Psychophysical conditions and hormonal secretion in nurses on a rapidly rotating shift schedule and exposed to bright light during night work

Abstract

The psychophysical conditions of 15 young female nurses, working in a rapidly-rotating shift system (2-2-2-2), modified according to some psychophysiological criteria, and exposed to short period (4 × 20 min) of bright light (2350 Lux) during their night duty, were studied in order to evaluate their adaptation to night work and to test a possible positive effect on it of bright light. Subjective evaluations of work load and psychophysical conditions, performance measures, hormonal excretion (cortisol, 6-sulphatoxymelatonin and catecholamines), oral temperature and activity-sleep logs were taken during the shiftwork cycle, comprising one morning, one afternoon and two consecutive nights under normal and bright light. The results showed that this rapidly-rotating shift system had little effect upon the normal circadian rhythms of the body. Moreover, the lengthening of the night shift to 10 h can be considered to be acceptable, provided that work load is reduced and there are sufficient rest pauses available. On the other hand, the reduction to 7 h of the length of the day shifts and delayed start of the morning shift to 07:00 h appeared to be convenient both in relation to the work load and sleep duration. Some positive effects of bright light upon psychophysical conditions and performance efficiency were noted, while hormonal excretion and body temperature did not show any effect of bright light; in particular, melatonin excretion was not suppressed appreciably by the bright light used.     

Appropriate use of bright light promotes a durable adaptation to night-shifts and accelerates readjustment during recovery after a period of night-shifts

The present study examines the stability of bright light circadian readjustment during two consecutive dim light night-work periods and circadian synchronization during the recovery after a night-shift period. A sample of 10 subjects was divided into 2 groups (control group : 6 subjects; experimental group: 4 subjects). All subjects worked during 5 days, between 23:00 and 07:00 h and then went to sleep. Subjects received 2500-3000 lux between 02:00 and 05:00 h during 5 days for the control group and 3 days for the experimental group. During recovery after the night-shift periods, three cycles of bright light were administered at two different times: 12:00-15:00 h for two of six subjects from the control group and 10:00-13:00 h for all subjects (4) of the experimental group. By the fifth cycle of night-work the maximum of urinary aMT6s excretion that occurs at 05:00 h in the baseline condition was shifted to 12:00 h for the control and experimental groups (delay in hours: 7 +/- 1.6 (control); 7 +/- 1(experimental)). This result suggests that three cycles of bright light are sufficient to induce a significant phase delay and that this delay remained stable when night-work proceeded under dim light. The phase delay of the circadian aMT6s excretion by exposure to bright light was accompanied by an improvement of the quality of day sleep and level of cognitive and psychomotor performances for control and experimental groups. No significant difference was observed in the two groups for daytime sleep and nocturnal performance. The two bright light periods used during the three days of recovery induced a complete synchronization in five of six subjects. One subject showed a partial sychronization probably because he remained at the laboratory under dim light during the day and had few family and social contacts.     

Appropriate use of bright light promotes a durable adaptation to night-shifts and accelerates readjustment during recovery after a period of night-shifts

Abstract

The present study examines the stability of bright light circadian readjustment during two consecutive dim light night-work periods and circadian synchronization during the recovery after a night-shift period. A sample of 10 subjects was divided into 2 groups (control group: 6 subjects; experimental group: 4 subjects). All subjects worked during 5 days, between 23:00 and 07:00 h and then went to sleep. Subjects received 2500-3000 lux between 02:00 and 05:00 h during 5 days for the control group and 3 days for the experimental group. During recovery after the night-shift periods, three cycles of bright light were administered at two different times: 12:00-15:00 h for two of six subjects from the control group and 10:00-13:00 h for all subjects (4) of the experimental group. By the fifth cycle of night-work the maximum of urinary aMT6s excretion that occurs at 05:00 h in the baseline condition was shifted to 12:00 h for the control and experimental groups (delay in hours: 7±1.6 (control); 7±1 (experimental)). This result suggests that three cycles of bright light are sufficient to induce a significant phase delay and that this delay remained stable when night-work proceeded under dim light. The phase delay of the circadian aMT6s excretion by exposure to bright light was accompanied by an improvement of the quality of day sleep and level of cognitive and psychomotor performances for control and experimental groups. No significant difference was observed in the two groups for daytime sleep and nocturnal performance. The two bright light periods used during the three days of recovery induced a complete synchronization in five of six subjects. One subject showed a partial synchronization probably because he remained at the laboratory under dim light during the day and had few family and social contacts.     

