Factors determining maximum expiratory flow in dogs.

Abstract

By measuring esophageal pressure and end and side intrabronchial pressures simultaneously, along with flow and volume during forced deflations in dogs, the site of equal pressure points (EPP) were located and the factors determining the resistance of airways upstream from them were measured. These factors, along with lung elastic recoil pressure, are regarded as the determinants of maximum expiratory flow ([image]max). At high lung volumes EPP were in large extrapulmonary airways and pressures required to accelerate gas (Pca) from alveoli to EPP greatly exceeded the pressure required to overcome frictional resistance (Pfr). At low lung volumes EPP moved upstream into the lung beyond the reach of the pressure catheter, Pca decreased markedly, and Pfr increased. In normal lungs at high volumes, the cross-sectional area at EPP (to which Pca is inversely related) and lung elastic recoil are the most important determinants of [image]max. At low lung volumes [image]max is determined by lung recoil and the frictional resistance of airways upstream from EPP.