The Influence of Internal Time,Time Awake,and Sleep Duration on Cognitive Performance in Shiftworkers

To date, studies investigating the consequences of shiftwork have predominantly focused on external (local) time. Here, we report the daily variation in cognitive performance in rotating shiftworkers under real-life conditions using the psychomotor vigilance test (PVT) and show that this function depends both on external and internal (biological) time. In addition to this high sensitivity of PVT performance to time-of-day, it has also been extensively applied in sleep deprivation protocols. We, therefore, also investigated the impact of shift-specific sleep duration and time awake on performance. In two separate field studies, 44 young workers (17 females, 27 males; age range 20–36 yrs) performed a PVT test every 2?h during each shift. We assessed chronotype by the MCTQ^Shift (Munich ChronoType Questionnaire for shiftworkers). Daily sleep logs over the 4-wk study period allowed for the extraction of shift-specific sleep duration and time awake in a given shift, as well as average sleep duration (“sleep need”). Median reaction times (RTs) significantly varied across shifts, depending on both Local Time and Internal Time. Variability of reaction times around the 24 h mean (≈ ±5%) was best explained by a regression model comprising both factors, Local Time and Internal Time (p < .001). Short (15th percentile; RT_15%) and long (85th percentile; RT_85%) reaction times were differentially affected by Internal Time and Local Time. During night shifts, only median RT and RT_85% were impaired by the duration of time workers had been awake (p?<?.01, consistent with the highest sleep pressure), but not RT_15%. Proportion of sleep before a test day (relative to sleep need) significantly affected median RT and RT_85% during morning shifts (p?<?.01). RT_15% was worst in the beginning of the morning shift, but improved to levels above average with increasing time awake (p < .05), whereas RT_85% became worse (p < .05). Hierarchical mixed models confirmed the importance of chronotype and sleep duration on cognitive performance in shiftworkers, whereas the effect of time awake requires further research. Our finding that both Local Time and Internal Time, in conjunction with shift-specific sleep behavior, strongly influence performance extends predictions derived from laboratory studies. (Author correspondence: roenneberg@lmu.de)     

The Effect of One Night's Sleep Deprivation on Temperature,Mood, and Physical Performance in Subjects with Different Amounts of Habitual Physical Activity

Eleven healthy males were studied twice. On one occasion (control, C), they slept (night 1) and then underwent a battery of tests at 4h intervals from 06: 00 day 1 to 02: 00 day 2; then, after a normal sleep (night 2), they were tested from 10: 00 to 22: 00 on day 2. On the second occasion (sleep deprivation, SD), the subjects remained awake during night 1. Each battery of tests consisted of measurements of tympanic membrane temperature, profile of mood states (POMS), muscle strength, self-chosen work rate (SCWR), perceived exertion, and heart rate (HR) while exercising on a stationary cycle ergometer. Subjects also kept a diary of their activities during the two days and answered a questionnaire about their habitual physical activity. Results showed a significant negative effect of sleep deprivation on most mood states on day 1, but no effect on the other variables. By day 2, mood had tended to recover, though muscle strength tended to be worse in both control and sleep-deprivation experiments. There was also a more general tendency for negative effects to be present at the end of day 1 (02: 00) or at the beginning of day 2 (10: 00). There was limited support for the view that subjects who were habitually more active showed less negative effects after sleep deprivation and responded less adversely to the poor sleep achieved on the university premises (night 2). These results stress the considerable interindividual variation in the responses to sleep loss and, therefore, the difficulty associated with giving general advice to individuals about work or training capability after sleep loss.     

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)     

A Reliability and Validity Study of the Bergen Shift Work Sleep Questionnaire in Nurses Working Three-Shift Rotations

The “Bergen Shift Work Sleep Questionnaire” (BSWSQ) was developed to systematically assess discrete sleep problems related to different work shifts (day, evening, night shifts) and rest days. In this study, we assessed the psychometric properties of the BSWSQ using a sample of 760 nurses, all working in a three-shift rotation schedule: day, evening, and night shifts. BSWSQ measures insomnia symptoms using seven questions: >30-min sleep onset latency, >30-min wake after sleep onset, >30-min premature awakenings, nonrestorative sleep, being tired/sleepy at work, during free time on work days, and when not working/on vacation. Symptoms are assessed separately for each work shift and rest days, as “never,” “rarely,” “sometimes,” “often,” “always,” or “not applicable.” We investigated the BSWSQ model fit, reliability (test-retest of a subsample, n?=?234), and convergent and discriminant validity between the BSWSQ and Epworth Sleepiness Scale, Fatigue Questionnaire, and Hospital Anxiety Depression Scale. We also investigated differences in mean scores between the different insomnia symptoms with respect to different work shifts and rest days. BSWSQ demonstrated an adequate model fit using structural equation modeling: root mean square error of approximation?=?.071 (90% confidence interval [CI]?=?.066–.076), comparative fit index?=?.91, and chi-square/degrees of freedom?=?4.41. The BSWSQ demonstrated good reliability (test-retest coefficients p?<?.001). We found good convergent and discriminant validity between BSWSQ and the other scales (all coefficients p?<?.001). There were significant differences between the overall/composite scores of the various work shifts. Night shift showed the highest score compared to day and evening shifts as well as to rest days (all post hoc comparisons p?<?.001). Mean scores of different symptoms also varied significantly within the individual work shifts. We conclude that the BSWSQ meets the necessary psychometric standards, enabling systematic study of discrete insomnia symptoms in different work shifts. (Author correspondence: elisabeth.flo@psykp.uib.no)     

