Daytime sympathetic hyperactivity in OSAS is related to excessive daytime sleepiness

The aim of this study was to investigate the relationships among sympathetic hyperactivity, excessive daytime sleepiness (EDS) and hypertension in obstructive sleep apnoea syndrome (OSAS). Ten newly diagnosed OSAS patients with untreated EDS and daytime hypertension underwent polysomnography (PSG) and daytime measurements of plasma noradrenaline (NA), ambulatory blood pressure (BP), muscle sympathetic nerve activity (MSNA) by microneurography and objective assessment of EDS before and during 6 months of compliance-monitored continuous positive airway pressure (CPAP) treatment. One month after the start of CPAP, BP, MSNA and NA were significantly lowered, remaining lower than baseline also after 3 and 6 months of treatment. CPAP use caused a significant improvement of sleep structures, and reduced EDS. A statistical correlation analysis demonstrated that EDS was not correlated with sleep measures obtained from baseline PSG (% sleep stages, apnoea and arousal index, mean oxygen saturation value), whereas daytime sleepiness was significantly correlated with MSNA. Furthermore, MSNA and BP showed no correlation. Our data obtained from selected patients suggest that the mechanisms inducing EDS in OSAS are related to the degree of daytime sympathetic hyperactivity. Additionally, resting MSNA was unrelated to BP suggesting that factors other than adrenergic neural tone make a major contribution to OSAS-related hypertension. The results obtained in this pilot study need, however, to be confirmed in a larger study involving more patients.     

Topography of homeostatic sleep pressure dissipation across the night in young and middle‐aged men and women

Decline in slow‐wave activity (SWA) across the night is believed to reflect dissipation of the homeostatic sleep drive. This study evaluated the effects of age, sex and topography on SWA dissipation. The sleep electroencephalogram of 48 young [22 women, 26 men; mean = 23.3 years; standard deviation (SD) = 2.4] and 39 middle‐aged (21 women, 18 men; mean = 51.9 years; SD = 4.6) healthy volunteers was analysed. Spectral analysis (0.5–22.0 Hz) was performed per non‐rapid eye movement period for Fp1, F3, C3, P3 and O1. SWA (1.0–5.0 Hz) dissipation was modelled using linear and exponential decay functions applied to each age and sex subgroup data set for each derivation. The relative adequacy of both functions was compared using Akaike’s information criterion. Results suggest that the exponential model provides a better data fit than the linear fit independently of age, gender and brain location. In women, age reduced the span (distance between the y intercept and the asymptote) of SWA decay in Fp1, F3, P3 and O1. In men, however, the effect of age on the span of SWA decay was limited to Fp1 and F3. In all age and sex subgroups, anterior regions showed a higher span than posterior regions. The asymptote was lower in anterior regions in young but not in middle‐aged subjects. These results suggest that the homeostatic process operates on a larger scale in anterior regions. Importantly, ageing reduced the scale of homeostatic dissipation in both sexes, but this effect was more widespread across the brain in women.     

Sleep bruxism is associated to micro-arousals and an increase in cardiac sympathetic activity

Sleep bruxism (SB) subjects show a higher incidence of rhythmic masticatory muscle activity (RMMA) than control subjects. RMMA is associated with sleep micro-arousals. This study aims to: (i) assess RMMA/SB episodes in relation to sleep cycles; (ii) establish if RMMA/SB and micro-arousals occur in relation to the slow wave activity (SWA) dynamics; (iii) analyze the association between RMMA/SB and autonomic cardiac activity across sleep cycles. Two nights of polygraphic recordings were made in three study groups (20 subjects each): moderate to high SB, low SB and control. RMMA episodes were considered to occur in clusters when several groups of RMMA or non-specific oromotor episodes were separated by less than 100 s. Correlations between sleep, RMMA/SB index and heart rate variability variables were assessed for the first four sleep cycles of each study group. Statistical analyses were done with SYSTAT and SPSS. It was observed that 75.8% of all RMMA/SB episodes occurred in clusters. Micro-arousal and SB indexes were highest during sleep cycles 2 and 3 (P < 0.001). Within each cycle, micro-arousal and RMMA/SB indexes showed an increase before each REM sleep (P 相似文献   

