Automatic sleep spindles detection--overview and development of a standard proposal assessment method.

Since the 1970s, various automatic sleep spindles procedures have been implemented and presented in the literature. Unfortunately, their results are not easily comparable because the databases, the assessment methods and the terminologies employed are often radically different. In this study, we propose a systematic assessment method for any automatic sleep spindles detection algorithm. We apply this assessment method to our own automatic detection process in order to illustrate and legitimate its use. We obtain a global sensitivity of 70.20%, for a false positive proportion (relative to the total number of visually scored sleep spindles) of only 26.44% (False positive rate = 1.38% and specificity = 98.62%).

Automatic K-complexes detection in sleep EEG recordings using likelihood thresholds.

In this paper, we present an automatic method for K-complexes detection based on features extraction and the use of fuzzy thresholds. The validity of our process was examined on the basis of two visual K-complexes scorings performed on 5 excerpts of 30 minutes. Results were investigated through all different sleep stages. The algorithm provides global true positive rates of 61.72% and 60.94%, respectively with scorer 1 and scorer 2. The false positive proportions (compared to the total number of visually scored K-complexes) are of 19.62% and 181.25%, while the false positive rates estimated on a one 1 second resolution are only of 0.53% and 1.53%. These results suggest that our approach is completely suitable since its performances are similar to those of the human scorers.

Removal of ECG artifacts from EEG using a modified independent component analysis approach.

In this paper, we introduce a new automatic method for electrocardiogram (ECG) artifact elimination from the electroencephalogram (EEG) or the electrooculogram (EOG). It is based on a modification of the independent component analysis (ICA) algorithm which gives promising results while only using a single-channel EEG (or EOG) and the ECG. To check the effectiveness of our approach, we compared its correction rate with those obtained by ensemble average subtraction (EAS) and adaptive filtering (AF). For this purpose, we applied these algorithms to 10 excerpts of polysomnographic sleep recordings containing ECG artifacts and other typical artifacts (e.g. movement, sweat, respiration, etc.). Two hundred successive interference peaks were examined in each excerpt to compute correction rates. We found that our modified ICA was the most robust to various waveforms of cardiac interference and to the presence of others artifacts, with a correction rate of 91.0%, against 83.5% for EAS and 83.1% for AF.

Automatic sleep spindle detection in patients with sleep disorders.

In this paper, we present a new automatic method for sleep spindle detection. It consist of a generalisation of the Schimicek's method that takes more types of artefacts into account and uses variable thresholds regarding the statistical properties of the signal. Validity of our process is examined on the basis of visual spindle scoring performed by an expert. Results obtained are compared to those obtained by Schimicek's method. For a specificity of 90%, we obtain a sensitivity of 76.9% while Schimicek's method has a sensitivity of 70.4%. Moreover an increase of the area under the ROC curve is observed and confirms that the detection process is improved.

Operating characteristics of the negative expiratory pressure technique in predicting obstructive sleep apnoea syndrome in snoring patients.

BACKGROUND: This study examines the operating characteristics of the expiratory flow response to a negative pressure (NEP) applied to the mouth in the prediction of obstructive sleep apnoea syndrome (OSAS) in snoring patients. METHODS: Two hundred and thirty eight patients with normal spirometric values were studied. Full laboratory polysomnography was performed and an NEP of -5 cm H(2)O was applied in the sitting and supine positions. RESULTS: A significant correlation was found between the degree of flow limitation measured by NEP in both positions (expressed as the percentage of the expired tidal volume over which NEP induced flow did not exceed spontaneous flow) and the apnoea-hypopnoea index (AHI). This correlation was significantly higher in the supine position (p<0.0001) where an expiratory flow limitation cut off value of >/=27.5% of the tidal volume produced a sensitivity of 81.9% and a specificity of 69.1% in predicting OSAS. CONCLUSION: These findings show that the degree of instability of the upper airway measured by NEP is correlated with the severity of OSAS. NEP had moderate sensitivity and specificity and may be useful in predicting OSAS in a clinic based population.

