Systematic autoregulation counteracts the carotid baroreflex

The interaction between autoregulation and baroregulation and its effect on the gains of the short-term pressure regulatory system were studied by performing open- and closed-loop experiments in the same five anesthetized, vagotomized dogs and by analyzing the data using a novel model. With carotid pressure constant (no baroregulation), the pressure-flow data were convex to the flow axis, indicating the presence of autoregulation. When baroregulation was present, the data were convex to the pressure axis. The proposed model was able to fit the data as measured in both cases. From the fitting procedure, the zero-flow pressure intercept, the autoregulation resistance gain, and the baroregulation resistance gain were estimated. It is concluded that if autoregulation is present it affects the values of baroreflex gains estimated from both closed- and open-loop experiments. The autoregulation gain can be estimated from steady-state systemic pressure-flow data measured after vagotomy and with the carotid pressure constant. Then, from measurements of systemic pressure-flow data performed after restoring the hydraulic connection between carotid and aortic areas, the gains of the carotid baroreflex can be estimated with the aid of the proposed model.