Week 9: Hypoxia Flashcards
Who is Kilian Jornet?
A mountain runner with a v02max of ~90ml/L. Holds the record time for unsupported accent of Everest at 26hrs (typically takes >1 wk). Training at altitude benefitted his physiology and performance.
Main stressors we face at altitude are…..
Hypoxia, low air pressure or hypo barrier and cold ambient temperatures.
We experience increased physiological stress at altitude (>1600m) due to:
- Reduced ….. ….. of oxygen (P02), resulting in hypoxia, due to lower …… pressure (PB)
- Decreased ambient temperature (~…. …… ….. ) and humidity, increasing heat loss and dehydration
- So if it’s 15 degrees at the base of mountain, it will be below freezing by around ….. metres of altitude
- That’s partially a result of the increase ….. ….. at altitude and as the wind travels up a mountain, the air gets cooled and dries out substantially (reducing the water content or humidity of the air).
- Increased solar/UV radiation intensity and wind speed, increasing dehydration rate
- Decreased availability of …… ….. for rehydration
These environmental effects coupled with a lack of fresh liquid water increase the …… rate of altitude which lends itself to additional …… strain.
Partial pressure
Barometric
~1 degree per 150m
2300m
Wind exposure
Liquid water
Dehydration
Cardiovascular strain
The atmospheric barometric pressure changes with increasing altitude.
At sea level barometric pressure is around …. millimetres of mercury - we know that oxygen constitutes about …..% of the air we breathe so that gives us a partial pressure of oxygen of …. millimetres of mercury.
As we increase our altitude we can see that barometric pressure ….. reducing the ….. of the air. As the air gets thinner this leads to a lower effective oxygen percentage that we can breathe in. At 2000 metres we are effectively at …..% of the oxygen level we experience at sea level. At 5500 metres we are at half and by the time we reach 9000m (just above the peak of Everest) we would experience around ……% of the oxygen you and I are breathing at sea level.
This reduction in ….. (partial pressure of oxygen) at altitude affects the ….. between the ….. and ….. and therefore ….. transport & the ability of gas to exchange across the membrane. When we lose the pressure gradient between the air in our circulatory system the efficiency of ….. ….. ….. across that membrane is reduced affecting our ability to lower haemoglobin with oxygen to transport around the body to supply oxygen to our tissues. Now this explains why we might feel breathless at altitude and the commonly observed decrease in endurance performance
760
21%
159
Decreases
Density
78%
30%
P02
Gradient
Blood & tissues
Oxygen
Passive gas exchange
Altitude: Cardiorespiratory responses
- Peripheral chemoreceptors (….. & ….. bodies) detect reduced arterial 02 driving ….. (Hypoxic ventilation response) to compensate and increase arterial 02 saturation (Sa02)
- HVR results in respiratory …… (increase PH) and increased …… ……
- Increased ……. activation results in increased heart rate and cardiac output at rest and sub-maximal intensities to compensate for lower P02 – exacerbated by cold and exercise
- At maximal intensities, there is a reduction in peak …… ….. and …… output, limiting 02 supply
- Decrease in plasma volume (5d @ 2380m decreased ……-…..%) resulting in increased …….
- Increased a-v02 difference helps offset reduction in arterial Hb 02 saturation
Carotid & aortic bodies
Hyperventilation
Alkalosis
Respiratory dehydration
Sympathetic
Heart rate & cardiac output
15-20%
Hematocrit
Altitude: Metabolic response
* Greatly reduced ….. ….. ….. with increasing altitude due to increased HR & ….. gas diffusion/Hb onloading
* Increase in ……. and …… production due to increased metabolic demand
* Lower PC02 at altitude causes body to excrete ….. reserve of …… buffer (HCO3) via kidneys, reducing buffering capacity
* Increased …… …… ….. and carbohydrate needs, but decreased appetite (nausea) and gut absorption
* Muscle fibre atrophy and reduced muscle mass
Arterial oxygen saturation
Reduced
Glycolysis & lactate
Alkaline
Bicarbonate
Basal metabolic rate
Altitude: Performance effects
* Aerobic power (V02max) …… …… with increased altitude
* Little effect below 1500m – then VO2 max decreases by around …..% for every additional …… metres of altitude gain
* Increased pulmonary ventilation but no change in …… ……. diffusion and decreased …… 02 saturation
Decreases curvilinearly
1% per 100m
02 diffusion & decreased HB
- Resting V02 is ~……/kg/min and walking ~11ml/kg/min
- At Mt Everest peak (8848m), individuals have ~…..% V02max
- Kilian Jornet – fastest unsupported Everest ascent with 90ml/kg/min V02max would have an effective V02max of ……/kg/min
- Not accounting for the level of dehydration and plasma volume contraction he would have experienced
3.5ml/kg/min
70% of V02max
27ml/kg/min
Performance effects continued….