High leg motor activity in sleep apnea hypopnea patients: efficacy of clonazepam combined with nasal CPAP on polysomnographic variables.

The association of sleep apnea hypopnea syndrome (SAHS) with high leg activity in the same patient is a dilemma for the physician, as clonazepam, used to treat periodic leg movement syndrome (PLMS) can aggravate apneas, while nasal continuous positive airway pressure (nCPAP) can exacerbate PLMS. The present study aimed to compare nCPAP alone (n), nCPAP combined with clonazepam (n+c) and clonazepam alone (c) in patients with mild to moderate SAHS associated with high leg activity. Fourteen patients with an apnea hypopnea index (AHI) between 10 and 50 h(-1) and a leg movement index with regard to time in bed [LMI (TIB)] > 15 h(-1) on baseline polysomnography (b) were recorded on three consecutive nights with n, n+c and c, respectively. Leg movements were detected, using actigraphy, and were subsequently categorized into periodic, apnea- or hypopnea-related and nonperiodic movements (defined as neither periodic nor related to a respiratory event). The three treatments were successful in improving breathing [AHI b 26.1 (3.2) n 11.8 (2.4) n+c 5.0 (0.7) c 14.9 (1.8) h(-1)], leg activity [LMI (TIB) b 391 (4.8) n 22.5 (4.4) n+c 23.9 (3.9) c 22.6 (3.7) h(-1)] and sleep fragmentation [stage shift index b 373 (2.6) n 28.6 (1.6) n+c 25.6 (1.8) c 26.6 (1.6) h(-1)]. All types of movements were reduced, the effect being significant for respiratory events related and nonperiodic movements. Combination therapy was more effective than nCPAP alone in reducing the AHI and in improving sleep efficiency. We conclude that in patients with mild to moderate SASH associated with high leg activity, nCPAP improves nocturnal breathing and clonazepam reduces leg activity. More unexpectedly nCPAP is beneficial on leg activity and clonazepam on breathing, probably through a decrease in sleep fragmentation. The best results are obtained with combination therapy.

The SleepStrip: an apnoea screener for the early detection of sleep apnoea syndrome.

Sleep apnoea svndrome (SAS) is a largely undiagnosed and prevalent disorder. It is associated with cardiovascular morbidity as well as excessive daytime sleepiness and poor quality of life. In the present study the SleepStrip, a novel screening device is introduced, which is low cost and easy to use and is aimed for widespread use. The results of three independent validation studies, which compared the SleepStrip score (Sscore) against "gold standard" polysomnographically-determined apnoea/ hypopnoea index (AHI), are reported both separately and combined. Four hundred and two patients suspected of SAS underwent full polysomnography recordings concomitantly with the use of the SleepStrip. For all samples combined, the correlation between AHI and Sscore was r=0.73, sensitivity and specificity values ranged from 80-86% and 57-86% respectively, and the area under the curve derived from receiver-operating characteristic curves ranged from 0.81-0.92 at varying AHI thresholds. Though not intended as a substitute for polysomnography, the SleepStrip may provide initial screening information, which may be useful in both clinical and experimental settings.

Compliance with nasal continuous positive airway pressure assessed with a pressure monitor: pattern of use and influence of sleep habits.

