[Circadian rhythms variability of arterial pressure: methodological aspects for the measurement]

To study the differences among the methods used for estimating daytime and nighttime ambulatory blood pressure values, and to analyze their determinant factors.

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; b) 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 c) short-time, having a nighttime period from midnight to 6:00 h, and a daytime one from 08:00 to 22:00 h.

Daytime mean values of SBP and DBP were similar for the three methods. Nighttime mean values of SBP 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 SBP 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.

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.