Relation of body temperature and restraint to altitude tolerance in the rat

¹ U.S. Naval School of Aviation Medicine, Pensacola, Florida and Laboratory of Physical Biology, National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland

A comparison of the altitude tolerance of restrained and nonrestrained adult male (225–300 gm) and adult female (150–225 gm) Sprague-Dawley rats exposed to an altitude of 33,500 ft. at various rates of ascent with various prealtitude exposure treatments was made. Animals restrained immediately before altitude exposure with rapid ascent (2000 ft/min) to altitude die significantly sooner than do nonrestrained control animals. Slow stepwise ascent to altitude (2 –4 hr. to reach terminal altitude) increased the altitude tolerance of both the restrained and nonrestrained animals but much more for the restrained animals. When body temperatures were dropped to 25°C before altitude exposure there were no deaths (up to 6 hr.) in either the restrained or nonrestrained animals. A lesser body temperature fall provided less protection. It appears that restraint may affect altitude tolerance in the rat by hastening the body temperature fall ordinarily associated with altitude exposure and by increasing the oxygen requirements as a result of the struggling to escape restraint. Since the former increases altitude tolerance and the latter reduces it, restraint may significantly increase or significantly decrease altitude tolerance, depending on the experimental procedure.