Optimal definition of daytime and night-time blood pressure

OBJECTIVE: To review and categorize methods to define daytime and night-time blood pressures and to propose an optimal definition. METHODS: The methods can be divided into clock-time-independent and clock-time-dependent methods and, in addition, into wide methods, which use all pressure measurements for the entire 24 h period, and narrow methods, which exclude some of the measurements. RESULTS: The asleep and awake blood pressures, mostly defined as the in-bed and out-of-bed blood pressures, can be considered the optimum standard. Wide (square-wave fitting) and narrow (cumulative-sum analysis) clock-time-independent methods perform well with most subjects, but are problematic with reverse dippers because they identify periods of high and low blood pressure in these subjects that do not coincide with the day and the night. The results from fixed-time methods deviate from the awake and asleep blood pressures whens the predefined times do not coincide with the times subjects go to bed and arise; this is less of a problem for the narrow methods, in which data from morning and evening transition periods are discarded, than it is for the rigid time schedules of the wide methods. Reproducibilities of the various methods are roughly similar. CONCLUSION: We suggest that the optimal definition of daytime and night-time blood pressure is provided by the narrow clock-time-dependent method, in which data from morning and evening transition periods are excluded, because it is simple, reasonably accurate and reproducible and can be applied without disruption of the living habits of most subjects.