Flashcards in Performance at altitude Deck (16):
What metabolism during rest, unloaded cycling and the increase per watt?
- Resting: 250ml per minute
- Unloaded cycling: 500ml per minute
- Every watt is an additional 10ml
What is barometric pressure and how does it change from sea level to high altitude?
- A measure of the weight of a column of air directly over a given sport
Sea level: 760 mmHg weight and height of air column greatest
Everest: 251 mmHg smaller weight and height of air column
What is the key effect at high altitude?
Bert 1878: "Detrimental effects of high altitude are due to the diminished partial pressure of oxygen at reduced barometric pressure"
Describe the Oxygen transport cascade and how this differs with altitude?
- Transfer of oxygen from atmosphere to arterial blood to venous blood to mitochondria
- Lower barometric pressure lower PO2 and lower driving pressure into the mitochondria
What is the lowest PaO2 values ever recorded in humans at Everest and London? What is the reason for this?
- London: 148 mmHg
- Everest: 43.1 mmHg
- Lower driving pressure from atmosphere
What did the American Medical Research Expedition show? And the research from West et al (1983)
- Work rate and VO2 max are reduced by 70% at low inspired PO2 values
- VO2 max of 1 L/min gives just enough metabolic reserve to reach top of Everest
- Lactate threshold also severely reduced especially in well trained
What happens to maximum ventilation and maximum heart rate at high altitudes and why? West et al (1983)
- Maximum ventilation remained the same
- Max heart rate is decreased at lower VO2 explained by decreased work rate attained
What happens to ventilation at high altitude and how?
- Hypoxaemia (Low oxygen) stimulates aortic and carotid bodies
- Increased ventilation causes a reduction in PaCO2 (Respiratory alkalosis)
- Sustained low PaCO2 - kidneys secrete bicarbonate to constrain increase
- Increased sensitivity of peripheral and central chemoreceptors increases ventilation further - from bicarbonate release
What is the alveolar gas equation and how can it change with altitude?
PAO2 = PiO2- (PACO2 / RER)- To increase alveolar oxygen content need to decrease PACO2 by increasing ventilation
What happens to O2 saturation at high altitudes? What effect does this have?
- O2 aren't fully saturated when exercising at altitude because of reduced capillary transit time and lower alveolar PAO2 less driving pressure into capillary
What happens to the driving gradient at high altitude?
- Arterial saturation is lower and therefore the driving pressure into venous side during exercise is also lowered reducing the content
What cardiovascular adjustments are made to exercising at high altitude?
1) Higher HR at a submaximal work rate to compensate for reduced CaO2
2) Increase in O2 extraction
3) SV decreases after 2 weeks due to a decrease in plasma volume
4) Increase in [Hb] after 2 weeks due to activation of HIF-1 alpha
What is HIF-1 alpha and what is it's effect?
- A transcription factor and master regulator of hypoxia induced genes that stimulates EPO release from the kidneys to increase RBC production (polycythemia) from bone marrow
- Blood viscosity may increase in parallel
What is the effect of hypoxia on HIF- 1 alpha and the mitochondria
- 20-30% loss reported as HIF-1 alpha down regulates PGC-1 alpha
- Can reduce fibre size but may increase capillary density compensate for reduction in mitochondrial density
- VO2 max potentially lower
How does the live high train low concept effect performance?
- Live high: Increase amount of Hb in the blood due to being exposed to low PO2
- Train low: Performing exercise at sea level where normal work rates and intensities can be achieved