Unilateral carotid-cardiac baroreflex responses in humans

To determine the individual contributions of the right and left carotid sinus baroreflex control of the cardiac interval, we measured heart rate [as expressed by R-R interval (RRI)] and mean arterial pressure (MAP) responses elicited by pulsed trains of neck suction or pressure in 20 healthy men. Pulses were delivered using a customized neck collar device partitioned to allow for stimulation of only one side of the neck. Maximal cardiac gains for right, left, and bilateral baroreflexes were determined from the logistic function of RRI responses to changes in estimated carotid sinus pressure (ECSP). Maximal gains for right (5.44 +/- 1.33 ms/Torr ECSP) and left (4.22 +/- 1.44 ms/Torr ECSP, P > 0.05) carotid-cardiac responses did not differ. However, the bilateral gain (6.89 +/- 1.80 ms/Torr ECSP) was less than the simple sum of the right and left gains (9.67 +/- 2.20 ms/Torr ECSP, P < 0.01). We suggest that the right and left carotid-cardiac reflex responses are quantitatively similar in humans and exhibit an inhibitory interaction when compared with the bilateral response under conditions of supine rest in normotensive subjects.