Possible conversion of heat into work in the lung.

An infra-red thermometer has been used to monitor the surface temperature of double-sided surfactant films and excised sections of rabbit lung parenchymal tissue as their areas are changed by 2:1. The temperature fell upon expansion by 5.43 degrees C for the films and by 2.42 degrees C for the tissue secretions and rose upon compression. Upon removal of surfactant from the tissue sections, temperature changed in the opposite direction. The thermodynamic significance of these findings is discussed as providing a basis by which waste metabolic heat might be re-used in the lungs to provide the "engine" phenomenon previously deduced (1) on the basis of the inversion of the hysteresis between surface tension and area. This contribution to the work of breathing from a surface engine could be vital when there is a delicate balance between work demand and work supply for breathing in certain pathological states, e.g. with RDS.