DIURNAL BLOOD-PRESSURE VARIABILITY AND PHYSICAL-ACTIVITY MEASURED ELECTRONICALLY AND BY DIARY

In order for 24 h ambulatory blood pressure monitoring (ABPM) to be useful in clinical decision making, it is necessary to quantify ambient physical activity and to develop appropriate norms of ambulatory pressure for different levels of activity. The present study has compared the predictive value of physical activity determined by an electronic activity monitor or a written diary, for concomitantly recorded blood pressure during ABPM in healthy normotensive subjects. Each subject wore four activity monitors, on the right and left wrists, on the left ankle and at the waist, respectively. Linear regression analysis was performed for each subject to determine-the correlation between ABPM data (systolic and diastolic blood pressure and heart rate) and activity data (obtained from diaries and the four monitors). Significant differences in the degree of correlation were found for both the location of the activity monitor and the time (1/2, 2, 5, 10, 15, and 30 min preceding blood pressure measurement) over which activity was averaged (P < .05 by two-way analysis of variance). The best correlation was obtained with the activity monitor worn on the dominant wrist, and when activity was averaged over 2 to 10 min preceding blood pressure determination, accounting for 18 to 69% (mean 36 +/- 5%) of systolic blood pressure variation. Diaries performed similarly in these well-motivated subjects. It is concluded that because of the significant interaction between activity and blood pressure, ABPM data should be interpreted only in the light of concomitant activity data. The electronic activity monitor is an easy to use, reliable means of recording physical activity for this purpose, requiring no subject participation and performing at least as well as traditional diaries.