The challenge of chronodisruption assessment. The case of nursing staff shift workers

Introduction Shift work circadian disorders have been mainly evaluated by actigraphy (A) and classical methods of time series analysis. However, to determine the degree of chronodisruption (CD) it is necessary: a) to establish a marker of internal desynchronization (including different variables in ambulatory circadian monitoring or ACM such as skin temperature WT, body position P and light exposure L) and b) to modify classical procedures, based in a unique mean waveform analysis, to take account of the day to day differences in rhythms in response to scheduled work. The aim of this work is to determine the usefulness of ACM in conjunction with a new mathematical procedure to determine the severity of CD in nursing staff. Materials and methods Ten healthy day shift and ten night shift workers (6 males and 18 females, from 22 to 62 y. o.) participated in this study. Volunteers were monitored by ACM during 7–10 days using ACM (KronowiseTM, Chronolab, Univ. of Murcia) integrating five sensors: three built into a wristwatch (T, L; environmental temperature, ET) and two on a bracelet (A and P). Circadian status was inferred using the integrated variable TAP, calculated from T, A and P. Circadian robustness was assessed by the circadian function index (CFI) of TAP variable. Internal desynchronization was measured as difference between the non-parametric phase markers of T (M5 = five consecutive hours of maximum T) and A (L5 = five consecutive hours of minimum activity). The restfulness was calculated from L5 of TAP and expressed as a score from 0 to 10 (10 = very restfully sleep). Results Despite the stability in their working schedule, permanent nocturnal shift workers showed more CD than diurnals and lower circadian robustness, higher internal desynchronization between T and A rhythms and low values in the restfulness score. When a day-to-day time series analysis was performed instead of using the mean waveform, a significant improvement in the three CD markers was observed, although their values still were worse than those observed in diurnal workers. Conclusion The ACM allows a reliable assessment of the degree of chronodisruption in shift workers, however, mathematical procedures based on day to day analysis should be mandatory to avoid bias derived from the irregular life styles associated to nocturnal shifts. Acknowledgements To RETICEF (RD12/0043/0011), MINECO (BFU2010–21945-C02–01), and INNPACTO (IPT-2011–0833-900000) with FEDER cofounding to JAM.