Pulsatile activation of baroreceptors causes central facilitation of baroreflex

The reflex decrease in arterial pressure is greater and more sustained with elevated pulsatile than with elevated static carotid sinus pressure. The purpose of this study was to relate afferent baroreceptor activity (BRA) and efferent sympathetic nerve activity (SNA) during static and pulsatile pressure to evaluate the influence of pulsatile pressure on the central mediation of the baroreflex. The carotid sinuses were isolated in 11 dogs anesthetized with chloralose. Both vagosympathetic trunks were cut and both carotid sinuses exposed to static and pulsatile pressures over a range of mean carotid sinus pressures (40-180 mmHg). BRA was recorded from one carotid sinus nerve, and the other intact carotid sinus served to initiate reflex changes in lumbar or renal SNA and arterial pressure. For the same mean carotid sinus pressure, pulsatile pressure caused significantly greater inhibition of SNA than static pressure. More importantly, for the same or lesser levels of baroreceptor activity per second, pulsatile pressure caused significantly greater inhibition of SNA than static pressure. The inhibition of SNA was not sustained (i.e., there was "adaptation") with continuous baroreceptor input during static pressure, whereas the inhibition of SNA was sustained (i.e., there was no significant adaptation) with the phasic input during pulsatile pressure. Increases in pulse frequency from 1.4 to 2.5 and 3.7 Hz caused progressively less inhibition of SNA.(ABSTRACT TRUNCATED AT 250 WORDS)