Very slow response of the baroreflex regulation system: a tool for understanding cardiovascular control

The baroreflex loop control of blood pressure has been intensively studied during steady state, by assuming linearity and using Heart Rate (HRV) and Blood Pressure Variability (BPV) analysis. Since a step input response characterizes a linear system, it is used in patients undergoing carotid endarterectomy surgery, where restitution of blood flow in the artery, following removal of its atheromatous plaque, is assumed a step input to the baroreflex system. Also a model is constructed of linear and non-linear components; describing the sympathetic and parasympathetic systems, the baroreceptors and the vasomotor center. The model predicts the effect of carotid artery declamping, simulated by a step input to the "baroreceptor" component, on the mid and high frequency bands of the HRV and BPV as seen in patients. It also predicts the slow decline of heart rate and blood pressure following declamping, by describing the vasomotor center function as a Proportional and Integrator (PI) controller.