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Information on obstructive sleep apnea (OSA) is often latently detected in diagnostic tests conducted for other purposes, providing opportunities for maximizing value. This study aimed to develop a convolutional neural network (CNN) to identify the risk of OSA using lateral cephalograms.The lateral cephalograms of 5,648 individuals (mean age, 49.0±15.8 years; men, 62.3%) with or without OSA were collected and divided into training, validation, and internal test datasets in a 5:2:3 ratio. A separate external test dataset (n=378) was used. A densely connected CNN was trained to diagnose OSA using a cephalogram. Model performance was evaluated using the area under the receiver operating characteristic curve (AUROC). Gradient-weighted class activation mapping (Grad-CAM) was used to evaluate the region of focus, and the relationships between the model outputs, anthropometric characteristics, and OSA severity were evaluated.The AUROC of the model for the presence of OSA was 0.82 (95% confidence interval [CI], 0.80-0.84) and 0.73 (95% CI, 0.65-0.81) in the internal and external test datasets, respectively. Grad-CAM demonstrated that the model focused on the area of the tongue base and oropharynx in the cephalogram. Sigmoid output values were positively correlated with OSA severity, body mass index, and neck and waist circumference.Deep learning may help develop a model that classifies OSA using a cephalogram, which may be clinically useful in the appropriate context. The definition of ground truth was the main limitation of this study.

To examine the association of subjective age (SA) with sleep quality in an adult population.In the Korean Sleep and Headache Study, 2,349 participants (49.2% men; 48.1 ± 16.4 years old) were interviewed face-to-face using structured questionnaires between September and December 2018. SA was assessed by asking participants their perceived age in years and then compared with their chronological age (CA). Participants were assigned to three groups: feeling younger, feeling their age, and feeling older. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI). Association between SA and sleep quality was analyzed with multiple linear regression controlling for demographics, psychosocial, and sleep characteristics.The group feeling older (n = 404, 17.2%; men, 58.2%; age, 46.5 ± 16.2 years) had worse sleep quality than the groups feeling younger and feeling their age (PSQI score, 4.3 ± 2.7, 3.8 ± 2.4, 3.4 ± 2.1, respectively, p.001; prevalence of poor sleep quality, 29.0%, 18.4%, 13.5% respectively, p.001). The association between SA and the PSQI score remained significant after adjusting for confounders (β = 1.05, 95% confidence interval 0.26, 1.83; p.001). Stratified analyses by sex and CA showed that the association between SA and the PSQI score was significant only in women and in middle-aged and older group (aged 50-79), suggesting that sex and CA modified the association.Age perception was associated with self-reported sleep quality, independent of CA. SA may be a useful marker that complements the conventional assessment of subjective sleep quality.

This study aimed to evaluate the effect of sleep duration on brain structures in the presence versus absence of sleep apnea in middle-aged and older individuals. The study investigated a population-based sample of 2,560 individuals, aged 49-80 years. The presence of sleep apnea and self-reported sleep duration were examined in relation to gray matter volume (GMV) in total and lobar brain regions. We identified ranges of sleep duration associated with maximal GMV using quadratic regression and bootstrap sampling. A significant quadratic association between sleep duration and GMV was observed in total and lobar brain regions of men with sleep apnea. In the fully adjusted model, optimal sleep durations associated with peak GMV between brain regions ranged from 6.7 to 7.0 hours. Shorter and longer sleep durations were associated with lower GMV in total and 4 sub-regions of the brain in men with sleep apnea.

The relationship between napping and cognition remains controversial. This study aimed to investigate the association between napping and cognition according to sleep debt in the Korean adult population.A population-based nationwide cross-sectional survey was conducted in 2018. A two-stage stratified random sample of Koreans aged ≥19 years was selected and evaluated using questionnaires by trained interviewers. Cognitive function was assessed using the Mail-In Cognitive Function Screening Instrument (MCFSI). Sleep habits on weekdays and weekends, napping, and subjective sleep requirements were assessed using the questionnaires. Accumulated sleep debt was calculated by subtracting the weekly average sleep duration from subjective sleep requirements. Sleep quality, daytime sleepiness, insomnia, depression, demographics, and comorbidities were assessed. Participants were grouped into those with sleep debt ≤60 min and those with sleep debt60 min. Multiple linear regression was used to estimate the independent association between the factors and cognition.In total, 2,501 participants were included in the analysis. Naps were reported in 726 (29.0%) participants (nappers). The mean MCFSI score was higher in nappers (3.4±3.6) than in non-nappers (2.3±3.0) (In general, naps are associated with worse cognitive function in the Korean adult population. However, for those with sleep debt of60 min, naps for60 min were associated with better cognitive function.

Objective: Insomnia and depression are prevalent disorders that often co-occur. This study aimed to investigate the impact of clinically significant insomnia symptoms on the prevalence and clinical presentation of clinically significant depressive symptoms and vice versa.Methods: This study used data from the Korean Headache-Sleep Study (KHSS), a nationwide cross-sectional population-based survey regarding headache and sleep. Clinically significant insomnia symptoms were defined as Insomnia Severity Index (ISI) scores ≥ 10 and clinically significant depressive symptoms were defined as Patient Health Questionnaire-9 (PHQ-9) scores ≥ 10, respectively. We referred clinically significant insomnia symptoms and clinically significant depressive symptoms as insomnia symptoms and depressive symptoms, respectively.Results: Of 2,695 participants, 290 (10.8%) and 116 (4.3%) were classified as having insomnia and depressive symptoms, respectively. The prevalence of depressive symptoms was higher among participants with insomnia symptoms than in those without insomnia symptoms (25.9 vs. 1.7%, respectively, P < 0.001). Among participants with depressive symptoms, the PHQ-9 scores were not significantly different between participants with and without insomnia symptoms (P = 0.124). The prevalence of insomnia symptoms was significantly higher among participants with depressive symptoms than in those without depressive symptoms (64.7 vs. 8.3%, respectively, P < 0.001). The ISI scores were significantly higher among participants with insomnia and depressive symptoms than in participants with insomnia symptoms alone (P < 0.001).Conclusions: Participants with depressive symptoms had a higher risk of insomnia symptoms than did those without depressive symptoms. The severity of depressive symptoms did not significantly differ based on insomnia symptoms among participants with depressive symptoms; however, the severity of insomnia symptoms was significantly higher in participants with depressive symptoms than in those without depressive symptoms.

