Effect of a face mask on respiratory water loss during sleep in cold conditions

The purpose of this study was to test the hypothesis that a heat-and-moisture-retaining mask would result in a significant decrease in respiratory water loss among healthy subjects sleeping in a cold environment. The study was done in a backyard near a tertiary-care center during winter nights with ambient temperatures of less than 0 degrees C. Subjects were 10 healthy volunteers, 8 males and 2 females, aged 23-40 years, with a mean of 30.9 years. In a crossover design study, subjects slept alone in mountaineering tents on two nights (8 h each night) using sleeping bags and ground insulation. On one night, they wore heat-and-moisture-retaining masks designed for cold weather exercise. On the other night, they wore no mask. Subjects were weighed before and after each session to obtain an estimate of respiratory water loss. Comparisons were made of weight loss with and without the mask. We found the use of the masks resulted in decreased weight loss in all but one subject. The mean reduction in weight loss was 0.13 kg (SD +/- 0.18 kg). Using a one-tailed t-test, this difference was found to be significant (p < .05). We conclude that the use of a simple and inexpensive face mask can result in a meaningful decrease in overnight respiratory water loss while sleeping in a cold environment.