Diaphragmatic vasodilation elicited by pulmonary C-fiber stimulation

This study was performed to assess the effect of pulmonary C-fiber stimulation with capsaicin on vascular resistance in the diaphragm. Nine dogs were anesthetized with pentobarbital sodium and were instrumented with right and left ventricular catheters. The left phrenic artery was isolated and perfused from an extracorporeal reservoir. Right ventricular capsaicin injections (5-20 micrograms/kg) caused significant decreases in phrenic perfusion pressure (-16%), systemic arterial pressure (-32%), and heart rate (-19%). Injection of identical doses of capsaicin into the left ventricle led to no significant changes in phrenic arterial perfusion pressure or systemic arterial pressure but a 10% decrease in heart rate. Bilateral cervical vagotomy eliminated the response to both right and left ventricular injection of capsaicin, as did administration of the autonomic ganglion blocker hexamethonium bromide. The results indicate that pulmonary C-fiber stimulation reflexly vasodilates vessels in the diaphragm.