Blood volume changes and high and low pressoreceptor activity in cats.

Studies were undertaken in the cat to determine if moderate hemorrhage or volume expansion significantly altered carotid sinus and aortic baroreceptor activity. In addition, the experimental design provided the opportunity to compare gain of the two sets of receptors. A 20% blood volume expansion increased mean arterial blood pressure 5.2% and carotid sinus nerve activity 14.7%, whereas a 20% hemorrhage decreased mean arterial blood pressure 10.8% and carotid sinus nerve activity 32.3%. For the aortic baroreceptors, a 20% blood volume expansion increased mean arterial blood pressure 5.9% and nerve activity 10.5%, and a 20% hemorrhage decreased mean arterial blood pressure 8.9% and nerve activity 21.0%. The blood pressure-discharge curves for the carotid sinus and aortic baroreceptors were not different. The well-known high sensitivity of atrial receptors was also documented. We conclude that both high- and low-pressure receptors apprise the central nervous system of the status of intravascular volume and pressure.