Performance, sleep and circadian phase during a week of simulated night work

The current study investigated changes in night-time performance, daytime sleep, and circadian phase during a week of simulated shift work. Fifteen young subjects participated in an adaptation and baseline night sleep, directly followed by seven night shifts. Subjects slept from approximately 0800 hr until they naturally awoke. Polysomnographic data was collected for each sleep period. Saliva samples were collected at half hourly intervals, from 2000 hr to bedtime. Each night, performance was tested at hourly intervals. Analysis indicated that there was a significant increase in mean performance across the week. In general, sleep was not negatively affected. Rather, sleep quality appeared to improve across the week. However, total sleep time (TST) for each day sleep was slightly reduced from baseline, resulting in a small cumulative sleep debt of 3.53 (SD = 5.62) hours. Finally, the melatonin profile shifted across the week, resulting in a mean phase delay of 5.5 hours. These findings indicate that when sleep loss is minimized and a circadian phase shift occurs, adaptation of performance can occur during several consecutive night shifts.     

A compromise phase position for permanent night shift workers: circadian phase after two night shifts with scheduled sleep and light/dark exposure

Night shift work is associated with a myriad of health and safety risks. Phase-shifting the circadian clock such that it is more aligned with night work and day sleep is one way to attenuate these risks. However, workers will not be satisfied with complete adaptation to night work if it leaves them misaligned during days off. Therefore, the goal of this set of studies is to produce a compromise phase position in which individuals working night shifts delay their circadian clocks to a position that is more compatible with nighttime work and daytime sleep yet is not incompatible with late nighttime sleep on days off. This is the first in the set of studies describing the magnitude of circadian phase delays that occurs on progressively later days within a series of night shifts interspersed with days off. The series will be ended on various days in order to take a "snapshot" of circadian phase. In this set of studies, subjects sleep from 23:00 to 7:00 h for three weeks. Following this baseline period, there is a series of night shifts (23:00 to 07:00 h) and days off. Experimental subjects receive five 15 min intermittent bright light pulses (approximately 3500 lux; approximately 1100 microW/cm2) once per hour during the night shifts, wear sunglasses that attenuate all visible wavelengths--especially short wavelengths ("blue-blockers")--while traveling home after the shifts, and sleep in the dark (08:30-15:30 h) after each night shift. Control subjects remain in typical dim room light (<50 lux) throughout the night shift, wear sunglasses that do not attenuate as much light, and sleep whenever they want after the night shifts. Circadian phase is determined from the circadian rhythm of melatonin collected during a dim light phase assessment at the beginning and end of each study. The sleepiest time of day, approximated by the body temperature minimum (Tmin), is estimated by adding 7 h to the dim light melatonin onset. In this first study, circadian phase was measured after two night shifts and day sleep periods. The Tmin of the experimental subjects (n=11) was 04:24+/-0.8 h (mean+/-SD) at baseline and 7:36+/-1.4 h after the night shifts. Thus, after two night shifts, the Tmin had not yet delayed into the daytime sleep period, which began at 08:30 h. The Tmin of the control subjects (n=12) was 04:00+/-1.2 h at baseline and drifted to 4:36+/-1.4 h after the night shifts. Thus, two night shifts with a practical pattern of intermittent bright light, the wearing of sunglasses on the way home from night shifts, and a regular sleep period early in the daytime, phase delayed the circadian clock toward the desired compromise phase position for permanent night shift workers. Additional night shifts with bright light pulses and daytime sleep in the dark are expected to displace the sleepiest time of day into the daytime sleep period, improving both nighttime alertness and daytime sleep but not precluding adequate sleep on days off.     

