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Showing papers in "Journal of Sleep Research in 1995"


Journal ArticleDOI
TL;DR: The association between neurobiologically‐based sleepiness/fatigue and human‐error related accidents is reviewed and it concludes that fatigue contributes to human error and accidents in technology‐rich, industrialized societies in terms of human, environmental and economic impacts.
Abstract: SUMMARY This paper reviews the association between neurobiologically-based sleepiness/fatigue and human-error related accidents. It concludes that fatigue contributes to human error and accidents in technology-rich, industrialized societies in terms of human, environmental and economic impacts. The cultural utilization of time as expressed in 24-h work operations, combined with the widespread use of automation, will continue to escalate in the next century, further increasing the risks of fatigue-related accidents, as more people conduct vigilance-based activities at times other than the traditional daytime work hours. Fatigue management and prevention of fatigue-related catastrophes need to become a sustained priority for government, industries, labour, and the public. Scientific data are urgently needed on the most likely areas in which sleepiness-related performance failures contribute to accidents, and on the effectiveness of a wide range of potentially useful countermeasures.

887 citations


Journal ArticleDOI
TL;DR: There is a need for uniform methods to know the prevalence and incidence of sleep disorders, judged using the same criteria, and also the severity of each problem, i.e. how often a problem or a symptom happens/occurs.
Abstract: SUMMARY Sleep-related breathing disturbances, especially obstructive sleep apnoea syndrome (OSAS), are commonly encountered. Epidemiological studies from different countries have shown that poor sleep and complaints about insufficient sleep or poor sleep are often related to poor health. Different studies are, however, difficult to compare with each other. One of the main reasons for this is the frequent methodological differences between questionnaires. There is a need for uniform methods: we need to know the prevalence and incidence of sleep disorders, judged using the same criteria, and also the severity of each problem, i.e. how often a problem or a symptom happens/occurs. In 1988 the Scandinavian Sleep Research Society formed a task group for developing a standardized questionnaire that could be used as a basis for questionnaires used in the Nordic countries. In this article we describe the Basic Nordic Sleep Questionnaire (BNSQ). The main change compared to many previous questionnaires is the five-point scale (scale from 1 to 5) stressing on how many nights/days per week something happens. The basic scale is: 1, ‘never or less than once per month’; 2, ‘less than once per week’; 3, ‘on 1–2 nights per week’; 4, ‘on 3–5 nights per week’; and 5, ‘every night or almost every night’. For questions about specific rare events the first category may be divided into ‘never’ and ‘less than once per month’. Habitually occurring events such as ‘habitual snoring’ are defined here as snoring every night or almost every night. The BNSQ has been used widely in a variety of studies performed in Nordic countries during the last years, and it has proven to be a valid tool.

489 citations


Journal ArticleDOI
TL;DR: Severe subjective and physiological sleepiness occur in night work, afflict almost all individuals and are associated with a performance impairment severe enough to explain night‐work accident data.
Abstract: Severe subjective and physiological sleepiness occur in night work, afflict almost all individuals and are associated with a performance impairment severe enough to explain night-work accident data. The alertness deficit is caused by the displacement of work to the circadian phase which is least conducive to alert behaviour, by extension of the time spent awake and by the reduction of sleep length (due to circadian interference with sleep). Sleepiness will be extreme when the three causes are operative simultaneously. The three factors may be used quantitatively to predict sleepiness.

256 citations


Journal ArticleDOI
TL;DR: It is concluded that extended workshift schedules should be instituted cautiously and evaluated carefully, with appropriate attention given to staffing levels, workload, job rotation, environmental exposures, emergency contingencies, rest breaks, commuting time, and social or domestic responsibilities.
Abstract: Studies of overtime have pointed to fatigue as a potential factor producing, for example, a three-fold increase in accident rate after 16 h of work, increases in back injuries, hospital outbreaks of bacterial infection, or nuclear-power plant safety compromises. Fatigue has been measured more directly in studies of scheduled long workshifts, where performance decrements in both work-related tasks and laboratory-type behavioural tests have been observed, and significant loss of sleep and increases in subjective sleepiness have been reported. Analyses of accidents or injuries during scheduled extended workshifts, however, have produced equivocal results. Factors which could compound the fatiguing effects of extended workshifts, such as workload, noise, chemical exposure, or duties and responsibilities outside of the workplace, rarely have been studied systematically. It is concluded that extended workshift schedules should be instituted cautiously and evaluated carefully, with appropriate attention given to staffing levels, workload, job rotation, environmental exposures, emergency contingencies, rest breaks, commuting time, and social or domestic responsibilities.

