Muscle and skin sympathetic nerve traffic during the "White-Coat" effect

Background-Sphygmomanometric blood pressure measurements induce an alerting reaction and thus an increase in the patient's blood pressure and heart ra te. Whether and to what extent this "white-coat" effect is accompanied by d etectable changes in sympathetic nerve traffic has never been investigated. Methods and Results-In 10 mild untreated essential hypertensives (age 37.9/-3.8 years, mean+/-SEM), we measured arterial blood pressure (by Finapres) , heart rate (by EGG), and postganglionic muscle and skin sympathetic nerve activity via microneurography, Measurements were performed with the subjec t supine during (1) a 15-minute control period, (2) a 10-minute visit by a doctor unfamiliar to the patient who was in charge of measuring his or her blood pressure by sphygmomanometry, and (3) a 15-minute recovery period aft er the doctor's departure. The entire procedure was performed twice at a 45 -minute interval to obtain, in separate periods, muscle or skin sympathetic nerve traffic recordings, whose sequence was randomized. The doctor's visi t induced a sudden, marked, and prolonged presser and tachycardic response, accompanied by a significant increase in skin sympathetic nerve traffic (38.6+/-6.7%, P<0.01). In contrast, muscle sympathetic nerve traffic was sig nificantly inhibited (-25.5+/-4.1%, P<0.01). All changes persisted througho ut the doctor's visit and, with the exception of skin sympathetic nerve tra ffic, showed a slow rate of disappearance after the doctor's departure. Conclusions-Thus, the presser and tachycardic responses to the alerting rea ction that accompanies sphygmomanometric blood pressure measurement is char acterized by a behavior of the adrenergic nervous system that causes muscle sympathoinhibition and skin sympathoexcitation.