Shift Work Conditions Research Articles

Circadian-based lighting substantially improves vigilance in simulated night shift work conditions compared to standard lighting

Circadian-based lighting substantially improves vigilance in simulated night shift work conditions compared to standard lighting

Effects of working conditions on the perception of night work safety and health effects on nurses.

To examine night working conditions by shift work type and identify the effects of night working conditions on nurses' perceptions of shift work safety and health effects. Night work is the main factor affecting nurses' health. However, the safety of night working conditions has not been sufficiently examined in previous studies. This study used a cross-sectional research design and an online survey using a tool released by the Australian Manufacturing Workers' Union, and the responses of 348 shift work nurses in Korea were analyzed. Logistic regression analysis was used to examine the effects of shift work conditions on the perceived safety of night work and health effects. The STROBE reporting guidelines were utilized, and data were collected from December 1 to December 31, 2021. The adjusted logistic regression analysis showed that perceived threat to safety and the health effects of shift work were not significant according to shift type. However, night-shift-work nurses who worked alone (P=0.003), lacked an emergency recovery system (P=0.026), and had difficulty commuting perceived a threat to their health (P=0.007). Additionally, nurses who experienced loss of concentration (P=0.006) and inadequate rest time (P<0.001) perceived the health effects of shift work. Urgent monitoring of night work conditions is necessary for the 2-shift work type. Nurses must work night shifts together and an emergency system should be established for their safety. Night work conditions should be improved to prevent the hazards of night work and its negative health effects on nurses. This study suggests the necessity of a policy to enhance night work safety, including emergency coping systems and sufficient inter-shift rest time.

Time-of-day effects on speed and accuracy performance during simulated shiftwork

ABSTRACT Performance on tasks involving speed and accuracy fluctuate throughout the 24-h day negatively affecting shift workers and organizations. Two simulated work shifts common in occupational settings were used to assess performance on a vigilance and math task. In study 1, 33 sleep-deprived participants completed a nightshift. In study 2, 32 partially sleep-deprived participants completed a dayshift. These studies found that performance differed between the type of task and the type of simulated shift where performance during the nightshift was worse than during the dayshift. In addition, collapsing speed and accuracy on the math task into inverse efficiency scores provided a unique measure that captured the impact of circadian rhythms during shiftwork. The current study also indicated that participants adopted cognitive strategies including speed-accuracy tradeoff and regulatory foci regarding work motivation (prevention focus and promotion focus) when completing the tasks depending on time-of-day, type of shift, circadian rhythms, and amount of sleep deprivation. This suggests that researchers and organizations should consider cognitive strategies in addition to the physiological components of sleep deprivation and circadian rhythms when investigating and documenting the impact of time-of-day due to different types of shiftwork conditions on performance and safety.

Daily trend of blood pressure in staff under conditions of shift work of railway transport

Introduction. The results of the study of features of the daily rhythm of blood pressure in people who constantly work in a rotational shift schedule, arising under the influence of night shift work, are discussed.&#x0D; The purpose of the study was to determine the modifying effect of working night wakefulness on the parameters of the daily rhythm of blood pressure in persons employed in work with a night shift schedule.&#x0D; Materials and methods. The analysis was carried out, in two cohorts of 19 years – 62 years employees of locomotive crews of Russian Railways. The study included drivers, assistant locomotive drivers, for at least 1 year, with night shifts n = 30,566, the number of measurements = 4,497,122, but borderline (high normal) blood pressure.&#x0D; Results. The lowest levels of systolic blood pressure (SBP) were found to be recorded in a cohort of subjects per day with a night shift, the highest – in the general group of workers and in a cohort of subjects per day with a day shift.&#x0D; The daily trend of SBP was characterized by a regular change of phases in all observation groups. In the general group, a subgroup of persons with normotonia, in a cohort of subjects, when working on a day shift, a DECLINE curve of the same type in configuration was formed.&#x0D; Limitations. The representativeness of the sample size was ensured by the participation in the study of employees of locomotive crews with a range of ages &#x0D; of 19-62 years. The limitations of the study are related to the distribution of respondents by gender: there are no female respondents in the sample.&#x0D; Conclusions. Parameters of the daily rhythm of blood pressure sensitively react to changes in working hours. To the greatest extent, changes in the daily rhythm during the hours of night working wakefulness are typical for the indicators of the daily rhythm of diastolic blood pressure.

