The effect of body warming on respiratory system stress recovery in the rat

The mechanical characteristics of respiratory system tissues include visco-elastic behaviour. In particular, after mechanical unloading, i.e., a reduction in respiratory system volume, the lower stress achieved slowly increases, approaching higher constant value, due to visco-elastic stress recovery. We performed experiments in which constant deflation flow arrest was applied in rats to study the successive pressure-time course, which defines the visco-elastic stress recovery. To investigate the possible effects of temperature changes, measurements were performed at two body temperatures, 36.6 ± 0.3 and 39.0 ± 0.1 °C. We found that stress recovery is reduced by increasing body temperature. Pressure-time curves after deflation arrest were fitted by specific mathematical model, and a good agreement was found. Model parameters exhibited significant changes with body temperature variations, suggesting that temperaturedependent micro-structural rearrangement phenomena in the tissues of alveolar wall were involved in the stress recovery decrement with body temperature increase. Thus, visco-elastic phenomena in respiratory system tissues of mammals exhibit temperature dependence. The stress recovery changes with body temperature suggest that expiration is expected to be easier in condition of physiological body temperature than in the case of increased temperature.