Muscle and Skin Sympathetic Nerve Traffic During the “White-Coat” Effect

Abstract

Background —Sphygmomanometric blood pressure measurements induce an alerting reaction and thus an increase in the patient’s blood pressure and heart rate. Whether and to what extent this “white-coat” effect is accompanied by detectable 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 ECG), and postganglionic muscle and skin sympathetic nerve activity via microneurography. Measurements were performed with the subject 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 after 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 visit induced a sudden, marked, and prolonged pressor 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 significantly inhibited (−25.5±4.1%, P <0.01). All changes persisted throughout the doctor’s visit and, with the exception of skin sympathetic nerve traffic, showed a slow rate of disappearance after the doctor’s departure. Conclusions —Thus, the pressor and tachycardic responses to the alerting reaction that accompanies sphygmomanometric blood pressure measurement is characterized by a behavior of the adrenergic nervous system that causes muscle sympathoinhibition and skin sympathoexcitation.