P076 Comparing Four Different Simulated Shiftwork Schedules on Higher order Cognitive Function

Abstract Introduction Changes in cognitive performance during shiftwork due to fatigue and circadian misalignment are well-documented. However experimental evaluations of shiftwork schedules are often limited to basic tasks such as vigilance and attention. The current study evaluated several higher order cognitive functions such as memory and task switching during four simulated shiftwork schedules. Methods N=27 completed a 10-day laboratory shiftwork simulation. They were randomly assigned to one of four shiftwork conditions: Condition A, 4h-on/4h-off/8h-on/8h-off schedule; Condition B, 6h-on/6h-off schedule; Conditions C and D represented to different sections of a 4h-on/4h-on call/4h-off/4h-on/4h-on call/4h-off schedule. The Automated Neuropsychological Assessment Metrics (ANAM) was used to assess cognitive function. The tasks included in this analysis were Code Substitution (CDS/CDD), Pursuit Tracking (PUR), Matching to Sample (M2S), and Switching Task (SWT). Stability of performance during waking was compared between the conditions using Kruskal-Wallis tests. Results The analysis of cognitive performance tasks yielded mixed findings. Performance on all tasks was ranked from best to worst: Condition D (&amp;gt;Conditions A, B, C; all p &amp;lt; .05), Condition A (&amp;gt;Conditions B, C; p &amp;lt; .05 and p &amp;lt;.001, respectively), Condition B, Condition C. Regarding stability of higher order cognitive function across the waking day, Condition A exhibited the worst stability, and was the only condition whereby performance degraded across the wake period. Discussion These findings highlight the variability in cognitive capacities during different shiftwork schedules. It is important to examine higher order cognitive function, and other cognitive abilities during shiftwork, when evaluating different shiftwork schedules.

Circadian Adaptation of Melatonin and Cortisol in Police Officers Working Rotating Shifts.

Misalignment of behavior and circadian rhythms due to night work can impair sleep and waking function. While both simulated and field-based studies suggest that circadian adaptation to a nocturnal schedule is slow, the rates of adaptation in real-world shift-work conditions are still largely unknown. The aim of this study was to evaluate the extent of adaptation of 24-h rhythms with 6-sulfatoxymelatonin (aMT6s) and cortisol in police officers working rotating shifts, with a special attention to night shifts. A total of 76 police officers (20 women; aged 32 ± 5.4 years, mean ± SD) from the province of Quebec, Canada, participated in a field study during their 28- or 35-day work cycle. Urine samples were collected for ~32 h before a series of day, evening, and night shifts to assess circadian phase. Before day, evening, and night shifts, 60%-89% of officers were adapted to a day schedule based on aMT6 rhythms, and 71%-78% were adapted based on cortisol rhythms. To further quantify the rate of circadian adaptation to night shifts, initial and final phases were determined in a subset of 37 officers with suitable rhythms for both hormones before and after 3-8 consecutive shifts (median = 7). Data were analyzed with circular and linear mixed-effects models. After night shifts, 30% and 24% of officers were adapted to a night-oriented schedule for aMT6s and cortisol, respectively. Significantly larger phase-delay shifts (aMT6s: -7.3 ± 0.9 h; cortisol: -6.3 ± 0.8 h) were observed in police officers who adapted to night shifts than in non-adapted officers (aMT6s: 0.8 ± 0.9 h; cortisol: 0.2 ± 1.1 h). Consistent with prior research, our results from both urinary aMT6s and cortisol midpoints indicate that a large proportion of police officers remained in a state of circadian misalignment following a series of night shifts in dim-light working environments.

