Assessment of human sleep depth is being de-standardized by recently advised EEG electrode locations.

Human sleep depth was traditionally assessed by scoring electro-encephalographic slow-wave amplitudes at the globally standardized C4-M1 electrode derivation. Since 2007, the American Association of Sleep Medicine (AASM) has accepted three additional derivations for the same purpose. These might well differ in slow wave amplitudes which would bias the scorings. Some derivations might also introduce large inter-individual variability. We compared mean and variability of slow wave amplitudes between six derivations including the four AASM ones. Slow wave amplitudes in those derivations were simultaneously measured using automated analysis in 29 patients. Each amplitude was divided by the average from the six derivations, thus removing shared factors such as age, gender and sleep depth while retaining factors that differ between the derivations such as caused by local skull characteristics, electrode distance and neuronal dipole orientation. The remaining inter-individual variability differed significantly and up to a factor of two between the AASM derivations. The amplitudes differed significantly and up to 60% between the AASM derivations, causing substantial scoring bias between centres using different derivations. The resulting de-standardization most likely affects any patient group because the amplitude differences were consistent over diagnoses, genders, and age. Derivation-dependent amplitude thresholds were proposed to reduce the scoring bias. However, it would be better to settle on just one derivation, for instance Cz-Oz or Fpz-Cz because these have lowest variability while matching the traditional C4-M1 amplitudes.

Guidelines for the recording and evaluation of pharmaco-sleep studies in man: the International Pharmaco-EEG Society (IPEG).

The International Pharmaco-EEG Society (IPEG) presents guidelines summarising the requirements for the recording and computerised evaluation of pharmaco-sleep data in man. Over the past years, technical and data-processing methods have advanced steadily, thus enhancing data quality and expanding the palette of sleep assessment tools that can be used to investigate the activity of drugs on the central nervous system (CNS), determine the time course of effects and pharmacodynamic properties of novel therapeutics, hence enabling the study of the pharmacokinetic/pharmacodynamic relationship, and evaluate the CNS penetration or toxicity of compounds. However, despite the presence of robust guidelines on the scoring of polysomnography -recordings, a review of the literature reveals inconsistent -aspects in the operating procedures from one study to another. While this fact does not invalidate results, the lack of standardisation constitutes a regrettable shortcoming, especially in the context of drug development programmes. The present guidelines are intended to assist investigators, who are using pharmaco-sleep measures in clinical research, in an effort to provide clear and concise recommendations and thereby to standardise methodology and facilitate comparability of data across laboratories.

Measurement of sleep.

Rapid eye movement (REM) and non-REM sleep processes affect the electrical signals from brain, eyes and muscles. Recording these signals during sleep imposes special demands on electrodes, technicians and equipment. Both human and computerized signal analysis can then be applied to quantify the sleep processes. The most practical and state-of-the-art recording and analysis methods are discussed with emphasis on the most important details. Other analysis methods can be judged based on a few simple criteria.

A DC attenuator allows common EEG equipment to record fullband EEG, and fits fullband EEG into standard European Data Format.

OBJECTIVE: Traditional electroencephalogram (EEG) recorders reject low frequencies and DC and therefore cannot handle fullband EEG. Dedicated fullband recorders use non-standard file formats, because the standard format (EDF) cannot handle large DC electrode offset voltages. Both facts limit the development and use of fullband EEG. We developed a modification that allows conventional equipment to record fullband EEG, and adapts both types of recorders to EDF. METHODS: The modification is a simple filter that attenuates the DC component and thus makes the EEG fit within traditional equipment limitations and EDF. The review software automatically 'de-attenuates' the DC component, without loss of information. RESULTS: DC attenuation by a factor of 10 made both types of recorders store DC attenuated fullband EEG into EDF files. Recordings were made during 0.5-24h in 46 subjects. The DC de-attenuator automatically reconstructed the original fullband EEG within an amplitude range of ±100mV and with a resolution of 0.3µV. Using sintered Ag-AgCl electrodes attached with common procedures, reconstructed DC EEG in spontaneously moving subjects ranged between ±32mV. CONCLUSIONS: The modification works. Fullband recordings can now be analyzed by independent software, archived and exchanged. SIGNIFICANCE: Any EEG system can be made to record fullband EEG into standard EDF.

An E-health solution for automatic sleep classification according to Rechtschaffen and Kales: validation study of the Somnolyzer 24 x 7 utilizing the Siesta database.

