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

This study was designed to describe the interaction between physical activity (PA), quantified objectively by electronic activity monitors, and ambulatory blood pressure (ABP), and to test the hypothesis that modifying daily PA can effect significant changes in the diurnal variation in blood pressure and may result in altered dipping/nondipping status of an individual. Initially, 70 individuals underwent simultaneous ABP and electronic activity monitoring (actigraph devices manufactured by Gaewihler Electronics, Switzerland) over a 24-h period. Then, in a prospective study, the dipping/nondipping status of 43 subjects was assessed using ABP recorded over two 24-h periods of differing activity levels. Of the 70 subjects (age 49 +/- 11 years, 42 male) the diurnal variation in systolic blood pressure (20 +/- 12%, step-up from night [120 +/- 12 mm Hg] to day [144 +/- 13 mm Hg]) and diurnal variation in PA score (increment from sleep, 44 +/- 17 units) correlated significantly (R2 = 0.29; P < .05). Of the 43 subjects who underwent ABP monitoring 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 active day (chi2 = 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 of normotensive and hypertensive individuals. The magnitude of this effect underscores the importance of interpreting 24-h ABP data only in the presence of adequately quantified activity data.