Surface Tension as a Factor in Pulmonary Volume-Pressure Hysteresis

Abstract

During slow deep breathing the lungs of human subjects and experimental animals showed a degree of volume-pressure hysteresis which could not be accounted for on the basis of ordinary pulmonary flow resistance. To investigate the possible contribution of surface tension to this phenomenon, excised gas-free dog lungs were filled first with saline and subsequently with air. In the first instance, with surface forces minimized, the degree of hysteresis was small, and during both filling and emptying lung expansion was uniformly distributed. With air inflation, hysteresis was marked and expansion was nonuniform in contrast to deflation. It was concluded that much of the lungs' hysteresis observed in vivo during slow deep volume cycles is related to surface phenomena. Submitted on August 6, 1956