Split Sleep Research Articles

Sleep: Eye-Opener Highlights Sleep’s Organization

What can eyes tell us about what happens during sleep? Their movements split sleep into two distinct states- rapid-eye-movement (REM) or non-REM sleep. A new study now reveals that periodic pupil constrictions are linked to non-REM sleep plunging into deeper offline states and back about every minute.

Modeling the adenosine system as a modulator of cognitive performance and sleep patterns during sleep restriction and recovery.

Sleep loss causes profound cognitive impairments and increases the concentrations of adenosine and adenosine A1 receptors in specific regions of the brain. Time courses for performance impairment and recovery differ between acute and chronic sleep loss, but the physiological basis for these time courses is unknown. Adenosine has been implicated in pathways that generate sleepiness and cognitive impairments, but existing mathematical models of sleep and cognitive performance do not explicitly include adenosine. Here, we developed a novel receptor-ligand model of the adenosine system to test the hypothesis that changes in both adenosine and A1 receptor concentrations can capture changes in cognitive performance during acute sleep deprivation (one prolonged wake episode), chronic sleep restriction (multiple nights with insufficient sleep), and subsequent recovery. Parameter values were estimated using biochemical data and reaction time performance on the psychomotor vigilance test (PVT). The model closely fit group-average PVT data during acute sleep deprivation, chronic sleep restriction, and recovery. We tested the model’s ability to reproduce timing and duration of sleep in a separate experiment where individuals were permitted to sleep for up to 14 hours per day for 28 days. The model accurately reproduced these data, and also correctly predicted the possible emergence of a split sleep pattern (two distinct sleep episodes) under these experimental conditions. Our findings provide a physiologically plausible explanation for observed changes in cognitive performance and sleep during sleep loss and recovery, as well as a new approach for predicting sleep and cognitive performance under planned schedules.

The effect of split sleep schedules (6h-on/6h-off) on neurobehavioural performance, sleep and sleepiness

Shorter, more frequent rosters, such as 6h-on/6h-off split shifts, may offer promise to sleep, subjective sleepiness and performance by limiting shift length and by offering opportunities for all workers to obtain some sleep across the biological night. However, there exists a paucity of studies that have examined these shifts using objective measures of sleep and performance. The present study examined neurobehavioural performance, sleepiness and sleep during 6h-on/6h-off split sleep schedules. Sixteen healthy adults (6 males, 26.13y ± 4.46) participated in a 9-day laboratory study that included two baseline nights (BL, 10h time in bed (TIB), 2200h-0800h), 4 days on one of two types of 6h-on/6h-off split sleep schedules with 5h TIB during each ‘off’ period (6h early: TIB 0300h-0800h and 1500h-20000h, or 6-h late: TIB 0900h-1400h and 2100h-0200h), and two recovery nights (10h TIB per night, 2200h-0800h). Participants received 10h TIB per 24h in total across both shift schedules. A neurobehavioural test bout was completed every 2 h during wake, which included the Psychomotor Vigilance Task (PVT) and the Karolinska Sleepiness Scale (KSS). Linear mixed effects models were used to assess the effect of day (BL, shift days 1–4), schedule (6h early, 6h late) and trial (numbers 1–6) on PVT lapses (operationalised as the number of reaction times >500 ms), PVT total lapse time, PVT fastest 10% of reaction times and KSS. Analyses were also conducted examining the effect of day and schedule on sleep variables. Overall, PVT lapses and total lapse time did not differ significantly between baseline and shift days, however, peak response speeds were significantly slower on the first shift day when compared to baseline, but only for those in the 6h-late condition. Circadian variations were apparent in performance outcomes, with individuals in the 6h-late condition demonstrated significantly more and longer lapses and slower peak reaction times at the end of their night shift (0730h) than at any other time during their shifts. In the 6h-early condition, only response speed significantly differed across trials, with slower response speeds occurring at trial 1 (0930h) than in trials 3 (1330h) or 4 (2130h). While subjective sleepiness was higher on shift days than at baseline, sleepiness did not accumulate across days. Total sleep was reduced across split sleep schedules compared to baseline. Overall, these results show that while there was not a cumulative cost to performance across days of splitting sleep, participants obtained less sleep and reported lowered alertness on shift days. Tests near the circadian nadir showed higher sleepiness and increased performance deficits. While this schedule did not produce cumulative impairment, the performance deficits witnessed during the biological night are still of operational concern for industry and workers alike.

