Nocturnal blood pressure dipping: A consequence of diurnal physical activity blipping?

This study was designed to describe the interaction between physical activi ty (PA), quantified objectively by electronic activity monitors, and ambula tory blood pressure (ABP), and to test the hypothesis that modifying daily PA can effect significant changes in the diurnal variation in blood pressur e and may result in altered dipping/nondipping status of an individual. Ini tially, 70 individuals underwent simultaneous ABP and electronic activity m onitoring (actigraph devices manufactured by Gaewihler Electronics, Switzer land) over a 24-h period. Then, in a prospective study, the dipping/nondipp ing status of 43 subjects was assessed using ABP recorded over two 24-h per iods of differing activity levels. Of the 70 subjects (age 49 +/- 11 years, 42 male) the diurnal variation in systolic blood pressure (20 +/- 12%, ste p-up from night [120 +/- 12 mm Hg] to day [144 +/- 13 mm Hg]) and diurnal v ariation in PA score (increment from sleep, 44 +/- 17 units) correlated sig nificantly (R-2 = 0.29; P < .05). Of the 43 subjects who underwent ABP moni toring on a more active day, four had a nondipping BP profile; 12 of these same 43 subjects had a nondipping BP profile when monitored on a less activ e day (chi(2) = 4.9; P < .05). These results provide a quantitative description of the contribution of PA, including the sleep/awake status, to blood pressure variation in a group o f normotensive and hypertensive individuals. The magnitude of this effect u nderscores the importance of interpreting 24-h ABP data only in the presenc e of adequately quantified activity data. Am J Hypertens 2000; 13:601-606 ( C) 2000 American Journal of Hypertension, Ltd.