Pressor response to ambulatory blood pressure monitoring in normotensive subjects

The use of ambulatory blood pressure (BP) monitoring (ABPM) has provided a method of BP assessment that compensates for some of the limitations of conventional office values. Elimination of the “white-coat” effect is among the described advantages of ABPM. However, differences between consecutive days of monitoring in patients wearing the device for the first but not for the second and successive times [Hermida et al. Am J Hypertens. 2001;14:34], suggest a pressor response to ABPM. We have evaluated the extent and duration of this “ABPM effect” in normotensive subjects. We studied 170 volunteers (117 men), 23.2±3.7 (mean±SD) years of age, without medical history of hypertension and diurnal BP mean from ABPM consistently below 135/85 for systolic/diastolic BP. Subjects underwent ABPM at 30-minute intervals for 48 consecutive hours in up to six different occasions within 2 years, yielding 515 BP profiles. Circadian parameters established by population multiple-component analysis [Fernandez & Hermida. Chronobiol Int. 1998;15:191-204] were compared among consecutive days of monitoring by nonparametric testing. In normotensive volunteers evaluated for the first time, results indicate a highly significant (P<0.001) reduction during the second day of monitoring as compared to the first in the diurnal, but not in the nocturnal mean, of systolic and diastolic BP. This pressor effect increases BP on the average by a significant 4 and 3 mm Hg for systolic and diastolic BP for the first 4 hours of measurement. This effect can be documented as statistically significant independently of gender or day of the week of monitoring. The pressor effect was almost double in subjects who started ABPM in the evening (after 13:00 hours) as compared to subjects who started monitoring in the morning. This “ABPM effect” cannot be observed when the same subjects were evaluated for the second or successive times 3 months apart. ABPM for 48 consecutive hours in normotensive subjects reveals a statistically significant pressor response that could reflect a novelty effect in the use of the monitoring device for the first time, and that cannot be due just to regression to the mean. This “ABPM effect”, much higher in hypertensive patients [Hermida et al. Am J Hypertens. 2001;14:34], should be taken into consideration for a proper diagnosis of hypertension and evaluation of treatment efficacy by the use of ABPM. DGES, PM98-0106; PGICT00-PXI-32205PN; University of Vigo.