EFFECT OF GRAVITY ON THE BLOOD PRESSURE OF THE DOG

Abstract

Dogs, anesthetized with Na barbital or chloralose, were tilted from the horizontal to the upright, feet down (F.D.), position. This was usually accompanied by a sharp drop in intrafemoral and intracarotid blood pressure followed within 10 secs. by a compensatory rise of varying degree. The compensation, while seldom complete, was usually adequate to prevent serious cardiovascular embarrassment even when the animal was maintained in the F.D. position for several hrs. Repeated tilting did not seem to fatigue the compensating mechanisms unless the anesthesia was very deep or the animal in poor condition. Denervation of the carotid sinuses or cutting the vagus nerves, thus eliminating the 2 aortic nerves, uniformly diminished and sometimes eliminated the ability of the animal to compensate for gravity. Removal of both pressor receptor mechanisms usually resulted in complete absence of compensation and in many cases a drop in blood pressure to shock levels from which recovery was slight. The results suggested that the carotid sinus and aortic nerves are of importance in the response to gravity not only because of their pressor functions but because of their role in the response to lowered oxygen tension usually present when the animal is in the F.D. position.