Influence of Sympathetic Nerve Stimulation on Right Ventricular Outflow-Tract Pressures in Anesthetized Dogs

Abstract

Stellate ganglion stimulation in the anesthetized, open-chest dog consistently resulted in the generation of pressure differences which averaged 20 mm Hg across the infundibular region of the right ventricle. Before stimulation, peak systolic pressures in the sinus and conus were closely matched. Peak sinus pressure showed ah average increase of 184 and 162% during stimulation of the left and right stellate ganglia, respectively. Simultaneously, peak conus pressure showed average increases of 88 and 61% during left and right stellate ganglion stimulation, respectively. In addition, the maximal rate of intrasinus pressure development (dP/dt) was usually elevated above conus dP/dt, and this change contributed to the generation of early systolic pressure differences. Cervical vagosympathetic nerve stimulation following atropine administration also resulted in the generation of infundibular pressure differences, but the latter were less marked than those elicited during stellate ganglion stimulation. Elevations in main pulmonary arterial resistance abolished the induced pressure differences by allowing peak conus pressure to rise to the same extent as peak intrasinus pressure. Simultaneous electromagnetic flow recordings of pulmonary arterial blood flow during stellate ganglion stimulation revealed two-to five-fold increases in maximum flow acceleration with relatively little change in stroke volume. Infundibular pressure gradients which developed in early systole were associated with maximum flow changes in the pulmonary artery.ADDITIONAL KEY WORDS stellate ganglion stimulation pulmonary arterial occlusion pulmonary arterial blood flow sinus and conus regions of the right ventricle vagosympathetic stimulation right ventricular infundibulum • The early anatomical and embryological studies of Sir Arthur Keith (1, 2) demonstrated that the conus arteriosus of the developing embryo was incorporated into the right ventricular myocardium and formed the terminal portion of the infundibulum in the adult heart. The conus homologue on the left side was obliterated during the embryological development of the left ventricle. In lower forms, From the Department of Physiology, Loyola University, Stritch School of Medicine and the Graduate School, 1400 South First Avenue, Hines, Illinois 60141.This work was supported in part by U. S. Public Health Service Grants HE 08682 and CM 999 from the National Institutes of Health.Received October 14, 1968. Accepted for publication, January 24, 1969. such as the tortoise, the conus arteriosus is anatomically distinct from the rest of the right ventricular musculature, and Woodbury and Robertson (3) demonstrated that this region can act as a functional stricture to divert blood through the interventricular foramen to the left ventricle. Studies on the canine heart by March et al. (4) have shown that the inflow or sinus region of the right ventricle is activated before the infundibular region, thus demonstrating physiological inflow-outflow pressure differences. Recently Tobin et al...

Functional Anatomy of the Interventricular Septum

“…Regulation of flow into the aorta may be more dependent upon region II contractility and time of contraction which contribute to the pressure gradient front left ventricular chamber to aorta. The right ventricular conus, important in control of right ventricular outflow gradients [2,10], is reduced to a few fibers in the upper right septum and probably effects the output of that chamber to a lesser degree than the upper left septum does to left ven tricular output. The right septal musculature contracts in accord with the sinus region of the region of the right ventricular free wall and probably contributes considerably to the generation of pressure within the sinus region.…”

“…This structure is usually divided into a small, oval-shaped, pars membranácea and a large pars muscularis, the latter making up the great mass of its musculature. Much of the septum is anatomically associated with the proximal portions of the great arteries, and it is tempting to relate these structural features to the dramatically different pressures and pressure gradients developed across the right and left outflow tracts [2,9,10]. In cross-section, the interven tricular septum appears to be an integral part of the left ventricle; in fact, the septum is anatomically divisible into a relatively thin muscular sheet belonging to the right ventricle and a thick muscular layer forming a powerful part of the left ventricular wall [1], However, while the mus cular septum constitutes a massive central axis around which grossly dif ferent intraventricular pressures are developed, practically nothing is known about the functional partitioning of its regional contraction pat terns and the way in which contraction contributes to right and left intra ventricular pressure devlopment.…”

Sympathetic Control of Pulmonary Vascular Impedance in Anesthetized Dogs

“…The physical dimensions and frequency response characteristics of this device have been described (8). The main pulmonary artery was prepared to receive an electromagnetic flow probe by dissecting off the fat pads surrounding the vessel and freeing the vessel from connective tissue for a length of 1.5 cm.…”

Sympathetic Control of Right Ventricular Dynamics

“…Sinus dP/dt was consistently elevated above either impact or lateral dP/dt in the conus. In addition, the onset of development of sinus pressure preceded the onset of conus pressure [9,13,16]. Together, these alterations caused the generation of a pressure difference wave, which began to develop from sinus to conus prior to the onset of right ventri cular ejection.…”

“…Recent investigations dealing with right ventricular hemodynamics have revealed that positive inotropic stimuli can induce marked systolic pressure differences between the right ventricular inflow-tract and the pul monary arteries [13,18]. Simultaneous recordings of right ventricular sinus pressure and outflow-tract diameter indicate that during isopro terenol infusion right ventricular systolic pressure is markedly augmented and reaches maximum levels coincident with maximal reduction in outflow-tract diameter [18], These results indicate that positive inotropic stimulation of the right ventricle can induce the formation of a functional resistance to outflow by reducing the internal caliber of the infundibular zone.…”