Blood pressure responses to cyclic blood volume changes in awake and anesthetized dogs

A dynamic analysis of blood pressure regulation was performed in conscious and anesthetized dogs. The mean arterial pressure (MAP) responses to 5 and 10% sinusoidal changes in total blood volume with cycle lengths of 1, 4, and 8 min were measured in anesthetized 1) control dogs, 2) carotid and vagal baroreflex (CVB)-denervated animals, and 3) spinal-ablated dogs; in addition, the MAP responses to 10% sinusoidal blood volume changes with cycle lengths ranging from 0.25 to 8 min were measured in conscious control and CVB-denervated dogs. The presence of the baroreflexes in both the conscious and anesthetized control dogs essentially eliminated MAP excursions during the cyclic volume changes. The MAP changes in both the conscious and anesthetized denervated dogs were large. However, the responses in the anesthetized denervated dogs were linear, stationary, and cycle-length insensitive with respect to the sinusoidal forcing function, whereas the responses in the conscious CVB-denervated dogs were nonlinear, nonstationary, and cycle-length dependent. These results indicate that the cardiovascular system in the anesthetized CVB-denervated and spinal-ablated dogs is passive or "hydraulic" in nature; conversely, factors other than the carotid and vagal baroreflexes appear to exist that alter the arterial pressure responses to cyclic blood volume perturbations in the conscious CVB-denervated dogs.