Static volume-pressure curves of dog lungs--in vivo and in vitro.

Abstract

To evaluate esophageal pressure as a measure of pleural pressure in the dog, and to compare the static volume-pressure characteristics of in vivo and excised lungs, volume-pressure curves were obtained on 10 anesthetized and tracheosto-mized dogs. In 5 animals, esophageal pressure was compared to pleural pressure in the absence and presence of moderate and large pneumothoraxes. The differences were 3 cm H2O or less, except at the extremes of lung volume. A pneumothorax did not systematically alter the differences. The comparison of volume-pressure curves of excised and in vivo lungs showed small but systematic differences. Excised lungs contained more gas on deflation at moderate distending pressures and exhibited greater static hysteresis than living lungs. Differences in smooth muscle tension or vascular pressures probably contribute to the observed differences but cannot fully explain them. If alveolar surface tension deviates less from an equilibrium value in living than in excised lungs, changes similar to those observed would result.