223 citations


Journal ArticleDOI
TL;DR: Modafinil appears to be a good alternative to amphetamine for counteracting the debilitating mood and cognitive effects of sleep loss during sustained operations.
Abstract: Modafinil is an alerting substance that is considered safer than amphetamine with fewer side effects. Although modafinil has been used successfully to treat narcolepsy, relatively little is known about its ability to ameliorate fatigue and declines in mental performance due to sleep deprivation (SD) in a normal population. Forty-one military subjects received either 300 mg of modafinil, 20 mg of d-amphetamine, or placebo on 3 separate occasions during 64 hours of continuous cognitive work and sleep loss. Three drug treatments were given: at 23.30 hours and 05.30 hours during the first and second SD nights, respectively, and once at 15.30 hours during the third day of continuous work. Subjective estimates of mood, fatigue and sleepiness, as well as objective measures of reaction time, logical reasoning and short-term memory clearly showed better performance with both modafinil and amphetamine relative to placebo. Both modafinil and amphetamine maintained or increased body temperature compared to the natural circadian cycle observed in the placebo group. Also, from subject debriefs at the end of the study, modafinil elicited fewer side-effects than amphetamine, although more than the placebo group. Modafinil appears to be a good alternative to amphetamine for counteracting the debilitating mood and cognitive effects of sleep loss during sustained operations.

200 citations


Journal ArticleDOI
TL;DR: In this article, sleep/wake patterns and cognitive and functional status measures in a large sample of Alzheimer's disease subjects ranging from mild to moderate-severe in impairment were examined and regression analyses revealed that sleep and wake variables were highly correlated with and explained significant variance in cognitive/functional measures.
Abstract: Alzheimer's disease (AD), the most common dementing disorder of aging, is a progressive neurodegenerative disease of unknown etiology. Two of the common clinical features of AD are progressive cognitive and functional impairment, and disturbed sleep/wake patterns. We examined sleep/wake patterns and cognitive and functional status measures in a large sample of AD subjects ranging from mild to moderate-severe in impairment. All subjects survived at least 2 years after initial diagnosis. Regression analyses revealed that sleep/wake variables were highly correlated with and explained significant variance in cognitive and functional measures. More wakefulness during the night and longer REM latencies were associated with impaired cognition and function while more REM and slow-wave sleep were associated with preserved cognition and function. These results indicate that with advancing severity of the disease, sleep/wake patterns are disrupted in parallel with the disturbances in cognition and function that are the hallmarks of AD. Further, they suggest that the neural substrates underlying each process degenerate at somewhat comparable rates.

163 citations


Journal ArticleDOI
TL;DR: Two potential negative effects of naps, sleep inertia and effects on subsequent sleep periods, are discussed and combining strategies may be the most effective approach to managing fatigue engendered by 24‐h operational demands.
Abstract: Managing fatigue in complex operational settings requires attention to multiple factors, including hours of service, scheduling, education and training, counter-measures, technology, and research. Alertness-management strategies can be used to promote safety, performance, and productivity in operational settings. These strategies can involve both preventive (used prior to duty/shift) and operational (used during duty/shift) approaches. Studies have demonstrated the effectiveness of naps to improve subsequent performance and alertness. Strategic naps can be used effectively to promote performance and alertness in operational settings. Two potential negative effects of naps, sleep inertia and effects on subsequent sleep periods, are discussed. Sleep inertia can involve sleepiness and decreased performance immediately upon awakening from a nap. It should be a consideration prior to implementing nap strategies in work environments. A study of planned rest periods in long-haul flight operations demonstrated the effectiveness of in-flight naps to promote performance and alertness during subsequent critical phases of flight (descent and landing). Empirical evaluation of alertness-management strategies during regular operations will be critical to their implementation. Combining strategies may be the most effective approach to managing fatigue engendered by 24-h operational demands. Other considerations prior to implementing alertness-management strategies in operational environments are discussed.

134 citations



Journal ArticleDOI
TL;DR: The effects of changes in REMS latency on SWA were investigated by analysing simulations with a mathematical model and showed an initial increase and a later decline as a function ofREMS latency.
Abstract: Sleep interventions may have direct effects on slow-wave activity (SWA, i.e. power of the sleep EEG signal in the 0.75-4.5 Hz range) as well as indirect ones caused by changes in REM sleep (REMS) latency. The effects of changes in REMS latency on SWA were investigated by analysing simulations with a mathematical model. Mean SWA in the first non-REMS episode shows an initial increase and a later decline as a function of REMS latency. In the second non-REMS episode, mean SWA decreases with increasing REMS latency. These results of the simulations were validated with experimental data. In the evaluation of the effects of sleep interventions on SWA the effects of the timing of REMS have to be accounted for. The analysis of SWA over a sufficiently long constant amount of time spent in non-REMS proves to be relatively independent of REMS latency, which allows conclusions about the effects of sleep interventions on SWA per se.

