Physiology

The physiology of aeronauts and aviators, especially the effects of flight at high altitudes, became a topic of interest, for its own sake, and for that of the fliers.

Reports on blood pressure of aviators are discussed, for example, in a 1911 issue of Aero:

[...] Mountain climbing offers some analogy, but it differs in the fact that the transition from the high atmospheric pressure of the sea level to a low pressure takes place much more slowly, says the London Lancet.
In the Gazette Hebdomadaire des Science Médicales de Bordeaux of September 25, Prof. R. Moulinier has reported some interesting observations on the blood pressure of aviators who have ascended to high altitudes. On alighting after ascending to a height of 1,200 to 2,000 meters the aviator presents cyanosis of the extremities, probably from the low termperature of the high region of the atmosphere. Often there is congestion of the conjunctive. The pulse is slightly accelerated, but there is no palpitation, arrhythmia or epistaxis. There is often slight and transient headache and tinnitus aurium. Sometimes there is a tendency to sleep, and this may be felt even during flight.
After the flight the blood pressure is always increased. In one aviator at 5:30 p. m., before flight, the constant blood pressure in the radial artery was found with Pachon's sphygmometer to be 9 centimeters of mercury and the maximum pressure to be 18 centimeters: the pulse was 70. At 6 p. m., after a flight of 25 minutes during which at the twentieth minute he reached the height of 1,100 meters, the constant pressure was 12 centimeters of mercury and the maximum pressure was 19 centimeters: the pulse was 80.

The article goes on to underscore that these pilots were physically fit and well trained. Prof. Moulinier suggested that aviators should descend more gently if possible. The article points out that physical and psychical stress on pilots can lead to accidents.

Earlier, anecdotal reports had suggested the risks of altitude sicknsss: Francesco Zambeccari in 1803 and Henry Tracey Coxwell and James Glaisher in 1862 passed out during high-altitude ascents. Deafness seemed to be one of the few long-term risks of traveling to high altitude. Joseph Crocé-Spinelli and Théodore Sivel died, probably of oxygen deprivation, during a high-altitude ascension in the Zénith in 1875, with Gaston Tissandier passing out but living to tell the tale.