We investigated the prevalence of sleep problems, such as obstructive sleep apnea (OSA), insomnia, and daytime sleepiness in commercial motor vehicle (CMV) drivers compared with that in the general population. This is a cross-sectional study comparing sleep habits and sleep problems in 110 truck drivers with 1001 matched controls from the general population. The assessment was based on self-administered questionnaires that included the Berlin questionnaire, the insomnia severity index, and the Epworth sleepiness scale (ESS). Multivariate regression analysis was performed to determine whether CMV drivers were independently associated with these sleep problems compared with controls. The prevalence of a high risk of OSA and insomnia was 35.5% and 15.2%, respectively, in CMV drivers, which was significantly higher than in controls with a prevalence of 12.2% and 4.1%, respectively (P

OBJECTIVE This study was conducted to investigate sex differences in the prevalence and clinical presentation of migraine and probable migraine in a general population-based sample. BACKGROUND While there is research on sex differences in clinical characteristics and their impact on migraine headache, only few studies have investigated sex differences in probable migraine in population-based settings. Moreover, compared with Western countries, the prevalence of probable migraine in Asia is relatively high. This cross-sectional study was designed to investigate sex differences in the prevalence and clinical presentation of migraine and probable migraine in a general population-based sample. METHODS We used the data of the Korean Headache-Sleep Study, which is a nationwide survey on headache and sleep. RESULTS We interviewed 7430 people, and 3114 of them agreed to participate in our study (rejection rate, 58.1%). Among these people, 419 withdrew their participation during the interview. Ultimately, 2695 people completed our survey (cooperation rate, 36.3%). The prevalence of overall migraine and probable migraine was 350/1350 (25.9%) for women and 172/1345 (12.8%) for men (P

This study aimed to investigate sleep problems and comorbid conditions associated with fatigue in the general population. The data were obtained from a nationwide cross-sectional survey conducted in 2018. The Fatigue Severity Scale was used to assess fatigue. We examined sleep habits, such as workday sleep duration, chronotype, and free-day catch-up sleep, excessive daytime sleepiness (EDS), depression, and other comorbid conditions. We conducted multiple logistic regression analysis with the presence of fatigue as a dependent variable. Of 2,493 adults aged 19 to 92 years, 50% men, mean age was 47.9 ± 16.4 years. The average workday sleep duration was 7.1 ± 1.1 h, and the prevalence of fatigue was 31%. After adjusting for potential confounders, fatigue was associated with EDS (odds ratio [OR] 3.751, 95% confidence interval [CI] 2.928–4.805), depression (OR 3.736, 95% CI 2.701–5.169), perceived insufficient sleep (OR 1.516, 95% CI 1.249–1.839), free-day catch-up sleep (OR 1.123, 95% CI 1.020–1.235), less alcohol intake (OR 0.570, 95% CI 0.432–0.752), and physical inactivity (OR 0.737, 95% CI 0.573–0.948). On subgroup analysis, fatigue was additionally associated with short workday sleep duration (OR 0.899, 95% CI 0.810–0.997) in individuals without EDS. However, among those with EDS, only depression (OR 2.842, 95% CI 1.511–5.343) and less alcohol intake (OR 0.476, 95% CI 0.247–0.915) were associated with fatigue. Fatigue was significantly associated with depression independent of EDS. Further research is warranted to better understand the pathophysiological relationship between fatigue, depression, and sleep.

Background and Purpose While excessive daytime sleepiness can predate Parkinson’s disease in late-life, its association with parkinsonian-like (P-L) symptoms in middle age are unknown. Since neurodegeneration can appear decades before a diagnosis of Parkinson’s disease, identifying clinical features associated with this early progression is important. The purpose of this study was to determine the association of daytime sleepiness with P-L symptoms in a population-based sample of middle-aged Korean adults. Methods During 2013 and 2014, daytime sleepiness and P-L symptoms were assessed in 2,063 males and females aged 50–64 years who were participating in the Korean Genome and Epidemiology Study. The severity of daytime sleepiness was quantified by the score on the Epworth Sleepiness Scale (ESS). Self-reported P-L symptoms included nine motor disorders commonly associated with Parkinson’s disease. Participants with parkinsonism and related conditions are excluded. Results The prevalence of excessive daytime sleepiness (ESS score >10) was 7.0%. The frequencies of P-L symptoms ranged from 0.5% (for “trouble buttoning buttons”) to 18.4% (for “handwriting smaller than it once was”). After adjustment for covariates and multiple testing, the relative odds of P-L symptoms comparing the 80th and 20th percentiles of ESS scores was 1.6 (p=0.001) for “voice is softer than it once was,” 2.1 (p

Background and purpose Identifying changes in the prevalence, disability, and management patterns of migraine is important for reducing the burden of this disease. However, data on the changes in these variables are scarce. Methods We compared data obtained in the 2009 Korean Headache Survey and the 2018 Korean Sleep-Headache Survey. Results The 1-year migraine prevalence did not differ significantly between 2018 and 2009 [5.2% (114/2,200) vs. 6.0% (91/1,507), p=0.492]. The number of days with missed activity due to headache during the previous 3 months was larger in the 2018 survey than in the 2009 survey [1.1±2.9 vs. 0.3±1.0 days (mean±standard deviation), p=0.013]. The number of days with reduced productivity during the previous 3 months did not differ significantly between the two surveys (0.8±2.8 vs. 1.4±1.4 days, p=0.679). The proportion of subjects with a substantial-to-severe headache impact (Headache Impact Test-6 score ≥56) was marginally larger in the 2018 survey than in the 2009 survey [42.1% (48/114) vs. 29.7% (27/91), p=0.066]. The rate of lifetime medical consultations did not differ between the 2018 and 2009 surveys [34.2% (39/114) vs. 30.8% (28/91), p=0.615]. Conclusions Migraine prevalence was stable over the 9-year period between the surveys, but disability due to missed activity was greater in 2018 than in 2009 in Korea.