116 citations


Journal ArticleDOI
TL;DR: The existence of alpha activity which differs in generation site (thalamus), scalp distribution (frontal‐central), and behavioural correlates (e.g. enhancement to stimulation during wakefulness, concentration in the first‐half of the night during sleep, and absence of sleep disturbance) from occipital alpha activity is suggested.
Abstract: SUMMARY Alpha activity occurring during sleep is generally considered to reflect arousal processes and a shift toward wakefulness. This long-standing interpretation is based on physiological and behavioural arousal correlates of alpha activity presumed to have an occipital focus. In addition to the application of this interpretation to sleep/wake state determinations, there have been reports of nonrefreshing or nonrestorative sleep in clinical populations exhibiting dramatic amounts of alpha intrusion during sleep in the absence of awakening. Reports of the presence of alpha activity during sleep in normal subjects without sleep disruption or complaints of daytime sleepiness call into question the interpretation that this activity is associated with arousal. A re-examination of this literature, incorporating the results from recent investigations employing multi-site EEG recordings, electronic processing and source diple analyses of this activity, suggests the existence of alpha activity which differs in generation site (thalamus), scalp distribution (frontal-central), and behavioural correlates (e.g. enhancement to stimulation during wakefulness, concentration in the first-half of the night during sleep, and absence of sleep disturbance) from occipital alpha activity. Such marked differences in defining characteristics imply different functional correlates for these activities. In this context, it is proposed that this fronto-central alpha activity is associated with sleep-maintaining processes which may be enhanced in response to sleep-disturbing events.

98 citations


Journal ArticleDOI
TL;DR: The pattern of c‐fos expression after sleep deprivation was very similar to that observed after comparable periods of spontaneous wakefulness (Pompeiano et al. 1994), and the increase in c‐ fos expression was not simply proportional to the amount of previous wakefulness.
Abstract: This study examined the effects of sleep deprivation on the expression of the immediate early gene c-fos in the brain with both in situ hybridization and immunocytochemistry. Rats were manually sleep-derived for 3 h, 6 h, 12 h, and 24 h starting at light onset (08.00 hours), and for 12 h starting at dark onset (20.00 hours). c-Fos expression was found to be higher in sleep-deprived rats with respect to control animals in several brain areas. The increase was evident both in terms of c-fos mRNA and Fos protein, although with a different time course. Among the areas that showed a consistent induction of c-fos were many cortical regions, the medial preoptic area and the posterior hypothalamic area, some thalamic nuclei, and several nuclei of the dorsal pontine tegmentum. The pattern of c-fos expression after sleep deprivation was very similar to that observed after comparable periods of spontaneous wakefulness (Pompeiano et al. 1994). In general, the increase in c-fos expression was not simply proportional to the amount of previous wakefulness. In many areas, the highest levels of c-fos were seen after 3 h of sleep deprivation. These observations are discussed with respect to the homeostatic regulation of sleep and to the functional consequences of wakefulness in specific brain areas.

Journal ArticleDOI
TL;DR: The results from the few studies available show that sleep duration is clearly determined by the change over time between the night and the morning shift—no more than 5 or 6 hours of sleep is obtained before the morningshift if the shift starts at 06.00 hours or earlier.
Abstract: SUMMARY This review summarizes the effects on sleep duration and sleepiness of (1) the timing of shifts (start and finishing times) and (2) the scheduling of free time between shifts. The results from the few studies available show that sleep duration is clearly determined by the change over time between the night and the morning shift—no more than 5 or 6 hours of sleep is obtained before the morning shift if the shift starts at 06.00 hours or earlier. Therefore, it is suggested that the morning shift should not start before 07.00 hours. A late start of the morning shift will however, increase the sleepiness at the end of the night shift, as well as decrease the duration of the daysleep after the night shift. On the other hand, one may argue that the short daysleep after a night shift may be compensated for by an evening nap, whereas a short night sleep before a morning shift cannot (no time for nap). The review of studies concerning free time between shifts suggests that at least 16 hours is needed and that quick change-overs should be avoided. The free time after a spell of night shifts should be at least 48 hours since the shiftworker needs two main sleep episodes to recover from night work.

