Sleepiness/alertness on a simulated night shift schedule and morningness-eveningness tendency.

This study examined the influence of morningness-eveningness on night shift sleepiness in 15 subjects. Sleepiness was assessed during a five-night protocol involving the multiple sleep latency test (MSLT), repeated test of sustained wakefulness (RTSW) and the Stanford Sleepiness Scale (SSS). Daytime sleep was estimated by sleep diaries and wrist actigraphy. The sample was divided by median score on the Horne and Ostberg Morningness-Eveningness Questionnaire. Physiological sleep tendency was significantly worse between 0030 and 0430 hours for the Morning Tendency group than for the Non-Morning Tendency group. The Morning Tendency group reported obtaining less daytime sleep than the Non-Morning Tendency group; however, there was no difference between groups in total daytime sleep estimated by actigraphy. This preliminary study suggests that morning types are sleepier during night shift hours than non-morning types.     

Physiological sleep tendency on a simulated night shift: adaptation and effects of triazolam

Daytime sleep and nocturnal sleepiness were examined in 18 normal sleepers (9 young adults, 9 middle-age adults) for 5.5 days following acute sleep/wake schedule inversion. Triazolam and placebo were compared in a counterbalanced, crossover design. Triazolam improved daytime sleep, but did not produce significant changes in sleep tendency at night. Physiological sleep tendency in the early morning hours (0200 to 0600) was profound, but decreased significantly within 3 to 4 days following sleep/wake inversion, irrespective of treatment condition. Nocturnal performance data generally were consistent with changes in physiological sleep tendency. We conclude that extending daytime sleep by an average of approximately 50 min per day via administration of a hypnotic does not appear to significantly reduce circadian sleep tendency in the early morning hours. Further, considerable adaptation, in terms of sleep tendency, occurred within a weak of simulated night shift despite a relatively constant daytime sleep pattern.     

Promoting alertness with a short nap during a night shift

The use of a short (< 1 h) nap in improving alertness during the early morning hours in the first night shift was examined under laboratory conditions. The study contained four experimental, non-consecutive night shifts with a nap of either 50 or 30 min at 01.00 or 04.00 hours. An experimental night shift without a nap served as a control condition. Each experimental shift was followed by daytime sleep. Fourteen experienced male shift workers went through all of the experimental conditions. The results showed that the naps improved the ability to respond to visual signals during the second half of the night shift. Physiological sleepiness was alleviated by the early naps, as measured 50 min after awakening, but not at the end of the shift. Subjective sleepiness was somewhat decreased by the naps. The naps produced sleep inertia which lasted for about 10–15 min. Daytime sleep was somewhat impaired by the 50 min naps. The study shows that a nap shorter than 1 h is able to improve alertness to a certain extent during the first night shift.     

Impaired alertness and performance driving home from the night shift: a driving simulator study

Driving in the early morning is associated with increased accident risk affecting not only professional drivers but also those who commute to work. The present study used a driving simulator to investigate the effects of driving home from a night shift. Ten shift workers participated after a normal night shift and after a normal night sleep. The results showed that driving home from the night shift was associated with an increased number of incidents (two wheels outside the lane marking, from 2.4 to 7.6 times), decreased time to first accident, increased lateral deviation (from 18 to 43 cm), increased eye closure duration (0.102 to 0.143 s), and increased subjective sleepiness. The results indicate severe postnight shift effects on sleepiness and driving performance.     

Physiological sleep tendency and ability to maintain alertness at night

The maintenance of wakefulness test (MWT) and repeated test of sustained wakefulness (RTSW) were compared to the multiple sleep latency test (MSLT) during nighttime hours to evaluate differential sensitivity to variation in physiologic sleepiness/alertness. The degree of sleepiness varied by time of night and was further manipulated by varying prior sleep. Seven healthy normal sleepers were evaluated on the MWT, RTSW, MSLT, a digit symbol substitution test and the Wilkinson addition test in a protocol beginning at 2200 h and terminating at 0830 the following morning. A counterbalanced, crossover design compared an evening nap condition to a no-nap condition. The MWT and RTSW discriminated between nap and no-nap conditions, but the MSLT did not. This suggests that in some situations the MWT and RTSW may be more sensitive to changes in physiologic sleepiness/alertness than the MSLT. The data are discussed in terms of possible methodologic limits of the MSLT and the relationship between physiologic sleep tendency and the capacity to maintain alertness.     