The aim of the study was to assess compliance with nasal continuous positive airway pressure (N-CPAP) at home in patients with obstructive sleep apnoea syndrome (OSAS) and to search for predictors of compliance. We studied a cohort of 106 consecutive patients (91 men, 15 women) with a median apnoea hypopnoea index of 62.4 (range 21-132) h(-1), equipped at home with a Rem+ Soft device (Sefam, France), including a pressure monitor and a real-time clock. During the third and fourth months of treatment, the patients used their machine a median of 88% of days (16-100%), with a mean effective use of 5.6 (1.3-11.2) h per effective day. Residual apnoea index on N-CPAP, as recorded by the monitor, was 1.5 (0.3-27.6) h(-1). Mean clock-time for starting with N-CPAP was 23 h 54 min (21 h 34-01 h 42). The mean effective use per effective day correlated negatively with the minimal (and the mean) level of oxyhaemoglobin saturation (r(s) = -0.24, P < 0.05) while the percentage of days the machine was used correlated negatively with the percentage of slow wave sleep (r(s) = -0.22, P < 0.05) at baseline polysomnography. In a subset of 30 subjects, earlier start on N-CPAP correlated with longer use of the device in 22 patients (median r--0.48). We conclude that a pressure monitor allows reporting on compliance in terms of regularity (% of days the machine is used) and length of sleep on N-CPAP (effective use per effective day). These compliance variables show modest correlations with baseline polysomnographic features. Late bedtime should be discouraged as it might decrease compliance.

Frédéric Bremer 1892-1982: a pioneer in sleep research.

Frédéric Bremer was one of the pioneer neurophysiologists who dedicated their career to understanding the neural mechanisms involved in the control of sleep-wake regulation. This paper follows his career and his major achievements. We found that Bremer's interest in sleep resulted from his unexpected observations after transecting the brain at the midcollicular level in the "encéphale isolé" preparation. The sleep-like behaviour of the animal, accompanied by slow waves in the cortex, convinced him that sleep resulted from cortical deafferentation. He was further convinced that deafferentation was the cause of sleep when he found that transecting the brain at the medullary level did not much affect the sleep-wake cycle. As we show, Bremer's views that sleep is a passive phenomenon imposed on the brain because of deafferentation was shared by most of his contemporaries. Years later Bremer admitted that he interpreted his experimental findings wrongly. He continued to investigate sleep using his preparations and made important contributions to understanding the relationships between the brainstem reticular formation and the basal forebrain hypnogenic centres, as well as the importance of light on these relationships.

Genetic control of 24-hour growth hormone secretion in man: a twin study.

The aim of this study was to delineate the contributions of genetic and environmental factors in the regulation of the 24-h GH secretion. The 24-h profile of plasma GH was obtained at 15-min intervals in 10 pairs of monozygotic and 9 pairs of dizygotic normal male twins, aged 16-34 yr. Sleep was polygraphically monitored. Significant pulses of GH secretion were identified using a modification of the computer algorithm ULTRA. For each significant pulse, the amount of GH secreted was calculated by deconvolution. A procedure specially developed for twin studies was used to partition the variance of investigated parameters into genetic and environmental contributions. A major genetic effect was evidenced on GH secretion during wakefulness (with a heritability estimate of 0.74) and, to a lesser extent, on the 24-h GH secretion. Significant genetic influences were also identified for slow wave sleep and height. These data demonstrate that human GH secretion in young adulthood is markedly dependent on genetic factors.

Shortened REM latency as a psychobiological marker for psychotic depression? An age-, gender-, and polarity-controlled study.

BACKGROUND: Previous reports suggest that the clinical dichotomy separating psychotic and nonpsychotic depression corresponds to different neurobiological profiles. The aim of the present study is to further investigate the psychobiological correlates of these two particular depressive subtypes. METHODS: Thyroid-stimulating hormone response to thyrotropin-releasing hormone postdexamethasone cortisol levels, and electroencephalgraphic sleep characteristics of 44 psychotic major depressive patients were compared to those of 44 nonpsychotic depressives matched for age, gender, and polarity. RESULTS: Some biological disturbances usually associated with depression (increased wakefulness, diminished rapid eye movement latency, hypercortisolism, blunted thyroid-stimulating hormone response to thyrotropin-releasing hormone stimulation) seemed to be significantly more pronounced in the psychotic depressed group as a reflection of greater illness severity; however, shortened REM latency was not influenced by severity and seemed to be more specifically related to the co-occurrence of psychotic and depressive symptoms. CONCLUSIONS: Our data provide further support for the validity of the clinical dichotomy separating psychotic and nonpsychotic major depression independently of severity.