Background and purpose Nonketotic hyperglycemia often causes transient visual field defects, but only scattered anecdotes are available in the literature. Methods We report a patient with homonymous superior quadrantanopsia due to nonketotic hyperglycemia and provide a systematic literature review of the clinical features of 40 previously reported patients (41 in total, including our case) with homonymous visual field defects in association with nonketotic hyperglycemia. Results The typical visual field defect was congruous (84.6%), homonymous hemianopsia (87.8%) with macular splitting (61.5%) or sparing (38.5%). It was transient and repetitive in 54.5% of the patients, but it developed as a persistent form in the remainder. Positive visual symptoms such as hallucinations and phosphenes developed in 73.2% of patients. Brain MRI revealed corresponding abnormalities in most patients (84.8%), characterized by a low-intensity white-matter signal or a high-intensity gray-matter signal on T2-weighted or fluid-attenuated inversion recovery images with diffusion restriction or gadolinium enhancement. Most (97.0%) patients recovered completely, with 48.5% treated by glycemic control alone and the remainder also receiving antiepileptic agents. Conclusions Nonketotic hyperglycemia should be considered a possible cause of transient visual field defects, especially when it is associated with repetitive positive visual symptoms and typical MRI findings in hyperglycemic patients.

We investigated both independent and interconnected effects of 3 lifestyle factors on brain volume, measuring yearly changes using large-scale longitudinal magnetic resonance imaging, in middle-aged to older adults. We measured brain volumes in a cohort (n = 984, 49-79 years) from the Korean Genome and Epidemiology Study group, using baseline and follow-up estimates after 4 years. In our analysis, the accelerated brain atrophy in normal aging was observed across regions (e.g., brain tissue: -0.098 ± 0.01 mL/y, p0.001). An independent lifestyle-specific trend of brain atrophy across time was also evident in men, where smoking (p = 0.012) and physical activity (p = 0.014) showed the strongest association with the atrophy rate. Linear regression analysis of the interconnected effect revealed that brain atrophy is mitigated by intense physical activity in smoking males. Lifestyle factors did not show any significant effect on brain volume in women. These results provide important information regarding lifestyle factors that affect brain aging in mid-to-late adulthood. Our findings may aid in the identification of preventive measures against dementia.

Background and purpose Sufficient sleep is an essential part of good health and well-being. Tension-type headache (TTH) is the most common type of primary headache and has negative impacts on the quality of life and work performance. We aimed to determinethe relationship between TTH and insufficient sleep in the general population. Methods This study used data from the Korean Headache Sleep Study, which was a population-based survey about headache and sleep among Korean adults. Insufficient sleep was defined when the discrepancy between sleep need and average sleep duration was at least 1 hour. Results Among the 2,695 included subjects, 570 (21.2%) and 727 (27.0%) were classified as having TTH and insufficient sleep, respectively. The prevalence of insufficient sleep was significantly higher among subjects with TTH than among those without headaches (28.8% vs. 20.4%). For subjects with TTH, the scores on a visual analogue scale (4.7±1.8 vs. 4.3±1.9, mean±SD) and the Headache Impact Test-6 (44.9±7.0 vs. 43.6±6.1) were much higher in subjects with insufficient sleep than in those without insufficientsleep. Multivariable analyses revealed that insomnia [odds ratio (OR)=2.1], poor sleep quality (OR=1.7), and short sleep duration (OR=6.9) were significantly associated with insufficient sleep in subjects with TTH. Conclusions Our findings suggest that insufficient sleep is prevalent among subjects with TTH and is linked to an exacerbation of TTH. Therefore, the proper evaluation and management of sleep may lead to the better management of TTH.

Sleep, a vital process of human being, is carefully orchestrated by the brain and consists of cyclic transitions between rapid eye movement (REM) and non-REM (NREM) sleep. Autonomic tranquility during NREM sleep is characterized by vagal dominance and stable breathing, providing an opportunity for the cardiovascular-neural axis to restore homeostasis, in response to use, distress or fatigue inflicted during wakefulness. Abrupt irregular swings in sympathovagal balance during REM sleep act as phasic loads on the resting cardiovascular system. Any causes of sleep curtailment or fragmentation such as sleep restriction, sleep apnea, insomnia, periodic limb movements during sleep, and shift work, not only impair cardiovascular restoration but also impose a stress on the cardiovascular system. Sleep disturbances have been reported to play a role in the development of stroke and other cardiovascular disorders. This review aims to provide updated information on the role of abnormal sleep in the development of stroke, to discuss the implications of recent research findings, and to help both stroke clinicians and researchers understand the importance of identification and management of sleep pathology for stroke prevention and care.

Introduction Sleep patterns have been linked to various heath disease. Evaluating population-level trend of sleep could provide a comprehensive population health-forecasting model that has the potential to inform targeted interventions. Therefore, we aimed to examine the cross-sectional differences in sleep characteristics among Korean adults during a 9-year period of 2009-2018. Methods The data in this study were derived from two nationwide survey regarding sleep and headache in the representative sample of Korean adult population, namely the Korean Sleep Headache Study phase I (2009) and II (2018). The survey was conducted through door-to-door visit and face-to-face interview by using structured questionnaires. Total of 2,836 participants from Phase I (47.9±16.4 years old; female, 50.2%) and 2,501 participants (47.9±16.4 years old; female, 50.3%) from Phase II gave informed consents and completed the survey. For this study, we excluded those who worked as shift workers and missing data. From the MCTQ, we collected participants’ sleep schedule during workdays and free days over the past four weeks. Average sleep duration was a weighted mean of sleep duration on workdays and free days. Poor sleep quality was defined as PSQI >5. Excessive daytime sleepiness and Depression are performed with ESS and PHQ-9, respectively. Results During the 9 years, average sleep duration decreased by 21 minutes, especially more reduction on free days (workday: 7:17±1:58 vs. 7:06±1:06, p Conclusion Decreased sleep duration seems to be on the rise in the general adult population, which lead to a poor health status. Interventions to promote adequate sleep is urgently needed. Support (if any)

Background Sleep disturbances are closely related to migraine. Nevertheless, information regarding the impact of short sleep duration and poor sleep quality on the clinical presentation of migraine at population level is limited. Methods This study was a nationwide population-based survey on adults aged 19–69 years. Headache frequency (attacks/month) and intensity (visual analogue scale, 0–10) were documented. Short sleep duration and poor sleep quality were defined as average sleep duration 5, respectively. The association of sleep parameters with headache frequency and intensity was analysed among migraineurs. Results Of 2695 participants, 143 (5.3%) had migraine. Headache frequency was significantly higher among migraineurs with short sleep duration (2.0 [1.0–12.0] vs. 1.0 [0.3–4.0], p = 0.048) and poor sleep quality (2.0 [0.6–4.7] vs. 1.0 [0.2–3.0], p = 0.009) than among those without. However, headache intensity was similar between migraineurs with short sleep duration and poor sleep quality. Multiple linear regression analyses revealed that short sleep duration was a significant contributing factor for headache frequency (β = 0.210, p = 0.015). Conclusions Self-reported short sleep duration (

