Effects of ventilation on pulmonary arterial flow and vascular conductance

Abstract

The effects of the direction and of the rate of change of lung volume on the pulmonary vascular conductance were examined in the isolated lung lobe of the dog. The lobe was suspended in, filled with, and perfused with Ringer-Locke solution at selected constant pressures. Ventilation was produced by displacement of fluid into and out of the “pleural” space surrounding the lobe. During inflation of the lobe, the inflow rate decreased. The magnitude of the changes in the pulmonary arterial flow varied directly with the rate of change of volume of the lobe, and inversely with the conductance of the airways. For a given airway conductance or rate of change of lobar volume, the magnitude of the change in pulmonary arterial flow during deflation was greater than the magnitude of the change during inflation. These effects were augmented by the administration of acetylcholine or histamine. The results show that airway conductance and the rate of lobar volume change can significantly affect flow into the pulmonary artery and the mean pulmonary vascular conductance. These effects apparently result from changes in alveolar and transmural capillary pressures. The results also suggest that acetylcholine and histamine act directly on the bronchial smooth muscle, and thereby indirectly on the pulmonary vessels by raising alveolar pressure during deflation of the lung. The elevated alveolar pressure tends to collapse the pulmonary capillaries and thereby to reduce the pulmonary vascular conductance.