Evidence against a role for the growth hormone-releasing peptide axis in human slow-wave sleep regulation.

A complex interrelationship exists between sleep and somatotropic activity. In humans, intravenous injections of growth hormone-releasing hormone (GHRH) given during sleep consistently stimulate slow-wave (SW) sleep, particularly when given in the latter part of the night. In the present study, the possible somnogenic effects induced under similar conditions by GH-releasing peptide (GHRP) were investigated in seven young healthy men. Bolus intravenous injections of GHRP-2 (1 microgram/kg body wt) or saline, in randomized order, were given after 60 s of the third rapid-eye-movement period. All GHRP injections were immediately followed by transient prolactin elevations and by GH pulses of a magnitude within or around the upper limit of the physiological range. Except for a nonsignificant tendency to increased amounts of wakefulness during the 1st h after the injection, no effects of GHRP-2 administration on sleep were detected. There was in particular no enhancement of SW sleep. Thus, in contrast to GHRH, late-night single injections of GHRP-2 at a dosage resulting in similar GH elevations have no stimulatory effects on SW sleep. The present data provide evidence against the involvement of the GHRP axis in human SW sleep regulation.

Genetic and environmental influences on prolactin secretion during wake and during sleep.

To delineate the contributions of genetic and environmental factors in the regulation of human prolactin (PRL) secretion, the 24-h profile of plasma PRL was obtained at 15-min intervals in 10 pairs of monozygotic and 10 pairs of dizygotic twins. Sleep was monitored polygraphically. PRL secretory rates were derived from plasma concentrations by deconvolution. Diurnal (24-h) variations were quantified by a regression curve to define nadir, acrophase, and amplitude. Pulses of PRL secretion were identified using a computerized algorithm. A procedure specifically developed for twin studies was used to partition the variance into genetic and environmental contributions. Significant genetic effects were identified for daytime PRL concentrations, rhythm amplitude, and overall wave-shape of the daily PRL profile. In contrast, environmental effects were dominant for mean concentrations during sleep, total secretory output during sleep, overall 24-h concentrations, and total 24-h secretion. However, when interindividual variations in sleep fragmentation were taken into account, the estimates of genetic variance for PRL concentrations and secretion during sleep approached statistical significance. Significant genetic influences were identified for slow-wave sleep (SWS). Because SWS is associated with increased nocturnal PRL secretion, it is possible that genetic effects on PRL secretion during sleep reflect genetic influences on SWS. In conclusion, genetic factors determine partially both the basal daytime concentrations of PRL and the temporal organization of PRL secretion over the 24-h cycle in normal young men.

Does sleep EEG data distinguish between UP, BPI or BPII major depressions? An age and gender controlled study.

Clinical characteristics and sleep EEG data of 14 unipolar (UPR), 14 bipolar I (BPI) and 14 bipolar II (BPII) patients, matched for age and gender, were investigated during a major depressive episode. We observed a remarkable similarity in the clinical characteristics of the three samples and, concerning sleep EEG data, a trend to a higher percentage of awakening among BPI patients. Pairwise comparisons of the three subgroups showed that only the Newcastle rating scale score reached significant difference between BPI and UPR groups. We observed trends regarding the difference of awakening both between BPI and BPII groups and between BPI and UPR groups, difference of percentage of REM sleep between BPI and BPII groups and difference of Sleep Period Time between BPII and UPR groups. We also observed that the distribution of REM latencies in the BPI subgroup was different from the two others.

The dexamethasone suppression test and sleep electroencephalogram in nonbipolar major depressed inpatients: a multivariate analysis.