Background Recent studies have shown a significant association between restless legs syndrome (RLS) and primary headache disorders. Nevertheless, information regarding the association between tension-type headache (TTH) and RLS is limited. This study aimed to investigate the association between RLS and TTH in a population-based sample. Methods We selected a stratified random population sample of Koreans aged 19–69 years and assessed them using a semi-structured interview designed to identify RLS, headache type, and clinical characteristics of TTH. We determined the prevalence and clinical impact of RLS in participants with TTH. Results Of the 2695 participants, 570 (21.2%) and 142 (5.3%) were classified as having TTH and RLS, respectively. Among the 570 individuals with TTH, 113 (19.8%) also met the criteria for probable migraine (PM). The prevalence of RLS was significantly higher among individuals with TTH than among those with non-headache (6.0% vs 3.6%, p = 0.018). The prevalence of RLS was significantly higher in subjects with TTH who fulfilled PM criteria than in those with non-headache participants (8.0% vs. 3.6%, p = 0.018). However, RLS prevalence in individuals with TTH who did not fulfil PM criteria did not differ from that of participants with non-headache (5.5% vs. 3.6%, p = 0.063). TTH participants with RLS had higher visual analogue scale scores for headache intensity (5.1 ± 2.0 vs. 4.3 ± 1.8, p = 0.038), and higher prevalence of anxiety (20.6% vs. 8.8%, p = 0.022) and depression (14.7% vs. 3.5%, p = 0.002) than TTH participants without RLS. Multivariable analyses revealed that headache aggravation by movement (odds ratio [OR] = 2.4, 95% confidence interval [CI] = 1.1–5.2) and depression (OR = 3.5, 95% CI = 1.1–11.4) were significant indicators of RLS among individuals with TTH. Conclusions The prevalence of RLS was higher among individuals with TTH than among those with non-headache. Some clinical presentations varied in accordance with the presence of RLS among participants with TTH. Electronic supplementary material The online version of this article (doi:10.1186/s10194-017-0754-x) contains supplementary material, which is available to authorized users.

Study Objectives Sleep behaviors are related to brain structure and function, but the impact of long-term changes in sleep timing on brain health has not been clearly addressed. The purpose of this study was to examine the association of longitudinal changes in sleep timing from middle to late-life with gray matter volume (GMV), an important marker of brain aging. Methods We enrolled 1798 adults (aged 49–82 years, men 54.6%) who underwent magnetic resonance imaging (MRI) between 2011 and 2014. Midsleep time (MST) on free days corrected for sleep debt on workdays was adopted as a marker of sleep timing. Data on MST were available at the time of MRI assessment and at examinations that were given 9 years earlier (2003–2004). Longitudinal changes in MST over the 9-year period were derived and categorized into quartiles. Subjects in quartile 1 were defined as “advancers” (MST advanced ≥ 1 h) while those in quartile 4 were defined as “delayers” (MST delayed ≥ 0.2 h). Quartiles 2–3 defined a reference group (MST change was considered modest). The relationship of GMV with MST changes over 9 years was investigated. Results Nine-year change in MST were significantly associated with GMV. Compared to the reference group, advancers had smaller GMVs in the frontal and temporal regions. A delay in MST was also associated with smaller cerebellar GMV. Conclusions In middle-to-late adulthood, the direction of change in MST is associated with GMV. While advancers and delayers in MST tend to present lower GMV, associations appear to differ across brain regions.

Excessive daytime sleepiness (EDS) is a prevalent sleep-related complaint across the general population and has been reported to be associated with headache. Tension-type headache (TTH) is the most commonly encountered headache and accounts for a significant amount of disease burden. However, the association between EDS and TTH is currently scarce. In the present study, we investigated the impact of EDS on the prevalence and clinical presentation of TTH. We utilized data from the Korean Headache-Sleep Study, a national survey that sought to identify headache and sleep characteristics in Korean adults. Participants with an Epworth sleepiness scale score greater or equal to 11 were considered as having EDS. Of the 2,695 participants enrolled, 570 (21.2%) and 313 (11.6%) had TTH and EDS, respectively. EDS was highly prevalent in individuals with chronic tension-type headache (CTTH) than in those without headache (35.7 vs. 9.4%, p < 0.001). The prevalence of EDS in episodic tension-type headache (ETTH) individuals with a headache frequency

Introduction Increasing research suggests that subjective cognitive decline (SCD) in the absence of objective cognitive dysfunction may be a forerunner of non-normative cognitive decline and eventual progression to dementia. We investigated the association between chronotype and subjective cognitive functioning in the representative sample of the adult population. Methods We included subjects who participated in a nationwide cross-sectional survey of sleep and headache in 2018 in the Republic of Korea. A total of 2136 subjects (age 19-92, mean 48.3 ± 16.5 years old, 1062 male) was included in the analysis. To assess subjective cognitive functioning, we adopted the Mail-In Cognitive Function Screening Instrument (MCFSI). The MCSFSI is a brief, self-administered potential outcome measure developed by the Alzheimer’s Disease Cooperative Study (ADCS) to detect early changes in cognitive and functional abilities in individuals without clinical impairment. MCFSI scores ≥5 were considered abnormal for this study. As an indicator of chronotype, we adopted the “midpoint of sleep on free days corrected for sleep extension on free days (MSFsc).” MSFsc was calculated as follows: MSFsc = midpoint of sleep on free days − 0.5 × (sleep duration on free days − [5 × sleep duration on workdays + 2 × sleep duration on free days]/7). Participants whose MSFsc occurred before 04:00 AM, between 04:00 and 04:59 AM, and after 05:00 AM were classified as early, intermediate, and late chronotype, respectively. The associations between chronotype and subjective cognitive functioning were analyzed with logistic regression models adjusted for potential confounders. Results Subjective cognitive functioning was abnormal in 381 subjects (17.8%). A late chronotype was significantly associated with abnormal subjective cognitive functioning compared with an early chronotype independent of age, sex, average sleep duration, alcohol, smoking, regular exercise, anxiety, depression, body mass index (BMI), education years, and income status (OR 1.619, 95% CI 1.03 - 2.55, p=0.038). Abnormal subjective cognitive functioning was significantly associated with older age, female sex, lower education, higher BMI, anxiety, and depression. Conclusion This survey cohort results provide evidence at the population level that late chronotype is associated with abnormal subjective cognitive functioning. Support (if any)

