A polysomnographic study of morning and afternoon sleep quality during simulated night shift work

Shiftworkers differ as to scheduling their day sleep between night shifts. An experimental study was carried out to compare the effects of morning and afternoon sleep behaviour on sleep quality within and after a period of seven night shifts. Twelve young males participated in a repeated–measures design, six sleeping in the morning and six in the afternoon after night shifts. Sleep quality was evaluated by polysomnographic and subjective measures. Morning and afternoon sleepers showed some differences in the trend of sleep changes over successive sleep periods. However, at the end of the night shift week, there were no marked differences in sleep quality. Both morning and afternoon sleep were characterized by deep sleep, and short sleep onset latencies.     

A comparison of circadian rhythms in work performance between physically active and inactive subjects

This study compared circadian rhythms in physiological, subjective, and performance measures between groups exhibiting different levels of habitual physical activity. Fourteen male subjects, aged 19–29 years, were assigned to a physically active (group I, n=7) or a physically inactive (group II,n= 7) group on the basis of leisure–time physical activity. Rectal temperature, oral temperature, resting pulse rate, subjective arousal and sleepiness were measured at 02:00,06:00, 10:00, 14:00, 18:00 and 22:00 in a counter–balanced sequence for each subject. Whole–body flexibility, back and leg strength, grip strength (right and left), flight time in a vertical jump, PWC₁₅₀ and self–chosen work–rate were also recorded at each time point. At least 8h separated each test session. Subjects avoided exercise 48h prior to, and during the experiment. Data were subjected to the group cosinor method. Group I evidenced 1·5–2·5 times greater rhythm amplitudes than Group II for oral temperature, subjective arousal, sleepiness, flexibility, left and right grip strength, submaximal heart rate, and self–chosen work–rate (p<0·05). Oral temperature and arousal for Group I were lower than Group II only at 06:00. Early morning troughs in most of the performance measures were significantly greater for Group I (p<005). The groups did not differ with respect to phasing of the rhythms (p<005). These results confirm with physical performance measures that rhythm amplitudes are higher for physically fit subjects. This could be attributed to greater early–morning troughs in the measures for active individuals. Since the subjects were sedentary immediately prior to testing, it is plausible that these findings are training effects of physical activity.     

Sleep in a live-in mining operation: The influence of start times and restricted non-work activities

The amount of sleep obtained between shifts is influenced by numerous factors including the length of work and rest periods, the timing of the rest period relative to the endogenous circadian cycle and personal choices about the use of non-work time. The current study utilised a real-world live-in mining environment to examine the amount of sleep obtained when access to normal domestic, family and social activities was restricted. Participants were 29 mining operators (26 male, average age 37.4 ± 6.8 years) who recorded sleep, work and fatigue information and wore an activity monitor for a cycle of seven day shifts and seven night shifts (both 12 h) followed by either seven or fourteen days off. During the two weeks of work participants lived on-site. Total sleep time was significantly less (p < 0.01) while on-site on both day (6.1 ± 1.0 h) and night shifts (5.7 ± 1.5 h) than days off (7.4 ± 1.4 h). Further, night shift sleep was significantly shorter than day-shift sleep (p < 0.01). Assessment of subjective fatigue ratings showed that the sleep associated with both days off and night shifts had a greater recovery value than sleep associated with day shifts (p < 0.01). While on-site, participants obtained only 6 h of sleep indicating that the absence of competing domestic, family and social activities did not convert to more sleep. Factors including shift start times and circadian influences appear to have been more important.     

The prediction of the adaptation of circadian rhythms to rapid time zone changes

The aim of the study was to find out which factors could explain individual differences in the resynchronization speed of circadian rhythms of salivary melatonin and subjective alertness after transmeridian flights over 10 time zones. The mean age of the 40 female subjects was 33·0 ±6·9 years. The data were gathered by measurements of the circadian rhythms of melatonin excretion and ahertness at 2 h intervals in Helsinki (Finland) two days before westward flight to Los Angeles (USA), where the measurements were repeated on the 2nd day after the flights and on the 2nd day in Finland after return flight. This shift in the acrophases of the two circadian rhythms were used as dependent variables in regression analyses. The predictors used were length of day, marital status, amount of physical exercise, age, neuroticism, extroversion, and eveningness. Age, day length, marital status, and physical exercise explained the acrophase adaptation of the melatonin rhythm after westward flight, and day length, neuroticism, and extroversion after eastward flight. Marital status, neuroticism, and physical exercise explained the variation of the acrophase adjustment of the alertness rhythm after westward flight, and age and eveningness after eastward flight. It is concluded that the amount of daylight and personality are the best predictors of the circadian rhythm adaptation after transmeridian flights.     

