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CLINICAL STUDY

Sympathetic neural mechanisms in white-coat hypertension

^* Department of Cardiology, Leeds Teaching Hospitals, Leeds, United Kingdom

Manuscript received December 4, 2001; revised manuscript received March 19, 2002, accepted April 5, 2002.

^* Reprint requests and correspondence: Dr. Paul A. Smith, Cardio-Respiratory Unit, St. James’s University Hospital, Beckett Street, Leeds, United Kingdom.
paulsmith.leeds{at}ukgateway.net

OBJECTIVES: This study planned to establish whether sympathetic hyperactivity exists in white-coat hypertension (WHT) in the clinical setting, relative to matched groups with normotension (NT) and untreated essential hypertension (EHT).

BACKGROUND: White-coat hypertension differs from EHT by the presence of normal ambulatory blood pressure. Sympathetic hyperactivity exists in patients with EHT in the clinical setting and is believed to contribute to the development of target organ damage. Similar organ damage has been reported in WHT, yet little is known about sympathetic neural activity in this condition.

METHODS: Using microneurography, we examined groups of 12 matched subjects with WHT, EHT and NT during the same clinical setting to quantify muscle sympathetic nerve activity as multiunit discharge (MSNA) and single units (s-MSNA).

RESULTS: The s-MSNA in WHT (54 ± 4.2 impulses/100 beats) was greater (p < 0.05) than in NT (37 ± 5.4 impulses/100 beats) despite similar age and body mass index (BMI). The EHT values of s-MSNA (73 ± 5.2 impulses/100 beats) were significantly (p < 0.05) greater than in WHT despite similar age, BMI and blood pressure levels. The MSNA followed a similar trend. White-coat hypertension had a similar cardiac baroreceptor reflex sensitivity to NT, but this was impaired in EHT relative to both NT and WHT.

CONCLUSIONS: It was shown, in the clinical setting, that central sympathetic hyperactivity exists in WHT, albeit to a lesser degree than EHT. These findings suggest that WHT may not be entirely benign and that the observed sympathetic hyperactivity may be responsible for development of target organ damage in this group of patients.

Abbreviations and Acronyms   BMI   body mass index   BRS   cardiac baroreceptor reflex sensitivity   CVR   calf vascular resistance   EHT   essential hypertension   IVS   interventricular septal thickness   JNC   Joint National Committee   LVID   left ventricular internal diameter   LVM   left ventricular mass   LVMI   left ventricular mass index   MSNA   multiunit muscle sympathetic nerve activity   NT   normotension   PW   end-diastolic posterior wall thickness   s-MSNA   single-unit muscle sympathetic nerve activity   WHT   white-coat hypertension

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