The Investigation and Clinical Significance of Resonance in the Heart Rate and Vascular Tone Baroreflexes

The heart rate (HR) and vascular tone (VT) baroreflexes are control systems with negative feedback. As closed-loop control systems with delays, they possess resonance features at approximately 0.1 Hz and 0.03 Hz, which correspond to a ~5-s delay in the blood pressure (BP) response to HR changes and a ~15-s delay in VT response to BP changes, respectively. Unlike a single impact on the cardiovascular system (CVS) that elicits HR, BP, and VT oscillatory responses that fade over time, rhythmical stimulation of the CVS at 0.1 Hz or 0.03-Hz produces steady HR, BP, and VT oscillations with significantly higher amplitudes compared to stimulation at other frequencies. We posit that these baroreflex resonances are integral to the vast autonomic variability that underlies efficient and effective homeostatic reflexes. This paper characterizes the phenomenon of resonances in the CVS using a classic engineering approach and the ability to employ these resonances for clinical applications.