Journal ArticleDOI
TL;DR: Melatonin has clear circadian phase‐shifting effects in humans which have recently been formalized as a phase response curve and its potential use in circadian rhythm disorders has been investigated in field studies of jet lag and shift work and in simulated phase shift.
Abstract: SUMMARY The pineal hormone melatonin has clear circadian phase-shifting effects in humans which have recently been formalized as a phase response curve. Its potential use in circadian rhythm disorders has been investigated in field studies of jet lag and shift work and in simulated phase shift. A substantial amount of information indicates that in the majority of subjects it hastens adaptation of both subjective and objective measures to forced shifts in time cues with few reported side-effects. Field studies of its use in adaptation to shift work are sparse and preliminary but the first indications are positive. In some blind subjects with sleep disturbance it can stabilize sleep onset time without necessarily entraining all circadian rhythms and it can advance sleep timing in delayed sleep-phase insomnia. Acute suppression of core body tempera-ture may be an integral part of the phase-shifting mechanism.

Journal ArticleDOI
TL;DR: Modafinil allowed for sleep to occur, displayed sleep patterns close to that of the placebo group, and decreased the need for a long recovery sleep usually taken to compensate for the lost sleep due to total sleep deprivation.
Abstract: SUMMARY Polysomnograms were obtained from 37 volunteers, before (baseline) and after (two consecutive recovery nights) a 64-h sleep deprivation, with (d-amphetamine or modafinil) or without (placebo) alerting substances. The drugs were administered at 23.00 hours during the first sleep deprivation night (after 17.5 h of wakefulness), to determine whether decrements in cognitive performance would be prevented; at 05.30 hours during the second night of sleep deprivation (after 47.5 h of wakefulness), to see whether performance would be restored; and at 15.30 hours during the third day of continuous work, to study effects on recovery sleep. The second recovery night served to verify whether drug-induced sleep disturbances on the first recovery night would carry over to a second night of sleep. Recovery sleep for the placebo group was as expected: the debt in slow-wave sleep (SWS) and REM sleep was paid back during the first recovery night, the rebound in SWS occurring mainly during the first half of the night, and that of REM sleep being distributed evenly across REM sleep episodes. Recovery sleep for the amphetamine group was also consistent with previously published work: increased sleep latency and intrasleep wakefulness, decreased total sleep time and sleep efficiency, alterations in stage shifts, Stage 1, Stage 2 and SWS, and decreased REM sleep with a longer REM sleep latency. For this group, REM sleep rebound was observed only during the second recovery night. Results for the modafinil group exhibited decreased time in bed and sleep period time, suggesting a reduced requirement for recovery sleep than for the other two groups. This group showed fewer disturbances during the first recovery night than the amphetamine group. In particular, there was no REM sleep deficit, with longer REM sleep episodes and a shorter REM latency, and the REM sleep rebound was limited to the first REM sleep episode. The difference with the amphetamine group was also marked by less NREM sleep and Stage 2 and more SWS episodes. No REM sleep rebound occurred during the second recovery night, which barely differed from placebo. Hence, modafinil allowed for sleep to occur, displayed sleep patterns close to that of the placebo group, and decreased the need for a long recovery sleep usually taken to compensate for the lost sleep due to total sleep deprivation.

Journal ArticleDOI
TL;DR: Several laboratory studies indicate that careful application of bright light may cause the circadian system to shift to any desired phase, and studies of simulated night work demonstrate that night exposure to bright light can virtually eliminate circadian maladjustment among night workers.
Abstract: SUMMARY Night work is associated with increased sleepiness and disturbed sleep. Maladaptation of the circadian system, which is phase-adjusted to day time work and thus promotes sleepiness during its nadir at night and wakefulness (or disturbed sleep) during the day, contributes substantially to this problem. A major cause of suboptimal circadian phase adjustment among night workers is the exposure to morning light, which prevents the delay needed for optimal adjustment to night work. Several laboratory studies indicate that careful application of bright light may cause the circadian system to shift to any desired phase. Furthermore, studies of simulated night work demonstrate that night exposure to bright light can virtually eliminate circadian maladjustment among night workers. While the results are promising, there is still, however, an urgent need for longitudinal studies of bright light application in. real-life settings.

Journal ArticleDOI
TL;DR: Hypnotic medication reliably improves sleep during the day, in terms of increasing total sleep time (TST) and reducing awakenings and light sleep, and middle‐aged individuals may benefit more than young adults.
Abstract: Hypnotic medication reliably improves sleep during the day, in terms of increasing total sleep time (TST) and reducing awakenings and light sleep. Middle-aged individuals may benefit more than young adults. In addition, the time of day during which sleep is attempted may influence the efficacious dose of short-acting drugs. Available data suggest that improving sleep during the day may improve alertness/performance at night to a mild degree, but significant circadian-related sleepiness remains. Hypnotic medication may help minimize the cumulative effects of sleep loss associated with daytime sleep. Use for more than one week has not been adequately studied; however, as most night and rotating workers' schedules allow for night-time sleep for two or more nights per week, available evidence indicates that hypnotics can be used effectively on an intermittent basis, e.g. for the first 2-4 day-sleep periods of night shifts. Caffeine has been shown to increase alertness and improve psychomotor performance during usual night-shift hours when taken between 22.30 and 01.20 hours. Available data indicate that at approximate dosages of 250-400 mg, the beneficial effects persist until at least 05.30 hours. For most subjects, caffeine taken at the start of the night-shift does not interfere significantly with daytime sleep beginning at 09.00 hours. There is also some evidence that single doses of caffeine at the beginning of a night shift may be more alerting than divided doses. If caffeine is to be used therapeutically, avoidance of social use may be required to avoid tolerance to CNS stimulant effects. Despite the positive results of laboratory research examining hypnotics or caffeine as shiftwork countermeasures, field trials have not been conducted.

