Is the definition of daytime and nighttime blood pressure prognostically relevant?

Although the prognostic value of the day-night blood pressure (BP) changes is well established, the most appropriate method for definition of daytime and nighttime BP is still undefined. In a recent guidelines document of the European Society of Hypertension, there is no clear position in favor of one definition over other.

In the setting of the Progetto Ipertensione Umbria Monitoraggio Ambulariale study, we analyzed the prognostic impact of the day-night BP changes by using three widely used different definitions of day and night (large fixed-clock intervals, narrow fixed-clock intervals, diary) in 2934 initially untreated participants with essential hypertension.

Three hundred and fifty-six cardiovascular events and 176 deaths over a median follow-up period of 7 years were observed. Nondippers showed a higher risk of total cardiovascular events and all-cause mortality than dippers regardless of the definition of day and night. Furthermore, the area under a receiver-operated characteristic curve analysis did not differ among the different definitions of day and night (large fixed-clock intervals, narrow fixed-clock intervals, diary) for total cardiovascular events and all-cause mortality (all P=NS).

The data suggest that the prognostic value of the diurnal BP changes is comparable when day and night are defined using large fixed-clock intervals, narrow fixed-clock intervals, or actual time spent in and out of bed.