Partial and sleep-stage-selective deprivation

Occupational, family, and social pressures have led to a society that sleeps less. In 1960, a survey by the American Cancer Society found that people slept, on average, 8 h per night. This figure has dropped today to 6.7 h, a decrease of 15% in less than one generation. This fall may be due to medical conditions, sleep disorders, or medications that inhibit sleep, as well as lifestyle disrupters such as jet lag, exam stress, or parenting infants. With the change toward a 24-h society, working outside of the 9-to-5 day has also become increasingly prevalent. Shift workers commonly obtain less sleep than permanent daytime workers as daytime sleep is sacrificed to accommodate social, family, and leisure activities. Sleep deprivation causes between $43 billion and$56 billion worth of accidents annually, as well as contributing to a substantial number of injuries and deaths worldwide. Humans are biologically programmed to sleep at night, and going without sleep has a range of deleterious consequences for cognitive performance, health, and well-being. This article will first outline the methodologies used to investigate partial sleep deprivation in humans and animals and discuss the neurobehavioral, physiological, and psychosocial consequences of reduced sleep. The article will then describe the function of sleep stages, again summarizing methodologies and reviewing the findings from rapid eye movement (REM) and slow-wave sleep (SWS) selective sleep stage deprivation studies in humans and animals

A forced desynchrony correction

Aim: The forced desynchrony (FD) protocol is used widely in animal and human studies to investigate endogenous circadian and homeostatic processes. With different circadian phases systematically sampled on different experimental days, any longitudinal effect across the experiment can confound the findings. This study aims to assess a method of accounting for longitudinal effects within three FD data sets. It is hypothesised that the endogenous circadian rhythm of core body temperature will have a higher correlation to the circadian performance rhythm after the longitudinal effect is removed. Methods: Two dummy circadian rhythms (sine waves) were plotted and cross-correlated. A linear effect was added to one rhythm and their correlation was reassessed. The previous steps were repeated in reverse order on three FD data sets that contained longitudinal effects. Firstly, the cross-correlations between core body temperature and performance were assessed. A regression of day on performance revealed the linear longitudinal effect for each data set. This was then removed by subtracting the relative effect associated with each day. The cross-correlations between core body temperature and performance were then reassessed. Results: The cross-correlations between the dummy rhythms were higher before the longitudinal effect was added (from r =.75 to r =1). Similarly, the cross-correlations between core body temperature and performance improved after the longitudinal effect was removed from each day (from r =.74, .86 and .74 to r =.96, .93 and .92 respectively). Discussion: After the longitudinal effect was removed, the mean circadian rhythm of performance shared almost all of its variance with the average core body temperature – a measure of the endogenous circadian rhythm. This correction could explain the skewed performance rhythms depicted in many FD papers, as well as the discrepancy between the timing of performance nadirs reported in laboratory studies and in real world observations

More than hours of work: Fatigue management during high-intensity maritime operations

Objectives: This study examines the impacts of peak summer demand on operator workload and fatigue in a maritime environment. Methods: Participants (n = 12) were senior shipboard personnel who were working during the summer “double sailing” period for a roll-on roll-off ferry service. Wrist actigraphy was used to determine sleep opportunity and sleep duration, as well as prior sleep, total wake time, performance and alertness at the beginning and end of work periods. Results: Contrary to expectations, sleep was significantly greater, and both subjective estimates of fatigue and objective neurobehavioral performance were not impacted negatively by periods of increased work intensity. Conclusions: This study highlights a number of features of a fatigue-risk management system that appear to have been instrumental in ensuring adequate sleep and performance was maintained throughout periods of increased operational intensity. As a simple colloquial description of the fatigue-risk management system at play in this operation, it was fine to “work hard” if you were able to “sleep hard” as well. © 2018, © 2018 Taylor & Francis Group, LLC

Driving when distracted and sleepy: The effect of phone and passenger conversations on driving performance

This study investigates the effect of passenger and phone conversations on sleep-restricted driving. Six volunteers (50% male, mean age 24.8 ± 4.3 years) had their sleep restricted to 4 h in bed followed by a 20-min simulated drive on three separate occasions. Each drive included either a passenger conversation, a mobile phone conversation or a quiet passenger. The effect size of a phone conversation on lane deviation was large while passenger conversation was small. The main effect of conversation on lane deviation was non-significant (F(2,10) = 2.57, p = 0.126). Combining sleep-restricted driving with conversations warrants further investigation. © 2018, © 2018 The Author(s). Published by Taylor & Francis Group, LLC