Sleep patterns,shiftwork, and individual differences: a comparison of onshore and offshore control-room operators

Abstract

The sleep patterns of offshore control-room operators were compared with those of personnel carrying out similar work onshore, taking into account individual differences in age, number of years of shiftwork, and neuroticism. The dependent variables were self-reported sleep quality and duration for day-shift (D-S) and night-shift (N-S) work, and during leave periods (L-P) Offshore workers reported longer N-S sleep duration, and lower D-S sleep quality than those onshore, but the two groups did not differ in L-P measures. The effects of environmental differences (onshore versus offshore) on sleep patterns were more marked than those of the two different shift systems (weekly rotation and fast rotation) in operation onshore. Age was negatively related to both duration and quality of sleep; over and above age, number of years of shiftwork was negatively related to sleep duration. Neuroticism was also negatively related to sleep duration and, more strongly, to sleep quality. These findings are discussed in relation to the literature on shiftwork and sleep in general, and the characteristics of the offshore environment in particular     

Individual differences in circadian rhythm parameters and short-term tolerance to shiftwork: a follow-up study

The relationship between individual differences in the phase and amplitude of circadian rhythms and tolerance to shiftwork has been the subject of several studies. Those studies recorded circadian rhythms and shiftwork tolerance at approximately the same time. The present study aimed to examine the predictive relationships between the amplitude, phase, and mesor of 24 h rhythms obtained before exposure to shiftwork, and subsequent indices of tolerance measured after one and three years of shiftwork. The results revealed some stable relations between the various rhythm parameters and subsequent tolerance measures. Workers who had a higher mesor of positive moods, and a lower mesor of negative moods and fatigue, before entering shiftwork tended to tolerate shiftwork better. Further, those whose heart rate rhythm showed an earlier acrophase had better subsequent sleep quality scores, while those with a smaller amplitude of their temperature, negative mood and fatigue rhythms showed better night-shift tolerance.     

Qualitative changes in recall memory during day and night shifts

The effect of time of day on recall of words and drawings was studied in 29 French shiftworkers. Tests were carried out at 18:00, 22:00, 02:00 and 06:00. The task involved memorizing a list of 18 drawings for one half of the group, and 18 words (designating the corresponding figures) for the other half. At each time of day, the lists were presented both with and without an interpolated task. In the interpolated task condition, the first 9 items were followed by an interpolated imagery task and the last 9 by a spelling task, or vice versa. The results indicated an overall effect of time of day on the recall test, especially when memorizing drawings. At 18:00 in both the control and the interference condition, subjects recalled more words and drawings from the beginning of the list. Conversely, at 02:00, subjects recalled more words and drawings from the end of the list. The time spent in the interpolated comparison task varied with the time of day and was longer when memorizing drawings. The same time of day pattern of performance was found for spelling times. The implications upon issues concerning shiftwork and job demands are also discussed.     

Hours of work at sea: watchkeeping schedules,circadian rhythms and efficiency

Abstract

This review is concerned with the hours of work of personnel engaged in watchkeeping duties on board ocean-going vessels plying between distant ports. After an introduction to the general problem, existing research findings are considered in the context of the degree of adjustment shown by physiological and performance rhythms to the various watchkeeping systems in use on different types of ship. The findings are discussed in relation to a proposed programme of research aimed at determining the optimal system for maintaining efficiency in crews operating the modern, fully automated vessels now coming into service.     

Personality differences in the phase of circadian rhythms: a comparison of morningness and extraversion

Abstract

Individual differences in the phase of circadian (around 24 h) rhythms are thought to be important in determining adjustment to shift work and rapid time-zone transitions. Attempts to predict such phase differences on the basis of paper and pencil ‘personality’ tests have concentrated on extraversion and morningness, of which Kerkhof (1985), in a recent review of this literature, concluded morningness was the more important. However, the literature on which this conclusion was based suffers from a number of problems. The present study attempted to overcome these problems by examining the trends over a complete 24 h cycle for a range of performance and psychophysiological measures in students with extreme scores for both extraversion and morningness. In general, the results support KerkhoFs conclusion. However, reliable phase differences associated with morningness were confined to subjective ratings of alertness, oral temperature, and, in combination with extraversion, choice reaction time. Two alternative interpretations of this pattern of results are considered, and their practical implications discussed.     