0005 A circadian-informed lighting intervention markedly improves vigilance in a simulated night shift setting

Abstract Introduction Due to misalignment between circadian timing and the work/rest schedule, cognitive performance during night shift-work is often poor. This study tested a circadian-informed lighting strategy designed to improve on-shift cognitive performance through alerting effects, faster circadian adjustment to the shift-work schedule and promoting more sleep off-shift, compared to standard lighting. Methods A randomised controlled, within-subjects, counter-balanced cross-over study was performed to examine circadian-informed versus standard lighting on cognitive performance during a simulated 8-day night shift-work schedule. Nineteen healthy sleepers (12 males/7 females, mean±SD aged 28.7±10.4 years) underwent two separate 8-day experimental conditions in the sleep laboratory. The standard lighting condition mimicked current lighting on submarines (largely dim, blue-depleted light), while the circadian-informed lighting administered bright, blue-enriched and dim, blue-depleted lighting at times estimated to facilitate rapid circadian delay. After an adaptation sleep opportunity from 22:00 – 07:00 (day 1), participants remained awake for 27 hours to transition to sleeping during the day (10:00 - 19:00) and undertaking simulated night shift-work (00:00 - 08:00) at night on days 3-7. The primary performance outcome was the number of lapses (&amp;gt;500ms responses) on the psychomotor vigilance task (PVT), administered six times across each simulated work shift. Median reaction time and other PVT outcomes were also compared between lighting conditions. Results There were significant day-by-condition interactions on PVT lapses, p&amp;lt; 0.05. The circadian-informed lighting intervention resulted in ~50% fewer lapses by the final day compared to standard lighting (mean±SD 7.4±5.0 vs. 15.6±6.1 lapses). Similar effects were observed across other PVT outcomes. Conclusion Circadian-informed lighting resulted in markedly better vigilance than standard lighting under simulated night shift-work conditions. These findings indicate the considerable potential for automated lighting interventions to improve performance and safety in shift-workers. Support (if any) This research is supported by the Commonwealth of Australia as represented by the Defence Science and Technology Group of the Department of Defence through the Research Network for Undersea Decision Superiority (research agreement number: 9334), with additional financial support from Flinders University and lighting provision support from REDARC.

Machine learning estimation of human body time using metabolomic profiling

Circadian rhythms influence physiology, metabolism, and molecular processes in the human body. Estimation of individual body time (circadian phase) is therefore highly relevant for individual optimization of behavior (sleep, meals, sports), diagnostic sampling, medical treatment, and for treatment of circadian rhythm disorders. Here, we provide a partial least squares regression (PLSR) machine learning approach that uses plasma-derived metabolomics data in one or more samples to estimate dim light melatonin onset (DLMO) as a proxy for circadian phase of the human body. For this purpose, our protocol was aimed to stay close to real-life conditions. We found that a metabolomics approach optimized for either women or men under entrained conditions performed equally well or better than existing approaches using more labor-intensive RNA sequencing-based methods. Although estimation of circadian body time using blood-targeted metabolomics requires further validation in shift work and other real-world conditions, it currently may offer a robust, feasible technique with relatively high accuracy to aid personalized optimization of behavior and clinical treatment after appropriate validation in patient populations.

Polymorphism of genes of circadian rhythms in employees of a continuous production enterprise with a shift work schedule

