Viktor Avbelj

Jožef Stefan Institute | IJS · Department of Communication Systems

Optimal heart function depends on perfect synchronization between electrical and mechanical activity. In this pilot study, we aimed to investigate the electromechanical activity of the heart in healthy cats and cats with cardiomyopathy with phonocardiography (PCG) synchronized to an electrocardiography (ECG) pilot device. We included 29 cats (12 he...

The paper analyses the autonomy of a wireless body sensor that continuously measures the potential difference between two proximal electrodes on the skin, primarily used for measuring an electrocardiogram (ECG) when worn on the torso. The sensor is powered by a small rechargeable battery and is designed for extremely low power use. However, the aut...

Cardiovascular disease is among the leading causes of mortality in chronic obstructive pulmonary disease (COPD). Nonlinear heart rate variability (NHRV) measures are markers and predictors of cardiovascular disease, particularly arrhythmias. Our aim was to investigate NHRV in patients with COPD and changes after pulmonary rehabilitation. 20-minute...

Abstract - Analysis of synchronized phonocardiographic (PCG) and electrocardiographic (ECG) data provides insights into cardiac electromechanics that have previously not been investigated in the context of exercise-induced cardiac remodeling. This study aimed to obtain PCG data synchronized with ECG using an electronic stethoscope and an acoustic s...

Phonocardiogram, a graphic recording of auscultatory findings of the cardiac sound vibrations, was acquired through an add-on to a stethoscope: a microphone was inserted into the stethoscope tube and connected to a smart device. Phonocardiographic data were synchronised to electrocardiogram, a recording of cardiac electrical activity, that was obta...

A phonocardiographic device was constructed using a microphone connected to a stethoscope tube and a smartphone and synchronized with a wireless electrocardiographic sensor attached precordially to the animal's chest and connected to the smartphone via Bluetooth technology. Cardiac sounds and murmurs were recorded simultaneously with the animal's e...

The recent trend in electrocardiogram (ECG) device development is towards wireless body sensors applied for patient monitoring. The ultimate goal is to develop a multi-functional body sensor that will provide synchronized vital bio-signs of the monitored user. In this paper, we present an ECG sensor for long-term monitoring, which measures the surf...

Wireless body sensor, connected via Bluetooth technology to a smart device, was used to obtain ECG data in seven horses while they were standing, walking and trotting. Different positions of electrodes were tested. Measurements with the electrode distance of 8 cm, as proposed in the wireless sensor, gave reliable results only in standing horses, be...

Telesni EKG senzor, povezan preko Bluetooth tehnologije s pametno napravo, ki omogoča merjenje elektrokardiograma (EKG-ja), smo preizkusili pri 41 psih, 4 mačkah in 7 konjih. Primerjava s standardnim EKG-jem je pokazala, da je naprava zanesljiva za diagnostiko srčnega ritma, srčne frekvence ter standardnih meritev trajanja intervalov EKG-ja. Pri ko...

Background: Changes in cardiac autonomic regulation and P-wave characteristics are associated with the occurrence of atrial fibrillation. The purpose of this study was to evaluate whether combined preoperative non-invasive determination of cardiac autonomic regulation and PR interval allows for the identification of patients at risk of new-onset a...

Objectives To evaluate the diagnostic utility of electrocardiogram data obtained by a wireless sensor from 36 dogs and four cats with suspected arrhythmias caused by cardiac or systemic diseases. Materials and Methods Wireless electrocardiographic recordings were obtained via two precordial electrodes attached to an electrocardiogram sensor connec...

Heartbeat dynamics changes promptly and substantially in response to acute stress. This is due to direct neural connection of the heart and the central nervous system. An opportunity to analyze a video recording synchronized to a simultaneously recorded ECG arose after preparation of educational TV show about adrenaline. Although the scenario for t...

This monograph presents a comprehensive overview of the electrocardiography from the aspect of wireless and mobile monitoring and its potential for personalized health management. The topical focus is on the implementation and efficient application of user friendly m-Health systems. The target audience comprises biomedical engineers, medical doctor...

