Extent of Carotid Sinus Regulation of the Myocardial Contractile State in Conscious Dogs

Stephen F. Vatner; Charles B. Higgins; Dean Franklin; Eugene Braunwald

doi:10.1172/JCI106893

Extent of Carotid Sinus Regulation of the Myocardial Contractile State in Conscious Dogs

Stephen F. Vatner, Charles B. Higgins, Dean Franklin, and Eugene Braunwald

Published April 1, 1972 - More info

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Abstract

The effects of bilateral carotid artery occlusion (BCO) and carotid sinus nerve stimulation (CSNS) on left ventricular (LV) pressure (P), diameter (D), velocity of contraction (V), rate of change of pressure (dP/dt), and cardiac output were studied in conscious dogs instrumented with ultrasonic diameter gauges, miniature pressure gauges, and aortic electromagnetic flow transducers. The effects of BCO and CSNS were also studied after automatic blockade and were compared to similar alterations in pressure produced by norepinephrine, methoxamine, and nitroglycerin. When heart rate was maintained constant with atrial stimulation, BCO had little effect on ventricular contractility, increasing isolength systolic pressure (LV P_iso) by 36% while isolength velocity of myocardial shortening (V_iso) decreased by 12% and (dP/dt)/P fell by 8%. These effects could be explained largely by vasoconstriction, since elevating systolic pressure with methoxamine produced similar results, while norepinephrine increased V_iso by 36% and (dP/dt)/P by 56%. CSNS produced directionally opposite results from BCO; it decreased P_iso by 15%, V_iso increased by 11%, while (dP/dt)/P remained almost constant. These effects may be explained largely by vasodilatation since reducing systolic pressure to the same level with nitroglycerin produced similar results. When peripheral vasoconstriction was minimized by phenoxybenzamine pretreatment. BCO produced a slight positive inotropic effect (P_iso increased by 8%, V_iso by 4%, and (dp/dt)/P by 10%), while CSNS produced a slight negative inotropic effect (P_iso decreased by 3%, V_iso decreased by 5%, and (dP/dt)/P by 7%).

Thus, in the normal, healthy, conscious dog, the carotid sinuses exert relatively little control of the inotropic state of the left ventricle; moreover, this small inotropic action is masked by the more powerful effects on peripheral resistance.

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