Carotid baroreflex function ceasesduring vasovagal syncope

Abstract. Despite the arterial baroreflex control of heart rate andblood pressure, vasovagal syncope is a common cause of loss ofconsciousness in people exposed to stimuli that reduce thecentral blood volume, such as head-up tilt. Carotid baroreflexfunction was evaluated using a rapid pulse train of neckpressure and neck suction in three conscious volunteers whodeveloped a vasovagal episode during head-up tilt. The maximalgain of the carotid-heart rate and carotid-blood pressurebaroreflex function curves were identified as measures ofcarotid baroreceptor responsiveness. When presyncopal symptomsdeveloped, one further baroreflex assessment was obtained beforethe subjects were returned to the supine position. Thebradycardia and hypotension exhibited during pre-syncope andsyncope reflected a leftward and downward relocation of both thecardiac and vasomotor stimulusresponse curves. In addition,during the vasovagal syncope, baroreflex control was suppressedas blood pressure remained low during neck pressure stimuli. Inconclusion, arterial baroreflex function ceases during vasovagalsyncope.