Respiratory water loss as a function of ventilatory or environmental factors

Abstract

Since expired gas is not water-saturated (Ferrus et al., 1980, Respir. Physiol. 39: 367–381), its water content should depend on biological or environmental factors other than expired gas temperature. In order to verify this hypothesis, multiple linear regression relationships between Me H 2O , the mass of water expired per litre of BTPS ventilated gas and respiratory frequency (f) or period ( Tr), tidal volume ( Vt), ventilation (V̇), temperature of inspired gas (T I), density of inspired gas mixture (ϱ I), partial pressure of water in inspired gas ( Pi H 2O ) were computed from 345 experiments performed on 7 subjects. This analysis shows that M E H 2O is positively and significantly correlated to Ti (0.22 mg · dm −3 · °C −1), to Pi H 2O (0.14 mg · dm −3 · Torr −1), and to Tr (0.87 mg · dm 3 · s −1). Me H 2O is negatively and significantly correlated to f (−0.27 mg · dm −3(cy · min −1) −1) to ϱ i (−0.06 mg · dm −3(g · dm −3) −1) and to V̇ (−0.09 mg · dm −3(dm 3 · min −1) −1). There is no statistical correlation between Me H 2O and Vt. It is concluded that the respiratory water loss depends to a large degree on respiratory or environmental conditions. This dependence supports the previously published results suggesting that expired gas is not water saturated.