Pulmonary Vascular Response to Exercise in the Dog

Abstract

The effects of exercise on the pulmonary circulation were studied in seven experiments on five dogs. Pulsatile pulmonary arterial flow and pressure and left arterial pressure were measured by chronically implanted transducers; pulmonary vascular input impedance, resistance, and hydraulic power were computed. The average effects of running on a treadmill at 6.5 mph, as compared with the resting state, were an increase in cardiac output from 2.59 liters/ min to 5.30 liters/ min, a rise in mean pulmonary arterial pressure from 18 mm Hg to 28 mm Hg, and no consistent change in mean left arterial pressure. Pulmonary vascular resistance fell from 482 dyne sec cm at rest to 372 dyne sec cm -5 during exercise. Characteristic input impedance rose from 147 dyne sec cm-- at rest to 199 dyne sec cm -5 during exercise, and the oscillations of the impedance modulus with frequency decreased in magnitude. These changes were consistent with passive distention of the pulmonary vessels, decreasing the compliance of the large arteries and improving the impedance match between proximal and distal vessels.