Right ventricular responses to vagus stimulation of fibers to discrete cardiac regions in dog hearts

Abstract

To investigate the role on the right ventricular function of the parasympathetic nerves in discrete cardiac regions, we studied the effects of stimulation of the intracardiac parasympathetic nerves to the atrioventricular (AV) nodal area (AVPS) or sinoatrial (SA) nodal area (SAPS), and stimulation of the cervical vagus nerves (CVS) on the right atrial and ventricular function in the autonomically decentralized heart of the anesthetized dog. AVPS prolonged AV conduction time (AVCT) and decreased the ventricular rate without changes in atrial rate, right atrial `a' wave pressure (RAP), its first derivative (RAd P/d t), right ventricular pressure (RVP) and its first derivative (RVd P/d t) in the spontaneously beating heart. On the other hand, AVPS prolonged the AVCT in the atrium paced electrically and further decreased the ventricular rate with decreases in ventricular pressure responses but not atrial responses. SAPS decreased atrial and ventricular rates without AVCT changes and attenuated the right atrial and ventricular pressure responses. In the atrial paced heart, SAPS decreased the ventricular responses less than those responses in the spontaneously beating heart with similar decreases in the atrial pressure responses, but it changed neither the AVCT nor ventricular rate. On the other hand, CVS decreased the atrial and ventricular rate or pressure responses, and increased the AVCT. CVS in the paced heart also decreased the atrial and ventricular pressure responses with the prolongation of AVCT. The cardiac responses to parasympathetic stimulations were abolished by atropine. These results suggest that AVPS decreases ventricular rate without direct right ventricular pressure effects but the negative chronotropic effects of AVPS and SAPS decrease the ventricular pressure responses rate-dependently in the dog heart.