Autonomic markers of arousal during sleep in patients undergoing investigation for obstructive sleep apnoea, their relationship to EEG arousals, respiratory events and subjective sleepiness

Estimating the degree of sleep fragmentation is an important part of a respiratory sleep study and is conventionally measured using EEG micro arousals or is inferred indirectly from respiratory abnormalities such as apnoeas and desaturations. There is a need for less labour-intensive measures of sleep fragmentation, and transient rises in blood pressure and heart rate may fulfil this role. Forty unselected sleep clinic referrals undergoing investigation for possible obstructive sleep apnoea (OSA) were studied with one night of polysomnography. Three conventional indices of sleep fragmentation (EEG micro arousals, apnoea/hypopnoea index (AHI) and oxygen saturation dip rate (SaO₂ dips)) and two autonomic indices (heart rate and blood pressure rises) have been compared. Correlations between these five indices ranged from r=0.38 to r=0.73. Of the two autonomic indices, the correlations for blood pressure rises with SaO₂ dips and EEG micro arousals were stronger (r=0.71 and r=0.65, respectively) than those for heart rate rises (0.55 and 0.51). All indices of sleep fragmentation, apart from heart rate rises, were similar in their correlation with subjective sleepiness (r-values 0.21–0.36). Arousals implied from blood pressure rises (using pulse transit time) can be measured easily, are objective, and appear no worse at predicting subjective sleepiness than either EEG micro arousals or AHI. They may therefore provide a useful alternative to manual scoring of micro arousals from the EEG as an index of sleep fragmentation in sleep clinic patients undergoing investigation for possible OSA.     

Definition of excessive daytime sleepiness in the general population: Feeling sleepy relates better to sleep‐related symptoms and quality of life than the Epworth Sleepiness Scale score. Results from an epidemiological study

Many different subjective tools are being used to measure excessive daytime sleepiness (EDS) but the most widely used is the Epworth Sleepiness Scale (ESS). However, it is unclear if using the ESS is adequate on its own when assessing EDS. The aim of this study was to estimate the characteristics and prevalence of EDS using the ESS and the Basic Nordic Sleep Questionnaire (BNSQ) in general population samples. Participants aged 40 years and older answered questions about sleepiness, health, sleep‐related symptoms and quality of life. Two groups were defined as suffering from EDS: those who scored >10 on the ESS (with increased risk of dozing off) and those reporting feeling sleepy during the day ≥3 times per week on the BNSQ. In total, 1,338 subjects (53% male, 74.1% response rate) participated, 13.1% reported an increased risk of dozing off, 23.2% reported feeling sleepy and 6.4% reported both. The prevalence of restless leg syndrome, nocturnal gastroesophageal reflux, difficulties initiating and maintaining sleep and nocturnal sweating was higher among subjects reporting feeling sleepy compared to non‐sleepy subjects. Also, subjects reporting feeling sleepy had poorer quality of life and reported more often feeling unrested during the day than non‐sleepy subjects. However, subjects reporting increased risk of dozing off (ESS > 10) without feeling sleepy had a similar symptom profile as the non‐sleepy subjects. Therefore, reporting only risk of dozing off without feeling sleepy may not reflect problematic sleepiness and more instruments in addition to ESS are needed when evaluating daytime sleepiness.     

Sleep propensity varies with behaviour and the situation in which it is measured: the concept of somnificity

It is self-evident that we fall asleep more readily when lying down than when standing up. Nevertheless, the influence of this and more subtle changes in posture, activity and the situation in which sleep propensity is measured have been largely ignored. The term somnificity is introduced here, defined as the general characteristic of a posture, activity and situation that reflects its capacity to facilitate sleep-onset in a majority of subjects. The relative somnificities of different activities and situations in the Epworth Sleepiness Scale (ESS) were investigated in 23 groups, involving 2802 subjects from seven different countries. The means of the different ESS item-scores were ranked from highest to lowest in each group. There was a high concordance (Kendall's C=0.84, P < 0.0001) among these ranks for all groups, whether of normal subjects or patients with sleep disorders, regardless of age, sex, or average sleepiness in daily life assessed by total Epworth scores. The ESS item-ranks formed an ordinal scale of somnificities with five different levels. Analysis of raw ESS item-scores for all 987 individual Australian subjects showed the same pattern of somnificities with six different levels, but with a lower concordance (C=0.39, P < 0.0001). This was probably because of subject x situation-specific interactions that were averaged within groups. A conceptual model of sleepiness is outlined that includes interactions between separate sleep and wake drives as a possible way of including behavioural and situational influences on sleep propensity.     