Flat-out napping: The quantity and quality of sleep obtained in a seat during the daytime increase as the angle of recline of the seat increases

Some shiftwokers in the long-haul transportation industries (i.e. road, rail, sea, air) have the opportunity to sleep in on-board rest facilities during duty periods. These rest facilities are typically fitted with a seat with a maximum back angle to the vertical of 20°, 40°, or 90°. The aim of this study was to examine the impact of “back angle” on the quantity and quality of sleep obtained in a seat during a daytime nap. Six healthy adults (3 females aged 27.0 years and 3 males aged 22.7 years) each participated in three conditions. For each condition, participants had a 4-h sleep opportunity in a bed (02:00–06:00 h) followed by a 4-h sleep opportunity in a seat (13:00–17:00 h). The only difference between conditions was in the back angle of the seat to the vertical during the seat-based sleep periods: 20° (upright), 40° (reclined), and 90° (flat). Polysomnographic data were collected during all sleep episodes. For the seat-based sleep episodes, there was a significant effect of back angle on three of four measures of sleep quantity, i.e. total sleep time, slow-wave sleep, and rapid eye movement (REM) sleep, and three of four measures of sleep quality, i.e. latency to REM sleep, arousals, and stage shifts. In general, the quantity and quality of sleep obtained in the reclined and flat seats were better than those obtained in the upright seat. In particular, compared to the flat seat, the reclined seat resulted in similar amounts of total sleep and slow-wave sleep, but 37% less REM sleep; and the upright seat resulted in 29% less total sleep, 30% less slow-wave sleep, and 79% less REM sleep. There are two main mechanisms that may explain the results. First, it is difficult to maintain the head in a comfortable position for sleep when sitting upright, and this is likely exacerbated during REM sleep, when muscle tone is very low. Second, an upright posture increases sympathetic activity and decreases parasympathetic activity, resulting in a heightened level of physiological arousal. © 2018, © 2018 Taylor & Francis Group, LLC

Daily rhythms of hunger and satiety in healthy men during one week of sleep restriction and circadian misalignment

The impact of sleep restriction on the endogenous circadian rhythms of hunger and satiety were examined in 28 healthy young men. Participants were scheduled to 2 × 24-h days of baseline followed by 8 × 28-h days of forced desynchrony during which sleep was either moderately restricted (equivalent to 6 h in bed/24 h; n = 14) or severely restricted (equivalent to 4 h in bed/24 h; n = 14). Self-reported hunger and satisfaction were assessed every 2.5 h during wake periods using visual analogue scales. Participants were served standardised meals and snacks at regular intervals and were not permitted to eat ad libitum. Core body temperature was continuously recorded with rectal thermistors to determine circadian phase. Both hunger and satiety exhibited a marked endogenous circadian rhythm. Hunger was highest, and satiety was lowest, in the biological evening (i.e., ~17:00–21:00 h) whereas hunger was lowest, and satiety was highest in the biological night (i.e., 01:00–05:00 h). The results are consistent with expectations based on previous reports and may explain in some part the decrease in appetite that is commonly reported by individuals who are required to work at night. Interestingly, the endogenous rhythms of hunger and satiety do not appear to be altered by severe—as compared to moderate—sleep restriction

Working time society consensus statements: Individual differences in shift work tolerance and recommendations for research and practice

There is no standard definition of shift work universally, and no validated report of complete biological adjustment to shift work in workers. Similarly, the evidence for shift work tolerance is limited due to a small number of studies and a narrow range of outcome measures. This paper discusses evidence to date regarding individual differences in shift work tolerance and highlights areas for future research and recommendations for workplace practice. The few factors that are consistently associated with perceived or actual shift work tolerance are young age, low scores of morningness or being a late chronotype, low scores of languidity and neuroticism, high scores on extraversion, internal locus of control and flexibility and male sex. An important first step is to differentiate between factors that are potentially modifiable, such as those that are determined by lifestyle choices, and those factors specific to the working time arrangement. Identifying determinants of shift work tolerance and the ability to adjust to shift work, whether they are innate and/ or acquired mechanisms, is important so workers who are less likely to tolerate shift work well can be self-identified and supported with appropriate harm/risk minimization strategies. This paper also identifies important areas for future research with the goal of increasing the evidence base on which we can develop evidence-based harm mitigation strategies for shift workers. © 2019 National Institute of Occupational Safety and Health

Contacts versus connectors: The role of community fire safe group coordinators in achieving positive bushfire safety outcomes

