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The number of occasions to stay in a car overnight is increasing during disasters; however, the effects on sleep and the impact on daytime functioning are not well understood. We investigated the effect of seat angle when sleeping in a car and its impact on calculation performance the following day. Fifteen healthy males participated in three trials (sleeping in a car with the front seat angled at 45° and 60° in a laboratory and sleeping at home); sleep and calculation performance the following day were compared. Increased wake after sleep onset and decreased slow-wave sleep were observed in the 60° trial, that is, near-vertical, compared with the others. Subjective sleep quality and calculation performance in the 45° and 60° trials were poorer than those in the home trial. The effect of seat angle on sleep was confirmed objectively, but not subjectively, suggesting that a large seat angle might cause sleep impairment.

Abstract Study Objectives Conventional metrics of sleep quantity/depth have serious shortcomings. Odds-Ratio-Product (ORP) is a continuous metric of sleep depth ranging from 0 (very deep sleep) to 2.5 (full-wakefulness). We describe an ORP-based approach that provides information on sleep disorders not apparent from traditional metrics. Methods We analyzed records from the Sleep-Heart-Health-Study and a study of performance deficit following sleep deprivation. ORP of all 30-second epochs in each PSG and percent of epochs in each decile of ORPs range were calculated. Percentage of epochs in deep sleep (ORP < 0.50) and in full-wakefulness (ORP > 2.25) were each assigned a rank, 1–3, representing first and second digits, respectively, of nine distinct types (“1,1”, “1,2” … ”3,3”). Prevalence of each type in clinical groups and their associations with demographics, sleepiness (Epworth-Sleepiness-Scale, ESS) and quality of life (QOL; Short-Form-Health-Survey-36) were determined. Results Three types (“1,1”, “1,2”, “1,3”) were prevalent in OSA and were associated with reduced QOL. Two (“1,3” and “2,3”) were prevalent in insomnia with short-sleep-duration (insomnia-SSD), but only “1,3” was associated with poor sleep depth and reduced QOL, suggesting two phenotypes in insomnia-SSD. ESS was high in types “1,1” and “1,2”, and low in “1,3” and “2,3”. Prevalence of some types increased with age while in others it decreased. Other types were either rare (“1,1” and “3,3”) or high (“2,2”) at all ages. Conclusions The proposed ORP histogram offers specific and unique information on the underlying neurophysiological characteristics of sleep disorders not captured by routine metrics, with potential of advancing diagnosis and management of these disorders.

For decades, numerous seminal studies have built our understanding of the locus coeruleus (LC), the vertebrate brain’s principal noradrenergic system. Containing a numerically small but broadly efferent cell population, the LC provides brain-wide noradrenergic modulation that optimizes network function in the context of attentive and flexible interaction with the sensory environment. This review turns attention to the LC’s roles during sleep. We show that these roles go beyond down-scaled versions of the ones in wakefulness. Novel dynamic assessments of noradrenaline signaling and LC activity uncover a rich diversity of activity patterns that establish the LC as an integral portion of sleep regulation and function. The LC could be involved in beneficial functions for the sleeping brain, and even minute alterations in its functionality may prove quintessential in sleep disorders.

Obstructive sleep apnea (OSA) and insomnia are the two most common sleep disorders. The coexistence of these conditions, termed comorbid insomnia and sleep apnea (COMISA), has been increasingly recognized, with evidence suggesting a bi-directional relationship that exacerbates the severity of each disorder. This prospective recruited 170 consecutive patients with OSA, categorized into OSA alone and COMISA group. Among recruited patients, 68 (40%) were identified with COMISA. No significant differences were found in age, gender, or body mass index between COMISA and OSA alone groups. However, COMISA patients were more likely to have comorbid medical conditions, reported worse sleep quality, and exhibited higher levels of anxiety and depression. Sleep architecture and the distribution of the low arousal threshold endotype, a potential contributor to COMISA, did not significantly differ between patients with COMISA and OSA alone. Our results suggest that COMISA is prevalent among Asian patients with OSA and is associated with worse subjective sleep quality, adverse health conditions, and higher psychological distress. However, objective sleep architecture and arousal threshold endotypes do not significantly differ from OSA alone. Further research is needed to explore the pathophysiological mechanisms underlying COMISA and optimize treatment approaches.