Regional differences in cortical electroencephalogram (EEG) slow wave activity and interhemispheric EEG asymmetry in the fur seal

Slow wave sleep (SWS) in the northern fur seal (Callorhinus ursinus) is characterized by a highly expressed interhemispheric electroencephalogram (EEG) asymmetry, called ‘unihemispheric’ or ‘asymmetrical’ SWS. The aim of this study was to examine the regional differences in slow wave activity (SWA; power in the range of 1.2–4.0 Hz) within one hemisphere and differences in the degree of interhemispheric EEG asymmetry within this species. Three seals were implanted with 10 EEG electrodes, positioned bilaterally (five in each hemisphere) over the frontal, occipital and parietal cortex. The expression of interhemispheric SWA asymmetry between symmetrical monopolar recordings was estimated based on the asymmetry index [AI = (L?R)/(L+R), where L and R are the power in the left and right hemispheres, respectively]. Our findings indicate an anterior–posterior gradient in SWA during asymmetrical SWS in fur seals, which is opposite to that described for other mammals, including humans, with a larger SWA recorded in the parietal and occipital cortex. Interhemispheric EEG asymmetry in fur seals was recorded across the entire dorsal cerebral cortex, including sensory (visual and somatosensory), motor and associative (parietal or suprasylvian) cortical areas. The expression of asymmetry was greatest in occipital–lateral and parietal derivations and smallest in frontal–medial derivations. Regardless of regional differences in SWA, the majority (90%) of SWS episodes with interhemispheric EEG asymmetry meet the criteria for ‘unihemispheric SWS’ (one hemisphere is asleep while the other is awake). The remaining episodes can be described as episodes of bilateral SWS with a local activation in one cerebral hemisphere.     

Changes in brain cortical activity measured by EEG are related to individual exercise preferences

Exercise is well known to result in changes of brain cortical activity measured by EEG. The aim of this study was (1) to localise exercise induced changes in brain cortical activity using a distributed source localisation algorithm and (2) to show that the effects of exercise are linked to participants' physical exercise preferences.Electrocortical activity (5 min) and metabolical parameters (heart rate, lactate, peak oxygen uptake) of eleven recreational runners were recorded before and after incremental treadmill, arm crank and bicycle ergometry. Electroencephalographic activity was localised using standardised low resolution brain electromagnetic tomography (sLORETA).Results revealed an increase in frontal α activity immediately post exercise whereas increases after bike exercise were found to be localised in parietal regions. All three kinds of exercise resulted in an increase of β activity in Brodmann area 7. Fifteen and thirty minutes post exercise a specific activation pattern (decrease in frontal brain activity–increase in occipital regions) was noticeable for treadmill and bike but not arm crank exercise.We conclude that specific brain activation patterns are linked to different kinds of exercise and participants' physical exercise preferences.     

The daily variation in sleepiness and its relation to the preceding sleep episode—a prospective study across 42 days of normal living

Sleepiness is linked to accidents and reduced performance, and is usually attributed to short/poor prior sleep and sleepiness. However, while the link between reduced sleep and subsequent sleepiness is well established in laboratory experiments of sleep reduction, very little is known about the day‐to‐day variation of sleepiness in everyday life and its relation to the immediately preceding sleep episode. The purpose of the present study was to investigate the characteristics of this relation across 42 consecutive days. Fifty volunteers participated. Self‐reports of sleep were given in the morning and recorded with actigraphy; health was rated in the evening; and sleepiness was rated at eight points during the day (on a scale of 1–9). Results from mixed‐model regression analyses showed that, on average, total sleep time predicted sleepiness during the rest of the day across the 42 days, with sleepiness increasing with shorter preceding sleep (β = ?0.15 units h^?1, P < 0.001). Sleepiness also increased with earlier time of rising and lower‐rated sleep quality. Days off reduced sleepiness, but was accounted for by sleep. Self‐rated health improved when sleepiness was low during the same day (β = ?0.36 unit unit^?1 of rated health, P < 0.001), but the two were measured simultaneously. Napping was related to high sleepiness during the same day. Actigraphy measures of sleep duration showed similar, but somewhat weaker, effects than diary measures. It was concluded that the main determinants of daytime sleepiness in a real‐life day‐to‐day context were short sleep, poor sleep and early rising, and that days with high sleepiness ended with ratings of poorer health.     