Background Although probable migraine (PM) is common among headache sufferers, there is little knowledge of the prevalence and impacts of comorbid anxiety and depression in patients with PM. We assessed the prevalence and impact of anxiety and depression among PM sufferers in the general population. Methods We recruited Korean individuals aged 19–69 years via stratified random sampling and assessed headache type, anxiety, and depression among them using structured interviews. Results In a representative sample of 2695 individuals, 143 (5.3%) and 379 (14.1%) had migraine and PM, respectively. Fewer patients with PM had anxiety (17.7% vs. 30.1%, p = 0.002) and depression (8.7% vs. 16.8%, p = 0.007) compared to those with migraine. Prevalence of anxiety and depression was lower in people with PM than in those with migraine in univariable analysis, but insignificant after including headache intensity and headache frequency for adjustment. Headache frequency, headache intensity, and impact of headache were significantly higher among PM and migraine patients with anxiety and depression than among those without. Conclusions The prevalence of anxiety and depression was lower among individuals with PM compared to those with migraine. However, they were still prevalent and associated with an exacerbation of symptoms among individuals with PM.

Study Objectives To assess, using fractional anisotropy (FA) analysis, alterations of brain network connectivity in adults with obstructive sleep apnea (OSA). Abnormal networks could mediate clinical functional deficits and reflect brain tissue injury. Methods Structural brain networks were constructed using diffusion tensor imaging (DTI) from 165 healthy (age 57.99 ± 6.02 years, male 27.9%) and 135 OSA participants (age 59.01 ± 5.91 years, male 28.9%) and global network properties (strength, global efficiency, and local efficiency) and regional efficiency were compared between groups. We examined MRI biomarkers of brain tissue injury using FA analysis and its effect on the network properties. Results Differences between groups of interest were noted in global network properties (p-value < 0.05, corrected), and regional efficiency (p-value < 0.05, corrected) in the left middle cingulate and paracingulate gyri, right posterior cingulate gyrus, and amygdala. In FA analysis, OSA participants showed lower FA values in white matter (WM) of the right transverse temporal, anterior cingulate and paracingulate gyri, and left postcentral, middle frontal and medial frontal gyri, and the putamen. After culling fiber tracts through WM which showed significant differences in FA, we observed no group difference in network properties. Conclusions Changes in WM integrity and structural connectivity are present in OSA participants. We found that the integrity of WM affected brain network properties. Brain network analysis may improve understanding of neurocognitive deficits in OSA, enable longitudinal tracking, and provides explanations for specific symptoms and recovery kinetics.

Background Insomnia and migraine are closely related; insomnia aggravates migraine symptoms. This study was conducted to investigate the impact of migraine on the clinical presentation of insomnia symptoms. Methods The data of the Korean Headache-Sleep Study (KHSS) were used in the present study. The KHSS is a nation-wide cross-sectional population-based survey regarding headache and sleep in Korean adults aged 19 to 69 years. If a participant’s Insomnia Severity Index (ISI) score ≥ 10, she/he was classified as having insomnia. The clinical presentation of insomnia symptoms was assessed using total and subcomponent scores of the ISI. Results Of 2695 participants, 290 (10.8%) and 143 (5.3%) individuals were assigned as having insomnia and migraine, respectively. The proportions of migraine (12.8% vs. 4.4%, p

Background: Restless legs syndrome (RLS) is a common sleep disorder, although it has a low prevalence in Asian populations. However, the reported RLS prevalence in ­Korean adults is mostly 4.5–12.1%, which is higher than that reported in other Asian populations. This study aimed to diagnose RLS and exclude mimicking conditions in 2 independent samples of Korean adults, and to compare its prevalence to that from previous studies performed in Asian countries. Methods: Study populations included a (1) nationwide stratified random sample (n = 2,824; age 19–79 years) and (2) community-based cohort (n = 2,685; age 47–79 years). We applied the Cambridge-Hopkins diagnostic questionnaire to diagnose RLS and differentiate it from RLS mimics. Sleep-related symptoms, mood, and medical conditions were compared between the RLS and non-RLS groups. Prior studies of the RLS prevalence in Asia were systematically reviewed and compared to our findings. Results: The adjusted RLS prevalence was 0.4 and 1.3% in populations 1 and 2, respectively. In both populations, subjects with RLS had more depression. The prevalence of RLS mimics was 5.1 and 2.6%, in populations 1 and 2, respectively. The RLS prevalence in Asia was higher when RLS was defined by the presence of essential clinical features and lower when a differential diagnosis was additionally implemented. Conclusions: The RLS prevalence in Korean adults considering RLS mimics is comparable to that in adults from other Asian countries (< 2%). The reported RLS prevalence varies depending on the diagnostic method employed.

Objective We investigated seizure outcomes of patients with supratentorial meningiomas (ST-MNGs) treated with stereotactic radiosurgery (SRS). Methods One hundred and thirty-three patients with a total of 144 ST-MNGs, who were treated with SRS between 2009 and 2016, were included in this study. The mean age was 59.0 ± 11.9 years (range, 13–87 years). The mean follow-up duration was 49.8 ± 24.5 months (range, 9–96 months). The median tumor volume was 2.60 cm3 (range, 0.06–32.40 cm3), and the median marginal dose was 14.0 Gy (range, 11.0–20.0 Gy). Postradiosurgery peritumoral edema (PRPTE) was developed in 43 lesions (29.9%). Results New seizure attacks developed in 16 patients (12.0%) after SRS (first seizure attack in 14 [87.5%]; seizure aggravation in 2 [12.5%]). In 15 patients with new seizure attacks (93.8%), PRPTE was proved on magnetic resonance imaging. The mean interval between SRS and new seizure attack was 6.6 ± 7.1 (range, 0.23–28.8) months. Simple partial seizure was the most common type of seizure (n = 9 [56.3%]). Five patients (31.3%) were seizure-free with antiepileptic drug (AED) medication (3 [18.8%] withdrew AEDs during the follow-up period); however, the remaining 11 patients (68.7%) did not achieve seizure-free outcomes even with AED medication. Moreover, seizures became intractable in 8 patients (50.0%). From multivariate analysis, the significant predictors of post-SRS seizure attack were PRPTE (odds ratio, 53.99; 95% confidence interval, 5.214–559.1; P = 0.001) and brain-tumor contact-surface index (odds ratio, 2.466; 95% confidence interval, 1.183–5.138; P = 0.016). Conclusions The clinical outcomes of seizures after SRS for ST-MNGs fall short of our expectation, and seizures seem to be uncontrollable and even intractable.

