Dynamics of the short-term regulation of arterial pressure: frequency dependence and role of arterial compliance.

Abstract

The purpose of this study was to investigate the role of the interaction between peripheral resistance regulation and arterial compliance in the overall short-term regulation of mean arterial pressure. A nonlinear model previously proposed was linearised about control values of mean arterial pressure and cardiac output so that it could be reformulated in terms of transfer functions. The resulting pressure to pressure open-loop transfer function H(s) consists of a complex conjugate pair of poles (pertaining to the resistance regulating system) and a real pole (pertaining to the arterial system, 1/(R0 C), R0=control resistance). Such a structure suggests an interaction between the resistance regulation and the arterial compliance (C). Quantitative evaluation of this interaction was obtained by estimating the model parameters during partial vena cava occlusions in four cats. Using these parameters the time response of the open-loop control system to a pressure step was found to be underdamped and oscillatory in all four cats (damping factor ξ ranged from 0·20 to 0·66), the amplitude of oscillations depending on the value of ξ and on the relative amplitude of the arterial time constant (compliance and peripheral resistance) with respect to the time constant 1/(ξωn). Bode diagrams of H(jω) showed that the resonance peak due to the resistance regulating system may not be detectable, either because of the relatively high value of ξ or because it is masked by the pole of the arterial system.