Effects of melatonin administration on daytime sleep after simulated night shift work

Disturbed sleep and on-the-job sleepiness are widespread problems among night shift workers. The pineal hormone melatonin may prove to be a useful treatment because it has both sleep-promoting and circadian phase-shifting effects. This study was designed to isolate melatonin's sleep-promoting effects, and to determine whether melatonin could improve daytime sleep and thus improve night time alertness and performance during the night shift. The study utilized a placebo-controlled, double-blind, cross-over design. Subjects (n=21, mean age=27.0 +/- 5.0 years) participated in two 6-day laboratory sessions. Each session included one adaptation night, two baseline nights, two consecutive 8-h night shifts followed by 8-h daytime sleep episodes and one recovery night. Subjects took 1.8 mg sustained-release melatonin 0.5 h before the two daytime sleep episodes during one session, and placebo before the daytime sleep episodes during the other session. Sleep was recorded using polysomnography. Sleepiness, performance, and mood during the night shifts were evaluated using the multiple sleep latency test (MSLT) and a computerized neurobehavioral testing battery. Melatonin prevented the decrease in sleep time during daytime sleep relative to baseline, but only on the first day of melatonin administration. Melatonin increased sleep time more in subjects who demonstrated difficulty in sleeping during the day. Melatonin had no effect on alertness on the MSLT, or performance and mood during the night shift. There were no hangover effects from melatonin administration. These findings suggest that although melatonin can help night workers obtain more sleep during the day, they are still likely to face difficulties working at night because of circadian rhythm misalignment. The possibility of tolerance to the sleep-promoting effects of melatonin across more than 1 day needs further investigation.     

Timed exposure to bright light improves sleep and alertness during simulated night shifts.

Many of the health and safety problems reported by shift workers result from the chronic sleep deprivation associated with shorter, fragmented daytime sleep. This reduction in the quality and duration of sleep has been attributed to a change in the phase relationship between the work period and the circadian system, timing the propensity for sleep and wakefulness. This study examined the extent to which appropriately timed exposure to bright light would accelerate the circadian readjustment of physiological parameters thought to contribute to impaired performance in shift workers. A control (n = 7) and treatment group (n = 6) underwent a 3-day transition to simulated night work. The treatment group received a single 4-hour pulse of bright light (6,000 lux) between 2400 and 0400 hours on the first night shift and dim light (less than 200 lux) for the remainder of the study. The control group received dim light throughout. By the third night shift, the phase position of the core body temperature rhythm for the treatment group had delayed by 5-6 hours whereas the control group had delayed by only 2-3 hours. When compared to the control group, the greater delay in core temperature rhythm for the treatment group was associated with significantly higher alertness across the night shift and improved sleep quality during the day. By the third day sleep, mean sleep efficiency in the treatment group was not significantly different from normal night sleep. Similarly, onshift alertness was improved relative to the control group. The treatment group did not show the typical decline in alertness observed in the control group between 0300 and 0700 hours. These data indicate that a single 4-hour pulse of bright light between midnight and 0400 hours is effective in ameliorating the sleep and alertness problems associated with transition to night shift.     

