title: Reactivity of ambulatory blood pressure to physical activity varies with time of day.
abstract: Blood pressure (BP) fluctuates over a 24-hour period, but it is unclear to what extent this variation is governed completely by changes in physical activity. Our aim was to use a BP "reactivity index" to investigate whether the BP response to a given level of physical activity changes during a normal sleep-wake cycle. Hypertensive patients (n=440) underwent simultaneous 24-hour ambulatory BP, heart rate (HR), and activity monitoring. BP and HR were measured every 20 minutes. Actigraphy data were averaged over the 15 minutes that preceded a BP measurement. Individual BP and HR reactivity indices were calculated using least-squares regression for twelve 2-hour periods. These indices were then analyzed for time-of-day differences using a general linear model. Systolic BP and HR were generally more reactive to physical activity than diastolic BP. The highest reactivity of systolic BP (mean+/-SE=4+/-1 mm Hg per logged unit change in activity) was observed between 8:00 AM and 10:00 AM (P=0.014). Between 10:00 AM and 12:00 PM, BP reactivity then decreased (P=0.048) and showed a secondary rise in the early afternoon. These 24-hour changes in BP reactivity did not differ significantly between groups formed on the basis of early and late wake times (P=0.485), medication use, age, and sex (P>0.350). In conclusion, under conditions of normal living, the reactivity of BP and HR to a given unit change in activity is highest in the morning and shows a secondary rise in the afternoon.
authors.affiliation: Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool L3 2ET, United Kingdom. spshjone@livjm.ac.uk
authors.forename: Helen
authors.initials: H
authors.lastname: Jones
authors.forename: Greg
authors.initials: G
authors.lastname: Atkinson
authors.forename: Andrew
authors.initials: A
authors.lastname: Leary
authors.forename: Keith
authors.initials: K
authors.lastname: George
authors.forename: Michael
authors.initials: M
authors.lastname: Murphy
authors.forename: Jim
authors.initials: J
authors.lastname: Waterhouse
mesh_terms: D000328:Adult; D001794:Blood Pressure; D018660:Blood Pressure Monitoring, Ambulatory; D002940:Circadian Rhythm; D003971:Diastole; D005260:Female; D006339:Heart Rate; D006801:Humans; D006973:Hypertension / Q000175:diagnosis / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D013599:Systole