The circadian system plays an important role in regulating the functions of the human body. As a result of violations of the circadian system, functional disorders such as sleep disorders, carbohydrate metabolism, metabolic syndrome turning into obesity, cardiovascular pathology, oncological processes occur. One of the socially significant causes of circadian rhythm disorders is a shift work schedule.&#x0D; The study aims to explore the genetic status of employees and identify markers of predisposition to the formation of "intolerance" of shift work.&#x0D; Researchers have examined two groups of employees of the enterprise: observation group — 40 people gave 23–63 years old (30 women, 10 men) with a shift work schedule, the comparison group consisted of 51 people 24–62 years old (41 women, 10 men) of the administrative apparatus with a daily work schedule. Typing of polymorphic loci of the circadian system genes was carried out by sets of the company "Syntol" (Russia) using the Real-Time PCR method on a CFX96 device with allelic discrimination of fluorescence curves.&#x0D; Genotyping of the loci of the five main circadian genes allowed us to establish that the occurrence of the minor allele T of the MTNR1A melatonin receptor gene (rs34532313) in continuous production workers is 30%, which is five times higher than in workers with a standardized work schedule (p&lt;0.05). At the same time, workers with a shift schedule had a significant hypo-expression of serum serotonin (1.54 times, p&lt;0.05) relative to the comparison group.&#x0D; Continuous production workers have an increased occurrence of the minor allele of the MTNR1A melatonin receptor T gene (rs34532313) with a simultaneous decrease in the expression of serotonin catecholamine, which in shift work conditions can affect the formation of dysregulatory disorders of the functioning of homeostatic systems and the course of physiological metabolic processes. As a result, the polymorphism of the MTNR1A gene (rs34532313) can use as a marker of "intolerance" to shift work.&#x0D; Limitations. There are quantitative restrictions on the observation group of persons of different genders.&#x0D; Ethics. When conducting the study, the authors were guided by the Ethical principles of conducting medical research with the participation of a person as a subject, set out in the Helsinki Declaration of the World Medical Association of the last revision. The patients signed a voluntary informed consent for the examination.

Individual and Work-Related Psychological Characteristics Contributing to Subjective Well-Being in Air Rescue Employees

ObjectiveAir rescue staff are subject to stressors, including frequent traumatic events, shift work, and unfavorable conditions during rescue missions. We investigated subjective well-being among employees of the Swiss Air-Rescue organization and the potential determining factors, such as sense of coherence, self-esteem, coping, stress, and mental health status. MethodsAll employees (N = 142) received a questionnaire battery composed of the Trier Inventory for the Assessment of Chronic Stress, the Salutogenic Subjective Work Analysis, the Stress Coping Questionnaire, the Health and Stress Questionnaire, the Sense of Coherence Scale 13-item scale, the Inventory for the Measurement of Self-Efficacy and Externality, the Brief Symptom Inventory, the 12-item General Health Questionnaire, and the Posttraumatic Stress Diagnostic Scale. A discriminant analysis was conducted (input: subjective well-being, output: potential determining factors). A total of 48 participants provided complete data. ResultsThe discriminant analysis was significant (χ2 = 40.80, P < .001; correct classification: 89.4%) and revealed that sense of coherence (F1,45 = 40.46) and self-esteem (F1,45 = 36.20) were the most important discriminating factors for subjective well-being. ConclusionSense of coherence and self-esteem play an important role in the subjective well-being of emergency and rescue personnel. Fostering these traits should be included in preventive programs.

Endogenous Diurnal Patterns of Adrenal and Gonadal Hormones During a 24-Hour Constant Routine After Simulated Shift Work.

Night-shift work causes circadian misalignment, predicts the development of metabolic diseases, and complicates the interpretation of hormone measurements. To investigate endogenous circadian rhythms, dissociated from behavioral and environmental confounds, in adrenal and gonadal steroids after simulated shift work. Fourteen healthy adults (ages 25.8 ± 3.2 years) were randomized to 3 days of night or day (control) shift work followed by a constant routine protocol designed to experimentally unveil rhythms driven endogenously by the central circadian pacemaker. Blood was sampled every 3 hours for 24 hours during the constant routine to concurrently obtain 16 Δ4 steroid profiles by mass spectrometry. Cosinor analyses of these profiles provided mesor (mean abundance), amplitude (oscillation magnitude), and acrophase (peak timing). Night-shift work marginally increased cortisol by 1 μg/dL (P = 0.039), and inactive/weak derivatives cortisone (P = 0.003) and 18-hydroxycortisol (P < 0.001), but did not alter the mesor of potent androgens testosterone and 11-ketotestosterone. Adrenal-derived steroids, including 11-ketotestosterone (P < 0.01), showed robust circadian rhythmicity after either day- or night-shift work. In contrast, testosterone and progesterone showed no circadian pattern after both shift work conditions. Night-shift work did not alter the amplitude or acrophase of any of the steroid profiles. Experimental circadian misalignment had minimal effects on steroidogenesis. Adrenal steroids, but not gonadal hormones, showed endogenous circadian regulation robust to prior shift schedule. This dichotomy may predispose night-shift workers to metabolic ill health. Furthermore, adrenal steroids, including cortisol and the main adrenal androgen 11-ketostosterone, should always be evaluated during the biological morning whereas assessment of gonadal steroids, particularly testosterone, is dependent on the shift-work schedule.