The impact of a nap opportunity during the night shift on the performance and alertness of 12-h shift workers

The purpose of this workplace evaluation was to assess the effects on performance, alertness and subsequent sleep of strategic napping on 12-h overnight shifts. In a counterbalanced crossover design, 24 male aircraft maintenance engineers working in a forward rotating 12-h shift pattern volunteered to take part in the study for two work weeks. During the experimental week, each subject was given the opportunity to take a 20-min nap at work between 01:00 and 03:00 h on each of their two overnight shifts. On the control week no naps were taken on the night shifts. A computerized neurobehavioural test battery was employed to assess performance and subjective levels of fatigue at the beginning and end of each night shift, and pre- and postnap. Subjects were also asked to rate how near they had come to falling asleep while driving to and from work. The results revealed that taking a single 20-min nap during the first night shift significantly improved speed of response on a vigilance task measured at the end of the shift compared with the control condition. On the second night shift there was no effect of the nap on performance. Taking a short nap during either night shift had no significant effect on subjective ratings of fatigue, the level of sleepiness reported while driving to and from work, or subsequent sleep duration and sleep quality. Overall the results suggest some promise for a short duration nap taken in the workplace to counteract performance deficits associated with the first night shift.     

Sleepiness and nap sleep following a morning dose of clonidine

The effects of a single oral dose of clonidine on morning nap sleep and daytime sleepiness were evaluated in 18 normal young adult male volunteers aged 18-21 years. Polysomnography and subjective sleepiness (Stanford Sleepiness Scale and linear analog sleepiness rating scale) measures were obtained on 2 mornings. Half the subjects received placebo and half clonidine (0.25-0.3 mg) on both occasions. Subjects were instructed to stay awake on the first morning (wake) and to sleep on the second (sleep). Efforts were made to help subjects maintain arousal on the wake day. Results from the wake morning showed that clonidine subjects were significantly sleepier than placebo subjects as measured by introspection. In addition, clonidine subjects tended to have more polysomnographic signs of sleepiness (microsleeps) when not actively aroused. On the sleep morning, clonidine and placebo subjects slept for approximately 90% of the 3-h nap. Stage 1 and rapid-eye-movement (REM) sleep were significantly reduced and stage 2 sleep significantly increased in the clonidine group. In conclusion, a morning dose of clonidine produced profound sedation in waking subjects and marked REM suppression in sleeping subjects.     

The night before night shift: Chronotype impacts total sleep and rapid eye movement sleep during a strategically delayed sleep

Transition to night shift may be improved by strategically delaying the main sleep preceding a first night shift. However, the effects of delayed timing on sleep may differ between chronotypes. Therefore, the study aim was to compare the impacts of chronotype on sleep quality and architecture during a normally timed sleep opportunity and a delayed sleep opportunity. Seventy-two (36 female, 36 male) healthy adults participated in a laboratory study. Participants were provided with a normally timed sleep opportunity (23:00–08:00) and a delayed sleep opportunity (03:00–12:00) over two consecutive nights in a sleep laboratory. Sleep was monitored by polysomnography (PSG), and chronotype was determined from dim light melatonin onset (DLMO). A tertile split of DLMO defined early (20:24 ± 0:42 h), intermediate (21:31 ± 0:12 h), and late chronotype (22:56 ± 0:54 h) categories. Although there was no main effect of chronotype on any sleep measure, early chronotypes obtained less total sleep with delayed sleep than with normally timed sleep (p = 0.044). Intermediate and late chronotypes obtained more rapid eye movement (REM) sleep with delayed sleep than with normally timed sleep (p = 0.013, p = 0.012 respectively). Wake was more elevated for all chronotypes in the later hours of the delayed sleep opportunity than at the start of the sleep opportunity. Strategically delaying the main sleep preceding a first night shift appears to benefit intermediate and late chronotypes (i.e., more REM sleep), but not early chronotypes (i.e., less total sleep). Circadian processes appear to elevate wakefulness for all chronotypes in the later stages of a delayed sleep opportunity.     

