Blood pressure differences between consecutive days of ambulatory monitoring in hypertensive patients

The use of ambulatory lood pressure (BP) monitoring (ABPM) has provided a method of BP assessment that compensates for some of the limitations of office values. The most common approach is still to rely for diagnosis on the daily mean of a 24-hour profile [O'Brien & Staessen. Blood Pressure 1995;4:266-282]. With the objective to assess the reproducibility of BP between 2 consecutive days of ABPM, we studied 310 mild-to-moderate hypertensive patients (125 men), 54.9±0.7 (X±SE) years of age, who underwent ABPM at 20-minute intervals during the day and at 30-minute intervals during the night for 48 consecutive hours with an ambulatory Spacelabs 90207 device. Daily, diurnal and nocturnal mean values computed for each patient according to individual resting hours determined by diary and wrist actigraphy were compared between consecutive days of ABPM by paired t-test. Results indicate a highly statistically significant (P<0.001) reduction during the second day of ABPM as compared to the first in the diurnal (during daily activity) mean of SBP and DBP (2.28 and 1.70 mmHg, respectively), but not for HR (P=0.697). The nocturnal means of BP were, however, similar between both days of sampling (differences of -0.59 and 0.06 mmHg for SBP and DBP; P>0 612). As a consequence of the decrease in the BP during activity but not during nocturnal resting hours, there is a 7% increase (from 49 to 56%) of non-dippers when this classification is obtained on the basis of data sampled during the second day of ABPM as compared to the first. ABPM during two consecutive days reveals statistically significant differences in diurnal but not nocturnal BP that could reflect a novelty effect in the use of the device. These results indicate that an unique 24-hour profile of ABPM may be insufficient for a proper diagnosis of hypertension, evaluation of treatment efficacy, and identification of dipping status in relation to target organ damage.