Timed restricted feeding cycles drive daily rhythms in female rats maintained in constant light but only partially restore the estrous cycle.

Light at night is an emergent problem for modern society. Rodents exposed to light at night develop a loss of circadian rhythms, which leads to increased adiposity, altered immune response, and increased growth of tumors. In female rats, constant light (LL) eliminates the estrous cycle leading to a state of persistent estrus. The suprachiasmatic nucleus (SCN) drives circadian rhythms, and it interacts with the neuroendocrine network necessary for reproductive function. Timed restricted feeding (RF) exerts a powerful entraining influence on the circadian system, and it can influence the SCN activity and can restore rhythmicity or accelerate re-entrainment in experimental conditions of shift work or jet lag. The present study explored RF in female rats exposed to LL, with the hypothesis that this cyclic condition can rescue or prevent the loss of daily rhythms and benefit the expression of the estrous cycle. Two different feeding schedules were explored: 1. A 12-h food/12-h fasting schedule applied to arrhythmic rats after 3 weeks in LL, visualized as a rescue strategy (LL + RFR, 3 weeks), or applied simultaneously with the first day of LL as a preventive strategy (LL + RFP, 6 weeks). 2. A 12-h window of food intake with food given in four distributed pulses (every 3 h), applied after 3 weeks in LL, as a rescue strategy (LL + PR, 3 weeks) or applied simultaneously with the first day of LL as a preventive strategy (LL + PP, 6 weeks). Here, we present evidence that scheduled feeding can drive daily rhythms of activity and temperature in rats exposed to LL. However, the protocol of distributed feeding pulses was more efficient to restore the day–night activity and core temperature as well as the c-Fos day–night change in the SCN. Likewise, the distributed feeding partially restored the estrous cycle and the ovary morphology under LL condition. Data here provided indicate that the 12-h feeding/12-h fasting window determines the rest-activity cycle and can benefit directly the circadian and reproductive function. Moreover, this effect is stronger when food is distributed along the 12 h of subjective night.

Acute sleep loss increases CNS health biomarkers and compromises the ability to stay awake in a sex-and weight-specific manner

Night shift work impairs vigilance performance, reduces the ability to stay awake, and compromises brain health. To investigate if the magnitude of these adverse night shift work effects differs between sexes and weight groups, 47 men and women with either normal weight or obesity participated in one night of sleep and one night of total sleep loss. During the night of sleep loss, participants’ subjective sleepiness, vigilance performance, and ability to stay awake during 2-min quiet wake with eyes closed were repeatedly assessed. In addition, blood was collected in the morning after sleep loss and sleep to measure central nervous system (CNS) health biomarkers. Our analysis showed that women were sleepier during the night of sleep loss (P < 0.05) and spent more time in microsleep during quiet wake testing (P < 0.05). Finally, higher blood levels of neurofilament light chain, a biomarker of axonal damage, were found among women in the morning after sleep loss (P < 0.002). Compared with normal-weight subjects, those with obesity were more prone to fall asleep during quiet wake (P < 0.05) and exhibited higher blood levels of the CNS health biomarker pTau181 following sleep loss (P = 0.001). Finally, no differences in vigilance performance were noted between the sex and weight groups. Our findings suggest that the ability to stay awake during and the CNS health biomarker response to night shift work may differ between sexes and weight groups. Follow-up studies must confirm our findings under more long-term night shift work conditions.