Journal ArticleDOI
TL;DR: It seems reasonable to believe that in specific situations napping at the work place would be possible and used if authorized and encouraged and as a possible strategy to increase the vigilance level of night workers.
Abstract: SUMMARY It seems reasonable to believe that in specific situations napping at the work place would be possible and used if authorized and encouraged. Very short naps could have very positive long-term effects on biological functions. Training someone to sleep for short periods appears feasible if there is a high motivation to do so. Sleep inertia can be considered as one of the main limiting factors in napping strategy. Sleep inertia depends on different factors such as sleep stage preceding the awakening, temporal placement of the nap, duration of nap and wakefulness preceding it, etc. The effects of sleep inertia might be different depending on the type of task, and a reactivation technique applied immediately after awakening may remove it. Despite the fact that its implementation in industry raises some practical issues, napping can be considered as a possible strategy to increase the vigilance level of night workers.

Journal ArticleDOI
TL;DR: The SF 36 is sensitive to the effects of sleep disruption in subjects with obstructive sleep apnoea, is a useful outcome measure for treatment with CPAP and its value in other sleep disorders should be assessed.
Abstract: The objectives of this study were to test the sensitivity of the short form 36 health survey questionnaire (SF 36) to sleep disruption in patients with obstructive sleep apnoea (OSA) and assess its use as an outcome measure for treatment with nasal continuous positive airway pressure (CPAP). Two hundred and twenty-three subjects under investigation for snoring and/or daytime somnolence completed the questionnaire at presentation and again after a six month period. Subjects with OSA requiring treatment scored lower on all dimensions of the SF 36 (P < 0.05) than normative scores for the general population. The largest differences were for vitality (24%) and social functioning (27.9%). After six months of treatment with CPAP there was an improvement in all scores and the score for vitality was no longer significantly different from that of the general population. The SF 36 is sensitive to the effects of sleep disruption in subjects with obstructive sleep apnoea, is a useful outcome measure for treatment with CPAP and its value in other sleep disorders should be assessed.

Journal ArticleDOI
TL;DR: The findings lend support to the hypothesis that a K‐complex can be seen as a ‘defensive response’, or has a sleep protective function.
Abstract: The number of K-complexes recorded at the central-temporal EEG derivation (C3-T3) during 5 min periods for both the ascending and descending phase of Stage 2 of NREM sleep for cycles 1, 2 etc were counted in 10 subjects for each of the following five groups: normal persons, patients with a primary generalized form of epilepsy, narcolepsy, insomnia and obstructive sleep apnoea The differences in time spent in different stages of sleep were as expected for these types of patients A 2-within, 1-between factors, repeated measure ANOVA was applied to the data on K-complexes Overall, there was no significant difference between the number of K-complexes observed during the ascending and descending phases of the different sleep cycles Patients with a sleep disorder had significantly less well-defined K-complexes than the normals and the patients with a primary form of generalized epilepsy: for insomnia (P = 0035), for apnoea (P = 0011) and for narcolepsy (P = 0001) There was a significant, but very low correlation coefficient between the number of K-complexes observed during Stage 2 of NREM sleep and the time spent during that stage for all groups combined (Rho 027, P = 0002) and for the narcoleptic patients (Rho 044, P = 0017) In all, the findings lend support to the hypothesis that a K-complex can be seen as a 'defensive response', or has a sleep protective function