Effect of cognitive behavioural therapy for insomnia on sleep architecture and sleep EEG power spectra in psychophysiological insomnia

There is now an overwhelming preponderance of evidence that cognitive behavioural therapy for insomnia (CBT-I) is effective, as effective as sedative hypnotics during acute treatment (4-8 weeks), and is more effective in long term (following treatment). Although the efficacy of CBT-I in the treatment of chronic insomnia is well known, however there is little objective data on the effects of CBT-I on sleep architecture and sleep EEG power densities. The present study evaluated, first, subjective change in sleep quality and quantity, and secondly the modifications occurring in polysomnography and EEG power densities during sleep after 8 weeks of CBT-I. Nine free drug patients with psychophysiological insomnia, aged 33-62 years (mean age 47 +/- 9.7 years), seven female and two male participated in the study. Self-report questionnaires were administered 1 week before and 1 week after CBT-I, a sleep diary was completed each day 1 week before CBT-I, during CBT-I and 1 week after CBT-I. Subjects underwent two consecutive polysomnographic nights before and after CBT-I. Spectral analysis was performed the second night following 16 h of controlled wakefulness. After CBT-I, only scales assessing insomnia were significantly decreased, stages 2, REM sleep and SWS durations were significantly increased. Slow wave activity (SWA) was increased and the SWA decay shortened, beta and sigma activity were reduced. In conclusion CBT-I improves both subjective and objective sleep quality of sleep. CBT-I may enhance sleep pressure and improve homeostatic sleep regulation.     

Oculomotor changes are associated to daytime sleepiness in the multiple sleep latency test

Sleep onsets in the diurnal multiple sleep latency test (MSLT), following different sleep lengths of the preceding night sleep (8, 5, 4, 3, 2, 1 h) and following the corresponding recovery nights, were considered for a study on changes of oculomotor activity during sleep onset. The study aimed to assess the individual time course in spontaneous blinks (SBs) and slow eye movements (SEMs) during the sleep onset period and also the relationship with sleep latencies in the MSLT. Group analyses compared oculomotor changes between conditions characterized by a different level of daytime sleepiness. The results show a clear inverse relation between the two oculomotor measures, with a linear SB decrease and quadratic SEM increase across the wake-sleep transition. A 150 s sample of SB and SEM activity at the start of MSLT trials correlates with individual subsequent sleep latency. Finally, mean changes in daytime sleepiness as measured by the MSLT are paralleled by coherent oculomotor changes, with a significant linear decrease of SB as sleepiness increases as a consequence of previous sleep reduction. Both individual and group results show that endogenous blinking is associated with moderate changes in daytime sleepiness.     

The sleep EEG topography in children and adolescents shows sex differences in language areas

The topographic distribution of slow wave activity (SWA, EEG power between 0.75 and 4.5 Hz) during non-rapid eye movement (NREM) sleep was proposed to mirror cortical maturation with a typical age-related pattern. Here, we examined whether sex differences occur in SWA topography of children and adolescents (22 age-matched subjects, 11 boys, mean age 13.4 years, range: 8.7–19.4, and 11 girls, mean age 13.4 years, range: 9.1–19.0 years). In females, SWA during the first 60 min of NREM sleep was higher over bilateral cortical areas that are related to language functions, while in males SWA was increased over the right prefrontal cortex, a region also involved in spatial abilities. We conclude that cortical areas governing functions in which one sex outperforms the other exhibit increased sleep SWA and, thus, may indicate maturation of sex-specific brain function and higher cortical plasticity during development.     

