Measurement of vascular tone and stroke volume baroreflex gain.

The arterial baroreflex system (BRS) consists of at least three closed-loop control systems: the heart rate (HR), vascular tone (VT), and stroke volume (SV) BRSs. Whereas HR-BRS gain is well studied, VT-BRS and SV-BRS gain are not. This study aimed to develop a method for quantifying VT-BRS and SV-BRS gain using an established HR-BRS gain measurement approach. ECG and beat-to-beat blood pressure (BP) were recorded in 31 young healthy participants during three tasks. Sequences of R-to-R wave intervals (RRI) of the ECG, pulse transit time (PTT), and SV were measured to assess HR-, VT-, and SV-BRS gain using the cross-spectral technique of computing the BP-RRI, BP-PTT, and BP-SV transfer functions. Gain in each BRS arch was measured in individuals with intact BRS functioning. Functional overlap and independence was noted in the BRS arches. The implications of the proposed method are discussed.