Effects of unilateral and bilateral carotid baroreflex stimulation on cardiac and neural sympathetic discharge oscillatory patterns.

BACKGROUND Left and right carotid baroreflex afferents participate in generating the spontaneous variability of heart rate (HR), arterial pressure (AP), and muscle sympathetic nerve activity (MSNA), but the relative contribution of each side is unclear. Pathophysiological conditions unilaterally affecting carotid baroreceptor function might result in abnormal changes of HR, AP, and MSNA variability, thus markedly affecting prognosis. We tested the hypothesis that unilateral carotid baroreceptor perturbation might differentially affect HR, AP, and MSNA variability compared with stimulation of the opposite side. METHODS AND RESULTS In 12 healthy volunteers, 4 sinusoidal neck suction procedures (0.1 Hz, from 0 to -50 mm Hg) were applied at the right, left, and combined right and left sides of the neck, in concordance or with phase opposition. Respiration was controlled at 0.25 Hz. Power spectrum analysis assessed the changes in the 0.1-Hz oscillatory component of the R-R interval, systolic AP (SAP), and MSNA variability induced by rhythmic baroreceptor stimulation. Mean R-R interval, SAP, and MSNA were unchanged during all procedures. The increase of the 0.1-Hz component of R-R and SAP variability during right and combined right and left carotid baroreceptor stimulation was greater than the changes induced by left-sided stimulation. The increase in the 0.1-Hz oscillatory component of MSNA variability was similar during all neck suction procedures. CONCLUSIONS Right carotid baroreflex loading was as efficient as bilateral stimulation and more effective than left carotid suction in modulating R-R and SAP variability. There was no asymmetry in neural sympathetic discharge responses after single-sided carotid baroreceptor stimulation.