Effects of Sympathetic Nerve Stimulation on the Pulmonary Arterial Tree of the Isolated Lobe Perfused in Situ

Abstract

The hemodynamic response to sympathetic nerve stimulation (SNS) was studied in canine lung lobes isolated in situ and perfused with a pulsatile pump. For the same input pulse, both the rate of rise and the rate of fall of pulmonary arterial pressure increased during SNS; the peak systolic pressure was also higher during SNS, whereas diastolic pressure levels were either at, or below, control levels. The increase in pulse pressure produced little or no change in mean pulmonary artery pressure and resistance. During SNS, compliance per unit length in large arteries fell, pulse wave velocity increased, and elastic modulus increased. Phenoxybenzamine produced opposite changes. Norepinephrine injections increased resistance and produced smaller compliance changes than SNS. Flow loads imposed by short bursts of rapid pump rate at constant stroke volume caused increments of vascular volume which returned to control levels after return to the slower rate. Volume increments were smaller and restoration rates faster during SNS than during control. After phenoxybenzamine, volume increments were larger and restoration rates slower than control. The results indicate that the distensibility of the large pulmonary arteries and the precapillary bed is decreased during sympathetic stimulation, while calculated resistance is not changed.