Subclinical carotid atherosclerosis in the conditions of rotational shift work in the arctic: Data of preventive examination

Subclinical carotid atherosclerosis in the conditions of rotational shift work in the arctic: Data of preventive examination

Shift work and the onset of type 2 diabetes: results from a large-scale cohort among Japanese workers.

Data are limited regarding how shift work is linked to the development of type 2 diabetes, especially among workers at high risk of diabetes. We examined the risk of diabetes according to shift-work conditions over several years among Japanese adults. This prospective study enrolled 17,515 workers (age 40-78years). Shift work was self-reported at annual health examinations over time from 2004 to 2017 and categorized as shift workers or non-shift workers. Diabetes was defined as fasting plasma glucose, random glucose, HbA1c, and self-reported use of antidiabetic medications. The association of shift work and diabetes was quantified using Cox regression. During a follow-up of 8.1years in median, 2071 incident cases of diabetes were documented. Compared with non-shift work, shift work showed a significantly elevated hazard ratios of developing diabetes. Shift work showed a 19% (95% confidence intervals: 3-37%) higher hazard ratios for diabetes, after adjustment for demographic-, cardiometabolic-, and work-related factors. Further adjustment for lifestyle factors and body mass index did not materially change this association (a 16% increase; 95% confidence intervals, 1-34%). This relationship was replicated among workers with prediabetes. Engaging in shift work may increase the risk of developing diabetes independently of lifestyle factors and body mass index, even among prediabetic workers.

Factors affecting night sleep in rotational shift workers in the Arctic

Abstract Funding Acknowledgements Type of funding sources: None. Background Our previous studies revealed that half of arterial hypertension (AH) patients had a flat type of non-dipper curve of blood pressure daily profile (BPDP). Purpose To study and differentiate the leading component of sleep disturbance in conditions of the Arctic rotational shift work and evaluate its relationship with the data of ambulatory blood pressure monitoring (ABPM). Methods In September 2019, 180 patients with AH, including 79 males (M), (gr. 1) aged 48.7 ± 8.3 years and 68 females (F), (gr. 2) aged 50.0 ± 6.7 years (p = 0.06) were simultaneously examined in Yamburg (68 N) settlement in the Arctic Watch. Groups did not differ in rotational shift work duration (16.9 ± 8.7 and 16.2 ± 8.3 years, p = 0.72). Analysis of sleep quality (Pittsburg Sleep Quality Index - PSQI) with daytime sleepiness analysis (Epworth Sleepiness Scale) was carried out. Six components were investigated: 1 - subjective sleep (S) quality component; 2 - assessment of S latency; 3 - assessment of S duration; 4 – habitual S efficiency ; 5 – step disturbances of S; 6 - use of S medication; 7 - daytime S dysfunction with differentiation of global index (Global PSQI score). All individuals underwent ABPM with analysis of daily index of systolic blood pressure and diastolic blood pressure and BPDP. Results According to the survey, 22% had S disorders in M gr., 30% (24/81) in F gr., p = 0.23. Global assessment of S quality was also not dependent on gender: mode of assessment was 4 points (P), (24 individuals) in M, 5 P (17) in F (p = 0.91). Leading components of S quality disorder were the subjective S quality with 2 P, (16); the S latently had 2 P (11); the step disturbances of S had the 2 P (11) and the daytime S dysfunction had the 2 P (14) in M. In F, the 1st component (C)C (2 P – 13); the 2nd C - 2 P (16) prevailed and the 5th and the 7th C were less manifested. Moreover, F had S latency complaints oftener than M (p = 0.031). Analysis of interconnections with ABPM revealed "over dipper" BPDP in the 12.5%, "dipper" BPDP in 42.5% (51); "non dipper" BPDP in 41.7% (50); "night peaker" BPDP in 3.3%. In individuals with normal S quality, "dipper" BPDP prevailed (54%). At the same time, leading components did not have significant correlations with abnormal BPDP. Conclusion In conditions of rotational shift work in the Arctic, regardless of gender, sleep disturbances are more associated with poor habitual sleep efficiency and less associated with disturbances of BPDP. This is obviously explained by increased exhaustion due to the intense nature of rotational shift work in the Arctic region.