Sleepiness and sleep disorders in shift workers: a study on a group of italian police officers

STUDY OBJECTIVES: evaluation of shift-work effect on sleepiness, sleep disorders, and sleep-related accidents in a population of police officers. DESIGN: Aquestionnaire-based survey was used to gather information on age and physical characteristics, working conditions, sleep problems, and accidents. Sleepiness was measured by the Epworth Sleepiness Scale (ESS) while the presence of sleep disorders was evaluated by a score (SDS) drawn from indicators of insomnia, breathing disorders, periodic limb movements and restless legs syndrome, and hypersomnia. The effects of age, gender, body mass index, working conditions, and seniority on ESS, SD score, and accidents were analyzed by linear and logistic regression. SETTING: The self-administered questionnaires were filled in by police officers in the district of Genoa (Italy). PARTICIPANTS: 1,280 police officers: 611 shift workers (SW) and 669 non-shift workers (NSW). INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: The ESS score was not higher in SW than in NSW, while the SDS was significantly influenced by shift-work conditions and seniority in shift work. The occurrence of sleep-ascribed accidents was significantly increased in the SW group and related to the presence of indicators of sleep disorders. There was evidence for sleep disorders in 35.7% of SW and in 26.3% of NSW. CONCLUSIONS: Shift-work conditions and seniority may enhance sleep disorders and may favor sleep-related accidents, but they do not influence ESS score. Stressful conditions could cause sleepiness to be underestimated, or else they might overcome sleepiness. However, our data should alert occupational health physicians for the diagnosis and prevention of possible undetected intrinsic sleep disorders, which could possibly worsen shift workers' health and increase the risk of accidents.     

Scheduling of sleep/darkness affects the circadian phase of night shift workers

Shift work results in a misalignment between circadian timing and the sleep/wake schedule, leading to irregular and poor quality sleep. Inconsistent input from the daily light cycle further interferes with circadian entrainment. It has been hypothesized that scheduling the sleep/dark cycle on the night shift could aid in promoting adaptation to night shift work by facilitating appropriate phase shifts. In a simulated shift-work study, we compared the ability of two sleep/dark schedules to shift circadian phase. Our results indicate that scheduled sleep/darkness can aid in adaptation to night shift work by inducing both advance and delay phase shifts, depending on the timing of the sleep schedule, although the size of the phase shifts are not sufficient to produce complete adaptation to the night shift. These results have applications to night shift workers, particularly in occupations in which alterations in the timing of light exposure cannot be achieved during working hours.     

Recovery sleep at different times of the night following loss of the last four hours of sleep

The sleep of 8 women was restricted to the first half of the night for 1 night on two separate occasions. On each occasion, heavy loss of REM (64%) and stage 2 (60%) with only a relatively light loss (20%) of slow wave sleep resulted. The purpose of the present study was to investigate whether or not the circadian timing of recovery sleep, particularly the second 4 h, would affect the response of the sleep system to the differential loss of the sleep stages. Recovery sleep commenced at 2000 h (i.e., after a normal daily span of 16 h of wakefulness) and was either continuous or interrupted after 4 h with 4 h of enforced wakefulness. Thus, the second 4 h of recovery sleep occurred between either 0000-0400 h or 0400-0800 h, two periods of the night normally associated with low and high levels of REM, respectively. The composition of recovery sleep, particularly the level of REM sleep, was found to be relatively unaffected by circadian factors. Instead, the response of the sleep system was mainly determined by stage 4 debt. It was suggested that obtaining a daily stage 4 quota acts as the primary drive mechanism of the sleep system.     

Effect of the first night shift period on sleep in young nurse students

In young hospital nurses being exposed to a night shift work schedule for the first time in their occupational life, sleep quality is investigated quantitatively. A main sleep period and supplementary sleep periods were defined and analyzed to investigate sleep behavior and quality. A total of 30 young nurses (26 women, 4 men), mean age 20.2 ± 2.1 years participated. A 3 week nursing school period was followed by a 3 week work period with a 3–5 night shift sub-period and recovery days. Sleep–wake behavior was assessed with an actigraph, sleep diaries, Epworth sleepiness scale (ESS), and quality of life was assessed with a standard questionnaire (SF-36). Comparing the school period with the work shift period when excluding recovery days after night shift period significant increase of total sleep time within 24 h was found during the work days (ANOVA P < 0.05). During the night shift sub-period, there was just a small decline of the main sleep period at day (n.s.) which was not compensated by supplementary sleep episodes. The supplementary sleep during work day varied between 11 min (school period) and 18 min after recovery days from night shift (n.s.). Young healthy nurses tolerate the first night shift exposure very well, according to objective and subjective parameters related to quality of sleep. An increased sleep need during work days lead to longer total sleep time, but do not lead to longer supplementary sleep episodes. Young nurses tolerate the first rotating shift period and the first night shift period very well.     

