Aortic nervous activities in response to pulsatile and nonpulsatile pressure

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Abstract
Semiquantitative measurements of the aortic baroceptor nervous activities were made under pulsatile and nonpulsatile conditions in cats at various pressure levels induced by the occlusion of the ascending and descending aortas and by the intravenous administration of epinephrine. The mean aortic nervous activity changed almost linearly to changes in the absolute mean aortic pressure level between 80 and 240 mm Hg. Within this wide pressure range the gain of baroceptors varied from 1.7-2.3 in the aortic arch and was slightly greater in the left carotid sinus for steady mean pressure. Sensitivity to the systolic pressure was the greatest within the range from threshold pressure level to 140 mm Hg and then it decreased with increase in aortic pressure. The phasic discharge to the rate of rise in pulse pressure disappeared at the level of 98 [plus or minus] 3 (SE) mm Hg during falling mean pressure and appeared at the level of 67 [plus or minus] 4 (SE) mm Hg during rising mean pressure. No detectable difference was found in baroceptor sensitivity to changes in the absolute level in mean pressure induced by the intravenous administration of epinephrine (8 [mu]g/kg).