Journal ArticleDOI
TL;DR: It was found that bedtime was more often after 22.00 hours among adolescents than preadolescents both at weekends and on weekdays, and total sleep durations were longer in preadolescent than in adolescent groups, and longer during weekend nights than on weekday nights in all groups.
Abstract: SUMMARY A variety of epidemiological sleep parameters was evaluated in 574 Finnish schoolchildren (age 7 to 17 years) and in their parents (454 mothers and 390 fathers). Three questionnaire forms were set, one for the pupil and two for his/her parents including information of sleep habits, disorders, and social background of the pupil and his/her family. The pupils were grouped by age (two preadolescent groups: 7.1–9.3 y and 9.4–13 y, adolescents 13.1–17.1 y) and sex. It was found that bedtime was more often after 22.00 hours among adolescents than preadolescents both at weekends and on weekdays. At weekends the wake-up time was later in adolescents than preadolescents but on weekdays it was opposite in boys. On weekdays girls went earlier to bed than boys and woke up earlier than boys. Total sleep durations both on weekdays and at weekends were longer in preadolescent than in adolescent groups, and longer during weekend nights than on weekday nights in all groups. Girls experienced more dreaming and night waking, but boys snored more. Daytime sleepiness patterns were more common in adolescents than in preadolescents. Children who experienced daytime sleepiness more often had fathers with daily sleep urges. An association was found between age and sleep habits and some daytime sleepiness patterns; adolescents went to bed later and slept less, and had more problems with alertness during daytime than preadolescents. Some differences were also found between boys and girls. The daytime sleepiness of pupils correlated with the same symptom in fathers.

Journal ArticleDOI
TL;DR: Jet lag and day‐time sleepiness cannot be avoided in transmeridian operations, because work hours of aircrews interfere with the circadian system through irregular work‐rest schedules and rapid time‐zone transitions.
Abstract: SUMMARY Jet-lag and day-time sleepiness cannot be avoided in transmeridian operations, because work hours of aircrews interfere with the circadian system through irregular work-rest schedules and rapid time-zone transitions. Although the primary cause of accidents is usually the human factor, jet lag and sleepiness have seldom been officially identified as causes of inadequate functioning in the cockpit. However, research clearly indicates that flights at night and/or across time zones will impair performance and reduce safety. Research on countermeasures have focused on on-board napping, crew augmentation, behavioural strategies against jet-lag, light treatment and melatonin administration. Regrettably, scientific knowledge has been successfully transmitted to only a very few national authorities responsible for work hours of aircrews.

Journal ArticleDOI
TL;DR: It is concluded that only a minor part of the variation inSleepiness between individuals can be explained and preventive advice and medical surveillance focusing on individual differences in sleepiness are recommended.
Abstract: SUMMARY On-site studies of shiftwork show considerable differences in sleepiness between workers. Variation between individuals depends on different sleeping, coping and living habits of the workers, on possible sleep disorders, but also on more ‘permanent’ inter-individual factors that may influence sleepiness by changing either the circadian or homeostatic factors of sleep. The effects of circadian phase, age, sex, physical fitness, domestic and personality factors on shiftworkers' sleepiness and work-related accidents are reviewed. It is concluded that only a minor part of the variation in sleepiness between individuals can be explained. The present knowledge is not sufficient to carry out reliable ‘selection’ of individuals suitable for shiftwork. However, preventive advice and medical surveillance focusing on individual differences in sleepiness are recommended.

Journal ArticleDOI
TL;DR: To minimize the disturbances of the circadian system and the accumulation of sleep deficits, rapidly and clockwise‐rotating shift systems would seem to be preferable.
Abstract: This review paper deals with the issue of shift rotation, i.e. the number of consecutive shifts of the same type and the order of change between shifts. To minimize the disturbances of the circadian system and the accumulation of sleep deficits, rapidly and clockwise-rotating shift systems would seem to be preferable. Regarding consecutive night shifts, a week of night shifts seems to be the worst system with regard to performance and accidents. There is a lack of reliable data on the effects of permanent vs. rotating-shift systems on alertness, performance and accidents. This is also true for the comparison of forward (delaying) and backward (advancing) rotating-shift systems, although the former would seem to be associated with fewer problems. For both systems, controlled longitudinal studies are necessary.

Journal ArticleDOI
TL;DR: The difference in the relative amplitude between the two study groups suggests that the amount of clenching force is the primary factor responsible for the harmful effects of sleep bruxism on the masticatory apparatus.
Abstract: All-night polysomnographic recordings were made of clinically diagnosed sleep bruxists (n = 23) and non-symptomatic controls (n = 6) The total duration of masseter contraction (MC) episodes during sleep was 116 minutes per night in bruxists and 66 in controls (P < 001) The mean frequency of MC episodes was 110 per hour of sleep in bruxists and 64 in controls (P < 005) The mean relative amplitude of MC episodes reflecting clenching strength was 081 in bruxists and 056 in controls (P < 001) The percentage distribution of mixed and phasic MC episodes was 94% among bruxists and 88% in controls The remaining activity was classified as tonic in both groups The subclassification of rhythmic jaw movements (RJM), defined as three or more separate rhythmic contractions during MC episode were also evaluated The frequency of those MC episodes with RJM was 36 per hour of sleep in bruxists and 11 in controls (P < 0001) The difference in the relative amplitude between the two study groups suggests that the amount of clenching force is the primary factor responsible for the harmful effects of sleep bruxism on the masticatory apparatus The most significant difference was seen in those phasic and mixed MC episodes which also included the subclassification of rhythmic jaw movement The result suggests that relative amplitude and rhythmicity of MC episodes can be used as a basis to confirm the diagnosis and to evaluate the treatment effects of suspected sleep bruxists