Circadian rhythms and bright light: Recommendations for shift work

This paper starts with a brief review of the basic principles of human circadian rhythms relevant to understanding the problem of shift work. It then presents a more detailed critical review of the recent bright light literature, with an emphasis on methodological shortcomings, alternative interpretations, and areas that need further research. Evidence is presented which suggests that either a light-dark cycle (which includes bright light) or a sleep-wake schedule can act as a zeitgeber for human circadian rhythms. Current human phase response curves to bright light are reviewed. Light-work-sleep schedules are presented which have been designed to eliminate the physiologically based harmful consequences of shift work. These schedules include both bright light and sleep-wake schedule zeitgebers. Other practical applications of bright light treatment are mentioned.     

Countermeasures for night work performance deficits: The effect of napping or caffeine on continuous performance at night

Napping and caffeine consumption, two common strategies for improving alertness and performance on the night shift, were investigated in two separate studies. Performance was measured with a simulated assembly line task (SALT) during a single night work shift. Both strategies proved beneficial. Performance and subjective alertness were improved following either a 2.3-h evening nap or ingestion of caffeine (4 mg/kg) prior to the work shift. The effects were noted particularly at the trough of circadian alertness. Although neither napping nor caffeine countered the strong circadian influence on performance and alertness in the early morning hours, both strategies attenuated their sharp decline. Further research is required to determine the generalizability of these findings beyond a single night shift and in different populations of workers, such as older age groups, or chronic caffeine users.     

Dealing with shift work: Physical fitness, temperature, and napping

This paper reviews the effects of generally controllable factors such as physical conditioning, ambient temperature, and amount of prior sleep in adjustment to night work periods and shift work. One can expect a 5-10% decline in capacity for work in nocturnal work periods as compared to daytime work periods. This decreased capacity would dissipate if workers maintained a consistent sleep-wake routine for 8-16 days after moving to a new shift. Proven means for accelerating this adaptation are currently not available. The ability to perform work also declines as the length of the work period increases but depending upon individual tasks. Physical conditioning improves mood and general well-being, but no strong evidence currently indicates that conditioning increases tolerance or adjustment to shift work.

Increased ambient temperature increases the stress of work, although studies do not address heat as a factor in adjustment to shift work. While lower nocturnal temperature would be assumed to reduce heat stress during night shifts, supporting data does not exist. Studies have not addressed the negative consequences of cold stress or of rotating from night to day shifts with added heat stress.

The proper use of short sleep periods either as preparation for or as a response to a shift change can ameliorate some effects of shift rotation. Data indicate that performance on 'graveyard' shifts can be maintained close to baseline levels following true prophylactic naps while performance may decline by up to 30% when such naps are not taken. While there is evidence that naps or even rest periods without sleep are beneficial in improving mood in normal young adults, these data do not apply to 'replacement' naps. Studies of interjected naps imply that such naps do reduce sleep debt but do not imply that such naps are more beneficial than longer sleep periods. Naps appear to be most advantageous when the accumulated sleep debt is least.     

Using pharmacological aids to improve waking function and sleep while working at night

Non-refreshing or insufficient sleep, and impaired alertness on the job, are two nearly universal consequences of night work. The effects of drugs upon the sleep and alertness of night workers has only recently been studied and much work remains to be done. To date, it is clear that sleep during the day can be improved with sedative-hypnotic compounds, particularly the benzodiazepines. Despite improvement in sleep, alertness at night is improved only mildly, if at all, with short-acting sleeping agents and can be further impaired with long-acting drugs. The limited research examining alertness and performance during night shift hours after administration of CNS stimulants suggests significant benefits. The judicious use of CNS stimulants in this way needs further exploration. Precise pharmacological manipulation of the endogenous sleep/wake rhythm is primarily theoretical at this time but should be pursued.     

