Identification of obstructive sleep apnea and risk factors is important for reduction in symptoms and cardiovascular risk, and for improvement of quality of life. The population‐based Study of Health in Pomerania investigated risk factors and clinical diseases in a general population of northeast Germany. Additional polysomnography was applied to measure sleep and respiration with the objective of assessing prevalence and risk factors of obstructive sleep apnea in a German cohort. One‐thousand, two‐hundred and eight people between 20 and 81 years old (54% men, median age 54 years) underwent overnight polysomnography. The estimated obstructive sleep apnea prevalence was 46% (59% men, 33% women) for an apnea–hypopnea index ≥5%, and 21% (30% men, 13% women) for an apnea–hypopnea index ≥ 15. The estimated obstructive sleep apnea syndrome prevalence (apnea–hypopnea index ≥5; Epworth Sleepiness Scale >10) was 6%. The prevalence of obstructive sleep apnea continuously increased with age for men and women with, however, later onset for women. Gender, age, body mass index, waist‐to‐hip ratio, snoring, alcohol consumption (for women only) and self‐reported cardiovascular diseases were significantly positively associated with obstructive sleep apnea, whereas daytime sleepiness was not. Diabetes, hypertension and metabolic syndrome were positively associated with severe obstructive sleep apnea. The associations became non‐significant after adjustment for body mass. Women exhibited stronger associations than men. The prevalence of obstructive sleep apnea was high, with almost half the population presenting some kind of obstructive sleep apnea. The continuous increase of obstructive sleep apnea with age challenges the current theory that mortality due to obstructive sleep apnea and cardiovascular co‐morbidities affect obstructive sleep apnea prevalence at an advanced age. Also, gender differences regarding obstructive sleep apnea and associations are significant for recognizing obstructive sleep apnea mechanisms and therapy responsiveness.

The cardiac component of cardio-respiratory polysomnography is covered by ECG and heart rate recordings. However, their evaluation is often underrepresented in summarizing reports. As complements to EEG, EOG, and EMG, these signals provide diagnostic information for autonomic nervous activity during sleep. This review presents major methodological developments in sleep research regarding heart rate, ECG, and cardio-respiratory couplings in a chronological (historical) sequence. It presents physiological and pathophysiological insights related to sleep medicine obtained by new technical developments. Recorded nocturnal ECG facilitates conventional heart rate variability (HRV) analysis, studies of cyclical variations of heart rate, and analysis of ECG waveform. In healthy adults, the autonomous nervous system is regulated in totally different ways during wakefulness, slow-wave sleep, and REM sleep. Analysis of beat-to-beat heart-rate variations with statistical methods enables us to estimate sleep stages based on the differences in autonomic nervous system regulation. Furthermore, up to some degree, it is possible to track transitions from wakefulness to sleep by analysis of heart-rate variations. ECG and heart rate analysis allow assessment of selected sleep disorders as well. Sleep disordered breathing can be detected reliably by studying cyclical variation of heart rate combined with respiration-modulated changes in ECG morphology (amplitude of R wave and T wave).

This study is aimed at assessing the usefulness of different feature selection and classification methodologies in the context of sleep apnea hypopnea syndrome (SAHS) detection. Feature extraction, selection and classification stages were applied to analyze blood oxygen saturation (SaO2) recordings in order to simplify polysomnography (PSG), the gold standard diagnostic methodology for SAHS. Statistical, spectral and nonlinear measures were computed to compose the initial feature set. Principal component analysis (PCA), forward stepwise feature selection (FSFS) and genetic algorithms (GAs) were applied to select feature subsets. Fisher's linear discriminant (FLD), logistic regression (LR) and support vector machines (SVMs) were applied in the classification stage. Optimum classification algorithms from each combination of these feature selection and classification approaches were prospectively validated on datasets from two independent sleep units. FSFS + LR achieved the highest diagnostic performance using a small feature subset (4 features), reaching 83.2% accuracy in the validation set and 88.7% accuracy in the test set. Similarly, GAs + SVM also achieved high generalization capability using a small number of input features (7 features), with 84.2% accuracy on the validation set and 84.5% accuracy in the test set. Our results suggest that reduced subsets of complementary features (25% to 50% of total features) and classifiers with high generalization ability could provide high-performance screening tools in the context of SAHS.

