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

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.     

Shiftwork effects in nuclear power workers: A field study using portable computers

This field study of nuclear power shiftworkers reports the use of hand-held computers to record alertness levels, cognitive task performance and workload ratings. Subjective ratings and performance tasks (Search and Memory-5 (SAM-5); Choice Reaction Time (CRT) were completed on the computers at 2-h intervals during selected shifts in the work schedule by maintenance crews and reactor operators. Sleep duration and quality data were also obtained during the 35-day shift cycle. Workload remained relatively stable across shifts. The night-shift was associated with shorter sleep durations and poorer sleep quality. Significantly lower levels of alertness and poorer perforniance for components of the performance tasks were also observed on the night-shift. Tinic-on-shift effects on alertness were evident, where by for the night-shift, especially, alertness dropped dramatically during the early hours. Components of SAM-5 performance showed differential time-on-shift patterning relative to each shift whereas CRT was unresponsive to time-on-shift effects. Significant variations were observed in alertness and performance components during the 12-h night-shift. Perhaps paradoxically, performance on the 12-h night-shift appeared to improve rather than deteriorate during the early-hour period that was associated with the greatest drop in alertness. This was suggestive of extra effort expenditure during this critical period.     

Shiftwork effects in nuclear power workers: A field study using portable computers

Abstract

This field study of nuclear power shiftworkers reports the use of hand-held computers to record alertness levels, cognitive task performance and workload ratings. Subjective ratings and performance tasks (Search and Memory-5 (SAM-5); Choice Reaction Time (CRT) were completed on the computers at 2-h intervals during selected shifts in the work schedule by maintenance crews and reactor operators. Sleep duration and quality data were also obtained during the 35-day shift cycle. Workload remained relatively stable across shifts. The night-shift was associated with shorter sleep durations and poorer sleep quality. Significantly lower levels of alertness and poorer perforniance for components of the performance tasks were also observed on the night-shift. Tinic-on-shift effects on alertness were evident, where by for the night-shift, especially, alertness dropped dramatically during the early hours. Components of SAM-5 performance showed differential time-on-shift patterning relative to each shift whereas CRT was unresponsive to time-on-shift effects. Significant variations were observed in alertness and performance components during the 12-h night-shift. Perhaps paradoxically, performance on the 12-h night-shift appeared to improve rather than deteriorate during the early-hour period that was associated with the greatest drop in alertness. This was suggestive of extra effort expenditure during this critical period.     

Effects of sleep inertia on cognitive performance following a 1-hour nap

Abstract

This study investigated the effects of a 1-h nap on subsequent performance in spatial memory (SM) and logical reasoning (LR) tasks. The objective was to evaluate the duration of the effects of sleep inertia (SI). The performance was measured in two independent groups of subjects. The 1-h nap took place at 00:00 h in group 1 and at 03:00 h in group 2. In each task, the experimental design comprised one no-nap condition in which subjects had no sleep before the night tests, and a nap condition that comprised the 1-h nap followed by the test sessions. To measure the duration of SI effects, the subjects were tested in two 30-min sessions and the data in each session were analysed in sub-units of time of 3 min each. In each task the results showed no effects on accuracy, and no circadian effects of napping were found. In each task, analyses of pooled data of the two groups showed that the performance in the 1-h nap condition exhibited significant reductions of speed immediately following awakening, when compared with no-nap, reflecting SI effects. In SM, the slowing lasted 24 min, and 27 min in LR. Practical implications of the results are discussed.     

