Ballistocardiogaphic studies with acceleration and electromechanical film sensors.

The purpose of this research is to demonstrate and compare the utilization of electromechanical film (EMFi) and two acceleration sensors, ADXL202 and MXA2500U, for ballistocardiographic (BCG) and pulse transit time (PTT) studies. We have constructed a mobile physiological measurement station including amplifiers and a data collection system to record the previously mentioned signals and an electrocardiogram signal. Various versions of the measuring systems used in BCG studies in the past are also presented and evaluated. We have showed the ability of the EMFi sensor to define the elastic properties of the cardiovascular system and to ensure the functionality of the proposed instrumentation in different physiological loading conditions, before and after exercise and sauna bath. The EMFi sensor provided a BCG signal of good quality in the study of the human heart and function of the cardiovascular system with different measurement configurations. EMFi BCG measurements provided accurate and repeatable results for the different components of the heart cycle. In multiple-channel EMFi measurements, the carotid and limb pulse signals acquired were detailed and distinctive, allowing accurate PTT measurements. Changes in blood pressure were clearly observed and easily determined with EMFi sensor strips in pulse wave velocity (PWV) measurements. In conclusion, the configuration of the constructed device provided reliable measurements of the electrocardiogram, BCG, heart sound, and carotid and ankle pulse wave signals. Attached EMFi sensor strips on the neck and limbs yield completely new applications of the EMFi sensors aside from the conventional seat and supine recordings. Higher sensitivity, ease of utilization, and minimum discomfort of the EMFi sensor compared with acceleration sensors strengthen the status of the EMFi sensor for accurate and reliable BCG and PWV measurements, providing novel evaluation of the elastic properties of the cardiovascular system.

Ballistocardiography in sitting and horizontal positions.

The purpose of this study is to examine the effect of posture in the sitting and supine positions on ballistocardiography (BCG) measurements by using EMFi (electromechanical film) sensors. The experiment, measuring the subject's electrocardiography (ECG), BCG and carotid pulse (CP) signal, was repeated in the sitting and different horizontal positions. Additionally, the duration and the amplitudes of the BCG and CP signal components were studied. Certain properties of BCG differed significantly in the sitting and horizontal positions. Amplitudes of measured signals were larger, and time intervals were greater in the sitting position compared to the supine position. Thus, posture significantly influences cardiac performance evaluated by BCG. Sitting and supine positions are clearly distinguishable in the BCG signal. This provides new methods for evaluation of the hemodynamic changes induced by the body position.

Bioprofiling over grid for eHealthcare.

A trend in modern medicine is towards individualization of healthcare and, potentially, grid computing can play an important role in this by allowing sharing of resources and expertise to improve the quality of care. In this paper, we present a new test bed, the BIOPATTERN Grid, which aims to fulfil this role in the long term. The main objectives in this paper are 1) to report the development of the BIOPATTERN Grid, for biopattern analysis and bioprofiling in support of individualization of healthcare. The BIOPATTERN Grid is designed to facilitate secure and seamless sharing of geographically distributed bioprofile databases and to support the analysis of bioprofiles to combat major diseases such as brain diseases and cancer within a major EU project, BIOPATTERN (www.biopattern.org); 2) to illustrate how the BIOPATTERN Grid could be used for biopattern analysis and bioprofiling for early detection of dementia and for brain injury assessment on an individual basis. We highlight important issues that would arise from the mobility of citizens in the EU, such as those associated with access to medical data, ethical and security; and 3) to describe two grid services which aim to integrate BIOPATTERN Grid with existing grid projects on crawling service and remote data acquisition which is necessary to underpin the use of the test bed for biopattern analysis and bioprofiling.

A new method for measuring the ballistocardiogram using EMFi sensors in a normal chair.

Ballistocardiography is a non-invasive technique for the assessment of cardiac function. We built a measurement setup to measure the ballistocardiogram from a normal chair using EMFi sensors. The ballistocardiogram is recorded from a subject sitting on the chair. The measured signal is amplified by a specially-designed charge amplifier and digitized by a circulation monitor. A PC provides a user interface for the measurement devices, records the data and displays the results. Impedance cardiography and ECG serve as reference measurements for the ballistocardiography. To test the system, one healthy 24-year-old male and one healthy 22-year-old female were measured. It is concluded that the ballistocardiogram waveforms described in the literature can be recognized from the EMFi signal measured from a normal chair.

Automatic analysis of electro-encephalogram sleep spindle frequency throughout the night.

