Aortic baroreceptor discharge during nonhypotensive hemorrhage in anesthetized dogs

Abstract

We tested the hypothesis that arterial baroreceptor discharge remains constant during nonhypotensive hemorrhage. Aortic baroreceptor activity was recorded from anesthetized dogs during slow, continuous hemorrhage until 24 ml blood/kg body wt had been removed. The relationship between simultaneously recorded hemodynamic variables and single-unit aortic baroreceptor activity was evaluated by a unique computer program that sampled all variables 500 times/s and analyzed data from each consecutive cardiac cycle throughout the entire experiment. In three hemorrhages performed on three dogs, aortic blood pressure did not decrease during the experiment (nonhypotensive hemorrhage), but aortic nerve activity decreased progressively when data from individual cardiac cycles having identical mean aortic pressures were compared. Reduced baroreceptor activity correlated closely with progressive reductions in pulse pressure. In other hemorrhages, mean aortic pressure decreased by a variable amount; decreases in recorded single-unit baroreceptor activity occurred during each of these hemorrhages also. In summary, hemorrhage consistently caused decreases in the activity of aortic baroreceptors regardless of whether mean aortic pressure decreased or remained constant during hemorrhage. We conclude that experimental techniques employing nonhypotensive hemorrhage do not provide an effective method for selectively studying reflexes from cardiopulmonary receptors in the absence of changes in arterial baroreceptor input.

Human cardiovascular variability, baroreflex and hormonal adaptations to a blood donation

“…Heart rate was not altered, despite the overall sympathetic activation. This profile has not always been observed after blood donation or a mild drop in blood volume [2,[17][18][19][20]. Our results also contrast with those observed after a plasmaphoresis [21].…”

“…A mild drop in blood volume is usually considered to be a specific stimulus of low pressure cardiopulmonary baroreceptors [4]. However, non-hypotensive haemorrhage decreases the activity of aortic baroreceptors, regardless of whether there is a decrease in the mean aortic pressure [19]. Our protocol with its mild drop in blood volume and increased systolic and mean blood pressures probably did not involve arterial baroreceptors.…”

Mathematical modeling of gravitational effects on the circulation: importance of the time course of venous pooling and blood volume changes in the lungs

“…To introduce the fast vagal effects seen in tilt back, vagal efference is pulsatile, allowing a possible large effect within the same beat. Our baroreflex model is not only sensitive to the pressure level but also to P pulse (18). Sympathetic activity occurs in the diastolic silence of the baroreceptors (7,56).…”

“…Only when Ppulse was taken into account could the increase in HR be related to the decreased input (1). The role of changes in Ppulse in the baroreflex has been reported previously (18,48). The input to our baroreflex model is a combination of the systolic pressure and the integral of the pressure at the level of the receptors over the time of opening of the aortic valve (Eq.…”

“…The input to the baroreflex in our model is based on observations after hemorrhage reported previously (18) as well as our own measurements. Although HR increased after HUT for all subjects in our data set (n ϭ 20), the corresponding P mean and Pdiast at carotid level did not always decrease.…”