Assessing the delayed sleep phase disorder by ambulatory circadian monitoring

Introduction The circadian system is responsible for the generation of biological rhythms synchronized to environmental 24 h cycle. The delayed sleep phase disorder (DSPD) refers to a delay between the sleep-wake rhythm and the desired bed and rise times and patients suffer chronic difficulty to fall asleep, rising and impaired performance during day. The aim of this work is to test an innovative ambulatory circadian monitoring (ACM) system based on wrist temperature (T), motor activity (A), body position (P), light exposure (L) and environmental temperature (ET) rhythms, to evaluate patients affected by this syndrome. Materials and methods Fourteen patients between 10 and 86 yr old from the Sleep Unit of the Virgen de las Nieves Hospital and the Estivill Sleep Clinic, and 14 healthy volunteers (from 10 to 80 yr old) were included in the study. Their T, A, P, L and ET rhythms were registered by the ACM device Kronowise® (Cronolab, University of Murcia, Spain) during a week. Sleep-wake states were infered using the integrated variable TAP using Circadianware® software (Chronolab, Univ. Murcia). Results Reliable circadian phase markers can be calculated from all variables, being the timing of five consecutive hours of maximum values for T and sleep (TM5) and of five consecutive hours of minimum values for A, P, TAP and L (TL5), the most accurate ones. Most DSPD subjects showed a similar phase-delay with respect control subjects in the TM5 or TL5 in all ACM variables (02:30–04:30 h for control subjects vs. 06:00 to 09:40 h for DSPD). However, a 21% of DSPD patients exhibited internal desynchronization between T and A, P or sleep phases. DSPD subjects showed higher fragmentation, lower regularity in all variables, together with lower light exposures than the standard scores specially during the morning. Conclusion Our results showed that ACM provides objective markers to detect DSPD and chronodisruption. Besides differences in circadian phase, DSPS subjects showed more irregular, fragmented and less robust rhythms, worse sleep quality and less diurnal activation than controls, probably caused to the duty of sleep within a social schedule that differs from their endogenous biological propensity. Insufficient light exposure during early morning contribute to maintain their circadian phase delay. Acknowledgements Study supported by RETICEF (RD12/0043/0011), MINECO (BFU2010–21945-C02–01), TIN2009–14372-C03–01 to MC and INNPACTO (IPT-2011–0833-900000) to JAM.