The effect of body warming on respiratory mechanics in rats.

The temperature dependence of airway smooth muscle cells and alveolar surfactant activity, and of the elastin stress-strain relationship, suggests that body warming may affect respiratory mechanics in vivo, a possibility that has not yet been investigated. To examine this hypothesis, healthy rats were studied using the end-inflation occlusion method under control conditions and after an infrared lamp was used for body warming. Hysteresis areas, the inspiratory work of breathing, and its elastic and resistive components were also calculated. After body warming, static and dynamic elastance, ohmic airway resistance, mean value of hysteresis, the inspiratory work of breathing, and additional resistance due to pendelluft and stress relaxation were all decreased. These data suggest that body warming reduces the inspiratory work of breathing by improving the elastic and resistive mechanical properties of airways. This effect is evident even for limited temperature variations suggesting that it may occur in the event of spontaneous pathological conditions, such as fever.