Measurement of blood pressure circadian variability:: methodological aspects

BACKGROUND: TO study the differences among the methods used for estimating daytime and nighttime ambulatory blood pressure values, and to analyze their determinant factors. SUBJECTS AND METHODS: In 402 individuals mean values of systolic and diastolic blood pressure (SBP and DBP) during 24 h, daytime and nighttime, were calculated by three different methods: a) real-time, following a minidiary; bl long-time, having a nighttime period from 23:00 to 07:00 h, and a daytime one from 08:00 to 22:00 h, and cl short-time, having a nighttime period from midnight to 6:00 h, and a daytime one from 08:00 to 22:00 h. RESULTS: Daytime mean values of SEP and DBP were similar for the three methods. Nighttime mean values of SEP and DBP calculated using the long-time were significantly higher than those calculated with the real-time ((SBP -2.25 [5.3] mmHg, p < 0.05; DBP -1.17 [3.4] mmHg, p < 0,05). No differences were observed for both SEP and DBP with the real-time. The number of sleeping hours was the main determinant of the differences observed between the long-time and the real-time methods. The percentage of subjects with a non-dipping pattern were 17, 26 and 18% for real, long and short time methods, respectively, CONCLUSIONS: Daytime mean BP values are reproducible whatever the method used, but for estimating nighttime mean BP values short-time is the best of the fixed-time methods. Minidiary should be used if more accurate values are necessary or if the subjects sleep habits do not fit into the standard patterns.