Nonlinear Analysis of the Baroreceptor Reflex System

Abstract

The regulation of blood pressure by the baroreceptor reflex was examined in anesthetized dogs. The receptor feedback path was broken by surgical intervention, the input (carotid sinus pressure) was controlled by an external servo system, and simultaneous records of input and output (systemic arterial pressure) were obtained. A variety of pressure waveforms were applied to the carotid sinus so that the nonlinear behavior could be explored thoroughly. Most of the input waveforms consisted of relatively small signals about an operating point in the normal blood pressure range. The nonlinear behavior of the reflex was illustrated in a number of ways. Square waves, sinusoids, and short pulses produced asymmetric arterial pressure waveforms. An overshoot in the arterial pressure always followed the rising edge of the input square wave, but was generally absent following the negative-going part of the square wave. Either positive or negative pulses caused a transient drop in arterial pressure. The sinusoidal response was often distorted, with the falling portion of the output waveform steeper than the rising portion. The system behaved as a rectifier, or envelope-detector, as illustrated by 1) the decrease in mean arterial pressure when either the amplitude or the frequency of a sinusoidal input was increased and 2) the appearance in the arterial pressure waveform of a component correlated with the envelope of a modulated carrier. Another nonlinear phenomenon was the decrease in low-frequency sinusoidal gain caused by the addition of a high-frequency sinusoid to the sinus pressure waveform. This behavior indicates that if closed loop behavior in the intact animal is to be predicted from the open loop sinewave response, the effects of the cardiac pressure pulse must be considered. A model was constructed from standard electronic components to simulate the input-output behavior of the baroreceptor reflex. The model was able to simulate the response to high- and low-frequency sinusoids and to reproduce the essential features of the square-wave and pulse responses. On this basis the model was considered adequate for simulating the performance of the baroreceptor reflex in certain open loop and closed loop situations.

The loop gain of autonomic reflex function in orthostatic hypotension.

“…However, the differences were not statistically significant (p >0.02). In either 45 or 90° tilt, the gain values obtained from the SDVT experiment (LEVISON et al, 1966;CHEN, 1979;CHEN et al, 1979;CHEN and BISHOP, 1983). The sigmoid relationship between the input pressure (carotid sinus pressure) and the output pressure (SAP) reflects that the loop G is not a constant function, but decreases toward the saturation pressure (CHEN and BISHOP, 1983).…”

“…Another possibility for the unaltered PVP in the face of reflex sympathetic activation was a reduction in venous capacity without significant change in the pressure. The baroreflex G in arterial pressure compensation have been assessed using open-and closed-loop methods (LEVISON et al, 1966;ALLISON et al, 1969;DONALD and EDIS, 1971;MCRITCHIE et al, 1976;CHEN, 1979;CHEN et al, 1979;CHEN and BISHOP, 1983). CHEN and BISHOP (1983) were the first to correlate the G values from the open-loop experiment with the data from the closed-loop approach.…”

“…Our data revealed that the total baroreflex compensation in terms of the loop gain during the orthostatic stress averaged 2.36 and 1.63 for 45 and 90° head-up tilt, respectively. For a comparison, the gain values obtained from open-loop analysis of the carotid and aortic baroreflexes in anesthetized animals varied from 0.5-1.5 (LEVISON et al, 1966;KUMADA et al, 1970;CHEN, 1979;CHEN et al, 1979;CHEN and BISHOP, 1983). In the dog, aortic baroreceptors were shown to play a minor role in the antihypotensive function (ALLISON et al, 1969;DONALD and EDIS, 1971;EDIS,1971).…”

Bezold-Jarisch reflex attenuates dynamic gain of baroreflex neural arc

“…If we simply move the gain plot upward, the steady-state gain of ϳ5 would make the dynamic gain at 0.2 Hz unity, thereby causing system instability. A previous study (15) indicated that the arterial baroreflex system is marginally stable, suggesting that the absolute gain value of the total baroreflex is ϳ5. This assumption is based on linear analysis; the actual baroreflex system may only generate sustained oscillation, even with greater gain values, by virtue of system nonlinearity (14).…”

Bilateral Carotid Sinus Control of Ventricular Performance in the Dog

“…• Several quantitative analyses, with various levels of sophistication, have been reported for the dynamic baroreceptor control of systemic blood pressure (1)(2)(3)(4)(5). Because of the complexity of this system, however, the analyses developed have not included a rep-resentation of all the known functional components and their interconnections.…”