The impact of shiftwork on personnel at a nuclear power plant: An exploratory survey study

Shiftwork may constitute an additional risk factor in high-hazard industries where system failure could exact heavy human, environmental and economic costs. This exploratory survey study examined the impact of shiftwork upon nuclear power plant workers' perceived health, sleep, and social problem, as well as levels of alertness. Overall, the night shik proved to be the most problematic in ternis of decreases in alertness, sleep duration and quality, and disruptions to health, social and family life. The permanent shift preferences of the shiftworkers were also explored to establish the practicability of introducing a theoretically safer permanent mght shdt at such a facility. Importantly, the small proportion of the sample who showed a preference for a pemianent night shift was insufficient to provide operational cover. Although these shtftworkers reported experiencing less disruption on the night shift than those who would choose to work a permanent day shift, their preference appeared to be based upon a greater esprit de corps on this shift rather than on any predisposing individual characteristics. These results have practical implications for work scheduling in high-hazard industries.

The present study investigates the dimensional structure of the psychosocial work environment as assessed by Karasek's job characteristics scales and a set of factorial scales derived from the Dictionary of Occupational Titles (DOT) observers' ratings of occupational characteristics for census occupations. Scale scores on the Karasek and DOT were linked to information on occupation from the Epidemiologc Catchment Area (ECA) study sample. Scale intercorreladons and factor analysis were performed on those ECA subjects who reported ever having a full-time job (n=11,789). DOT'sS Substantive Complexity scale was positively correlated with Karasek's Skill Discretion and Decision Authority scales, and DOT's Physical Demands and Hazards scale was positively correlated with Karasek's Physical Demands scale. In addition, the DOT system compared to the Karasek system seems to assess psychosocial work domains less characteristic of traditional industrial jobs (interpersonal stress, expressive work). The content validity of the Karasek scales might be increased with the assessment of these domains. Giving support to Karasek's Demand/Control Model, the factor structure of the psychosocial work enviromnent in the probability sample of five US metropolitan populations yielded two major dimensions: Control, and Physical Demands.     

Ten-hour days and eight-hour nights: Can the Ottawa Shift System reduce the problems of shiftwork?

Most research on condensed working weeks has concentrated either on daywork only or on 12-h shifts. The Police Force in Ottawa, Canada, have been reporting positive experiences with a shift system which retains an 8-h night shift but which extends the day shifts to 10-h, thus enabling a 6-day rest period following night shifts. In the present study, the effects on well-being, personal, social and work disruption, alertness and sleep were evaluated when the same system was adopted by a police force in the UK. A survey was conducted at four police stations prior to the change and again 6 months after the change. Two of the stations did not change to the Ottawa system and hence formed a control group. The stations originally worked 8-h shifts with blocks of seven consecutive shifts. The results suggest that, in contrast to the control group the 'Ottawa' group experienced a significant improvement in well-being, a significant reduction in personal, social and work disruption, and a significant increase in average sleep duration over a shift cycle. Self-rated alertness at the end of shifts was no worse under the Ottawa system. However, the values were still very low at the end of the night shift and, with an average sleep duration between night shifts of only 6-4-h it suggests that the block of seven nights in the Ottawa system may need review.     

Workload and morning salivary cortisol in women

Previous studies have shown a link between work-related stress and the morning level of the stress hormone cortisol. The level of cortisol in the circulation is regulated by the hypothalamic-pituitary-adrenocortical (HPA) axis, dysregulation of which plays an important role in a number of disorders including hypertension, immune deficiency and being overweight (the 'metabolic syndrome'). The aim of this study was to investigate the association between workload and morning cortisol in women. Saliva samples were obtained four times during the first 45 min after awakening (0, 15, 30 and 45 min) in the morning on a work-free day from more than 200 women in full-time work who were born in 1955 and representing a normal population of a small city in Sweden. The amount of paid and unpaid work was reported in a questionnaire. Significant positive correlations were found between the amount of overtime at work and each of the four measurements of morning salivary cortisol (varying from r = .29 to r = .38, p < .01). In addition, participants with excessive overtime (more than 10 h/week) had on average about twice as high ( p < .01) morning cortisol levels as women with moderate overtime (< 10 h/week) or normal working hours (35-40 h/week). The results are consistent with earlier findings and suggest that morning cortisol is a sensitive indicator of work overload in women. However, additional research is necessary in order to reveal the specific pathways linking work-related stress to elevated morning cortisol.     

Behavioural techniques for enhancing alertness and performance in shift work

This paper reviews behavioural and cognitive methods for increasing alertness, enhancing performance, and decreasing long-term negative consequences due to shift work. Methods having the most potential for effective intervention include the short-term alerting effects of the optimal timing of work breaks, social activity during breaks, and sensory stimulation. Stress coping techniques and sleep hygiene information for workers and their families have the most potential for addressing long-tcrm effects of shift work. Recommendations for areas requiring further investigation include the altering effects of bright light, fresh air, and cold water; performance enhanccmcnt through psychophysiological self-regulation and imagery; and the impact on performance of second jobs and family responsibilities.     

