HUMAN PROBLEMS IN AVIATION — BRONX 405 



ing every pilot and air crewman in the basic physiological principles 

 that relate to life at high altitudes. In the Army, 60 modern replicas 

 of Paul Bert's "altitude chamber" have been erected at 45 airfields. 

 Under the direction of some 200 aviation physiologists, student fliers 

 in groups of 10 or 20 are placed in these chambers for several hours, 

 while the atmosphere is made to resemble that which they will later find 

 at 35,000 or 40,000 feet. Under careful supervision, they experience the 

 effects of inadequate oxygen and are taught to use the equipment avail- 

 able in combat aircraft for providing the additional oxygen they will 

 require. Finally, the "chamber flights" are supplemented with lectures 

 which give the physiological basis for the practical demonstrations. 

 Forty-five thousand men a month have been given such instruction, in 

 what is probably the largest medical training program ever developed 

 to overcome an occupational hazard. This is an essential part of the 

 training that fits the crews to fly the great bombing missions over the 

 Nazi's European fortress. 



The problems I have thus far discussed differ only in degree from 

 those encountered 50 years ago in slow-moving balloons. The high 

 speed which gives to modern aircraft a unique tactical advantage now 

 confronts the flight surgeon with quite new problems. For the air 

 crews not only ascend into an unnatural environment, but they do so 

 with terrific speed. Climbing at a rate of 80 feet a second, an airman 

 in G minutes reaches an altitude of 6 miles, where the barometric pres- 

 sure is but one-third that at sea level. This sudden change in the pres- 

 sure acting on the body unbalances the equilibrium of gas pressures 

 within its cavities and tissues. The painful inward pressure on the 

 ear drum when the eustachian tube cannot be opened is a familiar 

 experience of all who have flown. But only the military aviator going 

 quickly to 30,000 or 40,000 feet knows the excruciating pain caused by 

 the sudden liberation of gases from solution in the blood or other body 

 fluids. 



It has recently been shown that during these sudden changes of 

 pressure minute gas nuclei on the surface of cells or on the inner walls 

 of blood vessels rapidly expand in size, growing with the nitrogen, 

 carbon dioxide, and oxygen that is liberated from the surrounding 

 fluid as it is decompressed. As bubbles of gas are thus formed and 

 grow, some lodge in small terminal vessels where they obstruct the 

 flow of blood. Nerve endings may thus be deprived of oxygen and 

 pain results. Or regions of the brain are likewise put out of action, 

 with widespread and serious consequences. 



I must hasten to add that this widely accepted explanation of the 

 cause of the pain of decompression sickness is not conclusively estab- 

 lished. The theory has, however, served a useful purpose, for it has 

 led to a practical and fairly reliable method of prevention. Assum- 



