The relationship between subjective and objective sleepiness and performance during a simulated night-shift with a nap countermeasure

The aim of the present study was to investigate the relationship between perceived and actual sleepiness and performance during a simulated night-shift that included a 30-min night-nap as an on-duty sleepiness countermeasure. Twenty-four healthy young adults (nine males, fifteen females) participated in a repeated measures design comprising two experimental conditions: no night-nap and 30-min night-nap. Both groups were given a 2-h prophylactic afternoon sleep opportunity (1500-1700 h). Measures of subjective sleepiness (Stanford Sleepiness Scale, Karolinska Sleepiness Scale and Visual Analogue Scale), objective sleepiness (sleep latency tests), objective performance (Symbol-Digit Substitution Task) and reaction time (Psychomotor Vigilance Task) were taken before the night-nap (0230 h) and at several intervals post-nap. Time-series correlation analyses indicated that subjective sleepiness was less correlated with objective sleepiness and objective performance when participants were given a 30-min night-nap. However subjective sleepiness and reaction time performance was strongly correlated in both conditions, and there was no significant difference between the nap and no-nap conditions. Consistent with previous research, results of the present study indicate that subjective and objective indicators of sleepiness and performance may not always correspond, and this relationship may be reduced by the inclusion of a night-nap.     

The relationship between subjective and objective sleepiness and performance during a simulated night-shift with a nap countermeasure

The aim of the present study was to investigate the relationship between perceived and actual sleepiness and performance during a simulated night-shift that included a 30-min night-nap as an on-duty sleepiness countermeasure. Twenty-four healthy young adults (nine males, fifteen females) participated in a repeated measures design comprising two experimental conditions: no night-nap and 30-min night-nap. Both groups were given a 2-h prophylactic afternoon sleep opportunity (1500–1700 h). Measures of subjective sleepiness (Stanford Sleepiness Scale, Karolinska Sleepiness Scale and Visual Analogue Scale), objective sleepiness (sleep latency tests), objective performance (Symbol–Digit Substitution Task) and reaction time (Psychomotor Vigilance Task) were taken before the night-nap (0230 h) and at several intervals post-nap. Time–series correlation analyses indicated that subjective sleepiness was less correlated with objective sleepiness and objective performance when participants were given a 30-min night-nap. However subjective sleepiness and reaction time performance was strongly correlated in both conditions, and there was no significant difference between the nap and no-nap conditions. Consistent with previous research, results of the present study indicate that subjective and objective indicators of sleepiness and performance may not always correspond, and this relationship may be reduced by the inclusion of a night-nap.     

Who is sleepier on the night shift? The influence of bio-psycho-social factors on subjective sleepiness of female nurses during the night shift

Sleepiness is a common complaint during the night shift and may impair performance. The current study aims to identify bio-psycho-social factors associated with subjective sleepiness during the night shift. Ninety-two female nurses working rotating shifts completed a sociodemographic questionnaire, the Munich ChronoType Questionaire for shift workers, the Pittsburg Sleep Quality Index, and the Pre-sleep Arousal Scale. Subjective sleepiness was measured hourly during two night shifts using the Karolinska Sleepiness Scale, and activity monitors assessed sleep duration 24-h before each shift. Findings showed that increased sleepiness was associated with increased age in nurses with early chronotypes and with more children. High cognitive pre-sleep arousal, but not sleep, was associated with increased sleepiness, especially in late chronotypes. The impact of bio-psycho-social factors on night shift sleepiness is complex, and depends on mutual interactions between these factors. Nurses most prone to increased sleepiness must develop personal strategies for maintaining vigilance on the night shift.

Practitioner Summary: This study aims to identify bio-psycho-social factors associated with subjective sleepiness of female nurses during the night shift. Increasing sleepiness was associated with increased age in nurses with early chronotypes and with more children. Increased cognitive pre-sleep arousal, but not sleep, was associated with increased sleepiness, especially in late chronotypes.     

The effects of a self-selected nap opportunity on the psychophysiological,performance and subjective measures during a simulated industrial night shift regimen

This study compared the effects of a 1 h self-selected recovery period to those of a standard night shift arrangement (with a total break time of 1-h) over a simulated three-day night shift schedule in a laboratory setting. Results showed that the inclusion of the flexible nap scheme resulted in higher performance output, improvements in physiological strain responses and reduced sleepiness during each night shift and generally over the three-night cycle. Certain variables also revealed the impact of napping compared with the standard rest break condition on the circadian rhythm. The sleep diary records show that the inclusion of the current intervention did not significantly reduce daytime recovery sleep. The results suggest that the potential benefits of flexible napping may outweigh the logistical effort it requires in a workplace environment.

