The purpose of this study was to obtain an accurate measure of the temperature of respired air of subjects working on a treadmill at various ambient temperatures and ambient relative humidities (RH). The experiments were conducted in an environmental chamber at each of four different ambient temperatures (nominally 20, 30, 40 and 45° C) and at two different ambient RH (20% and 100%) for a total of eight different conditions. Each experiment consisted of four tests at each ambient condition, these being: (A) standing quietly; (B) walking on a treadmill at 3 km·h−1, 0% grade; (C) walking on a treadmill at 3 km·h−1, 5% grade; and (D) walking on a treadmill at 5 km·h−1, 5% grade. It was found that under these conditions the maximum temperature of the expired air is independent of work rate and also ventilation rate but varies significantly with both the temperature and humidity of the inspired air. At low ambient RH the expired air temperature was [mean (SD)] 31.2 (1.3), 33.3 (0.7), 34.0 (1.7) and 35.6 (0.7)°C for ambient temperatures of 20, 30, 40 and 45° C, respectively. At high ambient RH the expired air temperature was 32.0 (1.8), 35.3 (0.5), 37.6 (1.2) and 41.8 (0.8)°C at ambient temperatures of 20, 30, 40 and 45° C, respectively. Thus the expired air temperature was higher at the higher ambient temperatures and ambient RH. While similar results have been reported before, the techniques used in this study should provide a more accurate measure of these effects than those previously reported.
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Livingstone, S.D., Nolan, R.W., Cain, J.B. et al. Effect of working in hot environments on respiratory air temperatures. Europ. J. Appl. Physiol. 69, 98–101 (1994). https://doi.org/10.1007/BF00609400