Determination of the gain of baroceptive mechanisms on heart rate and arterial pressure variability signals

The performance of baroreceptive mechanisms is classically evaluated by measuring the lengthening of the heart period (HP) in response to a symbolic arterial pressure (SAP) rise. The authors present several methods for calculating the gain of the SAP-HP relationship through proper processing of cardiovascular variability signals. The spectral analysis of such signals makes it possible to enhance some parameters which satisfactorily describe the level of control elicited by the sympathovagal balance on cardiovascular functions. The advantages of this approach compared with the classical one, which uses an injection of i.v. vasoconstrictor drug as the input stimulation, are twofold. First, it is possible to measure α parameters in the patient even for long periods of recordings (up to 24 h or more) without using drugs which produce a change in the physiological short-term steady-state condition. Second, it is possible to use the parameters of cardiovascular variability signals for the design and validation of proper 'black-box' physiological modeling.