Reliability of nocturnal blood pressure dipping

Background Increasing evidence documents the fact that individuals whose bl ood pressure drops or 'dips' relatively little at night have a higher risk of numerous cardiovascular illnesses. Objective To examine the reliability of various measures of nocturnal blood pressure dipping. Methods This study examined 17 individuals with ambulatory blood pressure m onitoring on three 24 h recordings while they pursued a schedule similar to that of in-patients on a clinical research unit. Nocturnal dipping of bloo d pressure was scored three ways: as the drop in blood pressure between 10 p.m. and 6 a.m. ('clocktime'), as the drop in blood pressure tailored to ea ch individual's reported bedtime ('bedtime'), and as the drop in blood pres sure accompanying polysomnographically verified sleep ('sleeptime'). Results Adequate reliability was obtained for all three measures of dipping . There was, in general, a significant correlation across testing occasions (P < 0.05). The correlation coefficient ranged from 0.5 to 0.8, depending on which criterion of dipping was selected and whether the endpoint was sys tolic blood pressure, diastolic blood pressure, or mean arterial blood pres sure. Conclusions The reliability of systolic blood pressure dipping was somewhat lower than that of diastolic or mean arterial blood pressure dipping. Dipp ing appears to be a reliable construct. While no one definition of dipping was demonstrably better than another, the most sensible definition of dippi ng would allow some adjustment for defining 'night' on the basis of each in dividual's idiosyncratic bed time. (C) 2000 Lippincott Williams & Wilkins.