The chapter presents a clinical comparative study for obtaining in vivo measurements of intra-and extra-articular knee temperatures to assess the effectiveness of two cryotherapeutic methods-conventional cooling with gel-packs and computer-controlled cryotherapy with cryotherapeutic knee pad, both after anterior cruciate ligament reconstructive sur...

The use of ICT in the health care system is aimed to increase efficacy and decrease costs. We have designed a system and services for mobile monitoring of vital physiological parameters and environmental context. The system is based on a small multi-functional wireless body sensor for simultaneous measurement of ECG, temperature, heart rate, respir...

Background: The stability of an arterial baroreflex depends also upon the integrity of the afferent limb. For its quantification, we can use a noninvasive test such as baroreceptor sensitivity estimation during Valsalva manoeuvre. The aim of this study was to evaluate potential autonomic dysfunction in patients with unilateral severe carotid disea...

The introduction of information and communication technologies (ICT) into the integrated healthcare system could increase the self-management of health and therefore increase the efficacy and decrease the costs of overall health management. A personal mobile health monitoring system (PCARD) has been developed, which uses moderately-priced and user-...

Purpose: The arterial baroreflex depends on the integrity of the afferent limb, which can be quantified using the baroreceptor's sensitivity (BRS) during the Valsalva maneuver (VM). The aim of this study was to evaluate, using autonomic nervous system tests, the autonomic function in patients after a carotid artery angioplasty (CAS). Methods: We...

Presented is a wireless body sensor capable of measuring local potential differences on a body surface. By using on-sensor signal processing capabilities, and developed algorithms for off-line signal processing on a personal computing device, it is possible to record single channel ECG, heart rate, breathing rate, EMG, and when three sensors are ap...

Objectives. Arterial baroreflex plays a key role in short-term blood pressure balancing. It can also be quantified noninvasively with baroreceptor sensitivity during Valsalva manoeuver. The aim of the study was to evaluate the role of Valsalva manoeuver as a potential marker of possible autonomic dysfunction in patients after carotid artery angiopl...

Background: The multifractal approach of HRV analysis offers new insight into the mechanisms of autonomic modulation of the diseased hearts and has a potential to depict subtle changes in cardiac autonomic nervous control not revealed by conventional linear and non-linear analyses in various conditions like heart failure or stable angina pectoris....

The oscillometric method is the most widely used method for automatic non-invasive blood pressure measurements. An oscillometric device computes systolic and diastolic blood pressures from pressure oscillations in the cuff during slow deflation. Normally only the envelope of the pressure oscillations in the cuff is used. A closer look at these osci...

Respiration-related heart rate variability - respiratory sinus arrhythmia (RSA) - is clearly related to vagal activity. Usually it is analysed in frequency domain. An improved method for the assessment of the RSA in timedomain is proposed and evaluated on a control group of 12 healthy volunteers (9 male, 3 female; age 31-70). The method is based on...

Abstract Chronic obstructive pulmonary disease negatively affects the autonomic nervous system and increases risks of arrhythmias and sudden cardiac death. Electrocardiogram (ECG) recordings were used to compare parameters of heart rate variability and QTc interval in patients with COPD and healthy individuals. The effects of a 4-week program of re...

Body sensor networks for monitoring of bio-signals are technically feasible and economically relevant; however, their acceptance by patients and by medical experts is still not adequate. For patients, sensors are too obstructive, require technical skills, and introduce a perception of diminished safety and privacy. For medical experts, sensors and...

To obtain in vivo data about intra- and extra-articular knee temperatures to assess the effectiveness of two cryotherapeutic methods-conventional cooling with gel-packs and computer controlled cryotherapy following anterior cruciate ligament (ACL) reconstructive surgery. Twenty patients were arbitrarily assigned for cryotherapy after ACL reconstruc...

The beat-to-beat ST variability in the ECG signal is becoming an important indicator in neurocardiology. However, accurate determination of the ST variability is difficult because of uncertainty in the determination of the end point of the ST interval. T waves change their form because of breathing, heart movements, changing of lead positions etc....

A wireless multi-function biosensor that measures a potential difference between two proximal electrodes on the skin, enables monitoring of vital functions - heart activity and respiration. The sensor is designed as a small plaster-like reusable unit that can be easily fixed onto the body surface and is therefore minimally obtrusive for users. It i...