Effects of sleep inertia on cognitive performance following a 1-hour nap

This study investigated the effects of a 1-h nap on subsequent performance in spatial memory (SM) and logical reasoning (LR) tasks. The objective was to evaluate the duration of the effects of sleep inertia (SI). The performance was measured in two independent groups of subjects. The 1-h nap took place at 00:00 h in group 1 and at 03:00 h in group 2. In each task, the experimental design comprised one no-nap condition in which subjects had no sleep before the night tests, and a nap condition that comprised the 1-h nap followed by the test sessions. To measure the duration of SI effects, the subjects were tested in two 30-min sessions and the data in each session were analysed in sub-units of time of 3 min each. In each task the results showed no effects on accuracy, and no circadian effects of napping were found. In each task, analyses of pooled data of the two groups showed that the performance in the 1-h nap condition exhibited significant reductions of speed immediately following awakening, when compared with no-nap, reflecting SI effects. In SM, the slowing lasted 24 min, and 27 min in LR. Practical implications of the results are discussed.     

On-shift and daily variations in self-report and performance measures in rotating-shift and permanent night nurses

An intensive study was conducted of the influence of type of shift system, type of shift, and time-into-shift on a battery of on-shift and daily measures obtained from 61 female nurses over a 28-day period. Thirty-two rotating-shift nurses and 28 permanent night nurses recorded data on a hand-held computer at the start and end of each day, and every 2-h during their shifts. The measures included a sleep diary, self-ratings of mood, workload, and personal disruption, and two cognitive performance tasks. These results suggest that the permanent night nurses were no worse off and for some measures were actually better off than the rotating-shift nurses after controlling for differences in age and shiftwork experience; the night-shift was problematic for the rotating-shift nurses but so was the early shift; mood deteriorated and reaction time got slower over the course of the night-shift but extra long responses (which may correspond to lapses of attention) and rated workload were lower on the night-shift. The relatively large number of consecutive night-shifts worked by the rotating-shift nurses, the uneven distribution of workload between shifts, and the long night-shift may have contributed to these results.     

On-shift and daily variations in self-report and performance measures in rotating-shift and permanent night nurses

Abstract

An intensive study was conducted of the influence of type of shift system, type of shift, and time-into-shift on a battery of on-shift and daily measures obtained from 61 female nurses over a 28-day period. Thirty-two rotating-shift nurses and 28 permanent night nurses recorded data on a hand-held computer at the start and end of each day, and every 2-h during their shifts. The measures included a sleep diary, self-ratings of mood, workload, and personal disruption, and two cognitive performance tasks. These results suggest that the permanent night nurses were no worse off and for some measures were actually better off than the rotating-shift nurses after controlling for differences in age and shiftwork experience; the night-shift was problematic for the rotating-shift nurses but so was the early shift; mood deteriorated and reaction time got slower over the course of the night-shift but extra long responses (which may correspond to lapses of attention) and rated workload were lower on the night-shift. The relatively large number of consecutive night-shifts worked by the rotating-shift nurses, the uneven distribution of workload between shifts, and the long night-shift may have contributed to these results.     

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.     

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.     

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.     

A chronotype circadian model of charismatic leadership expressions and perceptions

We investigate the impact of the circadian process (24-h biological cycles that influence sleep/wake periods) and chronotypes (individual differences in the timing of those cycles) in charismatic leadership. We theorize that the expressions of charismatic signals by leaders, and the perceptions of those signals by followers are influenced by the circadian process. Moreover, considering that individuals vary in their sleep awake preferences (larks vs. owls), we argue that chronotype interacts with time of day to influence expressions and perceptions of charismatic leadership. In Study 1, we found that synchrony between leader chronotype and time of day affects expressions of charismatic leadership. In Study 2, we turned our attention to the followers' circadian process and found that synchrony between a follower's chronotype and time of day affects follower's perceptions of charismatic leadership. Our new model highlights how charismatic leadership can be driven by circadian process.     

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.     

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.     

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.     

