EFFECTS OF BRONCHOACTIVE AGENTS ON STATIC PRESSURE-VOLUME CHARACTERISTICS OF DOG LUNGS

Static pressure-volume characteristics of the lung in the thoracotomized dog have been studied during continuous infusion of bronchoconstrictor agents into the isolated bronchial arteries, or of sympathomimetic amines into the pulmonary arteries. At inflation pressures less than 20 mm Hg, static airway pressures were higher for a given volume during histamine or acetylcholine infusion than those of the controls. The difference in pressure was marked during inflation from the collapsed state; it was small when inflation was initiated from the end-inspiratory level. When the lung was fully expanded the difference in pressure was insignificant, i.e., drug infusion had no effect on airway pressures. During deflation the pressure-volume curve nearly retraced that of the controls, and pulmonary compliance calculated from the middle third of the deflation curves showed minimal differences. Infusions of epinephrine or norepinephrine into the pulmonary artery did not alter static pressure-volume characteristics. The present findings suggest that bronchoconstriction may lead to closure of some of the pulmonary air spaces by surface tension forces, resulting in a decrease in the number of units sharing a given air volume.