BACKGROUND: TO study the differences among the methods used for estimating
daytime and nighttime ambulatory blood pressure values, and to analyze thei
r determinant factors.
SUBJECTS AND METHODS: In 402 individuals mean values of systolic and diasto
lic blood pressure (SBP and DBP) during 24 h, daytime and nighttime, were c
alculated 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 daytim
e one from 08:00 to 22:00 h, and cl short-time, having a nighttime period f
rom 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 meth
ods. Nighttime mean values of SEP and DBP calculated using the long-time we
re significantly higher than those calculated with the real-time ((SBP -2.2
5 [5.3] mmHg, p < 0.05; DBP -1.17 [3.4] mmHg, p < 0,05). No differences wer
e 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-dipp
ing pattern were 17, 26 and 18% for real, long and short time methods, resp
ectively,
CONCLUSIONS: Daytime mean BP values are reproducible whatever the method us
ed, but for estimating nighttime mean BP values short-time is the best of t
he 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 pat
terns.