53.201 Physiology and the Effects of Flight

53.201.2 Explain how the partial pressure of oxygen changes as altitude increases.

As we climb into the atmosphere, the pressure around us reduces. 

For example, at 18’000 ft, the atmosphere has approximately half the weight as at the surface.  

Even though the pressure is reducing, the percentages of each gas remain the same.

The weight of any gas in the atmosphere is known as the partial pressure, and it is measured in mm of Mercury (Hg). 

On the surface, the pressure of the atmosphere is 760 mmHg, so the partial pressure of oxygen would be 160 mmHg (760 X 21%).

At 18,000 ft, the pressure of the atmosphere is 380 mmHg, so the partial pressure of oxygen would be 80 mmHg (380 X 21%).

53.201.4 Describe the primary physiological and behavioural consequences of hypoxia for flight crew and passengers.

53.201.6 List the main factors influencing variation in hypoxia onset (tolerance) between individuals.