Performance, alertness, and sleep after 3·5 years of 12 h shifts: A follow-up study

Control room operators at a continuous processing plant have been working a 12 h/3-4 day rotating shift schedule for over 3 years. After 7 months on this schedule, our initial assessment indicated decrements in performance and alertness, and a mild to moderate sleep debt, when the 12 h shift schedule was compared to the previously-worked 8 h shift schedule. In an effort to track long-term adaptation to the schedule, we conducted a 3 & 5 year follow-up evaluation using the same set of measures. Long-term follow-up testing revealed persistent decrements in performance and alertness attributable to 12 h shifts, and 1-3 h reductions in total sleep time after 12 h night shifts. Little deterioration in performance or alertness was observed across the workweek, which suggested day-to-day recovery from the extended workshift. The popularity of the 12 h shift schedule at this worksite indicates that the workers are willing to tolerate extra fatigue to derive other benefits from this schedule.     

A 14-h night-shift in the control room of a fire brigade

All 29 operators in the control room of a fire brigade performed test sessions during work and leisure time at 2-h intervals on a day with a 14-h night-shift, a day off and a day with a 10-h morning shift. The test sessions consisted of a visual search choice reaction time test and two Sternberg memory search tests (1 or 5 letters had to be memorized). Furthermore, the operators recorded their oral temperature and their subjective alertness before each test session. The subject also kept a diary of work and sleep times for 14 days. The circadian rhythm of body temperature was hardly changed by a single night-shift. Parallel to the body temperature, the subjective alertness fell significantly during the night-shift reaching a minimum value at 06:00 h. The mean reaction times increased non-significantly at the end of the night-shift and the results of the two Sternberg memory search tests showed no significant trends. The sleep of the operators after the night-shift was on average reduced to 5 hs 34 min. The results of subjective rating of alertness and reaction time test are interpreted as effects of the combined influences of circadian rhythmicity, sleep loss and time on professional task. Most results support the conclusion that a 14-h night-shift without extensive breaks is not acceptable.     

A 14-h night-shift in the control room of a fire brigade

All 29 operators in the control room of a fire brigade performed test sessions during work and leisure time at 2-h intervals on a day with a 14-h night-shift, a day off and a day with a 10-h morning shift. The test sessions consisted of a visual search choice reaction time test and two Sternberg memory search tests (1 or 5 letters had to be memorized). Furthermore, the operators recorded their oral temperature and their subjective alertness before each test session. The subject also kept a diary of work and sleep times for 14 days. The circadian rhythm of body temperature was hardly changed by a single night-shift. Parallel to the body temperature, the subjective alertness fell significantly during the night-shift reaching a minimum value at 06:00 h. The mean reaction times increased non-significantly at the end of the night-shift and the results of the two Sternberg memory search tests showed no significant trends. The sleep of the operators after the night-shift was on average reduced to 5 hs 34 min. The results of subjective rating of alertness and reaction time test are interpreted as effects of the combined influences of circadian rhythmicity, sleep loss and time on professional task. Most results support the conclusion that a 14-h night-shift without extensive breaks is not acceptable.     

The many meanings of sleep

Reductions in sleep are concomitant with night shift work. Data are presented showing that these robust differences in sleep are even present in experienced permanent night shift workers who most prefer to work nights. A model is presented which relates these reductions to chronic sleep deprivation. This, in turn, may be associated with performance decrements, and lead to accidents and illness. Better work schedule selection, worker training programs, and preventive medical action are unproven but promising approaches to overturning this model.     

A 14-h night-shift in the control room of a fire brigade

Abstract

All 29 operators in the control room of a fire brigade performed test sessions during work and leisure time at 2-h intervals on a day with a 14-h night-shift, a day off and a day with a 10-h morning shift. The test sessions consisted of a visual search choice reaction time test and two Sternberg memory search tests (1 or 5 letters had to be memorized). Furthermore, the operators recorded their oral temperature and their subjective alertness before each test session. The subject also kept a diary of work and sleep times for 14 days. The circadian rhythm of body temperature was hardly changed by a single night-shift. Parallel to the body temperature, the subjective alertness fell significantly during the night-shift reaching a minimum value at 06:00 h. The mean reaction times increased non-significantly at the end of the night-shift and the results of the two Sternberg memory search tests showed no significant trends. The sleep of the operators after the night-shift was on average reduced to 5 hs 34 min. The results of subjective rating of alertness and reaction time test are interpreted as effects of the combined influences of circadian rhythmicity, sleep loss and time on professional task. Most results support the conclusion that a 14-h night-shift without extensive breaks is not acceptable.     