Productivity on a weekly rotating shift system: circadian adjustment and sleep deprivation effects?

Abstract

There is little doubt that productivity and safety can be impaired on the night shift. Two main factors have been identified that may be responsible for this. On the one hand, the circadian rhythm in performance on at least simple tasks is at a low ebb at night, and adjusts only slowly over a span of night shifts. On the other, the day sleeps of shift workers taken between night shifts are of a reduced duration, and thus a cumulative sleep debt may accrue over successive night shifts. The former thus predicts that productivity should improve over a span of night duty, while the latter predicts that it should decline. We have examined the productivity of 53 female shift workers, and the sleeping habits of a sub-sample of 30 of them, on a weekly rotating shift system in order to assess the relative contribution of these two factors. Our results suggest that circadian adjustment to night work is the dominant factor for the first three or four successive nights shifts, but that sleep deprivation effects may then result in a decrease in productivity over subsequent nights. They also indicate that sleep deprivation, but not circadian adjustment, may affect the productivity of some workers when on the morning shift.     

A field study of sleep and fatigue in a regular rotating 12-h shift system

The aim of this study was to examine a regular rotating 12-h shift system (2D2N4Off) at an Australian Smelter. Sleep behavior, subjective fatigue and neurobehavioral performance were investigated over a 14-day period for 20 employees. Activity monitors, sleep/wake diaries, and 5-min psychomotor vigilance tasks were used. Sleep data showed differences between day and night shifts. While sleep prior to night1 was increased relative to day shifts, a reduced sleep length carried into the period leading to night2. Total wakefulness at the end of shift, and subjective fatigue were increased for night shifts, particularly night1. Decrements in performance data supported these findings. Both prior wakefulness and prior sleep are important in a 12-h shift system. Employees may “sleep in” after day shifts, rather than taking extra sleep prior to night work. Thus, sleep between day and night shifts is based on recovery rather than preparation.     

Circadian rhythms in deep body temperature,urinary excretion and alertness in nurses on night work

Fourteen volunteer nurses who worked on the night shift at a local hospital recorded their times of sleep, mealtimes and any illness or complaints for 12 consecutive days which included at least one spell of night work and rest days. Whilst awake they made regular assessments of their alertness and collected frequent urine samples for analysis of the rate of excretion of a number of constituents. Rectal temperatures were automatically recorded throughout the day and night. Volunteers were divided into those who worked 1–3 successive nights (short term) and those who worked longer ‘blocks’ (long term). There was no difference between the two groups when their subjective assessment of alertness during night work was considered and in both groups there was a similar change in circadian rhythms when rest days and work days were compared. However, there were differences in the amount of day-time sleep that was taken, the temperatures measured, both on and off duty, between 20.00 and 08.00 hours and the number of complaints recorded. These differences are discussed in terms of the ‘commitment’ of individuals to night work and of the possibility that this will change with family and social factors.     

Individual differences in tolerance to shiftwork: a review

Individual differences in the subjective health effects of shiftwork are reviewed. Circadian regulation and brain restitution (sleep) are the crucial mechanisms by which inter-individual factors can affect tolerance to shiftwork. On the other hand, shiftworkers can use different coping mechanisms by trying to schedule their lives and especially their sleeping habits to work at unusual hours. Individual factors related to shiftwork tolerance are discussed in two groups; first, the factors which affect primarily the circadian adjustment; and, second, the factors which mainly relate to the ability to sleep at unusual hours. The significance of circadian adjustment in shiftwork tolerance is outlined.     

The effect of four-day round trip flights over 10 time zones on the circadian variation of salivary melatonin and Cortisol in airline flight attendants

The effects of four-day round flights (Helsinki-Los Angeles-Seattle-Helsinki) were studied on the circadian rhythms of salivary melatonin (MT) and Cortisol (COR) in 35 flight attendants. The mean age of the subjects was 33 ± 7 years (median 34, range 21-50). Five 24 h profiles of unstimulated saliva were collected at 2 h intervals (except at 04:00) before, during, and after the four day flight. Salivary MT and COR were determined by radioimmunoassay. Both MT and COR exhibited a clear circadian rhythm with acrophases before the flight at 03:03 (MT) and 09:08 (COR). Two days after the westward flight from Helsinki to Los Angeles, the MT rhythm (circadian acrophase) had delayed 4 h 51 min and the COR rhythm 3 h 55 min compared to the control day before the flight. Two days later, during the last day in the USA, the MT rhythm had delayed 5 h 59 min and the COR rhythm 5 h 29 min as compared to the situation before the flight. After four days of the eastward flight from Seattle to Helsinki, the circadian acrophase of MT was still 1 h 35 min delayed compared to the control day before the westward flight. The results indicate that the restitution time of five days at the home base is on the average proper for recovery, if a four day round flight over 10 time zones takes four days or less. The resynchronization rate of salivary hormones after westward, outgoing flights is faster than the resynchronization rate after the eastward return flights.     