Background Probable migraine (PM) is a subtype of migraine that is prevalent in the general population. Previous studies have shown that poor sleep quality is common among migraineurs and is associated with an exacerbation of migraine symptoms. However, information on the prevalence and clinical implication of poor sleep quality among individuals with PM is scarce. Thus, the aim of this study was to assess the prevalence and clinical impact of poor sleep quality in individuals with PM in comparison with those with migraine. Methods Two-stage cluster random sampling was used to perform the survey for sleep and headache in Korean general population. Participants with Pittsburgh Sleep Quality Index > 5 were considered as having poor sleep quality. Results Of 2695 participants, 379 (14.1%) had PM and 715 (26.5%) had poor sleep quality. Prevalence of poor sleep quality was 35.4% in the PM group, which was lower than that in the migraine group (47.6%, p = 0.011), but higher than that in the non-headache group (21.4%, p

We performed a retrospective study to identify factors associated with preoperative and late postoperative seizures in primary supratentorial meningiomas.Between July 2003 and December 2014, we extracted 303 consecutive patients who underwent primary resection for supratentorial meningiomas at a single institution. Univariate analysis and multivariate logistic regression analysis were performed to determine the associations of seizure occurrence and outcome.Forty-nine (16.2%) of the total 303 patients presented with preoperative seizures. The risk factors independently associated with preoperative seizures were vasogenic edema (OR 4.44, p = 0.001), parasagittal or parafalcine location (OR 2.20, p = 0.020), and absence of neurologic deficit (OR 0.30, p = 0.003). Among these patients, 33 (67.3%) were seizure free postoperatively (Engel Class I). Of the 303 patients, we observed late postoperative seizures in 35 (11.6%) patients. The associated risk factors included history of preoperative seizure (OR 3.96, p = 0.002), bigger tumor size (OR 1.04, p = 0.002), and continuation of anti-epileptic drugs (OR 4.74, p = 0.001). We analyzed that meningiomas with a largest diameter of greater than 45.5 mm were 4.2 times more likely to have late postoperative seizures than those with less diameter (HR 4.20, p 0.001). Ten (28.6%) of the 35 patients with late postoperative seizures experienced poor seizure control. The independently associated predictive factors were high grade meningiomas (WHO Grade II or III) (OR 10.66, p = 0.030) and history of postoperative adjuvant therapy (OR 12.58, p = 0.040).Identifying factors associated with preoperative or late postoperative seizures may help guide treatment strategies, eventually improving the quality of life for patients with meningiomas.

Background Tension-type headache (TTH) represents the most common type of headache among the general population. Although such headaches are usually mild in severity, some individuals with TTH experience severe symptoms and psychiatric comorbidities. Such patients may also experience sleep disturbances, which have been associated with headache exacerbation. Nevertheless, information regarding the prevalence and impact of insomnia among individuals with TTH in a population-based setting is limited. Therefore, the aim of the present study was to evaluate the prevalence and impact of insomnia among individuals with TTH using data from the Korean Headache-Sleep Study (KHSS). Methods We analysed data from the KHSS—a nation-wide, cross-sectional, population-based survey on headache and sleep involving Korean adults aged 19 to 69 years. Insomnia was defined as an Insomnia Severity Index score ≥ 10. Results Among 2695 participants, 570 (21.2%) and 290 (10.8%) were classified as having TTH and insomnia, respectively. Among individuals with TTH, 113 (19.8%) met the criteria for probable migraine (PM). The prevalence of insomnia among individuals with TTH was significantly higher than that among individuals without headache (13.2% vs. 5.8%, p

Study objectives To determine if weekend catch-up sleep (CUS) impacts body mass index (BMI) in the general population. Methods A stratified random sample (2156 subjects; age 19-82 years old, 43.0 ± 14.5; 1183 male) from the general population was evaluated, in 2010, using face-to-face interviews about sociodemographic characteristics, height, weight, habitual sleep duration, and time-in-bed at night on weekdays and weekend, sleep-related profiles, mood and anxiety scales, and comorbid-medical conditions. Weekend CUS was identified when nocturnal sleep extension occurred over the weekend, and this was quantified. Average sleep duration, BMI, and chronotype were determined. The association of BMI with the presence and the amount of weekend CUS was analyzed, independent of average sleep duration, chronotype, and sociodemographic factors. Results BMI and average sleep duration was 23.0 ± 3.0 kg/m2 and 7.3 ± 1.2 hours, respectively. The weekend CUS group consisted of 932 subjects (43.2%) who slept longer on weekend than weekdays by 1.8 ± 1.1 hours. Weekend CUS subjects had a significantly lower BMI (22.8 ± 0.19 kg/m2) than the non-CUS (23.1 ± 0.19 kg/m2) group, after adjustment for age, sex, average sleep duration, chronotype, other sociodemographic factors, and anxiety/mood status (p = .01) The relationship between weekend CUS and BMI was dose-dependent (p = 0.02): Every additional hour of weekend CUS was associated with a decrease of 0.12 kg/m2 in BMI (95% confidence interval, -0.23 to -0.02). Conclusions Weekend sleep extension may have biological protective effects in preventing sleep-restriction induced or related obesity. The results suggest a simple population-level strategy to minimize effects of sleep loss.

Background Sleep disorder and sleep complaints are common in subjects with migraine. Although the association between sleep disorders and migraine has been reported, the association between perceived insufficient sleep and migraine has rarely reported. The aim of this study is to evaluate the association between insufficient sleep and migraine using the data of the Korean Headache-Sleep Study (KHSS). Methods The KHSS is a nation-wide cross-sectional population-based survey regarding headache and sleep for Korean adults aged 19 to 69 years. A difference of one hour or more between sleep need and average sleep time indicated insufficient sleep. Results Of 2,695 participants, 727 (27.0%) individuals were classified as having insufficient sleep. The prevalence of insufficient sleep among individuals with migraine (45.5%) was significantly higher compared to that among individuals with non-migraine headache (32.9%, p = 0.004) or among non-headache (20.4%, p