Abstract Study Objectives Objective sleep impairments in insomnia disorder (ID) are insufficiently understood. The present study evaluated whether whole-night sleep stage dynamics derived from polysomnography (PSG) differ between people with ID and matched controls and whether sleep stage dynamic features discriminate them better than conventional sleep parameters. Methods Eighty-eight participants aged 21–70 years, including 46 with ID and 42 age- and sex-matched controls without sleep complaints, were recruited through www.sleepregistry.nl and completed two nights of laboratory PSG. Data of 100 people with ID and 100 age- and sex-matched controls from a previously reported study were used to validate the generalizability of findings. The second night was used to obtain, in addition to conventional sleep parameters, probabilities of transitions between stages and bout duration distributions of each stage. Group differences were evaluated with nonparametric tests. Results People with ID showed higher empirical probabilities to transition from stage N2 to the lighter sleep stage N1 or wakefulness and a faster decaying stage N2 bout survival function. The increased transition probability from stage N2 to stage N1 discriminated people with ID better than any of their deviations in conventional sleep parameters, including less total sleep time, less sleep efficiency, more stage N1, and more wake after sleep onset. Moreover, adding this transition probability significantly improved the discriminating power of a multiple logistic regression model based on conventional sleep parameters. Conclusions Quantification of sleep stage dynamics revealed a particular vulnerability of stage N2 in insomnia. The feature characterizes insomnia better than—and independently of—any conventional sleep parameter.

Abstract Study Objectives The response of sleep depth to CPAP in patients with OSA is unpredictable. The odds-ratio-product (ORP) is a continuous index of sleep depth and wake propensity that distinguishes different sleep depths within sleep stages, and different levels of vigilance during stage wake. When expressed as fractions of time spent in different ORP deciles, nine distinctive patterns are found. Only three of these are associated with OSA. We sought to determine whether sleep depth improves on CPAP exclusively in patients with these three ORP patterns. Methods ORP was measured during the diagnostic and therapeutic components of 576 split-night polysomnographic (PSG) studies. ORP architecture in the diagnostic section was classified into one of the nine possible ORP patterns and the changes in sleep architecture were determined on CPAP for each of these patterns. ORP architecture was similarly determined in the first half of 760 full-night diagnostic PSG studies and the changes in the second half were measured to control for differences in sleep architecture between the early and late portions of sleep time in the absence of CPAP. Results Frequency of the three ORP patterns increased progressively with the apnea-hypopnea index. Sleep depth improved significantly on CPAP only in the three ORP patterns associated with OSA. Changes in CPAP in the other six patterns, or in full diagnostic PSG studies, were insignificant or paradoxical. Conclusions ORP architecture types can identify patients in whom OSA adversely affects sleep and whose sleep is expected to improve on CPAP therapy. Graphical abstract Graphical Abstract

Physical activity has been found to alter sleep architecture, but these effects have been studied predominantly in the laboratory and the generalizability of these findings to naturalistic environments and longer time intervals, as well as their psychological effects, have not been evaluated. Recent technological advancements in wearable devices have made it possible to capture detailed measures of sleep outside the lab, including timing of specific sleep stages. In the current study, we utilized photoplethysmography coupled with accelerometers and smartphone ambulatory assessment to collect daily measurements of sleep, physical activity and mood in a sample of N = 82 over multi-month data collection intervals. We found a robust inverse relationship between sedentary behavior and physical activity and sleep architecture: both low-intensity and moderate-to-vigorous physical activity were associated with increased NREM sleep and decreased REM sleep, as well as a longer REM latency, while higher levels of sedentary behavior showed the opposite pattern. A decreased REM/NREM ratio and increased REM latency were in turn associated with improved wellbeing, including increased energy, reduced stress and enhanced perceived restfulness of sleep. Our results suggest that physical activity and sleep account for unique variance in a person’s mood, suggesting that these effects are at least partially independent.

