The influence of physical activity on the variability of ambulatory blood pressure

The aim of this study was to assess the contribution of physical activity l evels to blood pressure (BP) variability, and to assess the effect age, gen der, body mass index, and use of antihypertensive medications on this relat ionship. We simultaneously monitored 24-h ambulatory BP by automated record er and activity by actigraphy in 431 patients. Mean activity scores for the 5, 10, 15, and 20 min preceding each BP measurement were calculated, and B P and heart rate were related to these variables using linear mixed model r egression. Various patient characteristics were added to the mixed model as covariates. Patients were heterogeneous in age (48 +/- 13 years), sex (49% men), and average 24-h BP (132/81 +/- 15/10 mm Hg). Mean daytime activity level was 44 +/- 15 U. During the daytime, systolic BP (r = 0.33), diastoli c BP (r = 0.29), and heart rate (r = 0.42) correlated best with the average activity for the 15 min preceding each measurement (P <.001). Variance was very high, with activity explaining from 0% to 62% of BP variability for d ifferent individuals. Men and the obese had a greater reactivity of systoli c BP to activity; older patients and those on antihypertensive therapy had a lower reactivity of heart rate. Blood pressure level is significantly ass ociated with physical activity, but the percentage of variance of BP explai ned by physical activity varies greatly between individuals. Correlation is strongest between BP and average activity integrated over the previous 15 min. Much of the variance in blood pressure remains unexplained. Am J Hyper tens 2000; 13:1067-1073 (C) 2000 American Journal of Hypertension, Ltd.