Study objectives Research points to impaired cognitive performance in sleep clinic patients with obstructive sleep apnea (OSA). However, inconsistent findings from various epidemiologic studies make this relationship less generalizable. The current study investigated the association between OSA and functional outcome measures, such as cognition, daytime sleepiness, and quality of life, in a Korean general population sample. Methods A total of 1492 participants from the Korean Genome and Epidemiology Study (KoGES) were included in the analyses. The presence of OSA measured by overnight polysomnography (PSG) was defined by apnea-hypopnea index (AHI) >5. Cognitive performance was determined with scores from a comprehensive neuropsychological battery. Excessive daytime sleepiness and quality of life were additionally measured through subjective reports. Results After adjusting for various demographic and medical characteristics, OSA was independently associated with lower performance in the Digit Symbol Test (52.73 ± 17.08 vs. 58.72 ± 18.03, OSA vs. not, p = .02). Hypoxia measures were not related to cognitive performance. OSA was associated with higher odds of displaying excessive daytime sleepiness (odds ratio = 1.72, 95% CI: 1.05-2.80), but there was no significant relationship between OSA and quality of life. Conclusions Cognition was unexpectedly unaffected overall. However, OSA was associated with impairment in a multidomain test that taps skills generally associated with frontal lobe function. The results suggest that research on protective and adaptive brain mechanisms to OSA stress can provide unique insights into the brain-sleep interface. As the study runs longitudinally, it will enable future studies on the impact of OSA on cognitive decline.

Stroke is very common in patients with sleep disordered breathing, especially in the elderly. We report the case of a 26-year-old man who had been referred to us with a sudden left side motor weakness of the body, headache, chronic fatigue, and witnessed sleep apneas. Intracerebral hemorrhage in the right external capsule and putamen was identified upon brain computed tomography. He had hypertension which had not been diagnosed previously. On polysomnography, apnea-hypopnea index was 73.0/h and arousal index was 74.7/h, indicating severe sleep apnea. Continuous positive airway pressure titration was conducted to determine the optimal pressure to alleviate the respiratory disturbances. Treatment with antihypertensive medication reduced blood pressure (BP) from 197/145 mm Hg to 130/80 mm Hg after 10 days of use. Co-treatment with the medication and auto-adjustable positive airway pressure additionally decreased BP to 110/60 mm Hg and normalized respiratory disturbances. In addition to BP, left hemiparesis, morning headache, daytime sleepiness, and chronic fatigue were all improved. Early treatment of OSA could help facilitate the rehabilitation of or recovery of weakness in such patients.

Antiepileptic drugs are commonly given for perioperative prophylaxis after brain tumor surgery, and there has been growing interest in levetiracetam, a second-generation antiepileptic drug. This retrospective study compared the seizure outcomes, side effects and durability of levetiracetam with valproic acid after a craniotomy for supratentorial brain tumors.Between 2009 and 2012, 282 consecutive patients with a supratentorial brain tumor underwent a craniotomy at Seoul National University Bundang Hospital. Of these patients, 51 (18.1%) and 231 (81.9%) were pre-operatively administered levetiracetam and valproic acid, respectively. The postoperative seizure outcomes (within 1 month after surgery) and the long-term side effects of both drugs were evaluated.Of the 51 patients in the levetiracetam group, 4 (7.8%) experienced postoperative seizures after brain tumor surgery, and 15 (6.5%) of the 231 patients in the valproic acid group experienced postoperative seizures (p = 0.728). The long-term complication rate of the valproic acid group (26.8%; 62/231) was significantly higher than that of the levetiracetam group (9.8%; 5/51) [p = 0.010]. In the valproic acid group, 10 hepatotoxicities, 20 hyperammonemias and 10 hematologic abnormalities (6 thrombocytopenias, 3 pancytopenias, and 1 leucopenia) occurred. Moreover, 89 patients (38.5%) in the valproic acid group changed or added other anticonvulsants because of side effects or uncontrolled seizures, whereas only 9 patients (17.6%) in the levetiracetam group changed or added other anticonvulsants (p = 0.005).The postoperative seizure control rates of levetiracetam and valproic acid were not statistically significantly different; however, levetiracetam may be superior to valproic acid in terms of its safety and durability after supratentorial tumor surgery.

STUDY OBJECTIVE Obstructive sleep apnea (OSA) contributes to the development of systemic hypertension, and hypertension strongly predicts the development of white matter change (WMC). Thus, it is plausible that OSA mediates WMC. The goal of the current study is to determine whether a contextual relationship exists between OSA and cerebral WMC. DESIGN Cross-sectional analyses conducted in a population-based study. SETTING Korean community-based sample from the Korean Genome and Epidemiology Study (KoGES) who attended examinations in 2011 at a medical center. PARTICIPANTS There were 503 individuals (mean ± SD, age 59.63 ± 7.48 y) who were free of previously diagnosed cardiovascular and neurologic diseases. MEASUREMENTS AND RESULTS Participants underwent 1-night polysomnography and were classified as no OSA (obstructive apnea-hypopnea index [AHI] < 5, n = 289), mild OSA (AHI 5-15, n = 161), and moderate to severe OSA (AHI ≥ 15, n = 53). WMC was identified with brain magnetic resonance imaging (MRI) and was found in 199 individuals (39.56%). Multivariate logistic regression analyses adjusted for covariates revealed that moderate to severe OSA was significantly associated with the presence of WMC (odds ratio [OR] 2.08, 95%, confidence interval [CI] 1.05-4.13) compared with no OSA. Additional adjustment of hypertension to the model did not alter the significance of the association (OR 2.03, 95% CI 1.02-4.05). CONCLUSIONS Moderate to severe OSA is an independent risk factor for WMC in middle-aged and older individuals. Thus, early recognition and treatment of OSA could reduce the risk of stroke and vascular dementia.

This study investigates health behaviors, health-related quality of life (HRQOL) and sleep among chronotypes in a community-based sample (n = 2,976). Analysis of covariance indicated evening types (E-types) had a significantly higher percentage of current smokers and more sleep-interfering behaviors compared to intermediate and morning types (M-type), and also lower physical activity and more sleep disturbance compared to M-types. E-types also had worse mental HRQOL compared to both chronotypes, and worse physical HRQOL compared to M-types. Exploratory analyses indicated E-types consumed more caffeinated beverages at night, smoked or ate heavy meals before bedtime, kept irregular sleep-wake schedules, and took more naps. Mediational analyses indicated that sleep-interfering behavior partially mediated the relationship between chronotype and sleep disturbance, and physical activity partially mediated the relationship between chronotype and mental HRQOL. E-types had more unhealthy behaviors, which may subsequently place them at higher risk for health problems.

