Effects of Carotid Sinus Nerve Stimulation on Blood-Flow Distribution in Conscious Dogs at Rest and during Exercise

The effects of stimulating the carotid sinus nerves on the distribution of cardiac output and peripheral vasoactivity was studied in intact, unanesthetized dogs instrumented with ultrasonic or electromagnetic flow probes on the ascending aorta, mesenteric, renal, and iliac arteries, and miniature pressure gauges in the aorta. A radiofrequency pacemaker was used to stimulate the nerves in dogs at rest, during treadmill exercise, and after autonomic blockade. Thirty-second periods of stimulation in the resting dog resulted in an average decrease in aortic pressure of 28%, cardiac output remained unchanged, total peripheral resistance fell 29%, mesenteric flow 12%, mesenteric vascular resistance 18%, renal flow 8%, and renal vascular resistance 22%. In the iliac bed flow increased by 90% while resistance declined by 62%. Heart rate decreased initially by 13%, and returned to control during stimulation. The bradycardia was determined to be predominantly due to vagal stimulation. During treadmill exercise carotid sinus nerve stimulation resulted in similar decreases in arterial pressure, mesenteric and renal resistance, and a further decrease in iliac resistance from exercise control values. Thus, electrical stimulation of the carotid sinus nerves in the conscious dog produced a differential pattern of peripheral vasodilatation, the most profound dilatation being observed in the hind-limb circulation. This release of sympathetic tone also occurred during stimulation in exercising animals when the muscular bed was already dilated on a metabolic basis.