The role of natural light rhythm in the development of desynchronosis in the conditions of rotational shiftwork in the Arctic

Purpose. To study the effects of a natural light cycle on circadian rhythms of blood pressure (BP) and heart rate conditions of rotational shiftwork in the Far North.

Material and Methods. Data of 24-h BP monitoring were analyzed in 373 male patients with hypertension stage II monthly round-trip sojourns to the Arctic compared with a similar group of 144 patients living in moderate climate (Tyumen, 57 N). The standard and chronobiological parameters of 24-h BP monitoring were analyzed in 93 randomly selected patients of the Far North group and 64 patients of the Tyumen group. The 24-h BP profile, circadian indices of systolic and diastolic BP, percentage contribution value, rhythm amplitude, acrophase, and diurnal mean value of 24-h BP rhythm were studied during the seasons of the year.

Results. The circadian rhythms of HR and BP in hypertensive patients in the conditions of rotational shiftwork in the Arctic showed the signs of internal desynchronosis and significantly differed from those in Tyumen patients independently of a season. The lack of natural light in the Far North during the polar day and polar night resulted in the flattened curves of circadian BP and HR rhythms in the hypertensive patients. Other major differences consisted in the low-amplitude profile of the spectrum and the loss of 24-h component in this group. The seasonal changes in HR in the comparison group were insignificant unlike those in the Far North group, which showed maximum flattening of HR rhythm during the polar day and polar night. Winter season (polar night) was the most adverse for the main group of patients in regard to their 24-h BP profile, which was characterized by the maximum degree of circadian rhythm flattening and the predominance of high-frequency oscillations in the spectrum.

Conclusions. The development of circadian and seasonal desynchronosis of the HR and BP rhythms in hypertensive patients in the conditions of rotational shiftwork in the Arctic was caused not only by the labour characteristics and the climatic factors, but also by the natural light rhythmicity in the high latitude.

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