Hypoxic Environment - Extreme Physiology

Altitude

<1600m = low altitude

1600m-2500m = low to moderate altitude (unnoticable effects)

2500m-4000m = moderate to high altitude (performance deficit)

4000m-6000m = high to very high altitude (human life not sustainable)

>6000m = extremely high altitude 

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Pressure and Altitude

At sea level = 760mmHg 

1600m = 600mmHg

2200m = 550mmHg

4800m = 385mmHg

8848m = 215mmHg

As altitude increases the proportion of oxygen in the air doesn't change - but the pressure affects how much enters our system.

In order to make up for lack of oxygen, the CO has to increase at a lower exercise rate 

Therefore it becomes limited much earlier on.

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Acute responses to hypoxia

At sea level - oxygen saturation is about 100%

At top of Everest - oxygen saturation is about 70%

At 50% oxygen saturation is when unconsciousness occurs

Ascent should be done slowly, oxygen saturation monitored and time should be taken to adapt

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Acclimatisation

Acute:

Heart rate increases almost instantaneously

Hyperventilation - blowing off more CO2

Chronic:

Increased red blood cell count - EPO activity increased

Capillary density increased - more delivery to cell

Takes about 14-28 days for chronic adaptions to set in

Optimum altitude = 2000-2500m

Optimal time = 28 days

Optimal hours per day at altitude = 22hrs/day

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Physiological adaptations

As altitude increases:

VO2 max decreases, work is limited at lower levels as the body has to compensate for lack of oxygen

Over time the heart rate decreases to adjust and is able to acclimatise to normal levels

Therefore back at sea level VO2 will increased as it no longer has to compensate for lack of oxygen

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Acute mountain sickness

Severe headache, nausea, vomitting, malaise, loss of appetite

Has a rapid onset of 3-96hrs

No protection with aerobic training

50% of people get AMS at 4205-5500m

Intracranial volume reserve may be anatomical risk factor in AMS

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High Altitude Cerebral Oedema

Caused by fluid shifts and increases in cranial and spinal pressure

Brain swelling, severe headache, confusion, disorientation, can lead to coma/death

People at risk are those who ascend too quickly

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High altitude pulmonary oedema

Fluid shifts in lungs due to changing pressure

Excessive rapid breathing, tachycardia, coughing, spluttering and production of frothey sputum

Rapid onset - 12-96hrs within ascent

Immediate treatment is required

Young, active males are particularly susceptible

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Physiological disadvantages of altitude

Increased ventilation

Decreased peripheral blood flow

Immunosupression

Dehydration

Increased oxidative stress

Disturbed sleep

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