The circadian disruption of night work alters gut microbiota consistent with elevated risk for future metabolic and gastrointestinal pathology

ABSTRACT

Day and night cycles are the most important cue for the central clock of human beings, and they are also important for the gut clock. The aim of the study is to determine the differences in the gut microbiota of rotational shift workers when working the day versus night shift. Fecal samples and other data were collected from 10 volunteer male security officers after 4 weeks of day shift work (07:00–15:00 h) and also after 2 weeks of night shift work (23:00–07:00 h). In total, 20 stool samples were collected for analysis of gut microbiota (10 subjects x 2 work shifts) and stored at ?80°C until analysis by 16 S rRNA sequencing. The relative abundances of Bacteroidetes were reduced and those of Actinobacteria and Firmicutes increased when working the night compared to day shift. Faecalibacterium abundance was found to be a biomarker of the day shift work. Dorea longicatena and Dorea formicigenerans were significantly more abundant in individuals when working the night shift. Rotational day and night shift work causes circadian rhythm disturbance with an associated alteration in the abundances of gut microbiota, leading to the concern that such induced alteration of gut microbiota may at least partially contribute to an increased risk of future metabolic syndrome and gastrointestinal pathology.     

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.     

完全睡眠剥夺对大脑注意网络冲突效应和脑电样本熵的影响*

目的: 本研究分析睡眠剥夺对个体选择性注意网络冲突效应和脑电样本熵的影响,探讨睡眠剥夺对大脑注意网络的影响。方法: 25名健康受试者参与36 h完全睡眠剥夺试验。试验于当天9:00开始,于次日21:00结束,试验采用自身前后对照设计。受试者在睡眠剥夺前后分别完成注意网络任务,同步采集受试者的脑电图。用脑电样本熵算法分析脑电图的delta、theta、alpha、beta和gamma频率段的脑电复杂度并对比各频段脑电样本熵在睡眠剥夺前、后的变化。结果: 同睡眠剥夺前比较,睡眠剥夺后与受试者的注意网络冲突效应密切相关的反应时显著下降(P＜0.01),正确率显著增加(P＜0.01)。脑电样本熵分析发现在beta频率段,与注意网络冲突控制相关的脑电样本熵值在睡眠剥夺后明显增大(P＜0.01)。其余脑电频率段脑电样本熵未发现显著差异。结论: 表明完全睡眠剥夺后大脑的注意网络冲突效应降低,表明睡眠剥夺后执行冲突控制能力的下降。     

Effects of sustained manual work and partial sleep deprivation on muscular strength and endurance

In a military field artillery trial, the effects of 8 days of sustained manual work and partial sleep loss on isometric right hand grip strength and upper and lower body anaerobic power (using the Wingate test) was investigated in 25 healthy young male soldiers. During the trial, the physical activity of each subject was essentially identical except that an experimental group (n = 18) manually handled a large quantity of artillery shells (weighing 45 kg) and charges (13 kg), whilst a control group (n = 7) merely simulated manual handling activities and did no lifting or loading of shells. The daily amount of sleep obtained by each group was similar (3 to 4 hours), as were their activity patterns and food and fluid intake. Isometric right hand grip strength for both groups fell progressively during the trial and did not return to pre-trial levels during 3 days of recovery. At the end of the 8 day trial, there were statistically significant reductions in the body weight (1.9%, p less than 0.001), % body fat (7.1%, p less than 0.001) and upper body mean power (7.3%, p less than 0.01) of the experimental group but not in the controls. Lower body peak and mean power were significantly increased at the end of the trial in both the experimental (14.7%, p less than 0.001 and 17.0%, p less than 0.001 respectively) and control (14.3%, p less than 0.01 and 15.0%, p less than 0.05 respectively) groups. Lower body power decrease was significantly increased (18.1%, p less than 0.05) in the experimental group but not in the controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

The impact of sleep timing and bright light exposure on attentional impairment during night work

