Printed in U.S.A. Respiratory Heat Exchange with Vizrying Temperatare and Hzlmidity of Inspired Air

I N THE COURSE 01 ~ STUDIES on human exposures to air temperatures ranging up to 240’F. (115.5Oc.) and humidities ranging up to 1.4 in. Hg (35.6 mm.) vapor pressure, the possibility of intolerable heating of the respiratory passages or lungs as a limiting factor had continuously been entertained. Actually under the conditions of the experiments this fear was not realized, and all symptoms specifically referable to the respiratory tract proved to be mild and without important effect upon the duration of the experiment. It became clear that, like sweat evaporation in its effect upon the skin, the evaporative cooling mechanism of the respiratory tract has great capacity to absorb sensible heat through humidification. A few preliminary measurements made in 1948 typically took the following temperature course: 0 I showed that ambient air at 220’F. ncJusuREMENT Inhalation: At portal of nose or mouth 1.5 in. within nose or mouth Exhalation