EFFECTS OF ACTUAL VERSUS ARBITRARY AWAKE AND SLEEP TIMES ON ANALYSES OF 24-H BLOOD-PRESSURE

Investigators conducting hypertension trials with ambulatory blood pre ssure (BP) monitoring have been analyzing study results using arbitrar y times for day (wakefulness) and night (sleep). We prospectively eval uated the impact of using arbitrary times instead of patient reported awake and sleep times on mean 24-h, awake, and sleep BP, BP loads, and the awake-sleep BP difference in 50 subjects. Daytimes and nighttimes were derived from popular, arbitrary times reported in the literature . Compared to actual awake and sleep periods, arbitrary day and night division caused no significant differences in the mean awake and sleep BPs. However, limits of agreement for BP values derived for the actua l and arbitrary times of wakefulness and sleep were substantial especi ally during sleep (awake systolic BP, -4 to 7 mm Hg; awake diastolic B P, -2 to 4 mm Hg; sleep systolic BP, -12 to 7 mm Hg; and sleep diastol ic BP -7 to 4 mm Hg). Sleep BP loads (proportion of BPs >120/80 mm Hg) were altered by greater than 10% in 20% to 30% of the subjects, depen ding on choice of time schedule. These data demonstrate that the calcu lation of BP and BP load during sleep may be altered by use of arbitra ry, rather than actual, times of wakefulness and sleep in 24-h studies of ambulatory BP.