Practitioner summary: Consensus on appropriate napping strategies for shift work remains a challenge. This simulated night shift laboratory study sought to determine the effects of a 1-h self-selected nap opportunity relative to a normal shift set-up. The nap improved performance and decreased sleepiness, without affecting daytime sleep.     

The night float paradigm to decrease sleep deprivation: good solution or a new problem?

In the late 1980s physician residency training programs developed the night float rotation, characterized by a sequence of 5 - 15 days of night work without any daytime duties, thereby involving an abrupt reversal of the wake - sleep schedule. We examined the effect of the night float rotation on sleep, mood and performance of pediatric residents. Residents completed sleep diaries daily, and tests of mood (Profile of Mood States) and attention (Conner's Continuous Performance Test) three times a week during the two-week night float rotation, and during equivalent blocks of time of their daytime rotations. Results show that, despite having ample opportunity to sleep during the day, while on night float rotation residents slept less than during the nights of their normal daytime rotations, 6.3 h +/- 2.5 h and 7.2 h +/- 1.7 h, respectively, p < 0.0001. Also, during night float compared to daytime rotations residents had increased fatigue-inertia scores, 8.7 +/- 4.1 and 4.8 +/- 2.4, respectively, p < 0.0001, and decreased vigor-activity scores 10.7 +/- 5.4 and 14.8 +/- 5.3, respectively, p = 0.02. The scores for attention were not significantly different between night float and daytime rotations. The correlation coefficients of fatigue with measures of attention were not statistically significant for daytime rotations. However, for night float fatigue correlated with omission errors, r = 0.51, p = 0.001 and with attentiveness r = - 0.36, p = 0.03. Training programs that adopt the night float rotation must be aware of potential deleterious effects of the night float rotation as they may lead to serious consequences on residents' performance and patients' safety.     

Sleepiness in long distance truck driving: an ambulatory EEG study of night driving

Eighteen truck drivers had their EEG recorded continuously during a night or evening drive between southern Sweden and Stockholm (500 km). They also carried out self ratings of sleepiness and performance every hour. The EEG was subjected to spectral analysis. The drivers were divided into two groups with a night group (n = 7) who drove between 20:30 to 07:20, and an evening group (n = 11) who drove between 18:20 and 04:00. The night group showed higher subjective sleepiness and lower subjective performance, and increased alpha and theta burst activity during the last three hours of the drive. The groups did not differ for the first 2-3?h of the drive. For the night group, a significant intraindividual correlation was found between subjective sleepiness and EEG alpha burst activity. End-of-the-drive subjective sleepiness and alpha burst activity were significantly correlated with total work hours and arrival time but not with age, diurnal type, prior (rated) sleep length, total break time, drive time or prior time awake. A regression analysis showed that total work hours and total break time predicted 66% of the variance of alpha burst activity during the end of the drive.     

The night float paradigm to decrease sleep deprivation: good solution or a new problem?

In the late 1980s physician residency training programs developed the night float rotation, characterized by a sequence of 5 - 15 days of night work without any daytime duties, thereby involving an abrupt reversal of the wake-sleep schedule. We examined the effect of the night float rotation on sleep, mood and performance of pediatric residents. Residents completed sleep diaries daily, and tests of mood (Profile of Mood States) and attention (Conner's Continuous Performance Test) three times a week during the two-week night float rotation, and during equivalent blocks of time of their daytime rotations. Results show that, despite having ample opportunity to sleep during the day, while on night float rotation residents slept less than during the nights of their normal daytime rotations, 6.3 h ± 2.5 h and 7.2 h ± 1.7 h, respectively, p < 0.0001. Also, during night float compared to daytime rotations residents had increased fatigue-inertia scores, 8.7 ± 4.1 and 4.8 ± 2.4, respectively, p < 0.0001, and decreased vigor-activity scores 10.7 ± 5.4 and 14.8 ± 5.3, respectively, p = 0.02. The scores for attention were not significantly different between night float and daytime rotations. The correlation coefficients of fatigue with measures of attention were not statistically significant for daytime rotations. However, for night float fatigue correlated with omission errors, r = 0.51, p = 0.001 and with attentiveness r = ?0.36, p = 0.03. Training programs that adopt the night float rotation must be aware of potential deleterious effects of the night float rotation as they may lead to serious consequences on residents' performance and patients' safety.     

