Anthony Dixon, North Carolina State University

Baroreflex Regulation of Heart Rate during Postural Change from Sitting to Standing: Model Development and Experimental Validation

Abstract:  During orthostatic stress in humans, the arterial and cardiopulmonary baroreflexes play a key role in maintaining arterial pressure by increasing both heart rate and sympathetic neural activity to vascular beds.  In this presentation, we present a mathematical model that can predict reliably the dynamics of heart rate regulation in response to postural change from sitting to standing. The model includes for input the blood pressure measured at the finger, models for the baroreceptor nerves firing rate, sympathetic and parasympathetic responses or tones, tone impulse function, concentrations of noradrenalin and acetylcholine, and heart rate. In addition, we formulate an inverse least squares problem for parameter estimation and successfully demonstrate that our mathematical model captures accurately the dynamics observed in physiological heart rate data obtained from three groups of subjects, young, healthy and elderly, and hypertensive elderly. Among our key findings in this work is that successful validation of these models against clinical data requires that we have to consider effects of vestibulosympathetic reflex in humans. To our knowledge, our mathematical model of baroreflex control of heart rate successfully captures, among other cardiovascular reflexes, the role of the vestibular system in regulating sympathetic neural activity.  Furthermore our model reveals that the transfer between the nerve firing and blood pressure is non-linear and follows a hysteresis curve. In particular, in young subjects, the hysteresis loop is wide, however, in healthy elderly and hypertensive elderly subjects the loop shifts to the right and the area of the hysteresis loop is diminished. Finally, for hypertensive elderly subjects the hysteresis loop is not closed indicating that, during postural transition from sitting to standing, the blood pressure resettles at a different steady state value.
This is joint work with Mette S. Olufsen, Eamonn Tweedy, Hien T. Tran, Johnny T. Ottesen, Lewis A. Lipsitz, and Vera Novak.

Undergraduate Mentors: Hien T. Tran and Mette Olufsen (NCSU)