[Heart cycle related sensitivity of the pressor receptor reflex before and after dissection of the carotid sinus nerves].

Both carotid sinus nerves of anesthetized, spontaneously breathing dogs were stimulated, before and after dissection, with brief, R-wave-triggered, submaximal electric impulses during different phases of the heart cycle. The resulting decrease of blood pressure and heart rate, related to the initial level and stimulation intensity is, respectively, about 2.5- and 4.5fold higher after denervation. Stimuli applied 90 ms after the R-wave provoke maximal lowering of mean arterial pressure. After dissection this maximum reappears, enhanced by the factor of 1.4, with stimuli delayed by 70 ms. Also, the initial decrease of heart rate in the first respiration cycle after onset of stimulation shows a maximum of 90 ms, which does not, however, change its position after dissection. Two mechanisms are discussed for the heart cycle related sensitivity of the pressor-receptor reflex: 1. Time-selective inhibition of the sympathetic activity controlling the smooth vascular muscles because of a central coincidence of the afferent signals from the sinus and aorta nerves with the electric stimuli, and 2. the heart cycle related sensitivity of the heart against efferent vagal control signals.