Differences in the circadian variation of blood pressure between normotensive and white coat hypertensive subjects

The prevalence and clinical significance of white coat hypertension (WCH) is still controversial. Although recent longitudinal studies have provided preliminary prognostic data on subjects with WCH as compared to patients with sustained hypertension, the possible relation between WCH and vascular risk is still under debate. Accordingly, we compared the circadian pattern of blood pressure (BP) variability between normotensive subjects and patients with WCH. We studied 186 subjects (85 mean), 49.5±14.7 (mean±SD) years of age, with diurnal BP mean below 135/85 for systolic/diastolic BP, and hyperbaric index (area of BP excess above a time-specified tolerance interval) below the previously established threshold for diagnosis of hypertension from data obtained by ambulatory BP monitoring [Hermida et al. Hypertension. 2000;35:118-125]. Among those subjects, 94 (47 men) had WCH (mean from 6 office BP measurements above 140 or 90 mm Hg for systolic or diastolic BP). BP was measured at 20-minute intervals during the day (07:00 to 23:00 hours) and at 30-minute intervals at night for 48 consecutive hours. Circadian parameters established by population multiple-component analysis [Fernandez & Hermida. Chronobiol Int. 1998;15:191-204] were compared between normotensive and WCH subjects by nonparametric testing. Patients with WCH are characterize by a significant increase in systolic (3.1 mm Hg; P<0.001) but not in diastolic BP (P=0.452 for comparison of 24-hour mean) as compared to normotensive subjects. The differences in systolic BP between normotension and WCH are much more pronounced during the first 6 hours after awakening, and they are almost irrelevant during nocturnal resting hours. The largest and highly significant difference between groups was found around the clock in pulse pressure (about 4 mm Hg in 24-hour mean, P<0.001). In patients studied by 48-hour ambulatory monitoring, WCH is characterized by a significant elevation in systolic BP and, especially, in pulse pressure as compared to truly normotensive subjects. If indeed pulse pressure is an independent predictor of risk and cardiovascular events, WCH could then be associated to a long-term worst prognosis in comparison to true normotension, an issue that deserves further investigation. DGES, PM98-0106; PGICT00-PXI-32205PN; University of Vigo.