A fully automatic method to analyse electro-encephalogram (EEG) sleep spindle frequency evolution during the night was developed and tested. Twenty all-night recordings were studied from ten healthy control subjects and ten sleep apnoea patients. A total of 22,868 spindles were detected. The overall mean spindle frequency was significantly higher in the control subjects than in the apnoea patients (12.5 Hz against 11.7 Hz, respectively; p<0.004). The proposed method further identified the sleep depth cycles, and the mean spindle frequency was automatically determined inside each sleep depth cycle. In control subjects, the mean spindle frequency increased from 12.0 Hz in the first sleep depth cycle to 12.6 Hz in the fifth cycle. No such increase was observed in the sleep apnoea patients. This difference in the spindle frequency evolution was statistically significant (p<0.004). The advantage of the method is that no EEG amplitude thresholds are needed.

Autoassociative MLP in sleep spindle detection.

Spindles are one of the most important short-lasting waveforms in sleep EEG. They are the hallmarks of the so-called Stage 2 sleep. Visual spindle scoring is a tedious workload, since there are often a thousand spindles in one all-night recording of some 8 hr. Automated methods for spindle detection typically use some form of fixed spindle amplitude threshold, which is poor with respect to inter-subject variability. In this work a spindle detection system allowing spindle detection without an amplitude threshold was developed. This system can be used for automatic decision making of whether or not a sleep spindle is present in the EEG at a certain point of time. An Autoassociative Multilayer Perceptron (A-MLP) network was employed for the decision making. A novel training procedure was developed to remove inconsistencies from the training data, which was found to improve the system performance significantly.

Vigilance stages and performance in OSAS patients in a monotonous reaction time task.

OBJECTIVES: To develop improved methods for objective assessment of daytime vigilance. This is important in the diagnosis and therapy control of sleep disorders associated with excessive daytime sleepiness (EDS). METHODS: Twenty-one patients with EDS due to obstructive sleep apnea were recorded during a daytime 90 min reaction time (RT) test in a monotonous situation. Two EEG, two EOG and a submental EMG channel were recorded simultaneously. The recordings were divided into short, stationary segments of variable length (0.5-2 s) and classified into 7 stages using our previously described system, which includes additional stages for drowsiness. RESULTS: The duration of RT was linearly correlated to the vigilance state (P<0.05). The appearance of slow eye movements (SEM) was more consistently related to performance impairment than EEG changes. CONCLUSIONS: Our system can provide a better tracking of vigilance changes than the standardized sleep stage scoring. A 1-2 h test is useful in the assessment of the performance of a subject suffering from EDS. We found that SEMs indicate more sensitive and consistent EDS-related performance impairment than changes in EEG activity.

A computer-assisted visual sleep scoring program.

The sleep analysis and scoring program WSCORE was developed under the European Neurological Network (ENN) project. The purpose was to implement an analysis and scoring system for ambulatory and standard polysomnography. In addition to visual Rechtschaffen & Kales scoring the program offers a possibility of free form visual scoring. It contains also analysis modules for Periodic Leg Movement Disorder, Hjort parameters, heart rate and EMG amplitude. A FTP client module was built into the program so that it can be used as a telemedicine application.

Optimization of sigma amplitude threshold in sleep spindle detection.

Sleep spindles are transient EEG waveforms of non-rapid eye movement sleep. There is considerable intersubject variability in spindle amplitudes. The problem in automatic spindle detection has been that, despite this fact, a fixed amplitude threshold has been used. Selection of the spindle detection threshold value is critical with respect to the sensitivity of spindle detection. In this study a method was developed to estimate the optimal recording-specific threshold value for each all-night recording without any visual scorings. The performance of the proposed method was validated using four test recordings each having a very different number of visually scored spindles. The optimal threshold values for the test recordings could be estimated well. The presented method seems very promising in providing information about sleep spindle amplitudes of individual all-night recordings.

Vigilance transitions in reaction time test: a method of describing the state of alertness more objectively.

Electrophysiological recordings are considered a reliable method of assessing a person's alertness. The aim of this study was to show, firstly, that changes in alertness during a Reaction Time Test (RTT) can be determined with certain adaptive scoring stages but not with R&K scoring and secondly, that the different adaptive stages can explain findings in reaction time. In 17 male patients (50.8+/-9.7 years, Body-Mass Index (BMI) 31.9+/-5.1 kg/m2) diagnosed with Obstructive Sleep Apnea Syndrome (OSAS) (Respiratory Disturbance Index (RDI) 53.3+/-24.1 /h sleep) a 90 min daytime vigilance test was performed twice, after the diagnostic polysomnographic investigation and after two nights spent with nCPAP. After a computerised adaptive segmentation analysis, a visual rule-defined classification system categorised alertness into one of 12 adaptive scoring stages. 6 of the 12 stages are described by the alertness conditions comparable to WAKE and NREM1.4 stages are nearly classified as NREM2-4, Rapid Eye Movement (REM) and Movement Time (MT), and one stage reflects the increase of alertness from drowsiness. The typical stage of an alert subject increased significantly from a median of 65.9% before therapy to 80.8% in the second investigation. The percentages of clearly drowsy stages decreased significantly. In contrast, there were no significant changes in the percentages of sleep stages according to R&K criteria for both investigations. According to R&K criteria 178 of 398 failed reactions (Reaction time >10 s) occurred in stage WAKE. According to adaptive scoring, only 12 failed reactions appeared in the alert stage. During the other failed reactions the electrophysiological recordings showed decreases in alertness. Neither the visual assessment nor the descriptive statistical results of R&K scoring were helpful to interpret the patient's alertness condition. In contrast, the patients' increases in alertness with nCPAP could be described by the adaptive scoring stages. This method could be a very useful procedure, when an expert opinion is necessary. It also has an actual context to the discussion of the effectiveness of CPAP in the treatment of OSAS.