The prevalence of hazardous incidents induced by attentional impairment during night work and ensuing commute times is attributable to circadian misalignment and increased sleep pressure. In a 10-day shift work simulation protocol (4 day shifts and 3 night shifts), the efficacies of 2 countermeasures against nighttime (2300 to 0700 h) attentional impairment were compared: (1) Morning Sleep (0800 to 1600 h; n = 18) in conjunction with a phase-delaying light exposure (2300 to 0300 h), and (2) Evening Sleep (1400 to 2200 h; n = 17) in conjunction with a phase-advancing light exposure (0300 to 0700 h). Analysis of the dim light salivary melatonin onset indicated a modest but significant circadian realignment in both sleep groups (evening sleep: 2.27 +/- 0.6 h phase advance, p < 0.01; morning sleep: 4.98 +/- 0.43 h phase delay, p < 0.01). Daytime sleep efficiency and total sleep time did not differ between them or from their respective baseline sleep (2200 to 0600 h; p > 0.05). However, on the final night shift, the evening sleep subjects had 37% fewer episodes of attentional impairment (long response times: 22 +/- 4 vs. 35 +/- 4; p = 0.02) and quicker responses (p < 0.01) on the Psychomotor Vigilance Task than their morning sleep counterparts. Their response speed recovered to near daytime levels (p = 0.47), whereas those of the morning sleep subjects continued to be slower than their daytime levels (p = 0.008). It is concluded that partial circadian realignment to night work in combination with reduced homeostatic pressure contributed to the greater efficacy of a schedule of Evening Sleep with a phase-advancing light exposure as a countermeasure against attentional impairment, over a schedule of Morning Sleep with a phase-delaying light exposure. These results have important implications for managing patients with shift work disorder.     

Integration of videooculography and encephalography for investigation of visual selective attention in humans

An original method of EEG recording in combination with eye tracking was developed. Due to the precise synchronization (which can include any amount of various recording devices), it is now possible to record short-time electrophysiological patterns evoked by some visual stimulus. The key feature of the method is the possibility to study not only single effects of a stimulus but to extract electrophysiological records corresponding to some part of complex image scanning.     

Restricted sleep regime in rhesus monkeys: differential effect of one night's sleep loss and selective REM deprivation.

The differential effect of either one night's total sleep deprivation (TSD) or of selective REM deprivation (REMD) was examined on post-deprivation daytime EEG patterns with respect to control, in the same group of rhesus monkeys. TSD resulted in significantly decreased wakefulness and increased amounts of NREM and REM on the first day following TSD. In contrast, highly significant REM elevation without alteration of other EEG states occurred for 3 days after REMD. Post-deprivation behavioural and photic-induced neural changes were minor. The results obtained after sleep deprivation in simians are comparable with similar findings in human subjects.     

Prolonged mild hypoxia modifies human circadian core body temperature and may be associated with sleep disturbances

Fatigue is often reported after long-haul airplane flights. Hypobaric hypoxia, observed in pressurized cabins, may play a role in this phenomenon by altering circadian rhythms. In a controlled cross-over study, we assessed the effects of two levels of hypoxia, corresponding to cabin altitudes of 8000 and 12,000 ft, on the rhythm of core body temperature (CBT), a marker of circadian rhythmicity, and on subjective sleep. Twenty healthy young male volunteers were exposed for 8 h (08:00-16:00 h) in a hypobaric chamber to a cabin altitude of 8000 ft and, 4 weeks later, 12,000 ft. Each subject served as his own control. For each exposure, CBT was recorded by telemetry for two 24 h cycles (control and hypoxic exposure). After filtering out nonphysiological values, the individual CBT data were fitted with a five-order moving average before statistical group analysis. Sleep latency, sleep time, and sleep efficiency were studied by sleep logs completed every day in the morning. Our results show that the CBT rhythm expression was altered, mainly at 12,000 ft, with a significant increase of amplitude and a delay in the evening decline in CBT, associated with alterations of sleep latency. Mild hypoxia may therefore alter circadian structure and result in sleep disturbances. These results may explain in part the frequent complaints of prolonged post-flight fatigue after long flights, even when no time zones are crossed.     

Improvement of the night sleep quality by electrocutaneous subthreshold stimulation synchronized with the slow wave sleep

Changes in sleep characteristics were studied under the non-wake-up stimulation with current pulses of less than 1 μA on average, applied to the palmar surface skin receptors during Δ-sleep. A significant increase in duration of the first and second cycles of deep sleep has been found, as well as a shorter latent period before the Δ-sleep onset and a longer time of the rapid sleep (REM phase). The sleep structure improvement was accompanied by the reduced reactive anxiety and depression and an increase in subjective physical efficiency.     

