The effect of sleep intervals on analysis of 24-h ambulatory blood pressure data

Twenty-four hour blood pressure exposure and circadian blood pressure variability may be important predictors of hypertensive end-organ damage. Since sleep is a major determinant of circadian blood pressure decline, day/night blood pressure changes may be affected by sleep intervals. The current study compares 24-h blood pressure results with and without adjustment for patient-specific sleep intervals. Forty male hypertensive patients (22 with renal insufficiency and 18 with normal renal function) underwent 24-h blood pressure study with SpaceLabs 90207 monitors. They also filled out sleep questionnaires to evaluate time awake and asleep during the day and night intervals. Data was analyzed with and without adjustment for daytime asleep and nighttime awake intervals. The percent change in systolic, diastolic, and mean arterial pressure as well as heart rate was not different statistically or clinically with or without adjustment for sleep intervals. Nevertheless, there was a progressive increase in the day versus night percent change in these hemodynamic parameters with adjustment for sleep intervals. When we used arbitrary cut-offs to define “non-dipper”, ie, less than 10% drop in a given hemodynamic parameter, and used patient-specific sleep intervals, clinically and statistically different numbers of “non-dippers” were seen versus sleep unadjusted data (19 v 12, using diastolic BP, P< .01). In conclusion, it may not be necessary to adjust for sleep intervals when relating 24-h blood pressure and day/night blood pressure variability to hypertensive end-organ damage. However, arbitrary cut-offs to define “non-dippers” may be greatly and capriciously affected by sleep/awake intervals. It may be appropriate to look at 24-h blood pressure and circadian blood pressure variability as continuous rather than dichotomous (“dipper”/“non-dipper”) variables when relating them to indices of hypertensive end-organ damage.