks/months
- > hypoxemia triggers EPO (erythropoietin; hormone that increases RBC) release from kidneys
- > increase RBC cell production in bone marrow
- > long term increase in hematocrit
how is Cardiac output affected by acute altitude exposure
increases (despite decrease in plasma volume)
- > at rest and sub max exercise (not max)
- > delivers more O2 to tissues per minute
- > increase SNS activity = increase HR
- > inefficient, short term adaptation (6-10days)
- after a few days muscles extract more O2*, decreased hypoxia
how are basal metabolic rates impacted…
basal metabolic rates increase with…
- > increase thyroxine and catecholamine secretions
- > must increase food intake to maintain body mass
- > more reliant on glucose vs fat
how is anaerobic metabolism affected by altitude
it increases, resulting in increased lactic acid
- > LA production will decrease over time
- > there is no explanation for this
why does appetite decline at altitude
- > paired with increase metabolism = 500kcal/day deficit
- > maintain iron intake to support increase in hematocrit
why does dehydration occur faster at altitude
- > increase water loss through skin, kidneys and urine
- > exacerbated by sweating/exercise
- > must consume 3-5L fluid/day
VO2max at altitude
decreases at altitude above 1500
- > due to decrease in arterial PO2 and Qmax
- > drops 8-11% per 1000m ascent