Background and Objective Many attempts have sought to devise an animal model of sleep fragmentation (SF) to understand the clinical effects of sleep loss, but no study has investigated the usefulness of the walking wheel method to interrupt sleep in rats. Methods Seven-week-old male Wistar rats were divided into a SF group and an exercise control (EC) group, with five rats in each. SF was achieved with a walking wheel using a 30 s on, 90 s off interval (total walking time 6 h/day). The EC group walked the same distance. Rat multiple sleep latency test was performed to measure sleepiness in rats. Sleep data were collected at baseline, and 4, 12, and 18 days after treatment. Percent (%) time spent awake and in non-rapid eye movement (NREM) and rapid eye movement (REM) sleep, NREM and wake bout number, NREM bout length, and mean sleep latency were analyzed. Results Numbers of NREM and wake bout were higher in the SF group, whereas the NREM bout length was smaller than in the baseline group. Unlike NREM, REM sleep (%) in the SF group was significantly lower than in the baseline and EC groups. Mean sleep latency was shortened in the SF group compared to the baseline and EC groups. EC did not differ significantly with respect to the amount of sleep time (%), bout number of NREM and wakefulness, NREM bout length, and mean sleep latency, compared to its own baseline. Conclusions Use of a walking wheel is an effective means of interrupting sleep in rats during a long-term period.

Previous reports have shown that cigarette smoking is associated with white matter hyperintensities (WMHs). However, it remains unclear whether this is true for all ages. We investigated the association between cigarette smoking, WMHs, and age. We retrospectively reviewed charts from 595 patients, who presented as outpatients from January 2007 to March 2010. Grading of periventricular WMHs (PVWMHs) and the scores of deep WMHs (DWMHs) was determined based on criteria established by the Rotterdam Scan Study. We compared the degree of WMHs between smokers and non-smokers, and those younger than the age of 65 years versus those above. In younger age group, smokers had higher grades of PVWMHs and more microbleeds than non-smokers. In the older age group, total burden of DWMHs was much greater in smokers than nonsmokers. Multivariate regression analysis showed that cigarette smoking was an independent risk factor for PVWMHs in the younger age group and for DWMHs in the older age group. The location of WMHs in association with smoking seems to differ among age groups. Age should be considered when interpreting the effects of smoking on the brain.

Background and Objective The association of sleep disturbance (SD) with cardiovascular disease is through its induction of autonomic dysregulation and inflammation, which also could be important pathophysiological mechanisms responsible for atrial fibrillation (AF). However, no study has fully elucidated the causal relationship between SD and AF. We investigated whether SD influences AF vulnerability in an in vivo rat model. Methods We divided 8-week-old Wister rats into 5 groups: 1) control, 2) 3-day SD, 3) 7-day SD, 4) 3-day sham SD, and 5) 7-day sham SD (n = 5 in each group), using the multiple platform method to create SD. We measured baseline heart rate, blood pressure (BP), and AF inducibility via burst atrial pacing (30 mA, 40 Hz, 30 seconds) by means of a transoesophageal electrode and used Sirius red staining to assess collagen deposition in the atriums. Results Baseline heart rate, diastolic BP and AF inducibility were significantly higher in the SD groups than in the control and sham condition groups (p < 0.05). However, there were no differences between the 3- and 7-day SD groups. Systolic BP and induced AF duration did not statistically differ among any of the experimental groups. The Sirius red staining showed no differences in collagen deposition among any of the experimental groups. Conclusions SD resulted in increase of AF inducibility in SD rats, suggesting that SD provides an atrial substrate for AF vulnerability, regardless of the disturbance period. However, induced AF duration showed no significant differences in SD rats.

Insomnia is a very common health problem affecting approximately 10-30% of the population in Western countries and approximately 23% of Korean adults.1-4 Medications based on chemical hypnotics, such as benzodiazepines, have the following adverse effects: diurnal ‘hangover’ effects, dependence, addiction, withdrawal symptoms, and subsequent drug-resistance.5 The demand for complementary and alternative medicines for treating insomnia is increasing, not only because patients wish to avoid the aforementioned adverse effects, but also because herbal/natural products are readily available and require no prescription from a doctor, in contrast to chemical drugs.6-8 Cynanchum wilfordii Hemsley (C. wilfordii)(Asclepiadaceae) is a perennial herb, whose roots have been widely used in Korea for treating insomnia, anxiety, anemia, senescence, and various geriatric diseases.9,10 However, despite its wide use in Korea, no objective studies evaluating its efficacy in treating or preventing insomnia exist. Therefore, in the present study, we evaluated C. wilfordii extract’s effects on the sleep-wake cycle in rats and compared it to valerian extract, an herbal product in widespread use for treating insomnia, to evaluate its possibilities as a natural hypnotic. Received: February 18, 2011 Revised: March 23, 2011 Accepted: April 1, 2011

Background and Objective Simulated altitude as a model for hypoxia has shown inconsistent results in terms of impaired cognition. We hypothesized that preserved periods of stable sleep even under hypoxia could explain stable cognitive function. Delta spectral power on electroencephalography during stable sleep as well as high frequency coupling on the electrocardiogram-based spectrogram was adopted as measures of sleep quality. Methods Eleven healthy, non-smoking subjects (7 men, 27 ± 1.5 years) were exposed to 9 hours of continuous hypoxia for 13 consecutive nights. Polysomnography was done at baseline and during 3 time points, at night 3, 7, and 14. In each study, delta spectral power was obtained during stable N2 and N3 sleep. Stable sleep was defined when there was no significant fragmentation in electroencephalography and fluctuation in electromyography and cardiorespiratory signals. The time threshold was 2 or 5 continuous minutes for N2 and 2 minutes for N3. The amount of high frequency coupling for the sleep period on the electrocardiogram-based spectrogram was computed. Randomized block ANOVA was used with electroencephalography delta power and high frequency coupling as dependent variables with post hoc Tukey test. Results Delta spectral power during stable sleep was not significantly different across the entire hypoxic exposures (p = 0.98 for N2; p = 0.32 for N3). High frequency coupling was different between pre-exposure and mid-exposure (night 7; 52.5 ± 23.6% vs. 39.0 ± 16.7%, p = 0.02) but returned to the baseline level at the post-exposure (night 14; 45.4 ± 18.2%, p = 0.39). Conclusions Both preservation of the proportion of stable sleep and unchanged delta power during these periods may help explain maintained cognition in conditions of chronic nocturnal hypoxic exposures.