Individual differences in night and continuously-rotating shiftwork: seeking anticipatory rather than compensatory strategy

Individual differences in adaptation to night or continuously-rotating shiftwork may reflect distinct strategies of coping with temporal challenges of the environment. Rather than studying compensatory mechanisms, we have chosen the anticipatory response of the sleep onset time preceding work in order to reveal the strategy used by workers submitted to those shift systems including night work. Comprehensive interviews, taking into account several aspects of the workers' lives, allowed for a classification of the subjects in terms of adaptation to their working schedules. Night workers go to bed once a day, whereas shiftworkers prefer to allocate their sleep onsets to two different periods of the day. For both cases, the more well-adapted an individual is, according to the classification obtained by the interviews, the more regular will be the choice of sleep onset times.     

Team adaptation to electronic communication media: evidence of compensatory adaptation in new product development teams

Prior research on the use of electronic communication media by teams performing complex tasks has led to contradictory findings. Much research has suggested that electronic communication media, due to not incorporating important elements found in face-to-face communication, pose obstacles for communication in comparison with the face-to-face medium. On the other hand, research has also suggested that teams interacting primarily electronically could perform quite well, sometimes even better, than face-to-face teams. A new theoretical framework, which builds on the notion of compensatory adaptation, has recently been advanced to explain these contradictory findings, arguing that (a) electronic communication media do pose obstacles to communication, and (b) individuals working in teams often compensate for obstacles posed by electronic communication media, which sometimes leads to team outcomes that are just as good or even better than those achieved by similar groups interacting primarily face-to-face. This study tests compensatory adaptation theory through a survey of 462 new product development teams, and finds general support for the theory. Important implications for research and practice are also discussed.     

NeuralSens: A neural network based framework to allow dynamic adaptation in wireless sensor and actor networks

Wireless Sensor and Actor Networks (WSANs) constitute a new way of distributed computing and are steadily gaining importance due to the wide variety of applications that can be implemented with them. As a result they are increasingly present everywhere (industry, farm use, buildings, etc.). However, there are still many important areas in which the WSANs can be improved. One of the most important aspects is to give the sensor networks the capability of being wirelessly reprogrammed so that developers do not have to physically interact with the sensor nodes. Many proposals that deal with this issue have been proposed, but most of them are hardly dependent on the operating system and demand a high energy consumption, even if only a small change has been made in the code. In this work, we propose a new way of wirelessly reprogramming based on the concept of neural networks. Unlike most of the existing approaches, our proposal is independent of the operating system and allows small pieces of code to be reprogrammed with a low energy consumption. The architecture developed to achieve that is described and case studies are presented that show the use of our proposal by means of practical examples.     

Role network measures to assess healthcare team adaptation to complex situations: the case of venous thromboembolism prophylaxis

Hospitals are complex environments that rely on clinicians working together to provide appropriate care to patients. These clinical teams adapt their interactions to meet changing situational needs. Venous thromboembolism (VTE) prophylaxis is a complex process that occurs throughout a patient’s hospitalisation, presenting five stages with different levels of complexity: admission, interruption, re-initiation, initiation, and transfer. The objective of our study is to understand how the VTE prophylaxis team adapts as the complexity in the process changes; we do this by using social network analysis (SNA) measures. We interviewed 45 clinicians representing 9 different cases, creating 43 role networks. The role networks were analysed using SNA measures to understand team changes between low and high complexity stages. When comparing low and high complexity stages, we found two team adaptation mechanisms: (1) relative increase in the number of people, team activities, and interactions within the team, or (2) relative increase in discussion among the team, reflected by an increase in reciprocity.

 

Practitioner Summary: The reason for this study was to quantify team adaptation to complexity in a process using social network analysis (SNA). The VTE prophylaxis team adapted to complexity by two different mechanisms, by increasing the roles, activities, and interactions among the team or by increasing the two-way communication and discussion throughout the team. We demonstrated the ability for SNA to identify adaptation within a team.