Effects of partial circadian adjustments on sleep and vigilance quality during simulated night work

In most situations, complete circadian adjustment is not recommended for night workers. With complete adjustment, workers experience circadian misalignment when returning on a day-active schedule, causing repeated circadian phase shifts and internal desynchrony. For this reason, partial circadian realignment was proposed as a good compromise to stabilize internal circadian rhythms in night shift workers. However, the extent of partial circadian adjustment necessary to improve sleep and vigilance quality is still a matter of debate. In this study, the effects of small but statistically significant partial circadian adjustments on sleep and vigilance quality were assessed in a laboratory simulation of night work to determine whether they were also of clinical significance. Partial adjustments obtained by phase delay or by phase advance were quantified not only by the phase shift of dim light salivary melatonin onset, but also by the overlap of the episode of melatonin production with the sleep-wake cycle adopted during simulated night work. The effects on daytime sleep and night-time vigilance quality were modest. However, they suggest that even small adjustments by phase delay may decrease the accumulation of sleep debt, whereas the advance strategy improves subjective alertness and mood during night work. Furthermore, absolute phase shifts, by advance or by delay, were associated with improved subjective alertness and mood during the night shift. These strategies need to be tested in the field, to determine whether they can be adapted to real-life situations and provide effective support to night workers.     

Increased production of evoked and spontaneous K-complexes following a night of fragmented sleep

STUDY OBJECTIVES: To determine whether K-complex production is better interpreted as being an arousal response or reflective of a sleep protective micro-state. DESIGN: A 3-night study--night 1 as a baseline night, night 2 as a sleep fragmentation night, followed immediately by night 3 as a recovery night. On nights 1 and 3, approximately 400 auditory stimuli were presented during nonREM sleep in the first two sleep cycles, using stimulus parameters previously found to be optimal for K-complex production. SETTING: The sleep research laboratory at the University of Melbourne. PARTICIPANTS: Six young healthy subjects (3 female). INTERVENTIONS: One night of sleep fragmentation. Ten-second auditory tones of up to 110 dB were presented throughout the entire night at approximately 1-minute intervals. MEASUREMENTS AND RESULTS: Sleep drive was increased on the recovery night, as indicated by increased amounts of slow wave sleep, increased sleep efficiency, and a reduction in stimulus-related alpha activity. The incidence of both evoked and spontaneous K-complexes increased significantly on the recovery night. When K-complex trials were averaged, neither N550 (Fz) amplitude nor latency differed between the 2 nights. When vertex sharp waves were averaged, N350 (Cz) amplitude was increased significantly on the recovery night. CONCLUSIONS: The increase in K-complex frequency together with the decrease seen in stimulus-related alpha activity supports the view that they reflect a sleep maintenance, rather than an arousal, response.     

Effects of night work, sleep loss and time on task on simulated threat detection performance