Shared responsibility for bushfire preparedness includes self-reliant communities with the skills, knowledge and ability to minimize the impacts of bushfires on their homes, properties and community. Community preparedness groups are a potentially effective way to achieve this self-reliance. Previous research shows that these groups increase people's knowledge and awareness of risk, their planning and preparations, and community cohesion and collaboration. However, these are not outcomes for all groups in all places. Groups face a perennial problem of low participation and ‘buy in’ from the local area due in part to individual differences in the desire to be part of a group, low levels of risk awareness, community turbidity, and low social capital. This paper proposes that the skills and characteristics of the group coordinator in responding to and overcoming these challenges are key to a group's longevity, collaboration and success. Using interviews and a survey with Community Fire Safe group coordinators and members affected by the 2015 Sampson Flat fire in South Australia, we found the key elements of successful coordination were active outreach to existing neighbourhood residents, newcomers and those ‘not into groups’ using face to face and personalized communication adapted for different people's needs. This active, determined persistence in communicating bushfire safety was motivated by an understanding that low interest can be overcome and that overcoming it is the key role of the group coordinator. Training for coordinators in the individual and group processes underpinning behavior change, in personalized communication, and adapting materials for diverse groups is likely to improve group outcomes

Using interstimulus interval to maximise sensitivity of the Psychomotor Vigilance Test to fatigue

There is some evidence that short interstimulus intervals (ISIs) on the Psychomotor Vigilance Test (PVT) are associated with longer and more varied reaction times (RTs). Preparation processes may impede RT following short ISIs, resulting in additional unexplained variance. The aims of this study were to investigate whether there is an effect of ISI on RT and errors within the PVT, and whether such an effect changes with three elements of fatigue: time of day, prior wake and time on task. Twelve male participants completed 49 PVTs across 7× 28 h periods of forced desynchrony. For analysis, RTs, reciprocal reaction times (1/RT), false starts and lapse responses within each 10 min session were assigned to a 1-s ISI group, a 2-min time of task group, a 2.5-h PW level and a 60° phase of the circadian rhythm of core body temperature (as a measure of time of day). Responses following short ISIs (2–5 s) were significantly slower and more varied than responses following longer ISIs (5–10 s). The likelihood of a lapse was also higher for short ISIs, while the probability of a false start increased as a function of ISI. These effects were independent of the influences of time of day, prior wake and time on task. Hence, mixed model ANOVAs comprising only long ISIs (5–10 s) contained stronger effect sizes for fatigue than a model of all ISIs (2–10 s). Including an ISI variable in a model improved the model fit and explained more variance associated with fatigue. Short ISIs resulted in long RTs both in the presence and absence of fatigue, possibly due to preparation processes or ISI conditioning. Hence, omitting short ISI trials from RT means or including an ISI variable in analysis can reduce unwanted variance in PVT data, improving the sensitivity of the PVT to fatigue

Simulated driving under the influence of extended wake, time of day and sleep restriction

Around a fifth of all road accidents can be attributed to fatigued drivers. Previous studies indicate that driving performance is influenced by time of day and decreases with sustained wakefulness. However, these influences occur naturally in unison,confounding their effects. Typically, when people drive at a poor time of day and with extended wake, their sleep is also restricted. Hence, the aim of the current study was to determine the independent effects of prior wake and time of day on driving performance under conditions of sleep restriction. The driving performance of fourteen male participants (21.8 +/- 3.8 years, mean +/-SD) was assessed during a 10 min simulated driving task with speed/lane mean, variability and violations (speeding and crashes) measured. Participants were tested at 2.5 h intervals after waking, across 7 * 28 h days with a sleep:wake ratio of 1:5. By forced desynchrony each driving session occurred at 9 doses of prior wake and within 6 divisions of the circadian cycle based on core body temperature. A mixed models ANOVA revealed significant main effects of circadian phase, prior wake and sleep debt on lane violations. In addition, three significant two-way interactions (circadian phase * prior wake, prior wake * sleep debt, sleep debt * circadian phase) and one three-way interaction (circadian * prior wake * sleep debt) were identified. The presence of the large interaction effects shows that the influence of each factor is largely dependent on the magnitude of the other factors. For example, the presence of the time of day influence on driving performance is dependent on the length of prior wake or the presence of sleep debt. The findings suggest that people are able to undertake a low-difficulty simulated drive safely, at least for a short period, during their circadian nadir provided that they have had sufficient sleep and have not been awake too long