The role of non‐rapid eye movement slow‐wave activity in prefrontal metabolism across young and middle‐aged adults

Electroencephalographic slow‐wave activity (0.5–4 Hz) during non‐rapid eye movement (NREM) sleep is a marker for cortical reorganization, particularly within the prefrontal cortex. Greater slow wave activity during sleep may promote greater waking prefrontal metabolic rate and, in turn, executive function. However, this process may be affected by age. Here we examined whether greater NREM slow wave activity was associated with higher prefrontal metabolism during wakefulness and whether this relationship interacted with age. Fifty‐two participants aged 25–61 years were enrolled into studies that included polysomnography and a ¹⁸[F]‐fluoro‐deoxy‐glucose positron emission tomography scan during wakefulness. Absolute and relative measures of NREM slow wave activity were assessed. Semiquantitative and relative measures of cerebral metabolism were collected to assess whole brain and regional metabolism, focusing on two regions of interest: the dorsolateral prefrontal cortex and the orbitofrontal cortex. Greater relative slow wave activity was associated with greater dorsolateral prefrontal metabolism. Age and slow wave activity interacted significantly in predicting semiquantitative whole brain metabolism and outside regions of interest in the posterior cingulate, middle temporal gyrus and the medial frontal gyrus, such that greater slow‐wave activity was associated with lower metabolism in the younger participants and greater metabolism in the older participants. These results suggest that slow‐wave activity is associated with cerebral metabolism during wakefulness across the adult lifespan within regions important for executive function.     

Comparison of the maintenance of wakefulness test (MWT) to a modified behavioral test (OSLER) in the evaluation of daytime sleepiness

The objectives were to evaluate the correlation between sleep onset as defined by the Oxford sleep resistance (OSLER) test and by simultaneous electroencephalography (EEG) and to determine the correlation between sleep latencies measured by the OSLER test and maintenance of wakefulness test (MWT) performed on the same day. This was a prospective, cross-sectional study carried out in a tertiary-care university-based sleep laboratory. Participants were 11 consecutive subjects presenting to the sleep center with clinical indications for nocturnal polysomnography and MWT. The interventions included MWT and OSLER test. Mean sleep latencies for the OSLER and MWT in each subject were closely correlated (ICC = 0.94, [Intra-class correlation]P < 0.05). Sleep latency by OSLER and simultaneous measurement of EEG also had excellent agreement (ICC = 0.91) with a bias of -0.97 min. The OSLER test is a practical and reliable tool for evaluating daytime sleepiness when compared with the MWT. No obvious systematic adaptation was seen during sequential OSLER test performance. Given its portability and minimal technical requirements, the OSLER test may be useful for large-scale applications in the evaluation of daytime wakefulness and vigilance.     

The aging slow wave: a shifting amalgam of distinct slow wave and spindle coupling subtypes define slow wave sleep across the human lifespan

Study ObjectivesSlow wave and spindle coupling supports memory consolidation, and loss of coupling is linked with cognitive decline and neurodegeneration. Coupling is proposed to be a possible biomarker of neurological disease, yet little is known about the different subtypes of coupling that normally occur throughout human development and aging. Here we identify distinct subtypes of spindles within slow wave upstates and describe their relationships with sleep stage across the human lifespan.MethodsCoupling within a cross-sectional cohort of 582 subjects was quantified from stages N2 and N3 sleep across ages 6–88 years old. Results were analyzed across the study population via mixed model regression. Within a subset of subjects, we further utilized coupling to identify discrete subtypes of slow waves by their coupled spindles.ResultsTwo different subtypes of spindles were identified during the upstates of (distinct) slow waves: an “early-fast” spindle, more common in stage N2 sleep, and a “late-fast” spindle, more common in stage N3. We further found stages N2 and N3 sleep contain a mixture of discrete subtypes of slow waves, each identified by their unique coupled-spindle timing and frequency. The relative contribution of coupling subtypes shifts across the human lifespan, and a deeper sleep phenotype prevails with increasing age.ConclusionsDistinct subtypes of slow waves and coupled spindles form the composite of slow wave sleep. Our findings support a model of sleep-dependent synaptic regulation via discrete slow wave/spindle coupling subtypes and advance a conceptual framework for the development of coupling-based biomarkers in age-associated neurological disease.     