The New Public Management and Managerial Roles: the Case of the Police Sergeant

This paper explores the introduction of New Public Management (NPM) techniques within the UK police service since the late 1990s, and in particular, the impact upon the role of the first line manager: the police sergeant. It draws upon qualitative data collected within 'City Police Service' by means of in-depth interviews with role sets of police sergeants, constables, inspectors and members of the senior management team in two police divisions. After evaluating a number of NPM precepts in the light of the findings, the paper makes a number of conclusions relating to the role of police sergeants. These echo the findings of other research on changes in managerial roles, including a shift towards more strategic responsibilities, but with a significant intensification of work, tighter control and scrutiny through organizational performance management systems, and less daily contact with their police constables. As elsewhere in the public sector, a shift towards becoming a 'practitioner manager' was apparent, but with respect to police sergeants the effect was to limit their ability to provide leadership and support for their constables, and to encourage a greater reliance upon peer group networks and on the constables they supervised.     

The impact of VDU use and psychosocial factors at work on musculoskeletal shoulder symptoms among white-collar workers

This investigation of white-collar workers ( n = 201) in Swedish industrial environments focused on an empirical examination of the relationships between work with visual display units (VDUs), psychosocial factors (skill discretion, appraised work load, job satisfaction), physical work load and musculoskeletal shoulder symptoms. This cross-sectional study was based upon questionnaire surveys carried out at industrial companies. The prevalence of shoulder symptoms during the previous year was 39%. Nearly one-half of the participants reported that they used a VDU for at least 4 h/day ('high VDU use'). High VDU use was related to increased Prevalence Odds Ratio (POR) for shoulder symptoms. After adjustment for physical work load, significant PORs were found in groups with high VDU use in combination with low job satisfaction (POR = 4.8) or high appraised work load (POR = 3.5), compared to groups with low VDU use in combination with high job satisfaction or low work load (reference groups).     

Editorial statement: Stress and work compensation

Shift work has been reported to predict health problems, and a possible explanation is that shift work may lead to poorer health habits, thereby increasing a person's vulnerability to illness. This study examined the association between shift work and health habits, as indicated by smoking, alcohol intake, physical activity and by being overweight. A questionnaire was sent to all 2795 female nurses working in the 10 hospitals of two Finnish health care districts. From the 2299 respondents, we selected those 506 shift workers who reported having always done shift work and those 183 day workers who had never done shift work. Shift workers were found to smoke more and to be overweight more often than day workers. These differences gradually increased in each successive age group, being 1.94 pack-years in smoking and 0.9 kg m^-2 in body mass index among nurses over 45 years of age. Shift work was not associated with alcohol intake or sedentary lifestyle. This evidence is compatible with the possibility that shift work in nurses increases smoking and being overweight to a degree that contributes to health problems, including coronary heart disease.     

Causes of accidents and the time of day

Abstract

The relationship between accidents and the time of day is not entirely clear. Although there is considerable evidence that performance is poorest in the early morning hours compared to at all other times, the degree to which this is translated into accidents is not understood. In this study work-related fatal accidents were analysed to determine whether the causes of these accidents vary with time. The analysis used a classification and coding system devised to describe the wider circumstances of the causes of fatalities. In terms of absolute numbers, fatalities were most common in the late morning or early afternoon. When these results were expressed in terms of the estimated number of workers at work, the proportion of fatal accidents occurring at night was more than double that occurring during the day. Behavioural factors were the most common cause of fatalities at all times, but most common in the early hours of the morning. Further analysis of the nature of the behavioural involvement showed that errors in automatic processing (skill-based errors) were the most common types of error and did not vary much with time of day. Rule-based errors were most common during the day whereas knowledge-based errors occurred mainly in the afternoon and night shifts. These results cast some doubt on the assumption that there is a direct relationship between the previously observed variations in performance across time and the ultimate safety outcome.