* Olympic Games (Mexico) held ~……. above sea level –> significant impact on physiology and performance
* Jumps, throws and short distance world records –> short explosive events (Bob Beaman broke the world record by 55cm in the long jump, Lee Evans broke his own 400m record – these events benefit because of the ….. ….. …… air density and resistance thereby improving velocity for the same work rate. It is a trade-off between ….. ….. and ….. …..
* Sports with high velocity or aerodynamic effect see a net benefit greater than the increased cardiorespiratory load
* Conversely endurance athletes eg Ron Clarke saw their performance plummet and several collapsed
* There was an exception, athletes who lived and trained at altitude performed well – eg ……, …… & ……
2280m
Reduced air density & resistance
Air resistance & mechanical power
Kenya, Ethiopia, Mexico
High altitude illness – acute mountain sickness
- AMS common during first several ….. or …. of altitude exposure above …… (particularly on descent)
- It’s thought that a weak ….. …… ….. & …… …… …. ……. …… …… ….. ….. ….. may be predictive AMS risk due to it contributing to increased C02 accumulation
- Weak …… and lower …… predictive, may contribute to C02 accumulation, and ROS may play a role
- Aerobic fitness not protective against AMS, and ….. may be more susceptible
- Symptoms include: (severe) headache, lethargy and weakness, dizziness, lack of appetite and nausea and insomnia or difficulty staying asleep
- Directly related to …… of ….. and final altitude – avoid by ascending no more than ……/day to allow body to adjust
- Treatment: non-prescription medicines for specific symptoms, …… ….., (symptoms may resolve in 24-48hrs – if no improvement they should descent …..-…… to gain relief)
Hours or days
2500m
Weak hypoxic ventilation & lower ability to saturate the arterial blood with oxygen
HVR & Sa02
Males
Speed of ascent
300m
Supplemental 02
500-1000m
High altitude illness – high altitude pulmonary edema
- High-altitude pulmonary edema (HAPE): potentially …… condition where lung …… leak & …… …… in the lungs
- Condition can occur in those who rapidly ascend to altitudes above …… and typically arises …..-……days after arrival at altitude
- Symptoms include: shortness of breath, development of …… with pink & frothy ……, excessive fatigue, ….. …. and fingernails (cyanosis), mental confusion
- Medical emergency with no known causes
- Treatment: immediate …… for medical assistance, administer supplemental oxygen, limit exertion
Fatal
capillaries
Fluid accumulates
2500m
2-4
Cough
Sputum
Blue lips
Descent
High altitude cerebral edema
* High altitude cerebral edema is a rare, life-threatening form of acute mountain sickness where …… ……. leak into the cranium causing …… accumulation causes brain …… and pressure
* Medical emergency with condition typically arising within ….-….. days of altitude exposure above ……
* Symptoms include: severe …… and ….., confusion and ….., appear drunk
* Treatment: immediate descent for medical assistance, administer supplemental oxygen and ……. (steroidal anti-inflammatory)
Cerebral capillaries
Fluid
Swelling
1-3 days
3000m
Exhaustion, weakness, irritability
Dexamethasone
Hypoxic training for performance
- Hypoxia-induced EPO stimulates ….. production, increasing …… & RBC ……
- But decreased ….. …… (and increased haematocrit) increases …… and peripheral resistance
- …… (formation of blood vessels) results in greater capillary density for increased surface area for 02 diffusion
- Increased …… and respiratory function (FVC & FEV) – possibly improved conditioning of diaphragm
- Muscle fibre ….. and decreased total muscle area due to body mass loss and dehydration
- If we can attain the benefits of altitude exposure ie increased red blood cell mass, capillary density & respiratory function while minimising the atrophy of muscle fibres and associated loss of power then that would be potentially very beneficial for endurance performance
RBC
Haemoglobin
Mass
Plasma volume
Viscosity
Angiogenesis
Ventilation
Atrophy
Altitude: Performance effects at sea level
* Hb concentration ….. in high-altitude natives
* Individuals exposed to altitude have increased RBC mass, but fast loss due to …..
* Not clearly proven that altitude training always improves sea-level performance
* …… status likely plays a role in determining responsiveness to altitude training
* Nutritional status (given increased metabolic demand) and planning are highly important
Higher
Neocytolysis
Training
Altitude: Optimising performance
Various methods have been suggested to improve performance including:
* Compete within ….. of arrival to altitude –> better to acclimatise to the environment
* Train at ….. to …… above sea level for atleast ….. weeks before competing
- Help develop some of the key physiological adaptations to assist with acclimatisation
* Increase v02max at ….. level to be able to complete at a lower relative intensity
- Most elite athletes are at or near peak V02max (high cost, potentially non-beneficial method)
General recommendation
* Live at ….. altitude, train at ….. altitude (LHTL)
* …../day for >….. total @1500-3000m (~3 weeks)
* This altitude range will provide sufficient stress without adverse outcomes
24hrs
1500m-3000m
Two
Sea
High
Low
14hr
300hrs
