Human brain distinctiveness based on EEG spectral coherence connectivity.

The use of EEG biometrics, for the purpose of automatic people recognition, has received increasing attention in the recent years. Most of the current analyses rely on the extraction of features characterizing the activity of single brain regions, like power spectrum estimation, thus neglecting possible temporal dependencies between the generated EEG signals. However, important physiological information can be extracted from the way different brain regions are functionally coupled. In this study, we propose a novel approach that fuses spectral coherence-based connectivity between different brain regions as a possibly viable biometric feature. The proposed approach is tested on a large dataset of subjects (N = 108) during eyes-closed (EC) and eyes-open (EO) resting state conditions. The obtained recognition performance shows that using brain connectivity leads to higher distinctiveness with respect to power-spectrum measurements, in both the experimental conditions. Notably, a 100% recognition accuracy is obtained in EC and EO when integrating functional connectivity between regions in the frontal lobe, while a lower 97.5% is obtained in EC (96.26% in EO) when fusing power spectrum information from parieto-occipital (centro-parietal in EO) regions. Taken together, these results suggest that the functional connectivity patterns represent effective features for improving EEG-based biometric systems.

Spontaneous variability and reactive postural beat-to-beat changes of integral ECG body surface potential maps.

There is virtually no information on spontaneous variability of ECG body surface potential maps (BSPMs) and on dynamics of their reactive changes in healthy subjects. This study evaluated quantitatively the depolarization (QRS) and repolarization (QRST) parameters derived from the respective integral BSPMs, constructed beat-to-beat, from continual body surface ECG records in 9 healthy men resting supine, during head-up tilting and sitting. Spontaneous variability of the BSPMs parameters, both at rest and during postural reactions, was characterized by significant respiratory and low frequency oscillations, more pronounced when related to repolarization. Head-up tilting and sitting-up evoked significant decrease in the QRST-BSPM amplitudes, widening of the angle alpha and reduction of nondipolarity indexes, compared to the respective supine values. All these changes were gradual, characterized by transition phenomena and prolonged after-effects. Tilting back to horizontal restored the resting supine values. The postural effects on depolarization were individually more variable and in the average showed a minimal QRS-BSPM amplitude increase. Beat-to-beat analysis of a train of ECG BSPMs provided the first evidence of spontaneous, non-random, respiratory and low frequency oscillations of the ventricular repolarization pattern, and the first insight into the dynamics of body posture associated changes in ventricular recovery.

A novel artificial intelligence method for weekly dietary menu planning.

OBJECTIVES: Menu planning is an important part of personalized lifestyle counseling. The paper describes the results of an automated menu generator (MenuGene) of the web-based lifestyle counseling system Cordelia that provides personalized advice to prevent cardiovascular diseases. METHODS: The menu generator uses genetic algorithms to prepare weekly menus for web users. The objectives are derived from personal medical data collected via forms in Cordelia, combined with general nutritional guidelines. The weekly menu is modeled as a multilevel structure. RESULTS: Results show that the genetic algorithm-based method succeeds in planning dietary menus that satisfy strict numerical constraints on every nutritional level (meal, daily basis, weekly basis). The rule-based assessment proved capable of manipulating the mean occurrence of the nutritional components thus providing a method for adjusting the variety and harmony of the menu plans. CONCLUSIONS: By splitting the problem into well determined sub-problems, weekly menu plans that satisfy nutritional constraints and have well assorted components can be generated with the same method that is for daily and meal plan generation.

Body surface potential field representation fidelity: analysis of map estimation procedures.

The first part of this study analyzed the spatial-temporal error distribution of the Lux-type limited lead system. Quantitative new evidence is reported that the 32-lead anterior subset estimates the further 160 leads with an average amplitude error less than 38.5 microV. The spatial error distribution revealed 8 sites where the error is the highest, primarily on the anterior side, independent of the clinical classification. The second part of the study examined inter-lead-system conversion strategies for interpolating the Lux-192 lead maps from the Montreal-63 data. The methodology based on the Laplacian interpolation yielded an average amplitude error of 143.7 microV and an average correlation of 0.87 for pattern fidelity. In this specific case a modified linear interpolation surpassed the Laplacian method. A presented example illustrates that even in cases when the fidelity of the signal information is heavily compromised the diagnostic information may remain less influenced.

Validity of viscoelastic models of blood vessel wall.