Obstructive sleep apnea in non-dialysis chronic kidney disease patients

There is an enormous increase in the burden of chronic kidney disease both in developing and developed countries. There is a paucity of data on obstructive sleep apnea (OSA) in chronic kidney disease (CKD) patients in India. We used a cross-sectional prospective observational study to determine the prevalence of OSA in non-dialysis CKD patients. Of the 647 CKD patients 302 patients were in stage II, III and IV. The study population was screened using the Berlin questionnaire and 87 patients were positive for OSA (28%). Among the 87, 37 patients were excluded based on the exclusion criteria. Fifty patients underwent a split night sleep study. Stage II, III CKD patients were clubbed as early CKD or group one and stage IV CKD patients were clubbed as late CKD or group two. The spilt night study revealed an 88% incidence of OSA of varying severity. A sub group analysis was done to assess the severity of OSA. A statistical significance (p < 0.05) between early and late CKD group was observed with respect to AHI and ODI. An improvement in the late CKD is observed and the Z values for AHI and ODI are 4.273 and 2.307, respectively. The prevalence and incidence of OSA was found to be 28% and 88% in non-dialysis CKD patients, respectively and the risk and severity of OSA increased with the progression of CKD stages and thus necessitating the need for screening the non-dialysis CKD population.

Investigation of the effectiveness of a split sleep schedule in sustaining sleep and maintaining performance

Shift work is common in today’s society, and is associated with negative health outcomes, and accidents and incidents. These detrimental effects can be primarily attributed to sleeping and working at an adverse circadian time. The aim of this study was to examine whether a split sleep schedule is as effective as a consolidated day shift or night shift schedule for maintaining performance and sustaining sleep. Fifty-three healthy male volunteers (mean ± SD age = 26.51 ± 4.07 years) underwent a randomized three condition study design. A split sleep condition involving two 5-h sleeping opportunities in 24 h [time in bed (TIB) 0300 h–0800 h and 1500 h–2000 h] was compared to a 10-h consolidated nighttime sleep (TIB 2200 h–0800 h) and 10-h consolidated daytime sleep (TIB 1000 h–2000 h). All participants underwent a baseline period of 10 h of nocturnal time in bed (TIB) followed by a 5-d simulated workweek spent in one of the three conditions. Polysomnography, psychomotor vigilance task, digit-symbol substitution task and subjective state were assessed. During the 5-d simulated workweek, participants in the nighttime sleep condition slept the most (total sleep time per day (TST) 8.4 h ± 13.4 min), followed by the split sleep condition (TST 7.16 h ± 14.2 min) and the daytime sleep condition (TST 6.4 h ± 15.3 min). Subjective sleepiness was highest in the daytime sleep condition and lowest in the nighttime sleep condition. No significant differences in performance were observed between the conditions. Compared to a nighttime consolidated sleep opportunity or split sleep, placement of a consolidated sleep opportunity during the day yielded truncated sleep and increased sleepiness. Further research in real-world situations is warranted to fully assess the efficacy of alternative split sleep schedules for improving safety and productivity.