Topographic sleep EEG changes in the acute and chronic stage of hemispheric stroke

After stroke, the injured brain undergoes extensive reorganization and reconnection. Sleep may play a role in synaptic plasticity underlying stroke recovery. To test this hypothesis, we investigated topographic sleep electroencephalographic characteristics, as a measure of brain reorganization, in the acute and chronic stages after hemispheric stroke. We studied eight patients with unilateral stroke in the supply territory of the middle cerebral artery and eight matched controls. All subjects underwent a detailed clinical examination including assessment of stroke severity, sleep habits and disturbances, anxiety and depression, and high‐density electroencephalogram examination with 128 electrodes during sleep. The recordings were performed within 10 days after stroke in all patients, and in six patients also 3 months later. During sleep, we found higher slow‐wave and theta activity over the affected hemisphere in the infarct area in the acute and chronic stage of stroke. Slow‐wave, theta activity and spindle frequency range power over the affected hemisphere were lower in comparison to the non‐affected side in a peri‐infarct area in the patients’ group, which persisted over time. Conversely, in wakefulness, only an increase of delta, theta activity and a slowing of alpha activity over the infarct area were found. Sleep slow‐wave activity correlated with stroke severity and outcome. Stroke might have differential effects on the generation of delta activity in wakefulness and sleep slow waves (1–8 Hz). Sleep electroencephalogram changes over both the affected and non‐affected hemispheres reflect the acute dysfunction caused by stroke and the plastic changes underlying its recovery. Moreover, these changes correlate with stroke severity and outcome.     

Reaction of sleepiness indicators to partial sleep deprivation,time of day and time on task in a driving simulator – the DROWSI project

Studies of driving and sleepiness indicators have mainly focused on prior sleep reduction. The present study sought to identify sleepiness indicators responsive to several potential regulators of sleepiness: sleep loss, time of day (TOD) and time on task (TOT) during simulator driving. Thirteen subjects drove a high‐fidelity moving base simulator in six 1‐h sessions across a 24‐h period, after normal sleep duration (8 h) and after partial sleep deprivation (PSD; 4 h). The results showed clear main effects of TOD (night) and TOT but not for PSD, although the latter strongly interacted with TOD. The most sensitive variable was subjective sleepiness, the standard deviation of lateral position (SDLAT) and measures of eye closure [duration, speed (slow), amplitude (low)]. Measures of electroencephalography and line crossings (LCs) showed only modest responses. For most variables individual differences vastly exceeded those of the fixed effects, except for subjective sleepiness and SDLAT. In a multiple regression analysis, SDLAT, amplitude/peak eye‐lid closing velocity and blink duration predicted subjective sleepiness bouts with a sensitivity and specificity of about 70%, but were mutually redundant. The prediction of LCs gave considerably weaker, but similar results. In summary, SDLAT and eye closure variables could be candidates for use in sleepiness‐monitoring devices. However, individual differences are considerable and there is need for research on how to identify and predict individual differences in susceptibility to sleepiness.     

Hypothalamic osmoregulation is maintained across the wake–sleep cycle in the rat

In different species, rapid eye movement sleep (REMS) is characterized by a thermoregulatory impairment. It has been postulated that this impairment depends on a general insufficiency in the hypothalamic integration of autonomic function. This study aims to test this hypothesis by assessing the hypothalamic regulation of body fluid osmolality during the different wake–sleep states in the rat. Arginine‐vasopressin (AVP) plasma levels were determined following intracerebroventricular (ICV) infusions of artificial cerebrospinal fluid (aCSF), either isotonic or made hypertonic by the addition of NaCl at three different concentrations (125, 250 and 500 mm ). Animals were implanted with a cannula within a lateral cerebral ventricle for ICV infusions and with electrodes for the recording of the electroencephalogram. ICV infusions were made in different animals during Wake, REMS or non‐REM sleep (NREMS). The results show that ICV infusion of hypertonic aCSF during REMS induced an increase in AVP plasma levels that was not different from that observed during either Wake or NREMS. These results suggest that the thermoregulatory impairment that characterizes REMS does not depend on a general impairment in the hypothalamic control of body homeostasis.