282 Effect of circadian misalignment on the sleep of police officers across a series of night shifts

Abstract Introduction Misalignment of behavior and circadian rhythms due to night work can impair sleep and waking function. While both simulated and field-based studies suggest that circadian adaptation to a nocturnal schedule is slow, the rates of adaptation in real-world shift-work conditions are still largely unknown. The aim of this study was to evaluate the extent of adaptation of 24-h rhythms in 6-sulfatoxymelatonin (aMT6s) and cortisol in police officers across night shifts and to compare their effect on sleep. Methods A total of 76 police officers (20 women; aged 32.3±5.5 years, mean±SD) from the province of Québec, Canada, participated in a field study comprising their 28- or 35-day work-cycle. Urine samples were collected for ~24-h before and after a series of 3–7 night shifts. Rhythms of urinary aMT6s were considered adapted if midpoints following night shifts occurred during participants’ average daytime sleep period. Cortisol was considered adapted if midpoints occurred within 2h of their average daytime sleep offset. Sleep was measured with actigraphy and sleep logs on a cell phone. Data were analyzed with circular and linear mixed-effects models. Results Analyses were based on a subset of 37 participants with rhythms of both hormones suitable for circadian phase assessment before and after their series of night shifts. After night shifts, the group acrophase of adapted rhythms (aMT6: n=11, cortisol: n=9) occurred significantly later than for non-adapted rhythms (aMT6s: 10.9 h vs. 3.4 h, p&amp;lt;.001; cortisol: 14.9 vs. 9.9 h, p&amp;lt;.001). Participants with adapted aMT6s rhythms obtained cumulatively more sleep per day throughout the series of shifts than those with non-adapted rhythms (average 6.4 h per day vs 5.8 h per day; p=.026). Conclusion Consistent with prior research, our results from both urinary aMT6s and cortisol midpoints indicate that a large proportion of police officers remained in a state of circadian misalignment following their night shifts. The minority of officers who adapted to night work were able to obtain more sleep across consecutive night shifts. Support (if any) Project funded by the Institut de Recherche Robert-Sauvé en Santé et en Sécurité du Travail (IRSST). A.K. received a postdoctoral fellowship from the Fonds de Recherche en Santé du Québec (FRQS).

ARTERIAL HYPERTENSION RISK PREDICTION IN CONDITIONS OF ROTATIONAL SHIFTWORK IN THE ARCTIC

Objective: To study features and dynamics of chronostructure of circadian blood pressure (BP) rhythm in normotensive patients and define their prognostic value with respect to arterial hypertension (AH) within prospective observation in conditions of Arctic rotational shiftwork. Design and method: During the prospective one-year study, in conditions of rotational shiftwork in the Arctic, 173 men with normal BP and with negative history of AH (mean age 40.2 ± 4.1 years) were examined. Work experience in the Arctic was 16.5 ± 6.8 years; work experience in rotational shifts was 11.2 ± 3.8 years and office BP was 123.4 ± 7.5/80.5 ± 5.5. All patients underwent ambulatory blood pressure monitoring (ABPM) 1 time in 3 months; individual cosinor-data analysis was carried out to determine circadian rhythm chronotypes. Results: According to the classification of P. Cugini, true normotension (50%) and atypical chronotypes: allonormotension (22%) and isonormotonia (28%) were revealed in individuals with normal BP. The prognostic value of circadian BP rhythm disturbances was explained by high frequency of atypical normotensive chronotype transformation into hypertensive ones. During the year of observation, AH developed in 26% of normotonics with atypical chronotypes. Based on results of the study of chronobiological parameters in individuals with normal BP, the role of autonomic nervous system in the formation of chronotypes of circadian BP rhythm in normotensive patients was assessed. Moreover, atypical chronotypes of BP highlighted as main disturbances of circadian rhythm in the conditions of the Arctic region. Atypical normotensive chronotypes were characterized by more evident structural changes of the heart and vessels. In conditions of the Arctic, chronobiological approach in comparison with standard analysis of ABPM indicated higher diagnostic sensitivity, specificity and efficiency. Logistic regression revealed prognostic significance of normotensive atypical chronotypes compared to main risk factors (smoking, low physical activity, body mass index, dyslipidemia, age, duration of work in the Arctic and rotational shiftwork experience, the mode and type of rotational shiftwork). Conclusions: Using multivariant analysis, there was received the model for determining a diagnostic indicator showing risk for AH development during one-year observation in normotensive individuals in condition of rotational shiftwork in the Arctic.

