title: Autonomic nervous stimulation affects left ventricular relaxation more than left ventricular contraction.
abstract: We studied the effects of stimulation of the vagal and also the sympathetic efferent cardiac nerves on left ventricular (LV) relaxation and contraction in 11 anesthetized, open-chest dogs. In each dog, we paced the ventricles at a fixed rate of 120 beats.min-1 and kept the systemic arterial pressure constant. The maximum rate of LV pressure decline, (dP/dt)min, and the time constant of LV isovolumic pressure decline, tau, were used as our indexes of LV relaxation. The maximum rate of LV pressure rise, (dP/dt)max, was used as our measure of LV contractility. Vagal stimulation decreased (dP/dt)min more than (dP/dt)max (P less than 0.01) when examined at frequencies that ranged from 2 to 12 Hz. Vagal stimulation at 12 Hz reduced (dP/dt)min by 26% (P less than 0.001) and increased tau by 57% (P less than 0.0001) but decreased (dP/dt)max by only 20%. Sympathetic stimulation, at frequencies that ranged from 2 to 12 Hz, increased (dP/dt)min more than (dP/dt)max (P less than 0.001). Sympathetic stimulation at 12 Hz increased (dP/dt)min by 130% (P less than 0.0001) whereas it increased (dP/dt)max by 60% (P less than 0.0001). Sympathetic stimulation at 12 Hz decreased tau by 74% (P less than 0.0001). Our studies suggest that cardiac autonomic nerve stimulation affects left ventricular relaxation more than left ventricular contraction.
authors.affiliation: Division of Investigative Medicine, Mt. Sinai Medical Center, Cleveland, OH 44106.
authors.forename: R J
authors.initials: RJ
authors.lastname: Henning
authors.forename: I
authors.initials: I
authors.lastname: Khalil
mesh_terms: D000818:Animals; D001341:Autonomic Nervous System / Q000502:physiology*; D001794:Blood Pressure; D004285:Dogs; D004558:Electric Stimulation; D006321:Heart / Q000502:physiology; D006352:Heart Ventricles; D009200:Myocardial Contraction; D013564:Sympathetic Nervous System / Q000502:physiology; D014630:Vagus Nerve / Q000502:physiology