Prevalence of shift work disorder among hospital personnel: A cross‐sectional study using objective working hour data

The prevalence of shift work disorder (SWD) has been studied using self‐reported data and the International Classification of Sleep Disorders, Second Edition (ICSD‐2) criteria. We examined the prevalence in relation to ICSD‐2 and ICSD‐3 criteria, work schedules and the number of non‐day shifts (work outside 06:00–18:00 hours) using objective working‐hours data. Secondly, we explored a minimum cut‐off for the occurrence of SWD symptoms. Hospital shift workers without (n = 1,813) and with night shifts (n = 2,917) and permanent night workers (n = 84) answered a survey (response rate 69%) on SWD and fatigue on days off. The prevalence of SWD was calculated for groups with ≥1, ≥3, ≥5 and ≥7 monthly non‐day shifts utilizing the working hours registry. ICSD‐3‐based SWD prevalence was 2.5%–3.7% (shift workers without nights), 2.6%–9.5% (shift workers with nights) and 6.0% (permanent night workers), depending on the cut‐off of non‐day shifts (≥7–1/month, respectively). The ICSD‐2‐based prevalence was higher: 7.1%–9.2%, 5.6%–33.5% and 16.7%, respectively. The prevalence was significantly higher among shift workers with than those without nights (p‐values <.001) when using the cut‐offs of ≥1–3 non‐day shifts. Shift workers with nights who had ≥3 days with ICSD‐3‐based SWD symptoms/month more commonly had fatigue on days off (49.3%) than those below the cut‐off (35.8%, p < .05). The ICSD‐3 criteria provided lower estimates for SWD prevalence than ISCD‐2 criteria, similarly to exclusion of employees with the fewest non‐day shifts. The results suggest that a plausible cut‐off for days with ICSD‐3‐based SWD symptoms is ≥3/month, resulting in 3%–6% prevalence of SWD.     

Sleepiness that cannot be overcome: Narcolepsy and cataplexy

Narcolepsy–cataplexy syndrome is characterized by excessive daytime sleepiness, cataplexy, sleep paralysis, hypnagogic hallucinations and disturbed nocturnal sleep. It is strongly associated with the genetic marker, human leucocyte antigen (HLA) DQB1*06:02. A deficit in the endogenous hypocretin/orexin system due to neuronal degeneration in the lateral hypothalamus, induced by an autoimmune‐mediated process, is the primary pathophysiology associated with the human disease. The important finding of an association with hypocretin genes in animal models of narcolepsy has led to the establishment of cerebrospinal fluid hypocretin measurements as a new diagnostic test for human narcolepsy. This is a fascinating story of translation of basic science research into clinical practice in sleep medicine during the past decade. Recent advances have shed light on the associations between respiratory medicine and narcolepsy–cataplexy research. The first is that upper airway infections, including H1N1 and/or streptococcal infections, may initiate or reactivate an immune response that leads to loss of hypocretin‐secreting cells and narcolepsy in genetically susceptible individuals. The second is that an increased incidence of sleep disordered breathing among narcoleptic subjects may relate to the impairment of central control of breathing, linked to hypocretin deficiency or carriage of HLADQB1*06:02, in animals and human subjects with narcolepsy, respectively, indicating neural dysfunction in an area where respiratory and sleep–wake systems are closely interrelated.     

The relationship between weight change and daytime sleepiness: the Sleep Heart Health Study

ObjectiveThrough a causal framework, we aim to assess the association between weight change and daytime sleepiness, and the role of obstructive sleep apnoea (OSA) in this relationship.MethodsFrom the Sleep Heart Health Study, we selected individuals who were: (1) 40–64 years old, with (2) body mass index (BMI) ≥18.5 kg/m², (3) no history of stroke, treatment for OSA, and tracheostomy at baseline. We used multiple linear regression to assess the relationship between five-year weight change and daytime sleepiness (assessed through Epworth Sleepiness Scale (ESS)) at five years, adjusting for daytime sleepiness, demographics, diabetes, subjective sleep duration, sleep disturbance, smoking status, weight, and use of antidepressants and benzodiazepines at baseline, in those with complete data (N = 1468). We further assessed the potential mediating role of OSA in this relationship.ResultsAt baseline, the study participants were on average 55 years old, 46% males, with mean BMI 28 kg/m²; and 25% had ESS>10. ESS at five years worsened by 0.36 units (95% confidence interval (CI) 0.12–0.61, p = 0.004) with every 10-kg weight gain. When stratified by sex, this relationship was only found in women (0.55, 95% CI 0.25–0.86, p < 0.001; p-interaction = 0.02). Approximately one-fifth of the relationship between weight change and daytime sleepiness was mediated by severity of OSA at five years.ConclusionWeight gain has a detrimental effect on daytime sleepiness, mostly through pathways other than OSA. This study provides further evidence and understanding of the relationship between obesity and excessive daytime sleepiness.     

Severe excessive daytime sleepiness induced by hydroxyurea

Excessive daytime sleepiness (EDS) has been reported with many drugs, either as an extension of a hypnotic effect (e.g. central nervous system depressants) or as an idiosyncratic response of the patient. Here, we report unexpected and severe subjective and objective EDS induced by hydroxyurea therapy, with a favorable outcome after withdrawal. Clinical history, sleep log, polysomnography, and multiple sleep latency tests confirming the absence of other EDS causes are presented.     

