Our story starts in December of 1941.

Following the Japanese bombing of Pearl Harbor on December 7th, the United States declared war on Japan.

Three days later, Germany and Italy declared war on the United States.

A few days after that, a 48 year-old physiologist from the University of Rochester called Wallace O. Fenn assembled a team of biologists with backgrounds in studying snakes, fruit flies and grasshoppers. 

Their intention: to win the war!

The importance of air power was one of the evolving lessons that had come out of WWI and various thinkers within the military establishments believed that the airforce that held the “higher ground” in terms of altitude would carry the day. Most airplanes of the time did not have pressurized cabins and while very little was known about gas exchange and lung physiology. What was known was that there simply was not enough oxygen for pilots to fly much beyond 12 000 feet.

To this day, hypoxia is one of the most important flight stressors to consider. We talk about this at length in the lesson on Dalton’s Law (part of the Flight physiology course). Essentially, the problem is that, because of the relatively low partial pressure of oxygen at altitude, there is no longer a sufficient pressure gradient to drive oxygen into the bloodstream.

A simplified form of the equation can be written:

PaO2= FiO2 (Patm-pH20) – PaCO2/0.8

Where PaO2 is the partial pressure of oxygen in the alveoli; FiO2 is the “fraction of inspired oxygen; Patm is the atmospheric pressure; pH2O is the saturated vapour pressure of water at body temperature and the prevailing atmospheric pressure and; PaCO2 is the arterial partial pressure of carbon dioxide.

If we solve this equation for different altitudes, we can see that the Sao2 is already critically low at 10 000 feet!