34.10 Hypoxia

34.10.2 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. 

For example, 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). 

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

Oxygen has to be of a certain pressure to be able to force itself through the lining of the lungs so that oxygen can be diffused into the blood stream. 

Within the lungs the presence of increased quantities of water vapour and carbon dioxide reduce the partial pressure of oxygen to 102 mmHg.

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

Oxygen has to be of a certain pressure to be able to force itself through the lining of the lungs so that oxygen can be diffused into the blood stream. 

The partial pressure of oxygen inside the lungs of 102 mm Hg is the minimum oxygen pressure a human needs to function normally.