Buffering blood pressure fluctuations by respiratory sinus arrhythmia may in fact enhance them: a theoretical analysis

TL;DR

This theoretical study uses a three-compartment model to analyze how respiratory sinus arrhythmia buffers blood pressure fluctuations, revealing that the effectiveness depends on body position and timing, and explaining paradoxical enhancement effects.

Contribution

It provides a novel theoretical framework showing the critical role of timing and body position in blood pressure buffering by respiratory sinus arrhythmia.

Findings

Buffering is effective only in upright position.

Ineffective control can paradoxically enhance blood pressure fluctuations.

Blood pressure control in the HF band is independent of arterial baroreceptor input.

Abstract

Using a three-compartment model of blood pressure dynamics, we analyze theoretically the short term cardiovascular variability: how the respiratory-related blood pressure fluctuations are buffered by appropriate heart rate changes: i.e. the respiratory sinus arrhythmia. The buffering is shown to be crucially dependent on the time delay between the stimulus (such as e.g. the inspiration onset) and the application of the control (the moment in time when the efferent response is delivered to the heart). This theoretical analysis shows that the buffering mechanism is effective only in the upright position of the body. It explains a paradoxical effect of enhancement of the blood pressure fluctuations by an ineffective control. Such a phenomenon was observed experimentally. Using the basis of the model, we discuss the blood pressure variability and heart rate variability under such clinical conditions as the states of expressed adrenergic drive and the tilt-test during the parasympathetic blockade or fixed rate atrial pacing. From the results of the variability analysis we draw a conclusion that the control of blood pressure in the HF band does not directly obtain the arterial baroreceptor input. We also discuss methodological issues of baroreflex sensitivity and sympathovagal balance assessment.