Sleep,Sleepiness, and Neurobehavioral Performance While on Watch in a Simulated 4 Hours on/8 Hours off Maritime Watch System

Seafarer sleepiness jeopardizes safety at sea and has been documented as a direct or contributing factor in many maritime accidents. This study investigates sleep, sleepiness, and neurobehavioral performance in a simulated 4?h on/8?h off watch system as well as the effects of a single free watch disturbance, simulating a condition of overtime work, resulting in 16?h of work in a row and a missed sleep opportunity. Thirty bridge officers (age 30?±?6 yrs; 29 men) participated in bridge simulator trials on an identical 1-wk voyage in the North Sea and English Channel. The three watch teams started respectively with the 00–04, the 04–08, and the 08–12 watches. Participants rated their sleepiness every hour (Karolinska Sleepiness Scale [KSS]) and carried out a 5-min psychomotor vigilance test (PVT) test at the start and end of every watch. Polysomnography (PSG) was recorded during 6 watches in the first and the second half of the week. KSS was higher during the first (mean?±?SD: 4.0?±?0.2) compared with the second (3.3?±?0.2) watch of the day (p?<?0.001). In addition, it increased with hours on watch (p?<?0.001), peaking at the end of watch (4.1?±?0.2). The free watch disturbance increased KSS profoundly (p?<?0.001): from 4.2?±?0.2 to 6.5?±?0.3. PVT reaction times were slower during the first (290?±?6?ms) compared with the second (280?±?6?ms) watch of the day (p?<?0.001) as well as at the end of the watch (289?±?6?ms) compared with the start (281?±?6?ms; p?=?0.001). The free watch disturbance increased reaction times (p?<?0.001) from 283?±?5 to 306?±?7?ms. Similar effects were observed for PVT lapses. One third of all participants slept during at least one of the PSG watches. Sleep on watch was most abundant in the team working 00–04 and it increased following the free watch disturbance. This study reveals that—within a 4?h on/8?h off shift system—subjective and objective sleepiness peak during the night and early morning watches, coinciding with a time frame in which relatively many maritime accidents occur. In addition, we showed that overtime work strongly increases sleepiness. Finally, a striking amount of participants fell asleep while on duty.     

补充支链氨基酸对睡眠剥夺大鼠行为和血清游离脂肪酸水平的影响

探讨补充支链氨基酸 (branched -chainaminoacids ,BCAA)对睡眠剥夺 (sleepdeprivation ,SD)大鼠的行为和血清游离脂肪酸 (freefattyacids,FFA)水平的影响。采用小站台水环境 (flower -pot)睡眠剥夺模型对大鼠进行睡眠剥夺。成年、雄性Sprague-Dawley大鼠 5 6只 ,按体重随机分为C(对照组、自由睡眠 )、2 4hSD(剥夺睡眠 2 4h)、2 4hSDB(睡眠剥夺 2 4h ,进食添加BCAA的饲料 )、4 8hSD、4 8hSDB、72hSD、72hSDB组 ,每组 8只。睡眠剥夺结束后 ,采用旷场实验 (openfieldtest,OPT)评价大鼠的精神行为。结果各睡眠剥夺组大鼠的OFT得分均显著高于对照组 (P <0 .0 5 ) ;其中以 4 8hSD组最高 ,72hSD组的OFT得分又显著低于 72hSDB组 (P <0 .0 5 )。睡眠剥夺各组大鼠血清FFA水平均显著高于非剥夺组 ,72hSDB组显著高于 72hSD组 (P <0 .0 5 )。结论为补充支链氨基酸可以改善睡眠剥夺大鼠的旷场实验行为 ,降低睡眠剥夺大鼠血清FFA水平。     

Acute Psychophysiological Relationships Between Mood,Inflammatory and Cortisol Changes in Response to Simulated Physical Firefighting Work and Sleep Restriction

This study examined how changes in wildland firefighters’ mood relate to cytokine and cortisol levels in response to simulated physical firefighting work and sleep restriction. Firefighters completed 3 days of simulated wildfire suppression work separated by an 8-h (control condition; n = 18) or 4-h sleep opportunity (sleep restriction condition; n = 17) each night. Firefighters’ mood was assessed daily using the Mood Scale II and Samn-Perelli fatigue scale. Participants also provided samples for the determination of salivary cortisol and pro- (IL-6, IL-8, IL-1β, TNF-α) and anti-inflammatory (IL-4, IL-10) cytokine levels. An increase in the positive mood dimension Happiness was related to a rise in IL-8 and TNF-α in the sleep restriction condition. A rise in the positive mood dimension Activation among sleep restricted firefighters was also related to higher IL-6 levels. An increase in the negative mood dimension Fatigue in the sleep restriction condition was associated with increased IL-6, TNF-α, IL-10 and cortisol levels. In addition, an increase in Fear among sleep restricted firefighters was associated with a rise in TNF-α. Elevated positive mood and immune activation may reflect an appropriate response by the firefighters to these stressors. To further understand this relationship, subsequent firefighting-based research is needed that investigates whether immune changes are a function of affective arousal linked to the expression of positive moods. Positive associations between negative mood and inflammatory and cortisol levels to physical work and restricted sleep provide useful information to fire agencies about subjective fire-ground indicators of physiological changes.     

A Neuronal Hub Binding Sleep Initiation and Body Cooling in Response to a Warm External Stimulus

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