The effects of two types of sleep deprivation on visual working memory capacity and filtering efficiency

Sleep deprivation has adverse consequences for a variety of cognitive functions. The exact effects of sleep deprivation, though, are dependent upon the cognitive process examined. Within working memory, for example, some component processes are more vulnerable to sleep deprivation than others. Additionally, the differential impacts on cognition of different types of sleep deprivation have not been well studied. The aim of this study was to examine the effects of one night of total sleep deprivation and 4 nights of partial sleep deprivation (4 hours in bed/night) on two components of visual working memory: capacity and filtering efficiency. Forty-four healthy young adults were randomly assigned to one of the two sleep deprivation conditions. All participants were studied: 1) in a well-rested condition (following 6 nights of 9 hours in bed/night); and 2) following sleep deprivation, in a counter-balanced order. Visual working memory testing consisted of two related tasks. The first measured visual working memory capacity and the second measured the ability to ignore distractor stimuli in a visual scene (filtering efficiency). Results showed neither type of sleep deprivation reduced visual working memory capacity. Partial sleep deprivation also generally did not change filtering efficiency. Total sleep deprivation, on the other hand, did impair performance in the filtering task. These results suggest components of visual working memory are differentially vulnerable to the effects of sleep deprivation, and different types of sleep deprivation impact visual working memory to different degrees. Such findings have implications for operational settings where individuals may need to perform with inadequate sleep and whose jobs involve receiving an array of visual information and discriminating the relevant from the irrelevant prior to making decisions or taking actions (e.g., baggage screeners, air traffic controllers, military personnel, health care providers).     

Circadian fluctuations in the muscular efficiency of athletes: with sleep versus sleep deprivation

The influence of time of day on muscular performance was studied. From part of the results of two different studies (EAS et EPS), the effects of sleep deprivation were appreciated. Seven times over the 24-h period, developed torque and myoelectric activity were estimated during maximal isometric voluntary contractions using an isokinetic dynamometer: elbow flexion for EAS in standardised sleep, and knee extension for EPS in complete sleep deprivation. The results showed nycthemeral changes in torque in both conditions (p < 0.005), with maximal values recorded at the beginning of night. Although during sleep deprivation (EPS) the rhythm followed neurophysiological factors, during EAS, this rhythm was accounted for by the variations in the contractile state of muscle.     

Different processing phases for features, figures, and selective attention in the primary visual cortex

Our visual system imposes structure onto images that usually contain a diversity of surfaces, contours, and colors. Psychological theories propose that there are multiple steps in this process that occur in hierarchically organized regions of the cortex: early visual areas register basic features, higher areas bind them into objects, and yet higher areas select the objects that are relevant for behavior. Here we test these theories by recording from the primary visual cortex (area V1) of monkeys. We demonstrate that the V1 neurons first register the features (at a latency of 48 ms), then segregate figures from the background (after 57 ms), and finally select relevant figures over irrelevant ones (after 137 ms). We conclude that the psychological processing stages map onto distinct time episodes that unfold in the visual cortex after the presentation of a new stimulus, so that area V1 may contribute to all these processing steps.     

Manifestations of selective visual attention in human parietal and temporal cortex according to evoked potentials

The event-related potentials (ERPs) in visual discrimination task in parietal and temporal cortical areas were recorded in 11 young adults during passive observation (involuntary attention) and target selection (voluntary attention). The voluntary selective attention resulted in: 1) increased ERP correlation between the parietal; and temporal cortical areas; 2) increased correlation of sequential ERPs in monopolar leads (P3, P4, T3, T4, T5, T6); and 3) increased correlation of sequential ERPs in bipolar leads (P3-T3, P3-T5, P4-T4, P4-T6). The findings suggest that voluntary attention maintains a concordant activity of the parietal and temporal cortical areas in execution of visual selection tasks.     