Ballet dancers are competitive athletes who undergo extreme physical and mental stress and work according to an irregular schedule, with long days of training, rehearsal, and performance. Their most significant potential risks entail physical injury and altered sleep. The elaborate training requirements for ballet dancers do not allow regular chronobiological patterns or a normal sleep-wake rhythm. Our aim was to investigate the sleep-wake rhythm and sleep quality during rehearsal phases prior to a ballet premiere. We used wrist actigraphy and sleep diaries for a period of 67 days before the ballet premiere performance to study 24 classical ballet dancers. We likewise applied the Epworth Sleepiness Score (ESS), Pittsburgh Sleep Quality Index (PSQI), SF-12 Quality of life Assessment, and d2 Test of Attention to assess quality of sleep, aspects of cognitive performance, and health status. We found significant reduction in sleep duration, from 418+/-43 min to 391+/-42 min, and sleep efficiency, from 81+/-4% to 79+/-5%, over the 67-day course of the rehearsal. We also found a decline in time in bed and an increase in wakefulness after sleep onset. Sleep onset latency did not change. However, the changes in sleep as documented by actigraphy were not reflected by the subjective data of the sleep diaries and sleep scores. As a result of the facts that total sleep efficiency and sleep duration values were already lower than usual for the dancers' age group at the beginning of the study and that mental acuity, concentration, and speed were likewise impaired, we observed exacerbated health deterioration in terms of sleep deprivation in ballet dancers during preparation for a premier. We conclude that individual activity-rest schedules, including daytime naps, may be helpful, especially during the stressful training and rehearsal experienced prior to ballet premieres.

The current study investigated the night-to-night variability and diagnostic accuracy of the oxygen desaturation index (ODI), as measured by ambulatory monitoring, in the diagnosis of mild and moderate obstructive sleep apnoea-hypopnoea syndrome.To assess the variability of the ODI, 35 patients were monitored at home during 7 consecutive nights by means of a portable recording device, the MESAM-IV1. The ODI variability factor and the influence of age, body mass index (BMI), alcohol, and body position were assessed. Furthermore, the diagnostic accuracy of the MESAM-IV was measured by comparison with polysomnographical outcomes in 18 patients.During home recording, the median ODI was 10.9 (interquartile range: 5.8-16.1) across the patients. Although the reliability of the ODI was adequate, the probability of placing the patient in the wrong severity category (ODI f15 or ODI w15) when only one single recording was taken is 14.4%. ODI variability was not significantly influenced by age, BMI, time spent in a supine position, or mild dosages of alcohol. A good correlation was found between the apnoea-hypopnoea index and the ODI.In conclusion, the findings suggest that the diagnostic accuracy of the MESAM-IV is strong, since the oxygen desaturation index is correlated with the apnoea-hypopnoea index. In most obstructive sleep apnoea-hypopnoea syndrome patients, oxygen desaturation index variability is rather small, and screening could be reliably based on single 1-night recordings. Eur Respir J 2004; 24: 987-993.

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Low REM stage scoring agreement exists for narcoleptics and SAHS, indicating the necessity to study sleep stage scoring agreement for a specific sleep disorder. Intensive training is needed for the scoring of sleep in international multiple center studies to improve the scoring agreement.

Ballet dancers are competitive athletes who undergo extreme physical and mental stress and work according to an irregular schedule, with long days of training, rehearsal, and performance. Their most significant potential risks entail physical injury and altered sleep. The elaborate training requirements for ballet dancers do not allow regular chronobiological patterns or a normal sleep-wake rhythm. Our aim was to investigate the sleep-wake rhythm and sleep quality during rehearsal phases prior to a ballet premiere. We used wrist actigraphy and sleep diaries for a period of 67 days before the ballet premiere performance to study 24 classical ballet dancers. We likewise applied the Epworth Sleepiness Score (ESS), Pittsburgh Sleep Quality Index (PSQI), SF-12 Quality of life Assessment, and d2 Test of Attention to assess quality of sleep, aspects of cognitive performance, and health status. We found significant reduction in sleep duration, from 418+/-43 min to 391+/-42 min, and sleep efficiency, from 81+/-4% to 79+/-5%, over the 67-day course of the rehearsal. We also found a decline in time in bed and an increase in wakefulness after sleep onset. Sleep onset latency did not change. However, the changes in sleep as documented by actigraphy were not reflected by the subjective data of the sleep diaries and sleep scores. As a result of the facts that total sleep efficiency and sleep duration values were already lower than usual for the dancers' age group at the beginning of the study and that mental acuity, concentration, and speed were likewise impaired, we observed exacerbated health deterioration in terms of sleep deprivation in ballet dancers during preparation for a premier. We conclude that individual activity-rest schedules, including daytime naps, may be helpful, especially during the stressful training and rehearsal experienced prior to ballet premieres.