title: The diurnal variation in blood pressure should be calculated from individually defined day and night times.
abstract: The aim of this study was to compare the nocturnal fall in BP parameters calculated from individually defined periods of day and night to values computed from collectively fixed day/night definitions. Day and night periods were defined according to 3 different methods: (i) the individually defined time of getting up and going to bed obtained from participant diaries (MethodIND); (ii) the mean time of rising and retiring in the group (MethodMEAN); and (iii) a daytime period from 07.00-22.00 h as recommended by The Scientific Committee (Method722). The ambulatory BP was recorded every 30 min over 24 h. One hundred and eighty-seven persons aged 40-66 years participated. With MethodIND, the BP load, systolic, diastolic and mean BPs were higher in the daytime and lower in the night-time compared to the results using Method722 and MethodMEAN. The nocturnal BP fall using MethodIND was larger than the fall calculated from every possible fixed division in the period from 3 h before till 3 h after the group mean time of getting up and going to bed (p < 0.001). The lowest frequency of non-dipping, defined as a nightly fall in systolic and diastolic BP below 10%, was observed using MethodIND (10%). Compared to MethodIND, 11% were misclassified as non-dippers by Method722 and 8% by MethodMEAN. We conclude that the diurnal blood pressure variation based on individually defined periods of day and night is larger than the variation based on any collectively fixed day/night definition. It is recommended that assessment of the nocturnal change in BP be based on individually defined periods of day and night.
authors.affiliation: Department of Cardiology, Odense University Hospital, Denmark.
authors.forename: O
authors.initials: O
authors.lastname: May
authors.forename: H
authors.initials: H
authors.lastname: Arildsen
authors.forename: E M
authors.initials: EM
authors.lastname: Damsgaard
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology*; D018660:Blood Pressure Monitoring, Ambulatory / Q000592:standards*; D002940:Circadian Rhythm; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged