Duration of sleep inertia after napping during simulated night work and in extended operations

Due to the mixed findings of previous studies, it is still difficult to provide guidance on how to best manage sleep inertia after waking from naps in operational settings. One of the few factors that can be manipulated is the duration of the nap opportunity. The aim of the present study was to investigate the magnitude and time course of sleep inertia after waking from short (20-, 40- or 60-min) naps during simulated night work and extended operations. In addition, the effect of sleep stage on awakening and duration of slow wave sleep (SWS) on sleep inertia was assessed. Two within-subject protocols were conducted in a controlled laboratory setting. Twenty-four healthy young men (Protocol 1: n = 12, mean age = 25.1 yrs; Protocol 2: n = 12, mean age = 23.2 yrs) were provided with nap opportunities of 20-, 40-, and 60-min (and a control condition of no nap) ending at 02:00 h after ～20 h of wakefulness (Protocol 1 [P1]: simulated night work) or ending at 12:00 h after ～30 h of wakefulness (Protocol 2 [P2]: simulated extended operations). A 6-min test battery, including the Karolinska Sleepiness Scale (KSS) and the 4-min 2-Back Working Memory Task (WMT), was repeated every 15 min the first hour after waking. Nap sleep was recorded polysomnographically, and in all nap opportunities sleep onset latency was short and sleep efficiency high. Mixed-model analyses of variance (ANOVA) for repeated measures were calculated and included the factors time (time post-nap), nap opportunity (duration of nap provided), order (order in which the four protocols were completed), and the interaction of these terms. Results showed no test x nap opportunity effect (i.e., no effect of sleep inertia) on KSS. However, WMT performance was impaired (slower reaction time, fewer correct responses, and increased omissions) on the first test post-nap, primarily after a 40- or 60-min nap. In P2 only, performance improvement was evident 45 min post-awakening for naps of 40 min or more. In ANOVAs where sleep stage on awakening was included, the test x nap opportunity interaction was significant, but differences were between wake and non-REM Stage 1/Stage 2 or wake and SWS. A further series of ANOVAs showed no effect of the duration of SWS on sleep inertia. The results of this study demonstrate that no more than 15 min is required for performance decrements due to sleep inertia to dissipate after nap opportunities of 60 min or less, but subjective sleepiness is not a reliable indicator of this effect. Under conditions where sleep is short, these findings also suggest that SWS, per se, does not contribute to more severe sleep inertia. When wakefulness is extended and napping occurs at midday (i.e., P2), nap opportunities of 40- and 60-min have the advantage over shorter duration sleep periods, as they result in performance benefits ～45 min after waking.     

Duration of Sleep Inertia after Napping during Simulated Night Work and in Extended Operations

Due to the mixed findings of previous studies, it is still difficult to provide guidance on how to best manage sleep inertia after waking from naps in operational settings. One of the few factors that can be manipulated is the duration of the nap opportunity. The aim of the present study was to investigate the magnitude and time course of sleep inertia after waking from short (20-, 40- or 60-min) naps during simulated night work and extended operations. In addition, the effect of sleep stage on awakening and duration of slow wave sleep (SWS) on sleep inertia was assessed. Two within-subject protocols were conducted in a controlled laboratory setting. Twenty-four healthy young men (Protocol 1: n?=?12, mean age?=?25.1 yrs; Protocol 2: n?=?12, mean age?=?23.2 yrs) were provided with nap opportunities of 20-, 40-, and 60-min (and a control condition of no nap) ending at 02:00?h after ～20?h of wakefulness (Protocol 1 [P1]: simulated night work) or ending at 12:00?h after ～30?h of wakefulness (Protocol 2 [P2]: simulated extended operations). A 6-min test battery, including the Karolinska Sleepiness Scale (KSS) and the 4-min 2-Back Working Memory Task (WMT), was repeated every 15?min the first hour after waking. Nap sleep was recorded polysomnographically, and in all nap opportunities sleep onset latency was short and sleep efficiency high. Mixed-model analyses of variance (ANOVA) for repeated measures were calculated and included the factors time (time post-nap), nap opportunity (duration of nap provided), order (order in which the four protocols were completed), and the interaction of these terms. Results showed no test x nap opportunity effect (i.e., no effect of sleep inertia) on KSS. However, WMT performance was impaired (slower reaction time, fewer correct responses, and increased omissions) on the first test post-nap, primarily after a 40- or 60-min nap. In P2 only, performance improvement was evident 45?min post-awakening for naps of 40?min or more. In ANOVAs where sleep stage on awakening was included, the test x nap opportunity interaction was significant, but differences were between wake and non-REM Stage 1/Stage 2 or wake and SWS. A further series of ANOVAs showed no effect of the duration of SWS on sleep inertia. The results of this study demonstrate that no more than 15?min is required for performance decrements due to sleep inertia to dissipate after nap opportunities of 60?min or less, but subjective sleepiness is not a reliable indicator of this effect. Under conditions where sleep is short, these findings also suggest that SWS, per se, does not contribute to more severe sleep inertia. When wakefulness is extended and napping occurs at midday (i.e., P2), nap opportunities of 40- and 60-min have the advantage over shorter duration sleep periods, as they result in performance benefits ～45?min after waking.     

The effects of extended nap periods on cognitive,physiological and subjective responses under simulated night shift conditions

Extended nap opportunities have been effective in maintaining alertness in the context of extended night shifts (+12?h). However, there is limited evidence of their efficacy during 8-h shifts. Thus, this study explored the effects of extended naps on cognitive, physiological and perceptual responses during four simulated, 8-h night shifts. In a laboratory setting, 32 participants were allocated to one of three conditions. All participants completed four consecutive, 8-h night shifts, with the arrangements differing by condition. The fixed night condition worked from 22h00 to 06h00, while the nap early group worked from 20h00 to 08h00 and napped between 00h00 and 03h20. The nap late group worked from 00h00 to 12h00 and napped between 04h00 and 07h20. Nap length was limited to 3 hours and 20 minutes. Participants performed a simple beading task during each shift, while also completing six to eight test batteries roughly every 2?h. During each shift, six test batteries were completed, in which the following measures were taken. Performance indicators included beading output, eye accommodation time, choice reaction time, visual vigilance, simple reaction time, processing speed and object recognition, working memory, motor response time and tracking performance. Physiological measures included heart rate and tympanic temperature, whereas subjective sleepiness and reported sleep length and quality while outside the laboratory constituted the self reported measures. Both naps reduced subjective sleepiness but did not alter the circadian and homeostatic-related changes in cognitive and physiological measures, relative to the fixed night condition. Additionally, there was evidence of sleep inertia following each nap, which resulted in transient reductions in certain perceptual cognitive performance measures. The present study suggested that there were some benefits associated with including an extended nap during 8-h night shifts. However, the effects of sleep inertia need to be effectively managed to ensure that post-nap alertness and performance is maintained.     

Daytime napping after a night of sleep loss decreases sleepiness, improves performance, and causes beneficial changes in cortisol and interleukin-6 secretion

Sleep loss has been associated with increased sleepiness, decreased performance, elevations in inflammatory cytokines, and insulin resistance. Daytime napping has been promoted as a countermeasure to sleep loss. To assess the effects of a 2-h midafternoon nap following a night of sleep loss on postnap sleepiness, performance, cortisol, and IL-6, 41 young healthy individuals (20 men, 21 women) participated in a 7-day sleep deprivation experiment (4 consecutive nights followed by a night of sleep loss and 2 recovery nights). One-half of the subjects were randomly assigned to take a midafternoon nap (1400-1600) the day following the night of total sleep loss. Serial 24-h blood sampling, multiple sleep latency test (MSLT), subjective levels of sleepiness, and psychomotor vigilance task (PVT) were completed on the fourth (predeprivation) and sixth days (postdeprivation). During the nap, subjects had a significant drop in cortisol and IL-6 levels (P < 0.05). After the nap they experienced significantly less sleepiness (MSLT and subjective, P < 0.05) and a smaller improvement on the PVT (P < 0.1). At that time, they had a significant transient increase in their cortisol levels (P < 0.05). In contrast, the levels of IL-6 tended to remain decreased for approximately 8 h (P = 0.1). We conclude that a 2-h midafternoon nap improves alertness, and to a lesser degree performance, and reverses the effects of one night of sleep loss on cortisol and IL-6. The redistribution of cortisol secretion and the prolonged suppression of IL-6 secretion are beneficial, as they improve alertness and performance.     

Mood,Alertness, and Performance in Response to Sleep Deprivation and Recovery Sleep in Experienced Shiftworkers Versus Non-Shiftworkers

Previous studies have shown increased sleepiness and mood changes in shiftworkers, which may be due to sleep deprivation or circadian disruption. Few studies, however, have compared responses of experienced shiftworkers and non-shiftworkers to sleep deprivation in an identical laboratory setting. The aim of this laboratory study, therefore, was to compare long-term shiftworkers and non-shiftworkers and to investigate the effects of one night of total sleep deprivation (30.5?h of continuous wakefulness) and recovery sleep on psychomotor vigilance, self-rated alertness, and mood. Eleven experienced male shiftworkers (shiftwork ≥5 yrs) were matched with 14 non-shiftworkers for age (mean?±?SD: 35.7?±?7.2 and 32.5?±?6.2 yrs, respectively) and body mass index (BMI) (28.7?±?3.8 and 26.6?±?3.4?kg/m², respectively). After keeping a 7-d self-selected sleep/wake cycle (7.5/8?h nocturnal sleep), both groups entered a laboratory session consisting of a night of adaptation sleep and a baseline sleep (each 7.5/8?h), a sleep deprivation night, and recovery sleep (4-h nap plus 7.5/8?h nighttime sleep). Subjective alertness and mood were assessed with the Karolinska Sleepiness Scale (KSS) and 9-digit rating scales, and vigilance was measured by the visual psychomotor vigilance test (PVT). A mixed-model regression analysis was carried out on data collected every hour during the sleep deprivation night and on all days (except for the adaptation day), at .25, 4.25, 5.25, 11.5, 12.5, and 13.5?h after habitual wake-up time. Despite similar circadian phase (melatonin onset), demographics, food intake, body posture, and environmental light, shiftworkers felt significantly more alert, more cheerful, more elated, and calmer than non-shiftworkers throughout the laboratory study. In addition, shiftworkers showed a faster median reaction time (RT) compared to non-shiftworkers, although four other PVT parameters did not differ between the groups. As expected, both groups showed a decrease in subjective alertness and PVT performance during and following the sleep deprivation night. Subjective sleepiness and most aspects of PVT performance returned to baseline levels after a nap and recovery sleep. The mechanisms underlying the observed differences between shiftworkers and non-shiftworkers require further study, but may be related to the absence of shiftwork the week prior to and during the laboratory study as well as selection into and out of shiftwork. (Author correspondence: sophie.wehrens@surrey.ac.uk)     

The effects of a nap opportunity in quiet and noisy environments on driving performance

While napping has previously been shown to alleviate the effects of sleep loss, before advocating the use of naps in transport accident campaigns it is necessary to consider whether a nap opportunity in a noisy uncomfortable environment can produce the same benefits as a nap opportunity in conditions that are conducive to sleep. To examine this, eight participants drove a driving simulator for 50 min at 11:00 h on three different test days. The simulator used has previously been found to be sensitive to the effects of sleep loss, alcohol consumption, and time of day. All three sessions were conducted after one night of sleep loss. Prior to driving during each session the participants either had a 60 min nap opportunity in a quiet or noisy environment, or no nap opportunity. Driving performance and reaction time while driving were measured, as were subjective sleepiness and ratings of sleep quality. No significant benefits of nap opportunities on driving performance were found. Levels of subjective sleepiness were not affected by the nap opportunity condition; however, sleep was rated as more refreshing and restful after a nap in a quiet environment compared to noisy environment. The measures of effect size reported suggest further research is required to unequivocally test the effects of nap opportunities on driving ability.     

The Effects of a Nap Opportunity in Quiet and Noisy Environments on Driving Performance

While napping has previously been shown to alleviate the effects of sleep loss, before advocating the use of naps in transport accident campaigns it is necessary to consider whether a nap opportunity in a noisy uncomfortable environment can produce the same benefits as a nap opportunity in conditions that are conducive to sleep. To examine this, eight participants drove a driving simulator for 50 min at 11:00 h on three different test days. The simulator used has previously been found to be sensitive to the effects of sleep loss, alcohol consumption, and time of day. All three sessions were conducted after one night of sleep loss. Prior to driving during each session the participants either had a 60 min nap opportunity in a quiet or noisy environment, or no nap opportunity. Driving performance and reaction time while driving were measured, as were subjective sleepiness and ratings of sleep quality. No significant benefits of nap opportunities on driving performance were found. Levels of subjective sleepiness were not affected by the nap opportunity condition; however, sleep was rated as more refreshing and restful after a nap in a quiet environment compared to noisy environment. The measures of effect size reported suggest further research is required to unequivocally test the effects of nap opportunities on driving ability.     

The Impact of Short,Irregular Sleep Opportunities at Sea on the Alertness of Marine Pilots Working Extended Hours

The aim of this study was to examine the impact of brief, unscheduled naps during work periods on alertness and vigilance in coastal pilots along the Great Barrier Reef. On certain routes, the duration of the work period can extend well beyond 24 h. Seventeen coastal pilots volunteered for the study, representing almost one‐third of the population. Participants collected sleep/wake and performance data for 28 days using a sleep and work diary and the palm PVT task. The average length of sleep on board was 1.4±1.0 h. Naps were taken regularly such that the average length of time awake between sleep periods on board a ship was 5.3±4.3 h. There was no change in mean reaction time across either the length of a pilotage or across the 24 h day. The results indicate that even though the naps were taken opportunistically, they tended to cluster at the high sleep propensity times. Further, frequent, opportunistic naps appeared to provide adequate recovery such that PVT performance remained stable. Pilots did report increases in subjective fatigue ratings at certain times of the 24 h day and at the end of a work period; however, these did not reach the high range. The fatigue‐risk minimization strategies employed by the Australian Maritime Safety Authority and the coastal pilots appear to be effective in maintaining alertness and vigilance while at work aboard ships.     

The impact of short, irregular sleep opportunities at sea on the alertness of marine pilots working extended hours

The aim of this study was to examine the impact of brief, unscheduled naps during work periods on alertness and vigilance in coastal pilots along the Great Barrier Reef. On certain routes, the duration of the work period can extend well beyond 24 h. Seventeen coastal pilots volunteered for the study, representing almost one-third of the population. Participants collected sleep/wake and performance data for 28 days using a sleep and work diary and the palm PVT task. The average length of sleep on board was 1.4+/-1.0 h. Naps were taken regularly such that the average length of time awake between sleep periods on board a ship was 5.3+/-4.3 h. There was no change in mean reaction time across either the length of a pilotage or across the 24 h day. The results indicate that even though the naps were taken opportunistically, they tended to cluster at the high sleep propensity times. Further, frequent, opportunistic naps appeared to provide adequate recovery such that PVT performance remained stable. Pilots did report increases in subjective fatigue ratings at certain times of the 24 h day and at the end of a work period; however, these did not reach the high range. The fatigue-risk minimization strategies employed by the Australian Maritime Safety Authority and the coastal pilots appear to be effective in maintaining alertness and vigilance while at work aboard ships.     

CONTRIBUTION OF CORE BODY TEMPERATURE,PRIOR WAKE TIME,AND SLEEP STAGES TO COGNITIVE THROUGHPUT PERFORMANCE DURING FORCED DESYNCHRONY

Shiftworkers are often required to sleep at inappropriate phases of their circadian timekeeping system, with implications for the dynamics of ultradian sleep stages. The independent effects of these changes on cognitive throughput performance are not well understood. This is because the effects of sleep on performance are usually confounded with circadian factors that cannot be controlled under normal day/night conditions. The aim of this study was to assess the contribution of prior wake, core body temperature, and sleep stages to cognitive throughput performance under conditions of forced desynchrony (FD). A total of 11 healthy young adult males resided in a sleep laboratory in which day/night zeitgebers were eliminated and ambient room temperature, lighting levels, and behavior were controlled. The protocol included 2 training days, a baseline day, and 7?×?28-h FD periods. Each FD period consisted of an 18.7-h wake period followed by a 9.3-h rest period. Sleep was assessed using standard polysomnography. Core body temperature and physical activity were assessed continuously in 1-min epochs. Cognitive throughput was measured by a 5-min serial addition and subtraction (SAS) task and a 90-s digit symbol substitution (DSS) task. These were administered in test sessions scheduled every 2.5?h across the wake periods of each FD period. On average, sleep periods had a mean (± standard deviation) duration of 8.5 (±1.2) h in which participants obtained 7.6 (±1.4) h of total sleep time. This included 4.2 (±1.2) h of stage 1 and stage 2 sleep (S1–S2 sleep), 1.6 (±0.6) h of slow-wave sleep (SWS), and 1.8 (±0.6) h of rapid eye movement (REM) sleep. A mixed-model analysis with five covariates indicated significant fixed effects on cognitive throughput for circadian phase, prior wake time, and amount of REM sleep. Significant effects for S1–S2 sleep and SWS were not found. The results demonstrate that variations in core body temperature, time awake, and amount of REM sleep are associated with changes in cognitive throughput performance. The absence of significant effect for SWS may be attributable to the truncated range of sleep period durations sampled in this study. However, because the mean and variance for SWS were similar to REM sleep, these results suggest that cognitive throughput may be more sensitive to variations in REM sleep than SWS. (Author correspondence: david.darwent@unisa.edu.au)     

Mood, alertness, and performance in response to sleep deprivation and recovery sleep in experienced shiftworkers versus non-shiftworkers

Previous studies have shown increased sleepiness and mood changes in shiftworkers, which may be due to sleep deprivation or circadian disruption. Few studies, however, have compared responses of experienced shiftworkers and non-shiftworkers to sleep deprivation in an identical laboratory setting. The aim of this laboratory study, therefore, was to compare long-term shiftworkers and non-shiftworkers and to investigate the effects of one night of total sleep deprivation (30.5 h of continuous wakefulness) and recovery sleep on psychomotor vigilance, self-rated alertness, and mood. Eleven experienced male shiftworkers (shiftwork ≥5 yrs) were matched with 14 non-shiftworkers for age (mean ± SD: 35.7 ± 7.2 and 32.5 ± 6.2 yrs, respectively) and body mass index (BMI) (28.7 ± 3.8 and 26.6 ± 3.4 kg/m(2), respectively). After keeping a 7-d self-selected sleep/wake cycle (7.5/8 h nocturnal sleep), both groups entered a laboratory session consisting of a night of adaptation sleep and a baseline sleep (each 7.5/8 h), a sleep deprivation night, and recovery sleep (4-h nap plus 7.5/8 h nighttime sleep). Subjective alertness and mood were assessed with the Karolinska Sleepiness Scale (KSS) and 9-digit rating scales, and vigilance was measured by the visual psychomotor vigilance test (PVT). A mixed-model regression analysis was carried out on data collected every hour during the sleep deprivation night and on all days (except for the adaptation day), at .25, 4.25, 5.25, 11.5, 12.5, and 13.5 h after habitual wake-up time. Despite similar circadian phase (melatonin onset), demographics, food intake, body posture, and environmental light, shiftworkers felt significantly more alert, more cheerful, more elated, and calmer than non-shiftworkers throughout the laboratory study. In addition, shiftworkers showed a faster median reaction time (RT) compared to non-shiftworkers, although four other PVT parameters did not differ between the groups. As expected, both groups showed a decrease in subjective alertness and PVT performance during and following the sleep deprivation night. Subjective sleepiness and most aspects of PVT performance returned to baseline levels after a nap and recovery sleep. The mechanisms underlying the observed differences between shiftworkers and non-shiftworkers require further study, but may be related to the absence of shiftwork the week prior to and during the laboratory study as well as selection into and out of shiftwork.     

A dose-response investigation of the benefits of napping in healthy young,middle-aged and older adults

Older adults experience more fragmented sleep, greater daytime sleepiness and, nap more often than younger adults. Little research has investigated the effects of napping on waking function in older adults. In the present study, waking cognitive performance was examined in 10 young (mean age = 28 years), 10 middle-aged (mean age = 42 years) and 12 older adults (mean age = 61 years) following 60-min, 20-min and no nap conditions. It was expected that the older adults would need a longer nap to accrue benefits. Napping led to improvements for all age groups in subjective sleepiness, fatigue and accuracy on a serial addition/subtraction task. Waking electroencephalogram (EEG) confirmed that the participants were more physiologically alert following naps. There were no age differences in subjective reports or cognitive tasks; however, older adults had higher beta and gamma in the waking EEG, suggesting that they needed increased effort to maintain performance. Overall, older adults had smaller P2 amplitudes, reflecting their difficulty in inhibiting irrelevant stimuli, and delayed latencies and smaller amplitude P300s to novel stimuli, reflecting deficits in their frontal lobe functioning. Although older adults did garner benefits from napping, there was no evidence that they required longer naps to experience improvement.

     

PRIOR NIGHT SLEEP DURATION IS ASSOCIATED WITH PSYCHOMOTOR VIGILANCE IN A HEALTHY SAMPLE OF POLICE ACADEMY RECRUITS

Aviation, military, police, and health care personnel have been particularly interested in the operational impact of sleep restriction and work schedules given the potential severe consequences of making fatigue-related errors. Most studies examining the impact of sleep loss or circadian manipulations have been conducted in controlled laboratory settings using small sample sizes. This study examined whether the relationship between prior night sleep duration and performance on the psychomotor vigilance task could be reliably detected in a field study of healthy police academy recruits. Subjects (N?=?189) were medically and psychiatrically healthy. Sleep-wake activity was assessed with wrist actigraphy for 7 days. Subjects performed the psychomotor vigilance task (PVT) for 5?min on a personal digital assistant (PDA) device before and after their police academy workday and on comparable times during their days off. Mixed-effects logistic regression was used to estimate the probability of having ≥1 lapse on the PVT as a function of the previous night sleep duration during the 7 days of field testing. Valid estimates of sleep duration were obtained for 1082 nights of sleep. The probability of a lapse decreased by 3.5%/h sleep the night prior to testing. The overall probability of having a lapse decreased by 0.9%/h since awakening, holding hours of sleep constant. Perceived stress was not associated with sleep duration or probability of performance lapse. These findings demonstrate the feasibility of detecting sleep and circadian effects on cognitive performance in large field studies. These findings have implications regarding the daytime functioning of police officers. (Author correspondence: Thomas.Neylan@ucsf.edu)     

Athletes underestimate sleep quantity during daytime nap opportunities

ABSTRACT

This study examined the difference between athletes’ self-reported and objective sleep durations during two nap opportunities. Twelve well-trained male soccer players’ sleep durations were assessed using polysomnography and a self-report question during a 60- and 120-min nap opportunity. Participants underestimated sleep compared to objective sleep assessments for both the 60-min nap opportunity (p = 0.004) and 120-min nap opportunity (p = 0.001). Soccer players underestimated their sleep duration by approximately 10 min per hour of nap opportunity. It is yet to be determined if athletes are likely to underestimate sleep duration during their main nighttime sleep period.     

Young Women With Major Depression Live on Higher Homeostatic Sleep Pressure Than Healthy Controls

There is mounting evidence for the involvement of the sleep-wake cycle and the circadian system in the pathogenesis of major depression. However, only a few studies so far focused on sleep and circadian rhythms under controlled experimental conditions. Thus, it remains unclear whether homeostatic sleep pressure or circadian rhythms, or both, are altered in depression. Here, the authors aimed at quantifying homeostatic and circadian sleep-wake regulatory mechanisms in young women suffering from major depressive disorder and healthy controls during a multiple nap paradigm under constant routine conditions. After an 8-h baseline night, 9 depressed women, 8 healthy young women, and 8 healthy older women underwent a 40-h multiple nap protocol (10 short sleep-wake cycles) followed by an 8-h recovery night. Polysomnographic recordings were done continuously, and subjective sleepiness was assessed. In order to measure circadian output, salivary melatonin samples were collected during scheduled wakefulness, and the circadian modulation of sleep spindles was analyzed with reference to the timing of melatonin secretion. Sleep parameters as well as non-rapid eye movement (NREM) sleep electroencephalographic (EEG) spectra were determined for collapsed left, central, and right frontal, central, parietal, and occipital derivations for the night and nap-sleep episodes in the frequency range .75–25?Hz. Young depressed women showed higher frontal EEG delta activity, as a marker of homeostatic sleep pressure, compared to healthy young and older women across both night sleep episodes together with significantly higher subjective sleepiness. Higher delta sleep EEG activity in the naps during the biological day were observed in young depressed women along with reduced nighttime melatonin secretion as compared to healthy young volunteers. The circadian modulation of sleep spindles between the biological night and day was virtually absent in healthy older women and partially impaired in young depressed women. These data provide strong evidence for higher homeostatic sleep pressure in young moderately depressed women, along with some indications for impairment of the strength of the endogenous circadian output signal involved in sleep-wake regulation. This finding may have important repercussions on the treatment of the illness as such that a selective suppression of EEG slow-wave activity could promote acute mood improvement. (Author correspondence: Christian.cajochen@upkbs.ch)     

Teen at work: the burden of a double shift on daily activities

The purpose of this study was to the evaluate time spent by working and nonworking adolescents on daily activities (work, home duties, school, transportation, other activities, leisure, sleep, and naps). Twenty-seven students, 8 male workers, 8 female workers, 5 male nonworkers, and 6 female nonworkers, ages 14-18 yrs participated in the study. They attended evening classes Monday-Friday (19:00-22:30h) in a public school in the city of S?o Paulo, Brazil. The students answered a comprehensive questionnaire on the characterization of their life, work, and health conditions. Simultaneously, they wore actigraphs (Ambulatory Monitoring, Inc.) and completed a diary of their daily activities (time spent at work, on home duties, commuting, leisure, other activities) for a minimum of 10 to a maximum of 17 consecutive days. The means of the variables were tested for differences by a two-factor (work and sex) ANOVA and Student-t test applied to pair-wise samples (weekdays and weekends). The average duration during weekdays of working time was 7 h 09 min and home duties 0 h 48 min. As for commuting time, there was a work effect [F(1,23) = 4.9; p = 0.04]; mean commuting time was 2 h 22 min for workers (males and females) and 1 h 25 min for nonworkers. There was a significant difference between workers and nonworkers [F(1,23) = 4.6; p = 0.04] regarding extra-cirricular class activities; workers spent a mean of 3 min/day on them as opposed to 1 h 14 min by nonworkers. The average daily time spent on leisure activities by workers was 6h 31 min; whereas, for nonworkers it was 7h 38min. Time spent in school amounted to 2h 47min for workers in comparison to 3h 22min by nonworkers. There was a significant work effect upon sleep [F(1,23)= 10.0; p <0.01]. The work effect upon nighttime sleep duration was significant [F(1,23)= 16.7; p <0.01]. Male workers showed a mean night sleep of 6 h 57 min and female workers 07h 15min. The average nighttime sleep duration for nonworkers was 9 h 06 min. There was a significant interactive effect between work and sex [F(1,23)= 5.6; p=0.03] for naps. Female workers showed took shortest nap on average (36 min; SD = 26 min), and female nonworkers the longest naps (1 h 45min; SD= 35min). Study and employment exert significant impact on the life and activities of high school students. Work affects sleep and nap duration plus the amount of time spent in school and other extra-curricular activities.     

Sleep,Sleepiness, Fatigue,and Performance of 12-Hour-Shift Nurses

Nurses working 12-h shifts complain of fatigue and insufficient/poor-quality sleep. Objectively measured sleep times have not been often reported. This study describes sleep, sleepiness, fatigue, and neurobehavioral performance over three consecutive 12-h (day and night) shifts for hospital registered nurses. Sleep (actigraphy), sleepiness (Karolinska Sleepiness Scale [KSS]), and vigilance (Performance Vigilance Task [PVT]), were measured serially in 80 registered nurses (RNs). Occupational fatigue (Occupational Fatigue Exhaustion Recovery Scale [OFER]) was assessed at baseline. Sleep was short (mean 5.5?h) between shifts, with little difference between day shift (5.7?h) and night shift (5.4?h). Sleepiness scores were low overall (3 on a 1–9 scale, with higher score indicating greater sleepiness), with 45% of nurses having high level of sleepiness (score ?>?7) on at least one shift. Nurses were progressively sleepier each shift, and night nurses were sleepier toward the end of the shift compared to the beginning. There was extensive caffeine use, presumably to preserve or improve alertness. Fatigue was high in one-third of nurses, with intershift fatigue (not feeling recovered from previous shift at the start of the next shift) being most prominent. There were no statistically significant differences in mean reaction time between day/night shift, consecutive work shift, and time into shift. Lapsing was traitlike, with rare (39% of sample), moderate (53%), and frequent (8%) lapsers. Nurses accrue a considerable sleep debt while working successive 12-h shifts with accompanying fatigue and sleepiness. Certain nurses appear more vulnerable to sleep loss than others, as measured by attention lapses. (Author correspondence: jgeiger@son.umaryland.edu)     

Time Course of Neurobehavioral Alertness During Extended Wakefulness in Morning- and Evening-Type Healthy Sleepers

The aim of the study was to evaluate the influence of chronotype (morning-type versus evening-type) living in a fixed sleep-wake schedule different from one's preferred sleep schedules on the time course of neurobehavioral performance during controlled extended wakefulness. The authors studied 9 morning-type and 9 evening-type healthy male subjects (21.4?±?1.9 yrs). Before the experiment, all participants underwent a fixed sleep-wake schedule mimicking a regular working day (bedtime: 23:30?h; wake time: 07:30?h). Then, following two nights in the laboratory, both chronotypes underwent a 36-h constant routine, performing a cognitive test of sustained attention every hour. Core body temperature, salivary melatonin secretion, objective alertness (maintenance of wakefulness test), and subjective sleepiness (visual analog scale) were also assessed. Evening-types expressed a higher level of subjective sleepiness than morning types, whereas their objective levels of alertness were not different. Cognitive performance in the lapse domain remained stable during the normal waking day and then declined during the biological night, with a similar time course for both chronotypes. Evening types maintained optimal alertness (i.e., 10% fastest reaction time) throughout the night, whereas morning types did not. For both chronotypes, the circadian performance profile was correlated with the circadian subjective somnolence profile and was slightly phase-delayed with melatonin secretion. Circadian performance was less correlated with circadian core body temperature. Lapse domain was phase-delayed with body temperature (2–4?h), whereas optimal alertness was slightly phase-delayed with body temperature (1?h). These results indicate evening types living in a fixed sleep-wake schedule mimicking a regular working day (different from their preferred sleep schedules) express higher subjective sleepiness but can maintain the same level of objective alertness during a normal waking day as morning types. Furthermore, evening types were found to maintain optimal alertness throughout their nighttime, whereas morning types could not. The authors suggest that evening-type subjects have a higher voluntary engagement of wake-maintenance mechanisms during extended wakefulness due to adaptation of their sleep-wake schedule to social constraints. (Author correspondence: jack.taillard@gmail.com)