Hot air breathing: effects of elevated wet bulb temperatures on tissue temperatures of the mouth

Six healthy young men breathed room air or one of nine hot humid air conditions on separate days for one hour while walking on a treadmill (40% VO2 max). Inspired wet bulb temperatures ranged from 18.9 (room air) to 49.3 degrees C. Tissue temperatures in the mouth were measured by means of thermocouples placed on the tongue and hard palate. Analysis of variance on repeated measures showed significant increases in both tongue and hard palate tissue temperatures (p less than 0.001) as a result of increasing wet bulb temperatures; however, core temperature and heart rate were not affected (p greater than 0.05). Ratings of subjective discomfort increased proportionally with increases in wet bulb temperature of the inspired air. It was concluded that wet bulb temperature of inspired air is a valuable measure to uses in studying temperature responses of mouth tissues when inhaling hot humid air, particularly when investigating human tolerance levels in order to recommend federal standards for the design of breathing apparatus.