Physical activity level is an independent predictor of the diurnal variation in blood pressure

Objective The aim of this study was to define the relationship between phys ical activity and the magnitude of the percentage fall in blood pressure at night (nocturnal dip). Methods We simultaneously monitored 24-h ambulatory blood pressure and meas ured physical activity by actigraphy in 434 patients. Blood pressure was me asured every 20 min; the actigraph integrated an activity score every 10 s. Mean daytime and night-time activity were calculated from mean scores for the 15 min preceding each blood pressure measurement. Nocturnal dip in syst olic and diastolic blood pressure (SBP and DBP) were regressed on mean (log -transformed) daytime activity. Mean night-time activity, age. gender, smok ing status, body mass index (BMI) and clinic blood pressure were added into a multiple linear regression. Results The patient group was heterogeneous in age, gender and mean 24-h bl ood pressure. Mean daytime activity level was significantly and positively associated with the magnitude of the nocturnal dip in both SBP and DBP. Inc reased night-time activity was significantly associated with a smaller noct urnal dip. Older patients had a smaller nocturnal dip per log unit daytime activity. Nocturnal dip in SBP was greater in males, and smaller in those t aking antihypertensive medications. Smoking, BMI and clinical blood pressur e level were not associated with the extent of the nocturnal dip after adju stment for other factors. Conclusions Daytime and night-time physical activity levels are independent ly and significantly predictive of the magnitude of the nocturnal dip in bl ood pressure. Variation in activity may confound interpretation of 24-h amb ulatory blood pressure monitoring, and contribute to the poor reproducibili ty of dipper status. J Hypertens 2000, 18:405-410 (C) Lippincott Williams & WiIkins.