Oto Janousek

Sleep scoring using artificial neural networks

Rapid development of computer technologies leads to the intensive automation of many different processes traditionally performed by human experts. One of the spheres characterized by the introduction of new high intelligence technologies substituting analysis performed by humans is sleep scoring. This refers to the classification task and can be solved - next to other classification methods - by use of artificial neural networks (ANN). ANNs are parallel adaptive systems suitable for solving of non-linear problems. Using ANN for automatic sleep scoring is especially promising because of new ANN learning algorithms allowing faster classification without decreasing the performance. Both appropriate preparation of training data as well as selection of the ANN model make it possible to perform effective and correct recognizing of relevant sleep stages. Such an approach is highly topical, taking into consideration the fact that there is no automatic scorer utilizing ANN technology available at present.

EEG biofeedback

EEG biofeedback is an up to date therapeutic system able to cure low concentration ability, attention deficit hyperactivity disorder (ADHD), learning disability or depressions. Biofeedback systems based on EDG, ECG, EMG or EEG are used in numerous rehabilitation and therapeutic centers. Designed EEG biofeedback acquires EEG signal with a use of BIOPAC Acquisition unit. The signal is amplified, filtered and digitized. The software part of the system is designed in LabVIEW; it handles system control, data processing and data and feedback visualization. Two simple graphical games are included. The games are designed to increase the patients efficiency of mind concentration or body and mind relaxation.

Classification of ventricular premature and ischemic beats in animal electrograms

Many approaches have been proposed for automatic classification of different pathological events in ECG signals. Present study is focused on analysis and classification of non-ischemic, moderate and severe ischemic, and VPB segments in data obtained in rabbit isolated hearts. It is shown, that use of low number of morphological parameters calculated from electrograms combined with even simple classification method allows achieving of accurate results (with overall accuracy up to 0.99) for four types of the segments.

Testing of features for fatigue detection in EOG

The article deals with the testing of features for fatigue detection in electrooculography (EOG) records. An optimal methodology for EOG signal acquisition is described; the Biopac data acquisition system was used. EOG signals were being recorded while 10 volunteers were watching prepared scenes. Three scenes were created for this purpose - a rotating ball, a video of driving a car, and a cross. Recorded EOG signals were processed and 20 features were extracted. The features involved blinks, slow eye movement (SEM), rapid eye movement (REM), eye instability, magnitude, and periodicity. These features were statistically tested and discussed in terms of fatigue detection ability. Some of the features were compared with published results. Finally, the best features - fatigue indicators - were selected.

Effect of increased left ventricle mass on ischemia assessment in electrocardiographic signals: rabbit isolated heart study

BackgroundDetailed quantitative analysis of the effect of left ventricle (LV) hypertrophy on myocardial ischemia manifestation in ECG is still missing. The associations between both phenomena can be studied in animal models. In this study, rabbit isolated hearts with spontaneously increased LV mass were used to evaluate the effect of such LV alteration on ischemia detection criteria and performance.MethodsElectrophysiological effects of increased LV mass were evaluated on sixteen New Zealand rabbit isolated hearts under non-ischemic and ischemic conditions by analysis of various electrogram (EG) parameters. To reveal hearts with increased LV mass, LV weight/heart weight ratio was proposed. Standard paired and unpaired statistical tests and receiver operating characteristics analysis were used to compare data derived from different groups of animals, monitor EG parameters during global ischemia and evaluate their ability to discriminate between unchanged and increased LV as well as non-ischemic and ischemic state.ResultsSuccessful evaluation of both increased LV mass and ischemia is lead-dependent. Particularly, maximal deviation of QRS and area under QRS associated with anterolateral heart wall respond significantly to even early phase (the 1st-3rd min) of ischemia. Besides ischemia, these parameters reflect increased LV mass as well (with sensitivity reaching approx. 80%). However, the sensitivity of the parameters to both phenomena may lead to misinterpretations, when inappropriate criteria for ischemia detection are selected. Particularly, use of cut-off-based criteria defined from control group for ischemia detection in hearts with increased LV mass may result in dramatic reduction (approx. 15%) of detection specificity due to increased number of false positives. Nevertheless, criteria adjusted to particular experimental group allow achieving ischemia detection sensitivity of 89–100% and specificity of 94–100%, respectively.ConclusionsIt was shown that response of the heart to myocardial ischemia can be successfully evaluated only when taking into account heart-related factors (such as LV mass) and other methodological aspects (such as recording electrodes position, selected EG parameters, cut-off criteria, etc.). Results of this study might be helpful for developing new clinical diagnostic strategies in order to improve myocardial ischemia detection in patients with LV hypertrophy.

