Systems analysis of the carotid sinus baroreflex system using a sum-of-sinusoidal input

The purpose of the present study was to determine the dynamic characteristics of the carotid sinus baroreflex system (CS) employing systems analysis. In 28 anesthetized and mechanically ventilated dogs with vagotomy, intracarotid sinus pressure (ICSP) was changed artificially. In protocol 1 (n = 7), we estimated the transfer function of the CS by means of a single sinusoidal input (SIN), the Gaussian white-noise input (GWN), and a sum-of-sinusoidal input (SUM). The transfer function of ICSP to systemic arterial pressure (SAP) was second-order delay with an identical corner frequency of 0.025 Hz and damping ratio of 0.7. The steady-state gain estimated using GWN (1.12 +/- 0.13) or SUM (1.13 +/- 0.08) was significantly smaller than SIN (1.69 +/- 0.25). In protocol 2, to find the reason why there was a difference among the estimated steady-state gains, we investigated the effect of ICSP pulsation on the open-loop gain of the CS. The maximum gain of the gain curve was decreased and the operating range was increased significantly with the 2-Hz pulsation. We could simulate the above phenomena by using a model with a nonlinear sigmoidal relationship between ICSP and SAP. The dynamic characteristics of the CS appeared to be changed by pulsation, but this phenomenon was attributable to the sigmoidal nature of the relationship between ICSP and SAP. Pulsation decreases the maximum gain and increases the operating range, which may contribute to stability of the CS and homeostasis of SAP.