The influence of split sleep-wake schedules and daytime sleep strategies on neurobehavioural performance

Demand for 24-h access to services and goods has led to an increase in the number of employees engaged in shiftwork. However, while shiftwork has become necessary to meet community expectations, it has serious consequences for health and safety. The risk of fatigue-related accidents and injuries is a significant problem for the shift working population. This is because shiftwork places restrictions on the opportunities available for workers to obtain sleep. Shiftworkers, especially those who work night shifts, must often stay awake for long hours and sleep at times inconsistent with their body clocks, so sleep loss is common. This dissertation evaluates alternative options for arranging sleep that could potentially optimise neurobehavioural function in circumstances where long nocturnal sleep episodes are not possible. Two main approaches were used to address these aims. The first was to assess the effectiveness of split sleep-wake schedules at sustaining neurobehavioural function around the clock – with and without sleep restriction – which could have implications for work rosters in certain safety-critical industries. The second approach was to assess the effectiveness of different arrangements of daytime sleep at ameliorating the decline of night-time performance, which could have implications for the sleep strategies shiftworkers employ before and after night shifts

Declining glucose metabolism across a week of sleep restriction

The incidence of diabetes has reached epidemic proportions and modern society is driven to sleep less. Sleep duration is associated with diabetes risk, and laboratory protocols have demonstrated increases in pre-diabetes indicators after sleep restriction (SR). The aim of this pilot study was to examine the daily effects of SR on glucose metabolism across a week

Food consumption and food choice following one week of sleep restriction : a pilot study

There is evidence to suggest that restricting sleep may result in overconsumption of food and poor food choices. This has been attributed to disruption in appetite hormones following sleep restriction (SR). The aim of this study was to investigate food consumption and food choices before and after either one week of SR or a control condition consisting of one week of 8 h time in bed (TIB)

Two for one? : Validating an energy expenditure monitor against polysomnography for sleep/wake measurement

Gold standard sleep measurement, polysomnography (PSG), is not always practical for field-based research due to time and expense. Wristwatch-like activity monitors that estimate sleep from wrist movement are often used instead. The Actical is an activity monitor designed to estimate energy expenditure. While not specifically designed to measure sleep, it records and stores data in a similar fashion to devices that are. Dual functionality could be useful for research spanning sleep and exercise behaviours, and thus the aim was to evaluate the Actical as an alternative to PSG for field research. Methods: Ten participants spent one night in bed (22:00-07:30 h) in temperature-controlled (21 1C) bedrooms. Each wore an Actical, set to record activity in 30-s epochs, on their non-dominant wrist, and electrodes were placed in the 10-20 arrangement for PSG. PSG data were manually scored as sleep/wake in 30-s epochs. Software provided sleep/wake estimates for Actical epochs at a medium- (default) and a low-activity threshold for wake. Actical sleep/wake data were compared with data from PSG on an epoch-by-epoch basis and in terms of total sleep time (TST), sleep efficiency (SE), and wake after sleep onset (WASO). Results: Actical identified 97 2% (M SD) and 98 1% of PSG-determined sleep epochs, at the low threshold and medium threshold for wake, respectively. Identification of PSG-determined wake was 31 13% and 22 9%, and overall agreements were 89 10% and 88 11%, respectively. TST was overestimated by 25 47 and 36 52 min, and SE by 5 8% and 6 9%; WASO was underestimated by 25 52 and 36 57 min, respectively. Discussion: Results suggest that overall epoch agreement between Acticals and PSG is good and identification of sleep is equally high at both thresholds; however, the lower threshold is better than the default for identifying wake. In addition, the biases of sleep parameters calculated using the Actical were smaller at the low threshold. The results indicated that the Actical is a satisfactory alternative tool for measuring sleep, particularly in field research

No first night shift effect observed following a nocturnal main sleep and a prophylactic 1-h afternoon nap.

Neurobehavioural impairment on the first night shift is often greater than on subsequent night shifts due to extended wakefulness. The aim of the study was to determine whether a 1-h afternoon nap prior to the first night shift is sufficient to produce neurobehavioural performance at levels comparable to the second night shift. Twelve male volunteers (mean age 22.9 years) participated in a laboratory protocol that simulated two 12-h night shifts. A nap preceded the first shift and a 7-h daytime sleep was scheduled between shifts. Neurobehavioural performance and subjective sleepiness measured across each night did not significantly differ between first and second shifts

Alternatives to polysomnography (PSG) : a validation of wrist actigraphy and a partial-PSG system

