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.

The relationship between EEG delta activity and autonomic activity as measured by SCSB during daytime sleep.

The aim of the present work was to study the applicability of the static-charge-sensitive bed (SCSB) method to sleep studies, by comparing autonomic nervous activity measured with the SCSB and EEG delta activity (0.5-2 Hz). Simultaneous polygraphic and SCSB measurements of the first sleep cycle (110 min) were recorded from seven subjects. The amount of delta activity filtered from the EEG was compared in 3 min epochs to an autonomic activity index (AAI) based on cardiac, respiratory and body movement activity. Individual Spearman rank order correlation coefficients between delta amplitude and the AAI varied from 0.17 to -0.60. Therefore, it is concluded that the relationship between the delta activity and the AAI is not systematic enough for defining 'depth' of sleep at any point in time by using the AAI. However, on average, the SCSB differentiates high and low delta values quite well. With some further improvement of the scoring system the SCSB is a useful tool in comparative sleep 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.

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.

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 new method to study blood pressure, heart rate and EEG as a function of reaction time.

A new method is presented to study the relationship between reaction time and blood pressure, heart rate and EEG. The method consists of a simultaneous recording of continuous invasive or non-invasive arterial blood pressure, ECG, EEG, EMG and EOG in a sound-isolated chamber while a monotonous visual reaction time test is running for about 90 minutes. The signals are A/D-converted and analyzed digitally after recording. One second average amplitudes are computed. Systolic, mean and diastolic blood pressure values are calculated, and the EEG is divided into the delta, theta, alpha, sigma and beta frequency bands. The signal amplitudes are averaged in three different reaction time categories, i.e., when the reaction is normal, delayed or missing. Preliminary tests suggest that interesting differences can be observed in the studied variables in different reaction time classes. This method can also be applied to the investigation of autonomic control and to treatment studies.

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.

A computerized analysis system for vigilance studies.

A digital signal analysis system for vigilance studies is presented. The analysis is based on adaptive segmentation, band pass filtering, nonlinear eye movement detection and rule-based decision making. A preliminary evaluation of seven subjects falling asleep showed that the system is able to detect small vigilance fluctuations reliably.

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.

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.

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.

Correlation between EEG and heart rate variation in deep enflurane anaesthesia.

Variations in heart rate during deep enflurane anaesthesia were studied in 11 women admitted for elective surgery. Correlation was found between heart rate variations and bursts and suppressions in the EEG patterns. The onset of bursts coincided with accelerating heart rate, and the onset of suppressions was combined with a fall in heart rate in all patients. The correlation is not explained by ventilation arrhythmia. Both the cortical electrical activity and heart rate fluctuation are probably controlled by the same subcortical factor.

Automatic identification of significant graphoelements in multichannel EEG recordings by adaptive segmentation and fuzzy clustering.

A new approach to visual evaluation of long-term EEG recordings is proposed. The method is based on multichannel adaptive segmentation, subsequent feature extraction, automatic classification of the acquired segments by fuzzy cluster analysis (fuzzy c-means algorithm), and on the distinguishing of thus identified EEG segments by colour directly in the EEG record. The black and white variant of the described automatic system is presented. The method was evaluated by applying it to simulated artificial data and to real EEG recordings; some of the illustrative results are shown. In addition, the performance of this system is evaluated and the first experience with its application to routine EEG recordings is discussed.

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.

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.