ABSTRACT
The presence of surfactant also allows the lung to remain inflated at relatively lower distending pressures than would otherwise be allowed by native surface tension forces at the air-liquid interface. These significant surface tension forces are the major determinant of the hysteresis of the lung, which is the difference in the pressure-volume relationship during inspiration versus expiration (Fig. 4). Lung hysteresis means that higher pressures are required to achieve a given lung volume during inspiration than are required during expiration. Thus, compared with an air-filled lung without surfactant, the air-filled lung lined with surfactant can be inflated at significantly lower transmural pressures. When surfactant function is deficient, as in the infant respiratory distress syndrome, alveolar collapse is common, with detrimental effects not only on gas exchange but also on the requirement for large pressures to inflate the lungs.