Voltage sensitive dye di-4-ANNEPS prolongs impulse conduction through ventricles, but not through AV node in isolated rabbit heart

Voltage sensitive dyes are widely used for recording of action potential in various cardiac studies. The elementary condition for its application is the fact that measured electrophysiological parameters would not be affected by the measuring procedure itself. The RR interval prolongation in the presence of the most frequently used voltage sensitive dye di-4-ANEPPS has been reported, but its exact mechanism is not known. In this study, the impact of di-4-ANEPPS on impulse conduction through the atrioventricular (AV) node and through cardiac ventricles in isolated rabbit heart was examined. The impulse conduction through AV node in the presence of di-4-ANEPPS was prolonged only during dye loading in the 14th, 16th and 17th minute. Only sporadic AV blocks were observed. In comparison, the prolongation of impulse conduction through cardiac ventricles was observed from the 13th minute of loading and persisted to the end of this phase as well as over the whole wash out phase.

The effect of heart orientation on high frequency QRS components in multiple bandwidths

Reduced power of high frequency (HF) oscillations inside the QRS complex reflects ischemic pathology in the heart. In order to show spatial and frequency dependencies, we examined the effect of heart orientation on power of high frequency components under normal and ischemia condition within various frequency bands. Root mean square (RMS) of the signal in QRS region within frequency bands from 150 Hz to 550 Hz and heart rotation around longitudinal axes (360°) were computed from four rabbit isolated hearts. Experimental protocol included control, ischemic and reperfusion phases. This pilot study shows that RMS level of HF signal in non-ischemic heart differs within lead orientation and its maximum lies in a region around specific angle. Relative decrease in RMS value also depends on lead position. When depicted in spatial-frequency plane with polar coordinates, these relative changes contributes to specific patterns under both normal and ischemic conditions, which should be further examined.

The effect of voltage-sensitive dye di-4-ANEPPS on heart rate variability in Langendorff-perfused isolated rabbit heart

Optical mapping of heart electrical activity in Langendorff-perfused isolated hearts is based on voltage-sensitive dyes, of which the most commonly used one is di-4-ANEPPS. Prolongation of action potential duration by di-4-ANEPPS was reported in isolated cells; however, this phenomenon was not observed in the whole heart model. In order to search for other adverse phenomena of di-4-ANEPPS use, its effect on heart rate variability (HRV) was investigated during staining and washout periods in jive New Zealand White rabbit isolated hearts. Time domain, frequency domain and non-linear HRV parameters (21 in total) revealed that there are no significant changes between control, staining and washout periods. Voltage-sensitive dye di-4-ANEPPS does not affect HRV when applied into the isolated heart coronary system. It can be concluded that di-4-ANEPPS may be safely used in studies combining optical mapping and HRV analysis.

Frequency domain HRV analysis of ischemia manifestation at isolated rabbit hearts

The ischemia manifestation was analyzed using heart rate variability (HRV) parameters in frequency domain. Assessment of HRV was based on analysis of consecutive normal R-R intervals during 5 minutes interval in seven section of measured ECG: control period, ischemia I-III periods and reperfusion I-III periods. Seven rabbits were used for experiment.

Influence of ischemia on left ventricular depolarization in isolated rabbit hearts perfused according to Langendorff

The aim of this study was to search for relation between electrical activity recorded from whole isolated heart and simultaneously from one cell. The QRS complex of electrogram (ECG) corresponds to the depolarization of the ventricles. The depolarization propagation is shown by monophasic action potential (MAP) recorded at appointed place during experiment. Electrogram changes observed during ischemia should be accounted for changes on cellular level. MAPs and ECG were recorded simultaneously. The activation time (AP), defined as distance from the earliest QRS deflection to MAP upstroke, changes with duration of ischemia. The excitement propagation and conduction in ischemic heart takes longer time in comparison to non-ischemic myocardium.