We propose a new body sensor for extracting the respiration rate based on the amplitude changes in the body surface potential differences between two proximal body electrodes. The sensor could be designed as a plaster-like reusable unit that can be easily fixed onto the surface of the body. It could be equipped either with a sufficiently large memo...

Visualization is a common way of data presentation in many fields where processing of visual information is further done by the human visual system. Signals from the heart (ECG) and from the brain (EEG) are normally presented as graphs and are also visually processed. Such signals can be transformed into sound (sonification) and then processed by t...

The spectrum of non-uniformly sampled signals is often needed for analysis of signals obtained from network of distributed sensors. In this paper, we analyze a method to retrieve the spectrum of this type of signals through interpolation, then re-sampling with uniform rate and performing Fourier transform at the end. We discuss this method based on...

A wireless bipolar body electrode has been developed, taking into account the limitations posed by signal-to-noise ratio, dimensions, wireless technology, limited power consumption and requirements for post-processing. A small set of wireless bipolar electrodes, placed at optimal locations on the body surface, are connected into a network that is a...

The development of new technologies for electrocardiographic (ECG) monitoring enables the optimization of ECG recording strategy, in terms of a number and a position of body electrodes. Emerging wireless technology, together with requirements for improved wearing comfort, dictates a special design of a wireless bipolar ECG lead, which is composed o...

An improved model of action potentials (AP) is proposed to increase the accuracy of simulated electrocardiograms (ECGs). ECG simulator is based on a spatial model of a left ventricle, composed of cubic cells. Three distinct APs, modeled with functions proposed by Wohlfard, have been assigned to the cells, forming epicardial, mid, and endocardial la...

Advanced nonlinear methods of measuring heart rate variability (HRV) derived from the mathematics of complex dynamics and fractal geometry have provided new insights into the abnormalities of heart rate behavior in various pathologic conditions. These methods have provided additional prognostic information compared with traditional HRV measures and...

De-novo ventricular arrhythmias are potentially life-threatening complications after beating-heart revascularization (off-pump CABG). Whether pulmonary hypertension can influence initiation of ventricular arrhythmias through increased sympathetic activity is controversial. In order to determine the influence of pulmonary hypertension on its relativ...

Non-linear analyses of heart rate dynamics reveal subtle changes not evident from conventional heart rate variability measures. Traditionally, the information was inferred from 24-hour ECG recordings, making it less suitable for clinical application. Moreover, only few studies have attempted to evaluate the reliability of non-linear analyses in rel...

An improved model of action potentials (AP) is proposed to increase the accuracy of simulated electrocar-diograms (ECGs). ECG simulator is based on a spatial model of a left ventricle, composed of cubic cells. Three distinct APs, modeled with functions proposed by Wohlfard, have been assigned to the cells, forming epicardial, mid, and endocardial l...

Arrhythmias attributable to altered autonomic modulation of the heart, with elevated sympathetic and depressed vagal modulation, occur to a similar extent after surgery performed on beating or arrested hearts. Coronary artery bypass grafting (CABG) with cardiopulmonary bypass has been associated with more frequent occurrence of arrhythmic events th...

Several hypotheses for the origin of the U wave in electrocardiograms have been proposed. We have set out to explore and test alternative modes for U-wave genesis via computer simulations. A spatial model of a left ventricle has been constructed from 12 layers composed of cubic cells. Each cell is assigned its own time-dependent action potential wi...

Reduced cardiac vagal modulation increases propensity to arrhythmias. Right decubitus position is a vagal enhancer in coronary and congestive heart disease. We evaluated vagal modulation before and after coronary artery bypass grafting (CABG) in 30 patients. Heart rate variability (HRV) indexes in frequency domain were calculated from 10-min digita...

Altered autonomic regulation after cardiac operations precipitates cardiac arrhythmias, affects repolarization, and increases the risk of sudden cardiac death. We sought to clarify how the 2 different techniques of coronary artery bypass grafting (CABG), namely conventional CABG using cardiopulmonary bypass (on-pump) and beating-heart CABG without...