Quantitative description of biomechanical behaviour of the blood vessel wall is needed for understanding normal and pathologic functions of the vascular system. In this study we investigated the stress relaxation of blood vessels. Strips were cut from the vessel wall and they were stretched in a stepwise manner until they tore. The mechanical stress (approximately 10(5)-10(6) Pa) induced in the strips was determined. This showed an initial steep rise and then a slow, near exponential decay (stress relaxation) after each step of stretch. For the mathematical description we used two technical models (the Maxwell and the Kelvin model--they are built of two elastic elements and of one viscous element), as well as a one-dimensional continuum mechanical model. The moduli of the models were identified with a curve fitting method. Our aim was to compare these models in order to elucidate, which one describes the rheological behaviour of the blood vessel more correctly. The results of our analysis show that the corresponding moduli diverge from each other in the Maxwell and Kelvin models: that is, they depend on the mode of the assumed connection between the mechanical units. In contrast, moduli of the continuous model are unambiguous. We conclude that the continuous model properly describes the stress relaxation of the vascular wall. Its advantage over the technical models is that moduli describing the viscoelastic behaviour of the tissue do not depend on the not wholly well-known structure of the wall components.

The main elements of the information system of the National Stroke Program (Smart Card - Telecommunication - Knowledge Bases).

The mortality of stroke in Hungary is 208 out of 100,000 inhabitants, which is very high in an international comparison. The age-group most in danger is between 35 and 50. There are 40-50 thousand hospital admissions each year because of stroke, the majority of them are unexpected crisis cases. In 1992, the government announced the National Stroke Program, which includes prevention, emergency, acute treatment and rehabilitation. Simultaneously with the medical-professional program, the National Stroke Program Information System (NSPI) has also been launched. Its aim is the direct backing up of the medical activity, the aiding of epidemiological tasks and preventive follow-up of patients. The system consists of an interactive database network in that it can guarantee accessibility, thus making every endeavour to assist in solving medical-professional problems with the help of modern information technology (smart care, telecommunication-device, etc.).

Statistical interpretation of body surface potential maps; aspects of adequate group representation and parameter selection.

Nonparametric approaches for studying adequate group representation accuracy vs. sample size relationship and two discriminative parameter searching methods of statistical body surface map analysis are discussed. A clinical application of the selection methods supports that body surface potential mapping provides significant additional diagnostic information with respect to the conventional 12 lead ECG.

Nonparametric identification of discriminative information in body surface maps.

A nonparametric method, based on the Kolmogorov-Smirnov (K-S) test was used to detect significant differences between classes of body surface maps (BSPM's). By systematic application of the method throughout the cardiac cycle, discriminative spatio-temporal information can be identified. In a second method, a Sebestyen linear transformation (SLT) was derived to give estimates of pairwise, linear separability of clinical classes. The utility of the method was illustrated by the pairwise comparison of 40 normal subjects (NOR), 40 patients with anterior myocardial infarction (AMI), and 40 with inferior myocardial infarction (IMI). The application examples demonstrated that: a) diagnostic information in low potential amplitude regions may surpass that in high amplitude regions, b) probability distributions of characteristic features showed small overlap in NOR versus AMI and NOR versus IMI dichotomies although they were not linearly separable, and c) the single best separating potential sample in the K-S sense for NOR versus AMI or NOR versus IMI dichotomies recovered 88 and 73% of the SLT performance, respectively.

[Clinical value of body surface mapping in the diagnosis of ischemic heart disease]. / Terheléses testfelületi potenciál térképezés (surface mapping) klinikai értéke az ischaemiás szívbetegség diagnosztikájában.

A series of 137 patients suffered in clinically documented angina pectoris were analyzed by 12-lead exercise ECG, exercise body surface potential mapping and exercise thallium scintigraphic methods and the results were compared to that of selective coronary angiography and left ventriculography. If coronary artery stenosis were considered to be significant in the presence of more than 70% vessel narrowing, the sensitivity figures were 76, 93 and 88% for exercise 12-lead ECG, exercise body surface potential mapping and exercise thallium scintigraphy, respectively. In considering 50% coronary artery narrowing to be significant, the same figures were 78, 94 and 89%. Specificity figures at the same order were 59, 65 and 80% for more than 70%, and 64, 70 and 88% for more than 50% coronary obstructions. Exercise body surface potential mapping and exercise thallium scintigraphy applied parallelly gave a sensitivity of 100% and specificity of 53%. False-negative and false-positive exercise body surface potential mapping and thallium scintigraphic tests were analysed taking into consideration left ventricular function indices and respective patients. The authors suggest that the outstanding high sensitivity of the above mentioned two tests applied parallelly reveals that they highlights partially different aspects of coronary artery disease, and that is why the overlapping between the methods is relatively small. The majority of false-positive tests characterize a pathological state, and in these cases the exact diagnosis should be cleared up by other noninvasive/invasive methods.