Abstract Study Objectives The COVID-19 pandemic has had dramatic effects on society and people’s daily habits. In this observational study, we recorded objective data on sleep macro- and microarchitecture repeatedly over several nights before and during the COVID-19 government-imposed lockdown. The main objective was to evaluate changes in patterns of sleep duration and architecture during home confinement using the pre-confinement period as a control. Methods Participants were regular users of a sleep-monitoring headband that records, stores, and automatically analyzes physiological data in real time, equivalent to polysomnography. We measured sleep onset duration, total sleep time, duration of sleep stages (N2, N3, and rapid eye movement [REM]), and sleep continuity. Via the user’s smartphone application, participants filled in questionnaires on how lockdown changed working hours, eating behavior, and daily life at home. They also filled in the Insomnia Severity Index, reduced Morningness–Eveningness Questionnaire, and Hospital Anxiety and Depression Scale questionnaires, allowing us to create selected subgroups. Results The 599 participants were mainly men (71%) of median age 47 (interquartile range: 36–59). Compared to before lockdown, during lockdown individuals slept more overall (mean +3·83 min; SD: ±1.3), had less deep sleep (N3), more light sleep (N2), and longer REM sleep (mean +3·74 min; SD: ±0.8). They exhibited less weekend-specific changes, suggesting less sleep restriction during the week. Changes were most pronounced in individuals reporting eveningness preferences, suggesting relative sleep deprivation in this population and exacerbated sensitivity to societal changes. Conclusion This unique dataset should help us understand the effects of lockdown on sleep architecture and on our health.

Dual orexin receptor antagonists (DORAs) represent a novel type of sleep medication that provide an alternative to the traditionally used positive allosteric gamma-aminobutyric acid (GABA)-A receptor modulators. Daridorexant is a new DORA that exhibited in phase 3 trials in insomnia not only a beneficial effect on sleep variables, measured objectively and assessed subjectively, but also an improvement in daytime functioning. Daridorexant was discovered through a tailored research program aimed at identifying an optimized sleep-promoting molecule with pharmacokinetic properties appropriate for covering the whole night while avoiding next-morning residual activity at efficacious doses. By specific binding to both orexin receptors, daridorexant inhibits the actions of the wake-promoting orexin (also called hypocretin) neuropeptides. This mechanism avoids a more widespread inhibition of neuronal pathways and associated side effects that are intrinsic to positive allosteric GABA-A receptor modulators. Here, we review the general pharmacology of daridorexant, based on nonclinical pharmacology studies of daridorexant, unpublished or already described, or based on work with other DORAs. Some unique features of daridorexant will be highlighted, such as the promotion of natural and surmountable sleep, the preservation of memory and cognition, the absence of tolerance development or risk of physical dependence, and how it can benefit daytime functioning.

Abstract Study Objectives Unrefreshing naps are supportive clinical features of idiopathic hypersomnia (IH) and are reported by more than 50% of IH patients. They are, however, not mandatory for the diagnosis, and their pathophysiological nature is not understood. This study aimed at verifying whether IH patients with and without unrefreshing naps constitute two subtypes of IH based on their demographic/clinical characteristics, and sleep architecture. Methods One hundred twelve IH patients underwent a polysomnography (PSG) followed by a multiple sleep latency test (MSLT). They completed questionnaires on excessive daytime sleepiness, mood, and sleep quality. They were met by sleep medicine physicians who conducted a semi-structured clinical interview and questioned them on refreshing aspects of their naps. Patients who reported unrefreshing naps were compared to patients reporting refreshing naps on questionnaires, MSLT and PSG variables, with age as a covariable. As sensitivity analyses, we performed the same comparisons in participants presenting objective markers of IH and those diagnosed with IH based only on clinical judgment (subjective IH), separately. Results In the whole sample, 61% of patients reported unrefreshing naps. These participants had less awakenings, a lower percentage of N1 sleep, less sleep stage transitions, and a higher percentage of REM sleep on the nighttime PSG compared to the refreshing naps subgroup. When subjective and objective IH patients were tested separately, more group differences were observed on PSG for subjective IH patients. Conclusions Patients with unrefreshing naps have less fragmented sleep compared to those with refreshing naps. Future studies should investigate whether this group difference indicates a weaker arousal drive. Graphical Abstract