Comparison of arbitrary definitions of circadian time periods with those determined by wrist actigraphy in analysis of ABPM data

Determining blood pressure (BP) values at different daily time periods is a well recognised measure to assess the risk of end-organ damage. However, t he use of various definitions of these periods, eg, day vs night, sleep vs wake or arbitrary definitions, makes clinical decisions based on available data difficult. In the present study, we compared BP loads in actual sleep- wake periods to default day-night definition provided by the ambulatory BP monitoring (ABPM) software (day 06.00-22.00; night 22.00-06.00) as well as to an arbitrary definition of sleep-wake periods in children published in J ournal of Pediatrics (Soergel at al, 1997) (awake 08.00-20:00 and sleep 00. 00-06.00). We used an actigraph, an accelerometer, to define the actual sle ep-wake periods in 46 patients with essential hypertension who are on vario us treatment regimens. BP data were obtained by using Spacelabs 90207 monit ors for a full 24 hours. There were significant differences between actual sleep-wake and default definition for BP load. No similar findings were not ed when arbitrary definition was used. The proportion of hypertensives was not significantly different when default and arbitrary definitions were use d. Classification of dippers and non-dippers is greatly affected by the def inition of sleep interval using the default method. Although some of the mi sclassifications were not statistically significant, their clinical importa nce must be considered. Determination of sleep and wake periods for analysi s of ABPM data should be based on careful determination of actual periods. Using other definitions may not provide complete information or accommodate for individual variation.