Influence of shift work in process industry on workers' occupational health,productivity, and family and social life: An ergonomic approach

Shift work is a major feature of modern work practices. It involves working at times considered unconventional for most workers, such as at night. Although the community often benefits from such work practices, shift work can be hazardous for both the workers and the community. There are increased risks for accidents and errors, increased sleepiness and fatigue due to difficulties sleeping, increased health problems, and disruptions to family and social life. More shift workers complained of sleep disturbance, poor sleep quality, tiredness at awakening, and sleepiness in work than did non‐shift workers. More shift workers also complained of gastrointestinal disturbances than did non‐shift workers. The aim of this article is to provide general information on shift work, work schedules, and the effects of work schedules on sleep, fatigue, performance, the health of the human operator, and productivity. © 2010 Wiley Periodicals, Inc.     

The effect of night-time naps on recovery from fatigue following night work

Abstract

A questionnaire was performed in order to investigate the effect of naps during duty on recovery from fatigue. Studies were performed on 12 male computer operators in each of two chemical plants working a four-team three-shift system. In one of the plants, the shift workers were able to take a 2 h nap during the night shift (nap group). In the other plant, no nap was taken (no-nap group). Before and after the two consecutive night shifts, both the nap and no-nap groups greatly extended their night sleeps, but the daytime sleep taken by the no-nap group during this period was significantly longer than that of the nap group on both the first and second days. No significant difference was found when comparing the length of the day sleep of the no-nap group with the total sleeping time (night-time nap plus subsequent day sleep) of the nap group. Therefore a night-time nap enables part of the essential sleep to be taken in advance of the day sleep following night work. During night work, both tbe nap and no-nap groups exhibited an increase in the sleepiness scores and also in the subjective feelings of fatigue concerning the complaints related to drowsiness, dullness and difficulty in concentration. However, it was found that for the no-nap group these effects continued for a large part of the recovery period following night work. It can therefore be surmised that naps taken during night-time work can be to a certain extent aid recovery from the fatigue caused by that work.     

Portable devices for measuring performance in the field: The effects of sleep deprivation and night shift on the performance of computer operators

The performance of twelve computer operators was measured in the field, on two new portable tests of reaction time, during the first night of the night shift at 0400 h and at the beginning day shift (0800 h), over three successive three-week comparisons. The results were: (i) mean reaction time increased significantly on the night shift as compared with the day: (ii) the adverse effect of the night shift was absent during the first comparison and became increasingly apparent on the second and third replications. These results: (i) provide evidence of inferior performance on the night as compared with the day shift in the field : (ii) show that data from previous studies of sleep deprivation in the laboratory are able to provide a good indication of what was to be expected in the field: (iii) emphasize the need for longitudinal studies in order to assess the true effects of stressful influences.     

Sleep and sleepiness following a behaviourally ‘active’ day

During 4 day periods in which a total of nine subjects expected to spend each daytime under relatively stereotyped environmental conditions, a substitution was made for 1 day (experimental day) on a random basis. Here, subjects spent the time in a variety of novel, interesting and perceptually stimulating environments. Sleep EEG recordings were made each night following an adaptation night. Self-assessment sleepiness ratings were made night and morning. Following the experimental day subjects felt significantly more sleepy at bedtime, and sleep onset latency was significantly reduced. Although sleep length was unchanged, deep (slow wave) sleep, particularly stage 4 sleep, was increased significantly. There was some increase in sleep disturbance. REM sleep was unaffected. Subjects awoke feeling refreshed the next day. There was a small but significant carryover of a further SWS increase in the first part of the following night.     

Systematic review of the relationship between quick returns in rotating shift work and health-related outcomes

A systematic literature search was carried out to investigate the relationship between quick returns (i.e. 11.0 hours or less between two consecutive shifts) and outcome measures of health, sleep, functional ability and work–life balance. A total of 22 studies published in 21 articles were included. Three types of quick returns were differentiated (from evening to morning/day, night to evening, morning/day to night shifts) where sleep duration and sleepiness appeared to be differently affected depending on which shifts the quick returns occurred between. There were some indications of detrimental effects of quick returns on proximate problems (e.g. sleep, sleepiness and fatigue), although the evidence of associations with more chronic outcome measures (physical and mental health and work–life balance) was inconclusive.

Practitioner Summary: Modern societies are dependent on people working shifts. This study systematically reviews literature on the consequences of quick returns (11.0 hours or less between two shifts). Quick returns have detrimental effects on acute health problems. However, the evidence regarding effects on chronic health is inconclusive.     