STUDY OBJECTIVES: To investigate the effects of night work and sleep loss on a simulated luggage screening task (SLST) that mimicked the x-ray system used by airport luggage screeners. DESIGN: We developed more than 5,800 unique simulated x-ray images of luggage organized into 31 stimulus sets of 200 bags each. 25% of each set contained either a gun or a knife with low or high target difficulty. The 200-bag stimuli sets were then run on software that simulates an x-ray screening system (SLST). Signal detection analysis was used to obtain measures of hit rate (HR), false alarm rate (FAR), threat detection accuracy (A'), and response bias (B"(D)). SETTING: Experimental laboratory study PARTICIPANTS: 24 healthy nonprofessional volunteers (13 women, mean age +/- SD = 29.9 +/- 6.5 years). INTERVENTIONS: Subjects performed the SLST every 2 h during a 5-day period that included a 35 h period of wakefulness that extended to night work and then another day work period after the night without sleep. RESULTS: Threat detection accuracy A' decreased significantly (P < 0.001) while FAR increased significantly (P < 0.001) during night work, while both A' (P = 0.001) and HR decreased (P = 0.008) during day work following sleep loss. There were prominent time-on-task effects on response bias B"(D) (P= 0.002) and response latency (P = 0.004), but accuracy A' was unaffected. Both HR and FAR increased significantly with increasing study duration (both P < 0.001), while response latency decreased significantly (P <0.001). CONCLUSIONS: This study provides the first systematic evidence that night work and sleep loss adversely affect the accuracy of detecting complex real world objects among high levels of background clutter. If the results can be replicated in professional screeners and real work environments, fatigue in luggage screening personnel may pose a threat for air traffic safety unless countermeasures for fatigue are deployed.     

Sleep structure and EEG power density in morning types and evening types during a simulated day and night shift

The objective of this study was to examine circadian and homeostatic regulation of sleep in humans. In 8 morning types (M-types) and in 8 evening types (E-types), sleep was recorded during 3 successive nights and, after shifting sleep to the daytime, during 3 consecutive days. Night sleep was highly similar in the M-types and E-types. Day sleep clearly differed from night sleep in both types: Day sleep was shorter and had a longer first REMS episode. Furthermore, EEG power density recorded during non-REMS in the delta and theta frequency bands was higher during all day-sleep periods. Remarkably, the enhancements did not occur in non-REMS episode 1 but were delayed. This was interpreted as an inhibition of EEG power density at the beginning of sleep, possibly caused by the time course of body temperature and/or by the higher REMS propensity. Also, clear differences between the types became apparent: Only in the E-types, the non-REMS episodes shortened in response to the shift in bedtime, and probably related to this, the time course of EEG power density over consecutive non-REMS episodes became almost flat. It was concluded that the circadian system exerts not only an influence on sleep duration and REMS propensity, but also affects the time course of the non-REMS process.     

Prediction of shiftworker alertness,sleep, and circadian phase using a model of arousal dynamics constrained by shift schedules and light exposure

Study ObjectivesThe study aimed to, for the first time, (1) compare sleep, circadian phase, and alertness of intensive care unit (ICU) nurses working rotating shifts with those predicted by a model of arousal dynamics; and (2) investigate how different environmental constraints affect predictions and agreement with data.MethodsThe model was used to simulate individual sleep-wake cycles, urinary 6-sulphatoxymelatonin (aMT6s) profiles, subjective sleepiness on the Karolinska Sleepiness Scale (KSS), and performance on a Psychomotor Vigilance Task (PVT) of 21 ICU nurses working day, evening, and night shifts. Combinations of individual shift schedules, forced wake time before/after work and lighting, were used as inputs to the model. Predictions were compared to empirical data. Simulations with self-reported sleep as an input were performed for comparison.ResultsAll input constraints produced similar prediction for KSS, with 56%–60% of KSS scores predicted within ±1 on a day and 48%–52% on a night shift. Accurate prediction of an individual’s circadian phase required individualized light input. Combinations including light information predicted aMT6s acrophase within ±1 h of the study data for 65% and 35%–47% of nurses on diurnal and nocturnal schedules. Minute-by-minute sleep-wake state overlap between the model and the data was between 81 ± 6% and 87 ± 5% depending on choice of input constraint.ConclusionsThe use of individualized environmental constraints in the model of arousal dynamics allowed for accurate prediction of alertness, circadian phase, and sleep for more than half of the nurses. Individual differences in physiological parameters will need to be accounted for in the future to further improve predictions.