The effects of a split sleep–wake schedule on neurobehavioural performance and predictions of performance under conditions of forced desynchrony

Extended wakefulness, sleep loss, and circadian misalignment are factors associated with an increased accident risk in shiftwork. Splitting shifts into multiple shorter periods per day may mitigate these risks by alleviating prior wake. However, the effect of splitting the sleep–wake schedule on the homeostatic and circadian contributions to neurobehavioural performance and subjective assessments of one’s ability to perform are not known. Twenty-nine male participants lived in a time isolation laboratory for 13 d, assigned to one of two 28-h forced desynchrony (FD) schedules. Depending on the assigned schedule, participants were provided the same total time in bed (TIB) each FD cycle, either consolidated into a single period (9.33 h TIB) or split into two equal halves (2 × 4.67 h TIB). Neurobehavioural performance was regularly assessed with a psychomotor vigilance task (PVT) and subjectively-assessed ability was measured with a prediction of performance on a visual analogue scale. Polysomnography was used to assess sleep, and core body temperature was recorded to assess circadian phase. On average, participants obtained the same amount of sleep in both schedules, but those in the split schedule obtained more slow wave sleep (SWS) on FD days. Mixed-effects ANOVAs indicated no overall difference between the standard and split schedules in neurobehavioural performance or predictions of performance. Main effects of circadian phase and prior wake were present for both schedules, such that performance and subjective ratings of ability were best around the circadian acrophase, worst around the nadir, and declined with increasing prior wake. There was a schedule by circadian phase interaction for all neurobehavioural performance metrics such that performance was better in the split schedule than the standard schedule around the nadir. There was no such interaction for predictions of performance. Performance during the standard schedule was significantly better than the split schedule at 2 h of prior wake, but declined at a steeper rate such that the schedules converged by 4.5–7 h of prior wake. Overall, the results indicate that when the total opportunity for sleep per day is satisfactory, a split sleep–wake schedule is not detrimental to sleep or performance. Indeed, though not reflected in subjective assessments of performance capacity, splitting the schedule may be of some benefit, given its reduction of neurobehavioural impairment at night and its association with increased SWS. Therefore, for some industries that require operations to be sustained around the clock, implementing a split work–rest schedule may be of assistance.

Sleep architecture of consolidated and split sleep due to the dawn (Fajr) prayer among Muslims and its impact on daytime sleepiness

BACKGROUND:Muslims are required to wake up early to pray (Fajr) at dawn (approximately one and one-half hours before sunrise). Some Muslims wake up to pray Fajr and then sleep until it is time to work (split sleep), whereas others sleep continuously (consolidated sleep) until work time and pray Fajr upon awakening.AIM:To objectively assess sleep architecture and daytime sleepiness in consolidated and split sleep due to the Fajr prayer.SETTING AND DESIGN:A cross-sectional, single-center observational study in eight healthy male subjects with a mean age of 32.0 ± 2.4 years.METHODS:The participants spent three nights in the Sleep Disorders Center (SDC) at King Khalid University Hospital, where they participated in the study, which included (1) a medical checkup and an adaptation night, (2) a consolidated sleep night, and (3) a split-sleep night. Polysomnography (PSG) was conducted in the SDC following the standard protocol. Participants went to bed at 11:30 PM and woke up at 7:00 AM in the consolidated sleep protocol. In the split-sleep protocol, participants went to bed at 11:30 PM, woke up at 3:30 AM for 45 minutes, went back to bed at 4:15 AM, and finally woke up at 7:45 AM. PSG was followed by a multiple sleep latency test to assess the daytime sleepiness of the participants.RESULTS:There were no differences in sleep efficiency, the distribution of sleep stages, or daytime sleepiness between the two protocols.CONCLUSION:No differences were detected in sleep architecture or daytime sleepiness in the consolidated and split-sleep schedules when the total sleep duration was maintained.