To date, the only standard for the classification of sleep-EEG recordings that has found worldwide acceptance are the rules published in 1968 by Rechtschaffen and Kales. Even though several attempts have been made to automate the classification process, so far no method has been published that has proven its validity in a study including a sufficiently large number of controls and patients of all adult age ranges. The present paper describes the development and optimization of an automatic classification system that is based on one central EEG channel, two EOG channels and one chin EMG channel. It adheres to the decision rules for visual scoring as closely as possible and includes a structured quality control procedure by a human expert. The final system (Somnolyzer 24 x 7) consists of a raw data quality check, a feature extraction algorithm (density and intensity of sleep/wake-related patterns such as sleep spindles, delta waves, SEMs and REMs), a feature matrix plausibility check, a classifier designed as an expert system, a rule-based smoothing procedure for the start and the end of stages REM, and finally a statistical comparison to age- and sex-matched normal healthy controls (Siesta Spot Report). The expert system considers different prior probabilities of stage changes depending on the preceding sleep stage, the occurrence of a movement arousal and the position of the epoch within the NREM/REM sleep cycles. Moreover, results obtained with and without using the chin EMG signal are combined. The Siesta polysomnographic database (590 recordings in both normal healthy subjects aged 20-95 years and patients suffering from organic or nonorganic sleep disorders) was split into two halves, which were randomly assigned to a training and a validation set, respectively. The final validation revealed an overall epoch-by-epoch agreement of 80% (Cohen's kappa: 0.72) between the Somnolyzer 24 x 7 and the human expert scoring, as compared with an inter-rater reliability of 77% (Cohen's kappa: 0.68) between two human experts scoring the same dataset. Two Somnolyzer 24 x 7 analyses (including a structured quality control by two human experts) revealed an inter-rater reliability close to 1 (Cohen's kappa: 0.991), which confirmed that the variability induced by the quality control procedure, whereby approximately 1% of the epochs (in 9.5% of the recordings) are changed, can definitely be neglected. Thus, the validation study proved the high reliability and validity of the Somnolyzer 24 x 7 and demonstrated its applicability in clinical routine and sleep studies.

Easy listening to sleep recordings: tools and examples.

BACKGROUND AND PURPOSE: To specify a simple conversion of neurophysiological signals contained in sleep recordings into standard audio files and to illustrate how our cerebral audio processor can then detect specific signal characteristics. METHODS: A software package (freely accessible from the Internet) has been developed that converts signals from standard EDF (or EDF+) format to standard audio (WAV) format, a process usually called audification. The software has been applied to sleep EEG, EOG and ECG. The software is easy to apply. RESULTS: A wide range of audified signals is described, stressing the analogy with familiar sounds. Audio properties of EEG in different sleep stages, EOG, ECG and respiration signals are discussed. Auditive presentation of the signals invokes brain processes that differ essentially from the commonly applied visual interpretation, including physiological frequency analysis. CONCLUSIONS: Such auditive interpretation may complement the visual one. The widespread use of EDF+ and multimedia computers makes such audification simple and straightforward.

SignalML from an EDF+ perspective.

Both SignalML and EDF+ offer a solution for the incompatibility between different data storage formats in biomedicine. This article discusses the SignalML approach from an EDF+ point of view.

Epidemiology of restless legs in The Netherlands.

The prevalence of restless legs syndrome (RLS) in various regions in the world has been estimated between 2.5 and 29%. For The Netherlands these figures are not known. Our observational and cross-sectional study was performed to estimate the prevalence of RLS in The Netherlands. A cross-sectional survey by postal questionnaire was carried out through a general practice in a small town in which one general practice serves 93% of the population. All men and women aged 50 years and older were invited to fill out the questionnaire on leg movements, quality of sleep and daytime symptoms. A total of 1485 (88.2%) persons returned their questionnaire and 1437 (85.4%) patients answered the questions on leg movements. A total of 102 (7.1%) inhabitants answered positively to the questions on leg movements and probably have RLS. The prevalence was higher in women and increased with age. People who complain of RLS have significantly more complaints of disturbances in initiating and maintaining sleep, sleepiness, tiredness during the day and less refreshing sleep. RLS is common in The Netherlands with an estimated prevalence of 7.1% in the population over 50 years of age.

European data format 'plus' (EDF+), an EDF alike standard format for the exchange of physiological data.

The European data format (EDF) is a widely accepted standard for exchange of electroencephalogram and polysomnogram data between different equipment and labs. But it hardly accommodates other investigations. EDF+ is a more flexible but still simple format which is compatible to EDF except that an EDF+ file may contain interrupted recordings. Also, EDF+ supports time-stamped annotations for the storage of events such as text annotations, stimuli, averaged signals, electrocardiogram parameters, apnoeas and so on. When compared to EDF, EDF+ can not only store annotations but also electromyography, evoked potentials, electroneurography, electrocardiography and many more types of investigations. Further improvements over EDF include the use of standard electrode names. EDF+ is so much like EDF that existing EDF viewers still display the signals in EDF+ files. Software development is limited mainly to implementing the annotations. EDF+ offers a format for a wide range of neurophysiological investigations which can become a standard within a few years.

Multi-centre comparison of five eye movement detection algorithms.

Although various investigators have suggested algorithms for the automatic detection of eye movements during sleep, objective comparisons of the proposed methods have previously been difficult due to different recording arrangements of different investigators. In this study the results of five eye movement detection algorithms applied to the same data were compared to visually scored data. The percentages of true and false detections are given for various threshold levels in rapid and slow eye movement detections. The methods gave best results when they were used with the same electrode montage they were designed for but the performance decreased when other montages were used. Subtracting the cross-talk of EEG delta activity improved the correctness of eye movement detections.