Stress states in nuclear operators under conditions of shiftwork

This study examined the stress states experienced by nuclear power operators at work under an existing shift system, time-on-shift effects and the manner in which these states may be moderated by achievement motivation and a sense of coherence. The results show an incidence of stress states during evening shifts and night-shifts in the operators, which are primarily characterized by increased distraction as well as by enhanced sleepiness and low irritability. The night-shift was found to be the most problematic one in terms of increased sleepiness and distractibility, and reduced alertness. An abrupt fall in alertness during the evening shift and a considerably increased distractibility at its end was observed. These facts, as well as the lack of recuperation from daily domestic activities and caring for children at the start of the shift, suggest that besides the night duty, the evening one also constitutes a serious challenge to operational safety at this nuclear facility. Correlations found between personality characteristics and sleepiness, distractibility and irritability, indicate personal resources as important modifiers of stress states. A narrowing in the effects of motivation and sense of coherence was found in the evening shifts and night-shifts. The results have practical implications for intentional modifications of personal resources at nuclear facilities.     

The after-effects of a prolonged period of day-sleep on subjective sleep quality

The effects of day-sleep on the quality ofsleep are not restricted to the night-work period itself. Effects can be measured during night-sleep in the period following night-work. A study on these after-effects, using a self-report instrument to measure sleep quality, is described. A total of N=7O operators wcrc observed over five consecutive undisturbed nights after a working period of seven morning shifts (N= 35) and after a working period of seven night-shifts (N= 35). The quality of sleep during the third night after the night-shift period was still significantly worse than the third night after the rnorning-shift period. No differential (after-)effects were observed with respect to differences in sleep duration.     

Sleep and napping in young shiftworkers: A 5-year follow-up

Abstract

The present study examined sleep characteristics in young workers who entered rapidly rotating shiftwork for the first time and stayed on shifts for 5 years. Data were collected when the subjects had shiftwork experience of approximately 1.5, 3.5 and 5.5 years and a mean age of 22, 24 and 26 years. Data are presented showing significant differences in the main sleep durations between situations within the shift cycle and a small reduction in overall sleep over the observed period, primarily due to a sleep reduction on afternoon shift days. Data on sleep quality did not show any change over this early period of shiftwork exposure. In addition, napping strategies did not change, with the exception of a small increase in those taking naps on night-shift days between 1.5 years and 3.5 years of shiftwork exposure. At all the observed phases there were more young shiftworkers taking a nap on the morning shift days than on the night-shift days. The data suggested that reduced sleeps on morning and night-shift days were not compensated by taking a nap, but rather with an increase in main sleep duration on afternoon shift days and days off. A weak tendency for individuals to be relatively long or short sleepers irrespective of sleep conditions could be seen.     

Stress states in nuclear operators under conditions of shiftwork

Abstract

This study examined the stress states experienced by nuclear power operators at work under an existing shift system, time-on-shift effects and the manner in which these states may be moderated by achievement motivation and a sense of coherence. The results show an incidence of stress states during evening shifts and night-shifts in the operators, which are primarily characterized by increased distraction as well as by enhanced sleepiness and low irritability. The night-shift was found to be the most problematic one in terms of increased sleepiness and distractibility, and reduced alertness. An abrupt fall in alertness during the evening shift and a considerably increased distractibility at its end were observed. These facts, as well as the lack of recuperation from daily domestic activities and caring for children at the start of the shift, suggest that besides the night duty, the evening one also constitutes a serious challenge to operational safety at this nuclear facility. Correlations found between personality characteristics and sleepiness, distractibility and irritability, indicate personal resources as important modifiers of stress states. A narrowing in the effects of motivation and sense of coherence was found in the evening shifts and night-shifts. The results have practical implications for intentional modifications of personal resources at nuclear facilities.     

Do eating and drinking habits interact with work schedule variables?

When compared to day workers, night-shift workers report that they eat fewer meals, have poorer appetites, are less satisfied with their eating habits, and eat at different times of the day. When demographic variables are held constant, there do not appear to be any significant differences between experienced day and night-shift workers in caffeine or alcohol consumption. Exceptions to and variations in these findings are probably due to the background influences of social and cultural variables. Eating and drinking behaviours do effect human performance and mood, but little relevant data have been gathered from experienced night-shift workers. There are no shiftworker data evaluating the effectiveness of the special diets or dietary recommendations that have been proposed for use by night-shift workers. Thus, attempts to manipulate night-shift worker eating and drinking habits require experimental test.