Effects of Surface-Active Aerosols and Pulmonary Congestion on Lung Compliance and Resistance

LUNG blood volume and surface tension forces are known factors contributing to the mechanical cost of breathing. In experi-mental and elinical states, pulmonary com-pliance decreases with lung congestion and increases with a reduction in pulmonary blood volume.'1 2 Surface tension forces have been known to influence respiratory mechanics since the work of von Neergaard,3 who dem-onstrated that more pressure was required to inflate air-filled than fluid-filled lungs. Sub-sequent observations have confirmed the me-chanical importance of surface tension pro-duced by an alveolar air-liquid interface, whieh includes a lipoprotein alveolar linina material that stabilizes surface forces.4 6 This study was designed to evaluate the relative contribution of surface forces and pulmonary congestion to the mechanics of breathing in man. Pulmonary compliance and resistance were determined before and after the nebulization of surface active agents in normal and abnormal hemodynamic states. Ethvl alcohol was used as an aerosol because of its low surface tension and beneficial effect reported invpulmonary edema.7 A superinone respiratory detergent containing silicone (Defomaire) was chosen for comparison be-cause of the unique surface effects of silicones. This report indicates that surface active aero-sols alter respiratory mechanies significantlv in normal man, but will not modify lung com-pliance in the presence of pulmonary conges-tion.