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PPL » Human Factors » Hypoxia

10.10 Hypoxia

10.10.2 Define hypoxia.

Hypoxia is a condition where there is a decrease in the amount of oxygen reaching body tissues.



10.10.4 State the partial pressure of oxygen both inside and outside the lungs at sea level.

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

At 18’000 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). 

At sea level, the pressure of the atmosphere is 760 mmHg, so the partial pressure of oxygen (outside the lungs) would be 160 mmHg (760 X 21%).

Within the lungs the presence of increased quantities of water vapour and carbon dioxide reduce the partial pressure of oxygen to 105 mmHg.


10.10.6 Explain the mechanical effect of the partial pressure of oxygen on oxygen transfer in the lungs.

The partial pressure of oxygen plays a mechanical role in oxygen transfer in the lungs.

When we breathe in, the air in the lungs has a higher partial pressure of oxygen compared to the blood in the capillaries surrounding the alveoli.

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