Short-term systemic autoregulation.

We studied total systemic autoregulation in closed-chest, chloralose-anesthetized dogs. Cardiac out-put (previously implanted electromagnetic flow probe on ascending aorta) and aortic pressure were varied by reducing venous return using a balloon catheter in the vena cava. Compensatory action of the baroreflex was prevented by bilateral vagotomy and isolation of both carotid sinuses. To avoid high vessel tone carotid sinus pressure was set at the original baseline value using a pressurized blood reservoir. With each balloon inflation aortic flow and aortic pressure decreased and stabilized in about 1 min. Pressure and flow were allowed to return to base-line values after each balloon inflation in an attempt to minimize the activation of slower regulatory mechanisms. The steady-state pressure-flow relations could be fitted with a sigmoidal curve. The mean quality (0 less than Q less than 1) of autoregulation in eight dogs was 0.41 +/- 0.08 (SD). Autoregulation was found in the pressure range from 42 to 140 mmHg. The early appearance of total systemic autoregulation suggests that, in the intact animal, it may counteract baroreflex control.