Alteration of period and amplitude of circadian rhythms in shift workers. With special reference to temperature, right and left hand grip strength.

48 male shift workers in various industries volunteered to document circadian rhythms in sleeping and working, oral temperature, grip strength of both hands, peak expiratory flow and heart rate. All physiological variables were self-measured 4 to 5 times a day for 2 to 4 weeks. Individual time series were analyzed according to several statistical methods (power spectrum, cosinor, chi squares, ANOVA, correlation, etc.) in order to estimate rhythm parameters such as circadian period (tau) and amplitude (A), and to evaluate subgroup differences with regard to tolerance to shift work, age, duration of shift work, speed of rotation and type of industry. The present study confirms for oral temperature and extends to other variables (grip strength of both hands, heart rate) that intolerance to shift work is frequently associated with both internal desynchronization and small circadian amplitude. The internal desynchronization among several circadian rhythms supports the hypothesis that these latter are driven by several oscillators. Many differences were observed between circadian rhythms in right and left hand grip strength: circadian tau in oral temperature was correlated with that in the grip strength of the dominant hand but not with that of the other hand; changes in tau s of the non-dominant hand were age-related but did not correlate with temperature tau; only the circadian A of the non-dominant hand was associated with a desynchronization. Thus, circadian rhythms in oral temperature and dominant hand grip strength may be driven by the same oscillator while that of the non-dominant hand may be governed by a different one. Internal desynchronization between both hand grip rhythms as well as desynchronization of performance rhythms reported by others provide indirect evidence that circadian oscillator(s) may be located in the human cerebral cortex.

Desynchronization of the oral temperature circadian rhythm and intolerance to shift work.

The present study tested the hypothesis that subjects with a good tolerance to shift work maintain the circadian period tau of their temperature rhythm equal to 24 h, while tau may differ from 24 h when subjects exhibit one or several clinical signs of intolerance. These latter are mainly: persisting sleep disturbance, persisting fatigue, changes in mood and behaviour, and digestive troubles, from gastritis to overt peptic ulcer. These symptoms were used here to classify the subjects studied. Medications, including all types of sleeping pills, are ineffective. As was the case in the present study, some subjects may tolerate shift work for 35 yr, reaching 57 yr of age without complaint, while others, after several months or many years, quite rapidly (within 6 months) develop symptoms of intolerance.

[Circadian rhythm of the grip strength of the right and left hands: desynchronization in some shift workers]. / Rythme circadien de la force des mains droites et gauches: désynchronisation chez certains travailleurs postés.

38 male shift workers and former shift workers volunteered to self-measure 4 to 8 times/24 hrs. their oral temperature (OT) as well as right and left hand grip strength (HGS) best performance during a 16 to 30 day span. Time series were analyzed individually according to two methods: day by day circadian acrophase drift and power spectrum. Mainly, but not exclusively, subjects with poor tolerance to shift work exhibited an internal desynchronization with a circadian period tau different from 24 hrs. which was the case for OT as well as right and left HGS; each could be different in tau between one another and from 24 hrs. These results suggest that oscillatory systems may be influenced by the neocortex apparently with difference between right and left side.

[Desynchronization of the circadian rhythm of oral temperature in young human subjects with poor tolerance for night work]. / Désynchronisation du rythme circadien de la température orale chez des hommes jeunes tolérant mal le travail de nuit.

15 night workers (mean age, 28 years; mean seniority 1.5 years) volunteered to measure their oral temperature (clinical thermometers 0.05 degrees C precision) 5 times/24 hrs. during a 21 day span. Time series were analyzed individually according to 3 methods. 11 of the subjects with a good tolerance had (with one exception) their prominent circadian period tau equal to 24 hrs. as well as a relatively large circadian amplitude (A from 0.19 to 0.42 degrees C). By contrast, subjects with a poor tolerance (sleep disorders, persisting fatigue, psychological troubles, etc.) had a tau value ranging from 24.9 to 25.7 hrs. associated with a relatively small rhythm amplitude (A from 0.04 to 0.13 degrees C). These results support the hypothesis that a desynchronisation of circadian rhythms help to explain why certain subjects do not tolerate shiftwork.

Amplitude of the oral temperature circadian rhythm and the tolerance to shift-work.

The aim of the study was to test the hypothesis of a relationship between the tolerance to shift-work and the amplitude of the oral temperature circadian rhythm. Forty eight shift-workers (Rhône-Alpes Region) volunteered for this chronophysiological investigation: a) 23 steel-industry workers (SI); shift-duration: 7 days (weekly rotation); b) 25 chemical-industry workers (CI); shift-duration 2 days. The subjects' ages were roughly similar with regard to groups (SI and CI) as well as sub-groups (good and poor tolerance of shift-work). The tolerance was evaluated conventionally, according to both the existence and intensity of 3 types of medical complaint: (1) digestive troubles: gastritis, colitis, peptic ulcer etc.; (2) persisting fatigue, unusual nerviness, etc.; (3) sleep alterations. The poor tolerance was observed mostly in subjects shift-working for 10 years or more. Regular large-scaled and retested medical Hg thermometers (1/20 Celsius precision) were used. Data were recorded 2-hourly, at fixed clock hours in order to obtain individual time series. Both conventional and cosinor statistical analysis show that, in both groups, the oral temperature circadian amplitude is larger in subjects tolerant to shift-work than in subjects that have become intolerant.