Does the compromised sleep and circadian disruption of night and shiftworkers make them highly vulnerable to 2019 coronavirus disease (COVID-19)?

ABSTRACT

Rotating and permanent night shiftwork schedules typically result in acute and sometimes chronic sleep deprivation plus acute and sometimes chronic disruption of the circadian time structure. Immune system processes and functionalities are organized as circadian rhythms, and they are also strongly influenced by sleep status. Sleep is a vital behavioral state of living beings and a modulator of immune function and responsiveness. Shiftworkers show increased risk for developing viral infections due to possible compromise of both innate and acquired immunity responses. Short sleep and sleep loss, common consequences of shiftwork, are associated with altered integrity of the immune system. We discuss the possible excess risk for COVID-19 infection in the context of the common conditions among shiftworkers, including nurses, doctors, and first responders, among others of high exposure to the contagion, of sleep imbalance and circadian disruption.     

Changes in the expression of steroid metabolism-related genes in rat adrenal glands during selective REM sleep deprivation

Selective REM sleep deprivation was carried out under the conditions designed to minimize the adverse influence of environmental conditions and restricted movement, and the influence of REM sleep deprivation on adrenocortical steroid metabolism was investigated by measuring the steady-state levels of mRNAs encoding steroid metabolism-related genes, steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage enzyme cytochrome P450 (P450scc) and steroid 5alpha-reductase (5alpha-R), in rat adrenal glands. Selective REM sleep deprivation caused a significant decrease in StAR mRNA and an increase in 5alpha-R mRNA levels without any notable change in P450scc mRNA levels in the adrenal gland. In contrast, non-selective sleep disturbance, resulting in the partial reductions of non-REM and REM sleep, tended to increase both StAR and P450scc mRNA levels without any statistical significance. These results indicate that REM sleep deprivation by itself may affect the expression of steroid metabolism-related genes in the adrenal gland, suggesting a possible relation between REM sleep and adrenocortical steroid metabolism.     

Combinations of bright light, scheduled dark, sunglasses, and melatonin to facilitate circadian entrainment to night shift work

Various combinations of interventions were used to phase-delay circadian rhythms to correct their misalignment with night work and day sleep. Young participants (median age = 22, n = 67) participated in 5 consecutive simulated night shifts (2300 to 0700) and then slept at home (0830 to 1530) in darkened bedrooms. Participants wore sunglasses with normal or dark lenses (transmission 15% or 2%) when outside during the day. Participants took placebo or melatonin (1.8 mg sustained release) before daytime sleep. During the night shifts, participants were exposed to a moving (delaying) pattern of intermittent bright light (approximately 5000 lux, 20 min on, 40 min off, 4-5 light pulses/night) or remained in dim light (approximately 150 lux). There were 6 intervention groups ranging from the least complex (normal sunglasses) to the most complex (dark sunglasses + bright light + melatonin). The dim light melatonin onset (DLMO) was assessed before and after the night shifts (baseline and final), and 7 h was added to estimate the temperature minimum (Tmin). Participants were categorized by their amount of reentrainment based on their final Tmin: not re-entrained (Tmin before the daytime dark/sleep period), partially re-entrained (Tmin during the first half of dark/sleep), or completely re-entrained (Tmin during the second half of dark/ sleep). The sample was split into earlier participants (baseline Tmin < or = 0700, sunlight during the commute home fell after the Tmin) and later participants (baseline Tmin > 0700). The later participants were completely re-entrained regardless of intervention group, whereas the degree of re-entrainment for the earlier participants depended on the interventions. With bright light during the night shift, almost all of the earlier participants achieved complete re-entrainment, and the phase delay shift was so large that darker sunglasses and melatonin could not increase its magnitude. With only room light during the night shift, darker sunglasses helped earlier participants phase-delay more than normal sunglasses, but melatonin did not increase the phase delay. The authors recommend the combination of intermittent bright light during the night shift, sunglasses (as dark as possible) during the commute home, and a regular, early daytime dark/sleep period if the goal is complete circadian adaptation to night-shift work.