Respiratory heat exchange in mammals

The dimensions of the maxillo-turbinate structures of a number of medium-sized and large mammals were determined using morphometric techniques. Estimates were obtained of the variation of gap width, perimeter and airway cross-sectional area along the organ. The time required for heat exchange in the turbinates of each animal was then determined for flow in a simple model based on that developed by Collins et al. (1971) and compared to the expected transit time for respired air. In all cases it was found that there was ample time for heating and humidification of the air when breathing at rest or moderate exercise. It was also shown that narrowing the air gap increased the effective time available for heat exchange despite the resulting reduction in transit time.