Altered autonomic regulation precipitates cardiac arrhythmias and increases the risk of sudden cardiac death. This risk is further increased by changes in ventricular repolarization. Autonomic regulation is deranged in patients after myocardial on-pump revascularization. We aimed to clarify how off-pump coronary artery bypass grafting (CABG) affect...

The amount and the character of interactions among breathing, heart beating and blood pressure are important issues in the evaluation of neurological state of each individual, which can be characterized by baroreflex sensitivity (BRS). Baroreflex control of the heart rate and blood pressure is one of the basic mechanisms which determine the blood p...

Complete allograft denervation occurs during heart transplantation. Partial ventricular sympathetic reinnervation may develop one year or later after transplantation and can be measured with iodine-123-meta-iodobenziylguanidine (MIBG) uptake. Aim of this study was to assess sinus node sympathetic reinnervation measured with heart rate variability a...

The repolarisation variability in body surface electrocardiograms has been evaluated by beat-to-beat QT interval variability. Interpolated R-peak time and template T-wave matching algorithms were used to determine the characteristic time points of the R-wave and T-wave, respectively. The T-wave time can be determined accurately and robustly by sear...

The right lateral body position has been proposed as an effective vagal enhancer. However, the possibility of breathing affecting heart rate power spectra in different body positions has not been assessed. The level of vagal modulation in various body positions in normal subjects was estimated by calculating heart rate power spectra. The results su...

Non-uniform recovery of excitability may be essential in triggering malignant ventricular tachycardia after cardiac surgery. Thirty-five channels ECG was recorded for 6 min in 27 patients before and after heart surgery and in 20 control subjects. Off-line analysis was performed. RR interval duration, RR SD, QT SD and power spectra of RR variability...

Non-uniform recovery of myocardial excitability may be essential in triggering malignant ventricular tachycardia in patients after cardiac surgery. Beat-to-beat heart rate and QT interval variability was investigated in 27 patients scheduled for elective coronary artery bypass graft surgery (CABG) and 20 control subjects. 35 channel ECG was recorde...

Heart rate variability (HRV) and its assessment using power spectral analysis revealed a possibility to quantify the characteristics of autonomic nervous system, related cardiovascular status and sympathovagal interaction. This study was designed to assess vagal tone in supine and right recumbent position in normal healthy subjects as many maneuver...

Body surface potential maps (BSPMs) recorded during pace mapping provide an important non-invasive means for identifying local cardiac events; recent clinical studies demonstrated that endocardial pacing sites can be resolved within less than 10 mm. We sought to determine whether similar spatial resolution could be achieved during epicardial pacing...

In the prospective study the authors tested the hypothesis that successful aortocoronary by-pass procedure performed in reversible ischemic areas of the cardiac muscle can be documented by the study of ST-40 ms isointegral maps prior and after aortocoronary revascularization with the combination of dipyridamole stress testing. Eight patients (1 fem...

Multichannel ECG is an important instrumentation for experimental and clinical electrophysiology. Both the software and the front-end design issues are described for a 128 channel system which can record the signals up to 100 seconds. The basic analysis and presentation of the acquired ECG signals are also given with examples of body surface potent...

: The Multichannel ECG (MECG) is an important instrumentation for both experimental and clinical electrophysiology. Software design issues for a 128-channel ECG with 14bits A/D conversion, 1 kHz/channel sampling rate, 100 second recording time, and optical connection to a standard personal computer are described. Data I/O with DMA capabilities were...

The paper describes and analyses a method for locating metal implants based on the interaction of a conductive object with a weak alternating magnetic field. Theoretical values for the boundary of detectability and the boundary of localability are introduced to show some technical characteristics, the diagnostic feasibility and limitations of the m...

). Data rates are never enough accurate. This inaccuracy could produce temporary loss of information, because of the limited length of circular buffers. Therefore, a mechanism for compensation of such inaccuracies has to be embedded in each multiplex unit. To implement this request a specific part of the transmission frame is reserved for the infor...

Background: Cardiac vagal modulation is reduced in patients with coronary artery disease or previous myocardial infarction. The propensity to lethal arrhythmias and oxygen consumption is thus increased. The objective of the present study was to assess the effect of different techniques used in coronary artery bypass grafting (CABG), namely on-pump...