Journal ArticleDOI
TL;DR: The phase shift created by bright light exposure did not seem to be large enough to have a systematic effect on sleep consolidation or on REM sleep parameters in any of the three groups, suggesting that these variables are less sensitive to alterations in phase of the circadian oscillator than early‐night sleep propensity.
Abstract: SUMMARY The aim of this work was to study the effects of bright light-induced circadian phase shifts on sleep propensity and sleep architecture while the timing of the sleep/wake cycle is kept constant. Twenty-three normal subjects underwent an 11-day study including: (i) baseline sleep and vigilance evaluation; (ii) baseline evaluation of the circadian temperature rhythm with a 40-h constant routine; (iii) five hours of bright light exposure on each of three days; (iv) post-treatment sleep and vigilance evaluation; (v) post-treatment circadian rhythm evaluation with a second 40-h constant routine. Subjects were divided into three groups: eight subjects were exposed to bright light in the morning (‘Morning group’), eight subjects were exposed in the evening (‘Evening group’), and seven subjects were exposed in the afternoon (‘Afternoon group’). After light exposure, the Morning group showed an advance of 1.23 h in the phase of the temperature rhythm, the Evening group showed a delay of 1.62 h, and the Afternoon group showed a non-significant advance of 0.5 h. In support of expectations, early-night sleep propensity was decreased by evening bright light, was increased in almost all subjects exposed to morning bright light, and was not changed by afternoon bright light exposure. The phase shift created by bright light exposure did not seem to be large enough to have a systematic effect on sleep consolidation or on REM sleep parameters in any of the three groups, suggesting that these variables are less sensitive to alterations in phase of the circadian oscillator than early-night sleep propensity.

Journal ArticleDOI
TL;DR: The roles of hypoxaemia, of mechanical changes related to partial or complete airway obstruction and of arousals during sleep in the haemodynamic and heart rate changes seen in association with sleep disordered breathing have been questioned.
Abstract: The roles of hypoxaemia, of mechanical changes related to partial or complete airway obstruction and of arousals during sleep in the haemodynamic and heart rate changes seen in association with sleep-disordered breathing have been questioned. Several experiments have been performed by these authors to investigate the role of arousals and mechanical changes in the blood pressure changes associated with sleep disordered breathing. Investigation of the role of arousals. Two different populations were used in this study; one of normal, young volunteers without sleep-disordered breathing monitored at baseline (normal sleep) who were submitted to auditory stimulation during sleep, causing sleep fragmentation, and another of obstructive sleep apnoeic patients who were monitored at baseline and after nasal CPAP treatment. Before treatment and after one month of treatment while still being treated with nasal CPAP, these subjects were submitted to the same auditory stimulation and sleep fragmentation as normal controls. The studied variables were systolic and diastolic blood pressure and heart rate. In normal controls, auditory induced arousals lead to an increase in diastolic as well as systolic blood pressure. The increase was related to the type of arousal but was also noted with K complexes to a lesser degree. In OSAS patients under treatment with nasal CPAP, similar increases were noted with auditory stimulation. Compared to baseline hypoxaemia and hyperventilation periods, however, the haemodynamic increase was, at its highest, only one-third of the mean pressure monitored during the baseline, end-of-apnoea hyperventilation period with EEG arousals. Investigation of the role of nasal CPAP on blood pressure (BP) while patients had no hypoxaemia (SaO2>92%) but still showed increased respiratory efforts indicated a persistence of higher systolic and diastolic pressures than when nasal CPAP completely eliminated increased efforts. Possible long-term impact of arousals and mechanical changes. A last study was performed on patients with upper airway resistance syndrome (UARS). Out of 112 patients, 6 were identified using the World Health Organization (WHO) protocol and ambulatory monitoring as having borderline high BP (140-160//90-98). Subjects were calibrated with nasal CPAP and were asked to use their equipment on a nightly basis. The CPAP machines were equipped with counters that could accurately measure the number of hours that the device was used. Patients were their own controls and were re-monitored one month later. Four subjects used their nasal CPAP at least 6 nights per week and more than 5 hours per night. One patient used his CPAP approximately 3 nights per week and more than 4 hours per night. One patient used his CPAP a total of 3 nights in the whole month. Blood pressure was unchanged in the patient who failed to use his CPAP, but was normalized in the 5 others, as were nocturnal recordings.