Local changes in the wake electroencephalogram precedes lane departures

The objective of this exploratory study is to investigate if lane departures are associated with local sleep, measured via source‐localized electroencephalography (EEG) theta power in the 5–9 Hz frequency range. Thirty participants drove in an advanced driving simulator, resulting in 135 lane departures at high levels of self‐reported sleepiness. These lane departures were compared to matching non‐departures at the same sleepiness level within the same individual. There was no correspondence between lane departures and global theta activity. However, at the local level an increased risk for lane departures was associated with increased theta content in brain regions related to motor function.     

Napping facilitates word learning in early lexical development

Little is known about the role that night‐time sleep and daytime naps play in early cognitive development. Our aim was to investigate how napping affects word learning in 16‐month‐olds. Thirty‐four typically developing infants were assigned randomly to nap and wake groups. After teaching two novel object–word pairs to infants, we tested their initial performance with an intermodal preferential looking task in which infants are expected to increase their target looking time compared to a distracter after hearing its auditory label. A second test session followed after approximately a 2‐h delay. The delay contained sleep for the nap group or no sleep for the wake group. Looking behaviour was measured with an automatic eye‐tracker. Vocabulary size was assessed using the Oxford Communicative Development Inventory. A significant interaction between group and session was found in preferential looking towards the target picture. The performance of the nap group increased after the nap, whereas that of the wake group did not change. The gain in performance correlated positively with the expressive vocabulary size in the nap group. These results indicate that daytime napping helps consolidate word learning in infancy.     

Sleepiness, Troika of Consciousness Cycle, and the Epworth Sleepiness Scale

Excessive daytime sleepiness (EDS) is an important indicator when diagnosing sleep-disordered breathing and evaluating its treatment results. However, there appears to be some confusion as to what exactly is sleepiness; Dorlands Illustrated Medical Dictionary does not help. The medical literature was reviewed in order to assemble a schematic model that would suggest a definition of sleepiness and how it can be measured. The derived model is entitled the troika of consciousness cycle (TCC). It assumes that the presence of wakefulness, nonrapid eye movement sleep (NREMS), and rapid eye movement sleep (REMS) is determined by the interactions of four drives: two promoting wakefulness and one each for the two sleep states. The TCC illustrates that inadequate sleep results in sleep debt, but that sleepiness is determined solely by the nearness of the secondary wake drive line to the NREMS drive line. Contact of these lines indicates dozing, a change in consciousness state, an observable event. The probability of this event may be defined as objective sleepiness; this is what the Epworth sleepiness scale (ESS) attempts to measure. Studies indicate that the ESS can determine EDS with greater sensitivity and selectivity than either the multiple sleep latency test or the maintenance of wakefulness test.     

Clinical implications of daytime sleepiness for the academic performance of middle school‐aged adolescents with attention deficit hyperactivity disorder

This study investigated the relative impact of total time slept per night and daytime sleepiness on the academic functioning of 100 middle school‐aged youth (mean age = 11.9) with attention deficit hyperactivity disorder (ADHD). The primary goal of the study was to determine if total time slept per night and/or daytime sleepiness, as measured by youth self‐report on the Pediatric Daytime Sleepiness Scale (PDSS), predicted academic functioning above and beyond symptoms of ADHD and relevant covariates, such as intelligence, achievement scores and parent education level. Self‐reported daytime sleepiness but not self‐reported total time slept per night was associated significantly with all academic outcomes. When examined in a hierarchical regression model, self‐reported daytime sleepiness significantly predicted parent‐rated homework problems and academic impairment and teacher‐rated academic competence above and beyond symptoms of ADHD and relevant covariates, but did not predict grade point average or teacher‐rated academic impairment. The implications of these findings for understanding more clearly the association between ADHD and sleep and the functional implications of this relationship are discussed.     

Assessment of vitamin D,exercise, and lipid profile associated with excessive daytime sleepiness in school children

Previous research reported associations of excessive daytime sleepiness (EDS) with a low vitamin D level, obesity, and sexual maturity. The aim of this study was to identify the association and rank the importance of these with EDS. This study examined 618 children who were 10–12 year-old. The pediatric daytime sleepiness scale (PDSS) was used to evaluate EDS and sleep patterns. EDS was defined as a total PDSS score above 17. We ranked the importance of the relationship of these factors with EDS using random forest analysis. EDS (n = 111, 18%) was positively associated with more advanced pubertal stage in girls, chronic cough, urticaria, and allergic rhinitis. Multivariable analysis with adjustment for confounding indicated that children with low level of 25-hydroxyvitaminD₃ (25(OH)D₃ (<20 ng/mL) and high-density lipoprotein-cholesterol (HDL-C) (<40 mg/dL) levels had an increased risk of EDS (25(OH)D₃:adjusted odds ratio [aOR] = 1.73; 95% confidence interval [CI]: 1.06 to 2.81; P = 0.028; HDL-C: aOR = 2.84; 95% CI: 1.05 to 7.68; P = 0.039). Random forest analysis indicated that 25(OH)D₃ level, exercise, and body mass index (BMI) were over three. This study indicated high levels of 25-(OH)D₃ and HDL-C and performing regular exercise decreased the risk of EDS.