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Reinberg A.,Rothschild | Riedel M.,Rothschild | Riedel M.,University of Tours | Brousse E.,Service Departemental dIncendie et de Secours de Saone et Loire | And 11 more authors.
Chronobiology International | Year: 2013

*This work is dedicated to the memories of Drs. Israel Ashkenazi and Erhard Haus, outstanding pioneers of medical chronobiology, dear colleagues, and distinguished gentlemen of exceptional human qualities.We investigated the circadian synchronization/desynchronization (by field-study assessment of differences in period, τ, of 16 coexisting and well-documented rhythms) of 30 healthy firemen (FM) exposed to irregular, difficult, and stressful nocturnal work hours who demonstrated excellent clinical tolerance (allochronism). Three groups of FM were studied (A=12 FM on 24-h duty at the fire station; B=9 FM on 24-h duty at the emergency call center; C=9 day-shift administrative FM) of mostly comparable average age, body mass index, career duration, chronotype-morningness/eveningness, and trait of field dependence/independence. The self-assessed 16 circadian rhythms were (i) physiological ones of sleep-wake (sleep log), activity-rest (actography), body temperature (internal transmitter pill probe), right-and left-hand grip strength (hand dynamometer), systolic and diastolic blood pressure (BP) plus heart rate (ambulatory BP monitoring device); (ii) psychological ones (visual analog self-rating scales) of sleepiness, fatigue, fitness for work, and capacity to cope with aggressive social behavior; and (iii) cognitive ones of eye-hand skill and letter cancellation, entailing performance speed (tasks completed/unit time) and accuracy (errors). Data (4-6 time points/24h; 2 591 480 values in total) were gathered continuously throughout two 8-d spans, one in winter 2010-2011 and one in summer 2011. Each of the resulting 938 unequal-interval time series was analyzed by a special power spectrum analysis to objectively determine the prominent τ. The desynchronization ratio (DR: number of study variables with τ=24.0h/number of study variables×100) served to ascertain the strength/weakness of each rhythm per individual, group, and season. The field study confirmed, independent of group and season, coexistence of rather strong and weak circadian oscillators. Interindividual differences in DR were detected between groups and seasons (χ2, correlation tests, analysis of variance [ANOVA]). Moreover, in each group, both in winter and summer, a normal distribution was observed in the number of FM with rhythms with τ=24.0h, e.g., ranging from 5/16 (large desynchronization) to 16/16 (no desynchronization). Such a normal distribution with intraindividual stability over time (i.e., seasons) is consistent with the hypothesis of an inherited origin of a differential propensity to circadian desynchronization and which is supported by the distribution of τs in winter and summer following the Dian-Circadian Genetic Model, i.e., with τ=24.0h, τ=24.0h+n(0.8h), and τ=24.0h-n(0.8h). © Informa Healthcare USA, Inc.

Touitou Y.,Rothschild | Reinberg A.,Rothschild | Smolensky M.H.,Rothschild | Smolensky M.H.,University of Caen Lower Normandy | And 8 more authors.
Indian Journal of Experimental Biology | Year: 2014

Circadian cognitive and physical rhythms plus 24 h patterns of accidents and work-related injuries (WRI) have been verified in numerous studies. However, rarely, if ever, have 24 h temporal differences in both work performance and risk of WRI been assessed in the same group of workers. We explored in a homogenous group of French firemen (FM) 24 h patterns of both lag time (LT) response duration to emergency calls for medical help (ECFM) for life-threatening out-of-hospital cardiac arrests (OHCA), used as a non-specific index of work performance, and W.R.I. Our studies demonstrate rather high amplitude statistically significant 24 h patterns of the two variables. The LT response duration was twice as long ~0500 h (slowest response) than ~1600 h (fastest response). In the same group of FM, the actual number WRI/h was greatest ~1600 h and lowest in the early morning hours. However, the 24 h pattern of the relative risk (RR) of WRIs, i.e., per clock hour number of WRI/(total number of responses to emergency calls x number of FM at risk per response), was very different, the RR being greatest ~0200 h and lowest in the afternoon. The 24 h pattern in LT response duration to ECMH for OHCA and RR of WRI was strongly correlated (r=+0.85, P<0.01), with the nocturnal trough (slowest response) in LT response duration coinciding with the nocturnal peak RR of W.R.I. These findings indicate the requirement for circadian rhythm-based interventions to improve the nocturnal compromised work performance and elevated risk of WRI of shift-working FM.

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