INTERACTIONS AMONG REFLEX COMPENSATORY SYSTEMS FOR POSTHEMORRHAGE HYPOTENSION

The open-loop gains of the carotid sinus, aortic, and cardiopulmonary baroreflex systems defined as the ratio of the posthemorrhage hypotension without a reflex to that with the reflex were estimated from experiments with a mild and quick hemorrhage (2 ml/kg body wt in 1-2 s) in 81 pentobarbital-anesthetized rabbits. The overall gain when all the nerves were intact was 7.4. After the carotid sinus nerves were sectioned the gain decreased to 3.0. After aortic nerve sectioning, the gain was 2.8, whereas vagotomy decreased it to 3.8. When both the carotid sinus and aortic nerves were cut, the gain was 0.9. When the aortic and vagus nerves were severed, it was 1.8. When the vagus and carotid sinus nerves were cut, it was 1.6. From these gain values the gain of the interacting component between the carotid sinus and aortic reflexes was calculated as 0.4; that between the aortic and cardiopulmonary reflexes was 0.5; and that between the cardiopulmonary and carotid sinus reflexes as 0.1. The gain of the interaction among all of these baroreflex systems was estimated to be 2.1. The results suggest that all these facilitatory interacting components play an important role in restoration of arterial pressure decrease caused by mild hemorrhage.