Could externally desynchronized circadian rhythm be resynchronized in shift workers?

The present study aimed at investigating the effect of shift work on circadian time structure of several variables, such as skin temperature (ST), heart rate (HR), peak expiratory flow rate (PEFR), subjective drowsiness (SDr), subjective fatigue (SF) and subjective attention (SA) in shift workers of a sub-urban cement factory. Six shift workers volunteered for this study. In each subject, above mentioned variables were monitored at least 4-6 times per day for over a period of one week. The study was conducted in two different spells. In the first spell (1994), circadian time structure of six shift workers was studied about 14 months after slowing down of overall functioning of the cement factory. In the second spell (1996), the circadian time structure of the same subjects was reexamined following about 30 months of slough in the cement factory. The results indicate that the rhythm desynchronization of ST, HR and PEFR was witnessed among shift workers in 1994. However, when all six shift workers were monitored again in 1996, the desynchronized rhythm became synchronized in most of the shift workers. Further, in the present study it was noticed that subjective variables, such as SF and SA are less prone to desynchronization as compared to other objective variables. The relative stability of rhythms in fatigue and attention could also be ascribed to the period of sleep-wake rhythm that remained either 24 h or very close to 24 h irrespective of the year of study. In conclusion, the findings of this study document rigorously that externally desynchronized circadian rhythms in shift workers could become normal following their transfer from shift work to diurnal work.