Ambulatory monitoring in humans: a new method to objectively assess circadian phase as compared with dim light melatonin onset (DLMO)

Abstract

Introduction It is important to develop a system able to detect the endogenous circadian phase easily, since current techniques imply either expensive hormonal quantification or uncomfortable monitorization of central temperature by rectal probes. Materials and methods In this work, a new ambulatory circadian monitoring system (ACM) was validated. To this, activity and position, wrist temperature rhythm as well as light exposure pattern were recorded for 10 days in 13 healthy subjects, thanks to an actimeter on the arm, a temperature sensor on the ventral side of the wrist and a pendant luxometer. DLMO was determined in saliva, and it was used as “the gold standard” to evaluate the accuracy of ACM to assess the circadian phase. Besides, subjects completed a sleep log and Horne-Ostberg morningness–eveningness, Pittsburgh Sleep Quality Index and Epworth Sleepiness Scale questionnaires to evaluate diurnal preference and its influence in sleep quality. Results The peripheral wrist temperature increase in the evening (and its new indexes WTOnset or WTOn and WT increase onset or WTiO) anticipated that of melatonin; while the decrease in motor activity, position and the composite variable TAP (including wrist temperature, activity and position), and the increase in sleep probability occurred after the increase in melatonin levels. The score of morningness–eveningness and sleep quality questionnaires showed high correlations with DLMO, confirming that the later the DLMO occurs higher eveningness and worse sleep quality are reported. Conclusion This ambulatory method allows accurately detecting the circadian phase while subjects maintain their normal life style. The proposed new phase markers based on wrist temperature rhythm (named WTOn and WTiO) would be appropriate in Clinics when it is important to know the subject circadian phase, like in cancer chronotherapy or light therapy. Acknowledgements Study supported by Instituto de Salud Carlos III, RETICEF (RD12/0043/0011), MINECO (BFU 2010-21945-C02-01and IPT-2011-0833-900000) with FEDER cofounding to JAM, and a research fellowship to MA Bonmati-Carrion (FPU2009-1051). We also thank Stockgrand Ltd. (UK) for the melatonin assay reagents. DJ Skene is a Royal Society Wolfson Research Merit Award holder.