Quality control of polysomnographic sleep data by histogram and entropy analysis.

OBJECTIVE AND METHODS: Sixteen polysomnographic recordings from 8 European sleep laboratories were analyzed. The histogram analysis was used to introduce quality control of all-night EEG recordings. RESULTS: It was found that the header information does not always provide the real saturation values of the recording equipment. The entropy measure was used for the quantitative analysis of the dynamic range of routinely used polysomnographic recorders. It was found that the recording equipment provides EEG data with entropy in the range of 8-11 bits. CONCLUSION: In the all-night sleep EEG were observed non-linearities. It is recommended that the equipment provide the saturation values in order to apply automated overflow detection.

Digital archival and exchange of events in a simple format for polygraphic recordings with application in event related potential studies.

This paper describes a simple method of event encoding as an extension to a previously defined standard format, the European Data Format (EDF). The specification ensures full backward compatibility with the existing definition. By using this extension, the format can be used to store both continuous recordings and selected epochs of recordings. The encoding is performed in a channel of event-codes or in a pseudo-channel for annotations. Standardisation of event encoding is discussed. Decoding of events or annotations from the extended format is implemented at the application level. Existing programs that do not support the new encoding scheme still operate correctly and can simply ignore the new channels in processing 'extended' data files. The event encoding is also compatible with EDF's capability to encode channels of different sampling frequency.

The detection of drowsiness and sleep onset periods from ambulatory recorded polygraphic data.

A 30 min sample recording at the sleep onset of 7 healthy male subjects was used to further develop a computer-scoring algorithm applied earlier for the analysis of MSLT recordings. The performance of this algorithm was tested on 7 patients with obstructive sleep apnea by using 6 h daytime recordings including drowsiness and sleep episodes. The total epoch-by-epoch agreement between visual and computer scoring was over 90% and the accurate detection rate of non-REM sleep was 64%. The hypnograms produced by the computer scoring corresponded sufficiently to those obtained by visual scoring. Our automatic scoring system can give a good estimation of the daytime vigilance profile but for clinical diagnosis the results have to be verified visually. However, by using modern digital recording, analyzing and scoring techniques the speed of analysis and thus the costs can markedly been reduced as compared to traditional visual analysis.

Nonlinear eye movement detection method for drowsiness studies.

Automatic long-term vigilance analysis systems require information about the occurrence and type of eye movements, in addition to information about other physiological signals. This paper presents a method to detect different types of eye movements in ambulatory recordings. The method is based on the application of a weighted FIR-median-hybrid filter in the preprocessing of the signal and on the novel use of linear correlation between two EOG signals which are obtained using a new, improved electrode montage. The evaluation of the method showed that it performed well in detecting isolated unambiguous eye movements, but differences were observed in comparison to visual scoring in borderline cases. The method was found to be suitable for use as part of a signal analysis system for drowsiness studies.

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.

Interactive computer program for the analysis of cardiovascular polysomnographic recordings.

A computer program for the analysis of blood pressure, heart rate, oxygen saturation and some other polysomnographic signals is presented. The program analyzes the signals, digitized by using a 100 Hz sampling frequency, in one second resolution. The analysis and calibration periods can be entered to the program by pointing at the appropriate positions of the displayed signal with a mouse. As analysis results the program can produce statistical tables or graphical representations of the measured variables as a function of time. The program can be used in routine polysomnographic cardiovascular analysis and due to its flexibility also in experimental studies.

Evaluation of a computerized system for recognition of epileptic activity during long-term EEG recording.

A new method of recognition of epileptic activity using adaptive segmentation in EEG during long-term intensive monitoring was developed in Tampere. The performance of the system was validated and compared to the commercially available discharge recognition system of Gotman. Twelve approximately 30 min EEG segments recorded during intensive monitoring from 6 patients were analysed. On these EEG segments two EEG specialists marked the occurrence of epileptic activity independently. Later they re-evaluated any differences in their scoring. This consensus file was used as a reference in validating the performance of the two computer programs. We found that the program developed in Tampere detected discharge activity more often than the Gotman system. Both systems performed poorly in spike recognition. In the specificity of the recognized segments, the Gotman system was better.