The objective of this study was to assess the validity of a sleep/wake activity monitor, an energy expenditure activity monitor, and a partial-polysomnography system at measuring sleep and wake under identical conditions. Secondary aims were to evaluate the sleep/wake thresholds for each activity monitor and to compare the three devices. To achieve these aims, two nights of sleep were recorded simultaneously with polysomnography (PSG), two activity monitors, and a partial-PSG system in a sleep laboratory. Agreement with PSG was evaluated epoch by epoch and with summary measures including total sleep time (TST) and wake after sleep onset (WASO). All of the devices had high agreement rates for identifying sleep and wake, but the partial-PSG system was the best, with an agreement of 91.6 % +/- 5.1 %. Attheir best thresholds, the sleep/wake monitor (medium threshold, 87.7 % +/- 7.6 %) and the energy expenditure monitor (very low threshold, 86.8 % +/- 8.6 %) had similarly high rates of agreement. The summary measures were similar to those determined by PSG, but thepartial-PSG system provided the most consistent estimates. Although the partial-PSG system was the most accurate device, both activity monitors were also valid for sleep estimation, provided that appropriate thresholds were selected. Each device has advantages, so the primary consideration for researchers will be to determine which best suits a given research design

Do split sleep/wake schedules reduce or increase sleepiness for continuous operations?

This study compared the impact of split and consolidated sleep/wake schedules on subjective sleepiness during the biological day and biological night. This was achieved using a between-group design involving two forced desynchrony protocols: consolidated sleep/wake and split sleep/wake. Both protocols included 7 × 28-h days with 9.33 h in bed and 18.67 h of wake each day. While the consolidated sleep/wake protocol had 1 × 9.33-h sleep opportunity and 1 × 18.67-h wake period each day, the split sleep/wake protocol had 2 × 4.67-h sleep opportunities and 2 × 9.33-h wake periods each day. For both protocols, subjective sleepiness was measured using the Karolinska Sleepiness Scale every 2.5 h during wake. A total of 29 healthy adult males participated, with 13 in the consolidated sleep/wake group (mean age = 22.5 yrs) and 16 in the split sleep/wake group (mean age = 22.6 yrs). On average, subjective sleepiness during wake periods of the split condition was significantly higher than that during the first half of wake periods of the consolidated condition, but was similar to the level during the second half. These findings were observed for wake periods that occurred during both the biological day and biological night. Previous data have shown that cognitive impairment at night is lower for split schedules than consolidated schedules, but the current data indicate that feelings of sleepiness are greater for split schedules than consolidated schedules for at least half of the time awake. Thus, it should be explained to people operating split sleep/wake schedules that although they may perform well, they are likely to feel sleepy

Are two halves better than one whole? : a comparison of the amount and quality of sleep obtained by healthy adult males living on split and consolidated sleep–wake schedules

The aim of this study was to compare the quantity/quality of sleep obtained by people living on split and consolidated sleep–wake schedules. The study had a between-groups design, with 13 participants in a consolidated condition (all males, mean age of 22.5 yr) and 16 participants in a split condition (all males, mean age of 22.6 yr). Both conditions employed forced desynchrony protocols with the activity:rest ratio set at 2:1, but the consolidated condition had one sleep–wake cycle every 28 h (9.33 + 18.67), while the split condition had one sleep–wake cycle every 14 h (4.67 + 9.33). Sleep was assessed using polysomnography. Participants in the split and consolidated conditions obtained 4.0 h of sleep per 14 h and 7.6 h of sleep per 28 h, respectively. Some differences between the groups indicated that sleep quality was lower in the split condition than the consolidated condition: the split sleeps had longer sleep onset latency (9.7 vs. 4.3 min), more arousals (7.4 vs. 5.7 per hour in bed), and a greater percentage of stage 1 sleep (4.1% vs. 3.1%), than the consolidated sleeps. Other differences between the groups indicated that sleep quality was higher in the split condition than the consolidated condition: the split sleeps had a lower percentage of wake after sleep onset sleep (11.7% vs. 17.6%), and a greater percentage of slow wave sleep (30.2% vs. 23.8%), than the consolidated sleeps. These results indicate that the split schedule was not particularly harmful, and may have actually been beneficial, to sleep. Split work–rest schedules can be socially disruptive, but their use may be warranted in work settings where shiftworkers are separated from their normal family/social lives (e.g., fly-in fly-out mining) or where the need for family/social time is secondary to the task (e.g., emergency response to natural disasters)

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

The efficacy of subjective ratings is limited during the biological night

Aims: Disturbed sleep is associated with sleepiness and impaired neurobehavioral performance. It is important to implement strategies to minimise the impact of performance impairment. It can be difficult for an individual to know when their performance is impaired by sleepiness. The aim of the present study was to examine whether the efficacy of subjective ratings varies as a function of circadian phase