Der Einfluß einer konstanten Herzfrequenz auf den Carotis-Sinus-Reflex am wachen Hund

Summary In healty, conscious dogs the heart rate was kept constant at 144 to 146 beats per minute either by vagal blockade with Atropine (0,5 mg/kg i.v.) or by electrical pacing of the heart. In the resting dog a carotid-sinus-reflex was elicited clamping both common carotid arteries with implanted pneumatic cuffs. Velocity in the ascending aorta (electromagnetic flowmeter), pressure in the descending thoracic aorta (implanted miniature pressure transducer) and pressure in the right carotid sinus using a catheter were measured. By analogue processing acceleration in the ascending aorta, stroke volume and stroke work of the left ventricle, and mean values were derived. Compared to the reflex under normal resting heart rates (64 beats per minute) the results show, that with a constant heart rate (144–146 beats per minute) blood pressure rises by about the same amount induced by a larger increase of the peripheral resistance. Because the fast increase of cardiac output regularly observed under normal conditions was eliminated, the time course of pressure elevation was slower when heart rate was kept constant. The elevated stroke work of the left ventricle during carotid occlusion cannot be explained by an increase of contractility due to enhanced sympathetic activity, because no such increase in contractility was found.It is suggested, that a low control heart rate allows fast reflex adjustment of blood pressure mediated by increases of cardiac output due to vagal inhibition. In contrast, when heart rate is high due to vagal blockade or electrical pacing, the reflex response is determined by slow changes of the total peripheral resistance.

Mit dankenswerter Unterstützung der Deutschen Forschungsgemeinschaft (S.F.B. 90).