Changes in specific airway resistance during prolonged breathing of moist air

Effects of increased water content of inspired air at 21–38 °C on specific airway resistance (sR aw ) in 107 healthy subjects were measured with a body plethysmograph. Mean sR aw increased insignificantly at 23 °C with 92% relative humidity (water content, 20.7 g∙m −3 ) for up to 71 h but became significant at 6 h with water content 25 g∙m −3 . Increases were greater when evaporated tap water was inhaled than when distilled water was used. It is postulated that the increase in sR aw is due to mucosal swelling and to contaminants in tap water. A theory of respiratory "water elimination" is proposed to replace the concept of respiratory water loss.