The evaluation of the Croatian version of the Epworth sleepiness scale and STOP questionnaire as screening tools for obstructive sleep apnea syndrome

Growing awareness of obstructive sleep apnea syndrome (OSAS) has increased the need for concise and reliable screening tools. The Epworth sleepiness scale (ESS) has been validated in numerous languages and ethnic groups, since it was originally designed for the English-speaking population. The STOP questionnaire was developed as a novel OSAS screening tool in surgical patients, but has not been validated in the general population. The present study was undertaken to provide reliable and validated ESS in the Croatian language and to evaluate the ESS and STOP as screening instruments for OSAS. The Croatian version of ESS and STOP questionnaire was administered to 217 patients referred to the Split Sleep Medicine Center and 208 healthy control subjects. Test-retest reliability was investigated in 20 healthy subjects. The ESS score was significantly higher for the patients referred to the Split Sleep Medicine Center compared to the control group (8.2 ± 5.0 vs. 5.9 ± 3.8, p < 0.001). Cronbach's alpha coefficient for the ESS Croatian version was 0.84 indicating an excellent internal consistency. Reproducibility revealed no significant difference in each item or in the total ESS scores. Receiver operating curve of the ESS for identification of cases with AHI >5/h was 0.64, and for the STOP questionnaire, it was 0.84. Both ESS and STOP questionnaires successfully distinguished healthy subjects from subjects with OSAS. The STOP questionnaire had better probability to correctly predict high-risk patients for OSAS compared to ESS. We propose that the STOP questionnaire could be used as an easy-to-use and accurate screening tool in identification of patients with risk for OSAS in the general population, but it has not been tested in the Croatian population yet.

Modeling fatigue-related truck accidents: Prior sleep duration, recency and continuity

A review of fatigue-management approaches proposed an alternative to hours of service (HOS) regulations based on prior sleep and wakefulness (PSW). This approach states that an individual must have ≥X h and ≥Y h sleep in the 24-h and 48-h periods prior to work, respectively; and that the continuous period for which they have been awake by the end of the shift must be less than or equal to the amount of sleep they have had in the prior 48 h. An a priori model with X = 5 and Y = 12 was suggested. This study investigated the ability to predict fatigue-related accidents using: (a) the a priori model; (b) an optimized model (manipulating X and Y); (c) models with continuous or split sleep; (d) HOS indicators; and (e) combined PSW and HOS models. Sleep and work histories were collected from 107 truck accidents (male drivers, aged 23–66 y), of which 62 had a probable cause of fatigue. The a priori model correctly classified 65%, and the optimized model (6.5 h in the prior 24 h and 8 h in the prior 48 h) nearly 71% of accidents. A simplified model of 6.5 h continuous sleep in the prior 24 h correctly classified nearly 75%. HOS indicators correctly classified <60% and combined models, approximately 73%. PSW or combined PSW/HOS approaches may more effectively manage fatigue than current HOS paradigms alone. Sleep duration, recency and continuity are of primary importance.

Response surface mapping of neurobehavioral performance: Testing the feasibility of split sleep schedules for space operations

The demands of sustaining high levels of neurobehavioral performance during space operations necessitate precise scheduling of sleep opportunities in order to best preserve optimal performance. We report here the results of the first split sleep, dose-response experiment involving a range of sleep/wake scenarios with chronically reduced nocturnal sleep, augmented with a diurnal nap. To characterize performance over all combinations of split sleep in the range studied, we used response surface mapping methodology. Waking neurobehavioral performance was studied in N = 90 subjects each assigned to one of 18 sleep regimens consisting of a restricted nocturnal anchor sleep period and a diurnal nap. Psychomotor vigilance task performance and subjective assessments of sleepiness were found to be primarily a function of total time in bed per 24 h regardless of how sleep was divided among nocturnal anchor sleep and diurnal nap periods. Digit symbol substitution task performance was also found to be primarily a function of total time in bed per 24 h; however, accounting for nocturnal sleep duration and nap duration separately provided a small but significant enhancement in the variance explained. The results suggest that reductions in total daily sleep result in a near-linear accumulation of impairment regardless of whether sleep is scheduled as a consolidated nocturnal sleep period or split into a nocturnal anchor sleep period and a diurnal nap. Thus, split sleep schedules are feasible and can be used to enhance the flexibility of sleep/work schedules for space operations involving restricted nocturnal sleep due to mission-critical task scheduling. These results are generally applicable to any continuous industrial operation that involves sleep restriction, night operations, and shift work.