Sample size and dimensionality in multivariate classification: implications for body surface potential mapping.

This paper presents empirically determined guidelines for specifying the number of features appropriate for multivariate classification studies for given sample sizes. Sample size was considered adequate if the mean distance between two sample sets, taken from the same continuous multivariate distribution and projected onto the best separating direction, remained below a prescribed level. To quantitate the sample size requirement, homogeneity of sample set pairs of equal size. N, taken from the same continuous multivariate distribution was studied as a function of dimensionality. M. Homogeneity was characterized by the maximum absolute distances (Dmax) between the corresponding pairs of empirical cumulative probability distributions on the best separating projection. Computer generated data sets were used to estimate the cumulative probability distribution, P(D)M.N, for sample sizes, N, ranging from 5 to 100 and the dimensionality, M, ranging from 1 to 4. An empirical relationship between the estimated step-polygons and the Kolmogorov type one dimensional limiting distribution L(z) has been established. Based on the sample size data of 34 key papers on clinical body surface potential mapping (BSPM) it is noted that in 30% of the cases only one, and in 6% of the cases only two parameters could be used for statistical group representation to ensure a reasonable reliability (Dmax less than 0.2). In 56% of the published cases the sample sizes could not guarantee this reliability even for one feature or parameter.

Sources of variability in normal body surface potential maps.

Within-group variability of body surface potential maps was assessed on data from 685 carefully validated normal subjects (348 men and 337 women). Sources of within-group variability were evaluated by subgrouping maps by patient sex, age, height, and weight. Contribution of reproducibility error to total variance was assessed in a separate group of 52 normal subjects in whom multiple maps were recorded. Total variance was significantly lower in women than in men. Total variance tended to decrease with age, and the greatest decrease occurred in men during the 3rd decade. The ratio of total variance to mean signal energy showed a slow decrease with age for each group. Results suggest that the dominant source of within-group variability arises from variability of cardiac electric sources while the influence of volume conductor variability is significantly less. Variability due to measurement reproducibility was approximately half of the total variance.

Detection and localization of ventricular preexcitation in Wolff-Parkinson-White syndrome (comparative study with body surface mapping).

21 patients with Wolff-Parkinson-White (WPW) syndrome were investigated through radionuclide imaging and body surface mapping. Ventricular preexcitation was localized by display of identical phase ventricular regions (phase display). In 79% of the cases radioisotope and body surface mapping methods have identical results for the site of preexcitation. In two patients of the control group (10 patients with Lown-Ganong-Levine (LGL) syndrome), false positive outside-of septum ventricular preexcitation was detected, i.e. an 80% specificity. It is concluded that phase display might be a suitable method in the diagnosis of WPW syndrome. The sensitivity of this method can be improved using several views.

Polarcardiographic (triaxicardiometric) study on the effect of isosorbide dinitrate on exercise-induced myocardial ischemia.

30 patients suffering from stable angina pectoris were studied by triaxicardiometric (polarcardiographic) method. Triaxicardiometry including the X, Y, Z Frank leads, azimuth (H degrees), elevation (V degrees) angle derivations and spatial magnitude (M) tracings were taken at rest and after submaximal bicycle ergometer exercise. After receiving 30 mg/day isosorbide dinitrate for a minimum of 5 days the whole procedure was repeated, stored by an analogue tape recorder and evaluated by a TPA/i computer. It has been stated that the method of triaxicardiometry has an excess sensitivity on the demonstration of ischemic alteration of anterior and posterobasal left ventricular wall compared to the traditional X, Y, Z leads. According to the pre- and post-exercise bicycle ergometer testing estimated by triaxicardiometry, isosorbide dinitrate caused a significant reduction of subendocardial myocardial ischemia.

Surface potential distribution on the human thoracic surface in left bundle branch block.

The sequences of myocardial excitation in the cases of human LBBB have been studied by the surface mapping technique. Analysis of the surface map patterns of 12 subjects has enabled 4 different types to be described. It is suggested that Type I represents a complete LBBB in the presence of an intact right bundle branch, while Types II and III show different degrees of conduction defect in the right bundle branch, too. The left ventricular activation of these 3 types has a similar pathway in phases II and III which is determined by orientation of the main subepicardial muscle layer coursing through the apex and terminating in the anterobasal region. The terminal anterobasal activation in the cases of LBBB has not only theoretical, but clinical significance, since in the presence of anteroseptal myocardial infarction the signs of necrosis must be hidden not in the early, but in the terminal parts of the QRS complex of conventional ECG. The lack of terminal anterior positivity of surface maps in the case of LBBB may be indicative of chronic anterior myocardial infarction.