EFFECTS OF PHOTOPERIODISM ON DAILY RHYTHMS OF BLOOD PRESSURE AND HEART RATE IN DIFFERENT SEASONS OF THE YEAR IN THE ARCTIC

Objective: To study the effect of the rhythm of natural light on circadian rhythms of blood pressure (BP) and heart rate (HR) in the Arctic. Design and method: Analysis of 24-hour BP monitoring was performed in 373 male patients with arterial hypertension (AH) stage II engaged in rotational shiftwork in the Arctic compared with the group of the same type of 144 patients living in moderate climate (Tyumen, 57 N) 93 randomly selected patients of the Northern group and 64 patients of the Tyumen group. Based on 24-hour ambulatory blood pressure monitoring chronobiological and standard parameters, daily BP profile, circadian BP and HR indices, percentage contribution value (PC), amplitude of a rhythm (RA), acrophase and BP MESOR in different seasons were analyzed. Results: In the conditions of Arctic shift work circadian BP and HR rhythms in patients with AH differed significantly compared with Tyumen patients regardless of season and were characterized by the absence of seasonality signs of BP and HR rhythms and the presence of inside desynchronosis of rhythms. Lack of natural light during the polar day and polar night leads to flattened HR and circadian BP in patients with AH in the Far North. The major differences were the loss of 24-hour period components and low-amplitude spectrum profile. Seasonal changes in the HR parameters were not significant in the comparison group versus northern group with a clear flattening of HR in the polar day period. In the main group of patients the worst condition for 24-hour BP profile was winter period (polar night) characterized by the peak flattening of circadian rhythms and the prevalence of high-frequency oscillations in the spectrum. Conclusions: In patients with AH in the conditions of Arctic shift work, formation of daily rhythm and absence of seasonality signs of HR and BP is associated with nature of work and climate factors, including natural light rhythm in the northern latitude.

Night shift schedule alters endogenous regulation of circulating cytokines

Night shift work is a risk factor for viral infection, suggesting that night shift schedules compromise host defense mechanisms. Prior studies have investigated changes in the temporal profiles of circulating cytokines important for priming and restraining the immune response to infectious challenges from night shift work, but not by way of a 24-h constant routine of continuous wakefulness devoid of behavioral or environmental influences. Hence the true endogenous pattern of cytokines, and the combined effect of sleep loss and circadian misalignment on these cytokines remains unknown. Here, 14 healthy young men and women underwent three days of either a simulated night shift or a simulated day shift schedule under dim light in a controlled in-laboratory environment. This was followed by a 24-h constant routine protocol during which venous blood was collected at 3-h intervals. Those who had been in the night shift schedule showed lower mean circulating TNF-α (t13 = -6.03, p < 0.001), without any significant differences in IL-1β, IL-8 and IL-10, compared with those who had been in the day shift (i.e., control) schedule. Furthermore, circulating IL-6 increased with time awake in both shift work conditions (t13 = 6.03, p < 0.001), such that temporal changes in IL-6 were markedly shifted relative to circadian clock time in the night shift condition. These results indicate that night shift work compromises host defense by creating cytokine conditions that initially impede anti-viral immunity (lower TNF-α) and may eventually promote autoimmunity (mistimed rise in IL-6).