The use of prophylactic naps and caffeine to maintain performance during a continuous operation

After a normal baseline night of sleep and a morning of baseline test performance, 24 young adult male subjects returned to bed from 16:00-20:00 prior to a 24?h period of sleep loss. Twelve subjects received caffeine 200?mg at 01:30 and 07:30. Performance tests (correctly completed addition problems, vigilance sensitivity, and logical reasoning correct responses) all indicated maintenance of baseline performance levels in the caffeine group after administration of caffeine while performance declined in the placebo group. Similar results were found for the Multiple Sleep Latency Test and Oral Temperature, which both remained near baseline levels throughout the observation period in subjects receiving caffeine. The results indicated that the combination of a prophylactic nap and caffeine was more effective in maintaining nocturnal alertness and performance than was the nap alone. Of more interest was the fact that the group which was given the combination of nap and caffeine was able to maintain alertness and performance at very close to baseline levels throughout a 24?h period without sleep.     

The role of naps in alleviating sleepiness during an irregular sleep-wake schedule

Abstract

Four groups of four subjects have been studied in an isolation unit on an irregular schedule of sleep and waking. Sleep periods of 6h duration were taken at irregular times during the 9-day protocol; they were arranged such that the waking periods lasted 6, 12 or 18 h and were also in an irregular sequence. One-hour naps were taken after 6 and 12 h of waking if the next sleep was not due then. Just before either a nap or a full sleep, subjects assessed their sleepiness and, on rising, they assessed how well sleep had been initiated and maintained. A mathematical model was developed which enabled the effects upon sleepiness of circadian rhythmicity, of the length of the waking period since the last full sleep (time-since-sleep), and of the subjective value of the previous full sleep or nap to be independently quantified. Results showed that there was a tendency for sleepiness to increase, in some cases quite markedly, as the irregular schedule proceeded. There were also effects upon sleepiness due to circadian changes and the amount of time since the last full sleep. These two effects were similar in size and larger than the benefits to be derived from a previous nap or full sleep that had been assessed at the time as having been a good one. We conclude that one-hour naps can play a small role in decreasing an individual's sleepiness and suggest possible means by which their subjective value might be increased.     

A quantitative model of work-related fatigue: empirical evaluations

Systematic and quantitative management of work-related fatigue within workplaces has been a challenging task due to a lack of useful tools. A previous paper provided background and development of a work-related fatigue modelling approach. The current paper outlines model evaluations using sleep deprivation experiments and recommendations of work scheduling. Previous studies have reported cumulative effects of sleep restriction (4-5 h per night) on a number of measures. Model predictions were correlated against psychomotor vigilance task lapses (r = 0.92) and reaction time responses (slowest 10%, r = 0.91) as well as sleep latency (r = -0.97). Further correlations were performed on four measures from a 64 h continuous sleep deprivation study; that is objective vigilance (r = -0.75) as well as subjective performance (r = -0.75), sleepiness (r = 0.82) and tiredness (r = 0.79). Evaluation against current scheduling recommendations illustrated consistency with the literature with the exception that forward rotation did not provide benefits over backward rotation. The results indicate that model predictions correlate well across a range of objective and subjective measures. This relationship also appears to hold for cumulative and continuous sleep deprivation protocols. Future studies will also focus on field-based evaluation.     

Can small shifts in circadian phase affect performance?

Small shifts in circadian timing occur frequently as a result of daylight saving time or later weekend sleep. These subtle shifts in circadian phase have been shown to influence subjective sleepiness, but it remains unclear if they can significantly affect performance. In a retrospective analysis we examined performance on the Psychomotor Vigilance Test before bedtime and after wake time in 11 healthy adults on fixed sleep schedules based on their habitual sleep times. The dim light melatonin onset, a marker of circadian timing, was measured on two occasions. An average 1.1?h shift away from a proposed optimal circadian phase angle (6?h between melatonin onset and midpoint of sleep) significantly slowed mean, median and fastest 10% reaction times before bedtime and after wake time (p?相似文献   

Vigilance on the civil flight deck: incidence of sleepiness and sleep during long-haul flights and associated changes in physiological parameters