BACKGROUND: The present study further examined relationships between postdexamethasone cortisol plasma values and sleep electroencephalogram (EEG) parameters. METHODS: The dexamethasone suppression test (DST) and polysomnographic recordings were performed in a sample of 300 inpatients with primary major depressive disorder (MDD) (102 men and 198 women, mean age 44 +/- 12 years, range 20-74 years) consecutively admitted to Erasme Hospital (Brussels, Belgium) between 1981 and 1992. RESULTS: The DST was abnormal in 40% of the sample. Postdexamethasone cortisol plasma values at 4:00 PM were significantly influenced by age, but not by gender. They were also significantly and positively correlated with weight loss, total scores on the Hamilton Depression Rating Scale, total scores on the Newcastle Scale, percentage of awakenings during sleep, and percent of stage 1. They were significantly and negatively correlated with percent of stage 2, slow-wave sleep, and REM sleep. Multiple regression analyses were conducted in two successive steps. First among clinical variables, only age and depressive symptom severity remained correlated with postdexamethasone plasma cortisol values. In the second step, with age and severity held constant, postdexamethasone plasma cortisol values were positively associated with amount of wake time and stage 1, and negatively with amount of slow-wave sleep. CONCLUSIONS: These findings provide further indirect support for an overarousal state in MDD with sympathoadrenal system hyperactivity and impaired sleep continuity. They also underline the importance of taking into account various clinical confounding factors in the interpretation of both DST and sleep EEG results.

Age related health dynamics and changes in labour market status.

We focus on aspects of health changes, the importance of cohort effects, age related health changes and the effect of labour market status and work history on health. We moreover assess the relative importance of gradual changes and sudden shocks in health changes and the role of work status on the likelihood of experiencing a health shock. A fixed effect panel data model is estimated on two waves of a survey of Dutch elderly. We find strong differences in health outcomes for different age cohorts and gender. We also find that health deteriorates with employment and labour market history.

[Sleep apnea and nocturnal ventilatory assistance (nCPAP): 5-year experience in the conventional system]. / Apnées du sommeil et assistance ventilatoire nocturne (nCPAP): cinq ans d'expérience dans le systeme conventionnel.

The reimbursement of nasal continuous positive airway pressure (nCPAP) by the Belgian social security, via a conventional system, has made since 1991 this treatment available to an increasing number of patients having moderate to severe sleep apnoea hypopnoea syndrome (SAHS). We have reviewed our experience in prescribing domiciliary nCPAP from 1991 to 1995. Three hundred twenty-five subjects with SAHS, predominantly male (89%) and/or obese (77%) subjects, have benefited. Mean use of nCPAP machine, assessed by reading the time counter, amounted 4.7 h per 24 h, with only 23% of non-compliant patients (use < 3 h per 24 h). In 205 patients nCPAP was effective in controlling SAHS-related symptoms. Cure, with successful weaning from nCPAP, was obtained in 16 patients, as a result of marked weight loss in 13 of them. Forty-six non-compliant subjects were not allowed by the physician to go on, and 40 subjects left nCPAP because of intolerance. Finally, 10 patients abandoned nCPAP because of inefficacy, ascribed to some associated condition, being predominant, and 8 patients died. Our results suggest that domiciliary nCPAP is an effective treatment for SAHS in a majority of subjects, but that this kind of treatment is prescribed lifelong, unless there is a marked weight loss. The Belgian conventional system, as it requires a regular follow-up, contributes to keep non-compliance within acceptable limits.

EEG sleep in non-affective psychiatric disorders.

Several sleep complaints and disturbances have been documented in psychiatric disorders. These modifications of sleep in anxiety disorders, alcoholism, schizophrenia, dementia and eating disorders are reviewed and discussed. At the present time, there is no evidence for any specific sleep pattern in non-affective psychiatric disorders. The co-morbidity of sleep disorders like sleep apnoea, periodic leg movements and parasomnia in psychiatric illness is not very well known at the present time.