A STUDY OF THE PHYSIOLOGICAL CHANGES WHICH OCCUR DURING ACCLIMATION TO HIGH ALTITUDE. THE CHANGES IN HEART SIZE IN MAN DURING PARTIAL ACCLIMATIZATION TO SIMULATED HIGH ALTITUDES.
NAVAL SCHOOL OF AVIATION MEDICINE PENSACOLA FLA
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Four healthy young men were partially acclimatized over a period of one month to simulated high altitudes in a decompression chamber. During the fourth week the subjects were able to remain at 22,500 feet and on occasions were taken to higher altitudes for short periods. The size of the heart shadow, as revealed in teleroentgenograms, was determined at frequest intervals. Measurements of the films of one subject were not made because the right border of the heart was obscured by the shadow of the spine. The results indicate that the heart shadow decreased slightly in size when the subjects were exposed to reduced atmospheric pressures. There is no reason to doubt but that this decrease in heart shadow size indicated an actual rather than an apparent decrease in heart size. Although our data do not directly bear on the cause of the decrease in heart size, it is believed to be due to decreased cardiac filling or smaller stroke volume or both. It is concluded that during an early stage of acclimatization to severe anoxia under the conditions of our experiment dilatation of the heart does not occur but, rather, the heart may decrease slightly in size. Some of the literature relating to the effect of anoxia on heart size is reviewed. Author