The study investigated sleepiness and sleep in aircrew during long-haul flights. The objectives were to identify loss of alertness and to recommend a practical approach to the design of an alerting system to be used by aircrew to prevent involuntary sleep. The flights were between London and Miami, covering both day- and night-time sectors, each with a duration of ~9 h. The subjects were 12 British Airways pilots. Various physiological variables were measured that could potentially be used to indicate the presence of drowsiness and involuntary sleep: brain electrical activity (electroencephalogram, EEG), eye movements via the electro-oculogram (EOG), wrist activity, head movements and galvanic skin resistance. The EEG and EOG identified sleepiness and sleep, as well as being potential measures on which to base an alarm system. Ten pilots either slept or showed evidence of sleepiness as assessed by the EEG and EOG. Many of the episodes of sleepiness lasted < 20 s, which could mean that the subjects were unaware of their occurrence and of the potential consequences on performance and vigilance. All physiological parameters showed changes during sleep, although only the EEG and EOG were modified by sleepiness. During sleep, skin resistance was increased, and wrist activity and head movements were absent for long periods. The study indicated that the measurement of eye movements (either alone or in combination with the EEG), wrist activity or head movement may be used as the basis of an alarm system to prevent involuntary sleep. Skin resistance is considered to be unsuitable, however, being related in a more general way to fatigue rather than to sleep episodes. The optimal way to monitor the onset of sleep would be to measure eye movements; however, this is not feasible in the flight deck environment at the present time due to the intrusive nature of the recording methodology. Wrist activity is therefore recommended as the basis of an alertness alarm. Such a device would alert the pilot after ~4–5 min of wrist inactivity, since this duration has been shown by the present study to be associated with sleep. The possibility that sleep inertia (reduced alertness immediately after awakening from sleep) could follow periods of sleep lasting 5 min needs to be considered. The findings reported here might be applicable to other occupational environments where fatigue and sleepiness are known to occur.     

Vigilance on the civil flight deck: incidence of sleepiness and sleep during long-haul flights and associated changes in physiological parameters

The study investigated sleepiness and sleep in aircrew during long-haul flights. The objectives were to identify loss of alertness and to recommend a practical approach to the design of an alerting system to be used by aircrew to prevent involuntary sleep. The flights were between London and Miami, covering both day- and night-time sectors, each with a duration of approximately 9 h. The subjects were 12 British Airways pilots. Various physiological variables were measured that could potentially be used to indicate the presence of drowsiness and involuntary sleep: brain electrical activity (electroencephalogram, EEG), eye movements via the electro-oculogram (EOG), wrist activity, head movements and galvanic skin resistance. The EEG and EOG identified sleepiness and sleep, as well as being potential measures on which to base an alarm system. Ten pilots either slept or showed evidence of sleepiness as assessed by the EEG and EOG. Many of the episodes of sleepiness lasted < 20 s, which could mean that the subjects were unaware of their occurrence and of the potential consequences on performance and vigilance. All physiological parameters showed changes during sleep, although only the EEG and EOG were modified by sleepiness. During sleep, skin resistance was increased, and wrist activity and head movements were absent for long periods. The study indicated that the measurement of eye movements (either alone or in combination with the EEG), wrist activity or head movement may be used as the basis of an alarm system to prevent involuntary sleep. Skin resistance is considered to be unsuitable, however, being related in a more general way to fatigue rather than to sleep episodes. The optimal way to monitor the onset of sleep would be to measure eye movements; however, this is not feasible in the flight deck environment at the present time due to the intrusive nature of the recording methodology. Wrist activity is therefore recommended as the basis of an alertness alarm. Such a device would alert the pilot after approximately 4-5 min of wrist inactivity, since this duration has been shown by the present study to be associated with sleep. The possibility that sleep inertia (reduced alertness immediately after awakening from sleep) could follow periods of sleep lasting 5 min needs to be considered. The findings reported here might be applicable to other occupational environments where fatigue and sleepiness are known to occur.     

The Effect of Repetition of Relevant and Irrelevant Tasks over Day and Night Work Periods

Abstract

The effects of repetition on the Wilkinson Vigilance Task and an unobtrusive performance measure (crossword completion) were examined in 18 subjects over two 8 h work periods. Vigilance trials alternated with breaks in 25min segments across a work period from 0900 to 1700 h and a period from 2400 to 0800 h. Performance decrements were seen in hit rate and on the irrelevant task measure across the night session, and in hit rate across the day session. Decrements were greater at night than during the day on both measures. The number of attempts on the vigilance task decreased across trials similarly in both testing sessions. It was concluded that specific task repetition results in performance decrements, even when circadian incremental effects would be predicted, and that the placement of such task repetition at night magnifies those decrements and extends them to intrinscially as well as extrinsically motivated tasks.     

Sleep-loss,Noise and Decisions

Abstract

Twelve subjects were given a visual detection task under three sleep schedules: normal 8 h sleep; 4 h sleep at night and 4 h sleep in the afternoon. Ninety-five dB white noise accompanied some tests. The results, in the form of confidence ratings, were analysed by means of statistical decision theory. Time on task made cautious performance more cautious, and sleep-loss made it more risky. Noise caused a rise in the risky criterion. There was some evidence that, in combination, noise and sleep-loss had mutually antagonistic effects on discriminability, and cancelled out each other's effects on the cautious criterion placement.