Sleep and Sleepiness of Fishermen on Rotating Schedules

Seafaring is a hazardous occupation with high death and injury rates, but the role of seafarer fatigue in these events is generally not well documented. The International Maritime Organization has identified seafarer fatigue as an important health and safety issue. Most research to date has focused on more regularly scheduled types of operations (e.g., merchant vessels, ferries), but there is relatively little information on commercial fishing, which often involves high day‐to‐day and seasonal variability in work patterns and workload. The present study was designed to monitor the sleep and sleepiness of commercial fishermen at home and during extended periods at sea during the peak of the hoki fishing season, with a view to developing better fatigue management strategies for this workforce. Sleep (wrist actigraphy and sleep diaries) and sleepiness (Karolinska Sleepiness Scale [KSS] before and after each sleep period) of 20 deckhands were monitored for 4–13 days at home and for 5–9 days at sea while working a nominal 12 h on/6 h off schedule. On the 12 h on/6 h off schedule, there was still a clear preference for sleep at night. Comparing the last three days at home and the first three days at sea showed that fishermen were more likely to have split sleep at sea (Wilcoxon signed ranks p<0.001), but the median sleep/24 h did not differ significantly by location (5.9 h at sea vs. 6.7 h at home). However, on 23% of days at sea, fishermen obtained<4 h total sleep/24 h, compared to 3% of days at home (p(χ2)<0.01). Sleep efficiency, mean activity counts/min sleep, and subjective ratings of sleep quality did not differ significantly between the last three days at home and the first three days at sea. However, sleepiness ratings remained higher after sleep at sea (Wilcoxon signed ranks p<0.05), with fishermen having post‐sleep KSS ratings ≥7 on 24% of days at sea vs. 9% of days at home (Wilcoxon signed ranks p<0.01). This work adds to the limited number of studies that objectively monitored the sleep of seafarers. It has the strength of operational fidelity but the weakness that large inter‐ and intra‐individual variability in sleep, combined with the small sample size, limited the power of the study to detect statistically significant differences between sleep at home and at sea. The clear preference for sleep at night during the 12 h on/6 h off schedule at sea is consistent with the expectation that this 18 h duty/rest cycle is outside the range of entrainment of the circadian pacemaker. High levels of acute sleep loss, and residual sleepiness after sleep, were much more common at sea than at home. The longer duration of trips during the peak of the fishing season increases the risk of performance impairment due to greater cumulative sleep loss than would be expected on typical three‐day trips. Key fatigue management strategies in this environment include that fishermen report to work as well rested as possible. Once at sea, the day‐to‐day variability in activities due to uncontrollable factors, such as fishing success, repairing gear, and weather conditions, mean that contingency planning is required for managing situations where the entire crew have experienced long periods of intensive work with minimum recovery opportunities.

Working on atypical schedules

Shift work has been associated with a number of health problems including cardiovascular disease, impaired glucose and lipid metabolism, gastrointestinal discomfort, reproductive difficulties, and breast cancer. The specific contributions of disturbed physiological rhythms, circadian misalignment, and sleep debt to the various medical problems encountered by shift workers remain to be clarified. Fatigue can be caused by extended on-duty and/or waking periods, inadequate sleep quantity, sleep disturbances, disruption of circadian rhythms, and difficult work and familial conditions. Fatigue-related accidents raise a safety concern for shift workers, especially at the end of the night when the circadian nadir of alertness interacts with increased time awake. Individuals vary greatly in their capacity to adjust to atypical work schedules and their tolerance to circadian misalignment. Predisposing individual and domestic factors have been identified, such as increasing age, being a single woman in charge of children, and split sleep patterns, all of which can affect the ability to adjust to atypical schedules. However, prior studies indicate that predisposing individual and social determinants are generally poor predictors of shift work tolerance in a given individual. In this manuscript, we review several countermeasures to improve adaptation to shift work.