Short-term control of cardiovascular function: estimation of control parameters in healthy humans.

In a previous study, we recorded short-term cardiovascular responses after a steep increase in arterial pressure in healthy humans [Am. J. Physiol. 266 (Heart Circ. Physiol. 35): H199-H211, 1994]. The aim of the present study was to develop a mathematical model of the baroreflex control of arterial pressure, to use this model with the previously recorded data to estimate unknown parameters in the reflex control loop, and then to analyze the overall open- and closed-loop performance of the system by model simulations with use of individual sets of optimal parameters. The mathematical model consists of a heart, a linear elastic arterial reservoir, and two parallel resistive vascular beds. The arterial baroreflex loop is modeled by two separate time domain processing objects, each with its own gain, time constant, and delay, to simulate the action of a sympathetic signal to the peripheral vascular bed and a parasympathetic signal to the heart. In repeated model simulations, the control parameters in the model were systematically adjusted by an automated algorithm that minimized the deviations between the time courses of the cardiovascular variables simulated by the model and the previously recorded responses in each individual. In all 10 subjects, the short-term cardiovascular responses were adequately simulated by using individual sets of parameters in the model. Open-loop transfer functions for arterial pressure control were obtained by using the individual sets of optimal model parameters in new simulation runs. Open-loop gain for arterial pressure control at nearly zero frequency (steady state) was between 0.9 and 4. Model simulations also indicated an underdampened response at 0.05-0.07 Hz in the closed-loop situation in four subjects, corresponding to peaks in the mean arterial pressor power spectra obtained from separate recordings of spontaneous variations in the resting situation.