ABSTRACT

Mechanoreceptors in the carotid sinus and aortic arch are the afferent limb of reflexes that regulate blood pressure. The vagal cardioinhibitory and sympathoinhibitory vascular effects of these reflexes have been studied for more than 60 years. It is undisputed that the baroreflexes buffer changes in arterial pressure via specific cardiovascular mechanisms; however, in addition to these peripheral effects, mediated by the autonomic efferents, stimulation of the baroreceptors also produces less known, but clearly documented, general inhibition of central nervous processes: Independent of changes in general circulation, the activation of baroafferent pathways by electrical nerve stimulation, mechanical stretch, or elevation of blood pressure will decrease somatic muscle tone, inhibit spinal somatic reflexes, induce synchronization of the electroencephalogram (EEG), increase cortical positivity, blunt pain sensations, reduce anxiety, and induce sleep or even clinically significant syncope (see below). Arousing emotional and pain stimuli elevate blood pressure, (Harshfield, Pickering, James, & Blank, 1990; Harshfield, Pickering, Kleinert, Blank, & Laragh, 1982; James, Yee, Harshfield, Blank, & Pickering, 1986; Jonsson & Hansson, 1977; Peterson, Augenstein, Tanis, & Augenstein, 1981; Pickering & Gerin, 1990; Pickering, Harshfield, Kleinert, Blank, & Laragh, 1982), and the CNS in-hibitory effects of barostimulation most simply can be seen to provide supplementary, homeostatic, negative feedback, that along with cardioinhibition and vasodilatation, helps to restore excessively elevated blood pressure to a safer level.