Journal ArticleDOI
TL;DR: In this article, it has been shown that the items of information which are repeatedly accessed during sleep and elaborated for insertion into the ongoing dream experience are better retained at delayed recall, and it is suggested that the use of the strategies applied in studying the information processing in normals may also be extended to sleep-disturbed individuals, in order to establish how memory functioning during sleep is influenced by sleep disturbances.
Abstract: SUMMARY Investigations into the role played by sleep in information processing have consistently shown that the retention of information is better when the memory storage is followed by a period of sleep than of waking. Less definitive evidence, however, is available as to whether the better performance is mainly due to (a) reduction of interference during sleep, (b) slowing down of decay, or (c) consolidation processes at work during sleep. Important insights as to whether consolidation takes place during sleep have recently been provided by the thematic continuity of dreams elaborated in the same night and by the repeated incorporation of pre-sleep stimuli into dream contents. The analysis of such aspects of dreaming indicates that the items of information which are repeatedly accessed during sleep and elaborated for insertion into the ongoing dream experience are better retained at delayed recall. Finally, it is suggested that the use of the strategies applied in studying the information processing in normals may also be extended to sleep-disturbed individuals, in order to establish how memory functioning during sleep is influenced by sleep disturbances.

Journal ArticleDOI
TL;DR: It is suggested that the relatively mild disturbances of sleep in shift work may contribute to reduced alertness although there are probably other, more potent, factors.
Abstract: SUMMARY This review of experimental studies focuses on the disturbances of sleep that may occur in connection with irregular work hours and their relation to ensuing alertness. Three aspects of sleep are covered: the duration of sleep, the stages of sleep, and the continuity of sleep. A sleep curtailment as small as 2 h has clear negative effects on alertness. Sleep disturbed as frequently as every minute clearly affects alertness, but such procedures also affect the stages of sleep and decrease total sleep time. However, fragmentation rates of one per 10 minutes also induce sleepiness without affecting sleep content or duration. There is no clear evidence for slow-wave sleep (SWS) being more important than other stages, but designs may not have been sensitive enough. In connection with fragmentation studies it is suggested, however, that the effects are stronger if more SWS is lost. In summary, the review suggests that the relatively mild disturbances of sleep in shift work may contribute to reduced alertness although there are probably other, more potent, factors.

Journal ArticleDOI
TL;DR: It was found that when a series of 1‐h naps was taken during the normal night period, oral temperature and psychomotor performance declined, but performance was relatively improved on the following evening, and it was concluded that the placement of sleep periods during extended work be based on knowledge of when maximal performance would be required.
Abstract: This study compared alertness and psychomotor performance over an extended work period in which participants received either a 4-h afternoon nap or four 1-h naps during the night. It was hypothesized that alertness and performance would be superior during the night following the 4-h afternoon nap and that the overall level of performance would be related to the amount of sleep obtained. It was found that when a series of 1-h naps was taken during the normal night period, oral temperature and psychomotor performance also declined. However, performance was relatively improved on the following evening. In contrast, with an effective 4-h prophylactic nap, performance remained near baseline levels across the night. It was concluded that the placement of sleep periods during extended work be based on knowledge of when maximal performance would be required.

Journal ArticleDOI
TL;DR: The results presented here suggest that independent of age and obesity the severity of sleep apnoea is an important determinant of circadian BP variation and nocturnal BP variability.
Abstract: The prevalence of hypertension in patients with obstructive sleep apnoea (OSA) is high and blood pressure profile is characterized by nocturnal blood pressure (BP) elevation and increased nocturnal BP variability Ambulatory 24-hour-blood pressure monitoring (ABPM) is a valid, non-invasive method to describe circadian BP variation Circadian BP profile and nocturnal BP variability were related to OSA severity (apnoea-hypopnoea index, mean low O2), age and body mass index (BMI) in 73 patients with OSA Prevalence of hypertension was 75%, and in 59% BMI was greater than 30 kg m-2 A nocturnal decline of at least 10% from daytime mean BP values (night/day BP ratio <09; dipper) was found in only 25% of hypertensive patients and 39% of normotensive patients Comparison between dippers and non-dippers showed significant differences in apnoea severity (apnoea-hypopnoea index 32 + 19 vs 50 + 23/h, P < 001; mean low O2 845 + 4 vs 802 + 58%, P < 001) but not for age and BMI In multiple regression analyses with age, body mass index, apnoea-hypopnoea index and mean low O2 as independent and BP ratios and BP variability as dependent variables, sleep apnoea severity was the only independent predictor for circadian BP rhythm and nocturnal BP variability The results presented here suggest that independent of age and obesity the severity of sleep apnoea is an important determinant of circadian BP variation and nocturnal BP variability