Pulmonary function in normal humans with exercise and temperature-humidity stress

Fifty-eight normal young male human subjects were exposed for 4 h to comfortable conditions (22 degrees C, 40% rh) or to heat stress conditions (30 degrees C, 60% rh) with or without exercise. Exercise amounted to two 15-min sessions of treadmill walking at 6.7 km X h-1 (4 mph) with a 10% grade beginning at 105 and 225 min after entry into the chamber. Measurements of 15 pulmonary function variables were made 1) before entry into the chamber, 2) 5 min after the first exercise period, 3) 5 min after the second exercise period, and 4) 24 h after the end of the exposure period. The exercise, estimated to use about two-thirds of the subjects' maximum oxygen intake, produced no statistically significant (P less than 0.01) changes in pulmonary function parameters. Heat stress produced significant changes in forced vital capacity, and possibly significant interactions were observed in peak expiratory flow and forced expiratory flow at 25% of vital capacity. Effects of the two factors appeared to be additive. Changes with exercise and heat stress were associated with reversal of a progressive decrease of airway resistance seen in subjects at rest in a comfortable environment.