Saulius Daukantas

A comparison of conductive textile-based and silver/silver chloride gel electrodes in exercise electrocardiogram recordings

BACKGROUND The goal of this study was to compare disposable silver/silver chloride and reusable conductive textile-based electrodes in electrocardiogram (ECG) signal monitoring during physical activity. MATERIALS AND METHODS The reusable electrodes were produced using thin silver-plated nylon 117/17 2-ply conductive thread (Statex Productions & Vertriebs GmbH, Bremen, Germany) sewed with a sewing machine on a chest belt. The disposable and reusable electrodes were compared in vivo according to ECG signal baseline drift, broadband electrode noise properties, and influence of electrode area to ECG signal morphology and frequency content. Twelve volunteers were included in this study. RESULTS Electroconductive textile-based ECG electrodes produce significantly more noise in a very low frequency band (0-0.67 Hz) and not significantly less of broadband noise (0-250 Hz) than disposable silver/silver chloride electrodes. Decreasing area of textile electrodes decreases fidelity of registered ECG signals at low frequencies. CONCLUSION Textile electrodes having adequate area can be used in more applications than only R-R interval monitoring.

Inertial sensor for objective evaluation of swimmer performance

In this paper, the development of an accelerometer based sensor and algorithms to extract useful information for evaluation of sportsman performance in swimming sport is presented. Several parameters were identified as useful and feasible to estimate from registered acceleration curves: ldquonumber of strokes per laprdquo, ldquoinstantaneous stroke raterdquo also durations of various swimming process intervals, periods and phases. Possible applications of extracted parameters were discussed.

Estimation of pulse arrival time using impedance plethysmogram from body composition scales

Long-term periodic monitoring of cardiovascular function in unobtrusive way has been a challenge in sensor research lately. This work presents the investigation of the method for pulse arrival time (PAT) estimation using body composition scales. It employs the electrocardiogram and the impedance plethysmogram (IPG) which are recorded from palm and plantar electrodes already integrated into body composition scales. Four subjects were involved in the experiment. The IPG was acquired from a single-foot and foot-to-foot and compared to the reference method - photoplethysmography. The range of correlation coefficient obtained in different methods varied from 0.7 to 0.94 showing that small PAT variations can be tracked using the IPG signals. Such results suggest that body composition scales could be supplemented with additional parameter for the assessment of arterial stiffness. This function will make them truly multi-parametric device for periodic health monitoring at home.

Assessment of pulse arrival time for arterial stiffness monitoring on body composition scales

This study presents a system that aims to estimate changes in arterial health status in an unobtrusive way. It might be especially useful in long-term self-monitoring of cardiovascular performance for successful treatment and empowerment of patients. This system applies the electrocardiographic and impedance plethysmographic signals acquired using modified body composition scales for the calculation of pulse arrival time, which is directly related to arterial stiffness. The proposed device was tested in a cohort of 14 subjects. The modified scales were compared to the commercial PulsePen tonometer and the results showed significant relationship between these different devices (rs=0.93, p<0.01). The system also showed the ability to track small pulse arrival time variations induced by paced respiration. These findings suggest that scales evaluating parameters of cardiovascular function have potential to become a convenient device for self-monitoring of arterial stiffness.

Algorithms and Results of Eye Tissues Differentiation Based on RF Ultrasound

Algorithms and software were developed for analysis of B-scan ultrasonic signals acquired from commercial diagnostic ultrasound system. The algorithms process raw ultrasonic signals in backscattered spectrum domain, which is obtained using two time-frequency methods: short-time Fourier and Hilbert-Huang transformations. The signals from selected regions of eye tissues are characterized by parameters: B-scan envelope amplitude, approximated spectral slope, approximated spectral intercept, mean instantaneous frequency, mean instantaneous bandwidth, and parameters of Nakagami distribution characterizing Hilbert-Huang transformation output. The backscattered ultrasound signal parameters characterizing intraocular and orbit tissues were processed by decision tree data mining algorithm. The pilot trial proved that applied methods are able to correctly classify signals from corpus vitreum blood, extraocular muscle, and orbit tissues. In 26 cases of ocular tissues classification, one error occurred, when tissues were classified into classes of corpus vitreum blood, extraocular muscle, and orbit tissue. In this pilot classification parameters of spectral intercept and Nakagami parameter for instantaneous frequencies distribution of the 1st intrinsic mode function were found specific for corpus vitreum blood, orbit and extraocular muscle tissues. We conclude that ultrasound data should be further collected in clinical database to establish background for decision support system for ocular tissue noninvasive differentiation.

Towards Long-term Monitoring of Atrial Fibrillation using Photoplethysmography

This study investigates the feasibility of long-term monitoring of atrial fibrillation (AF) using wrist-worn device, capable of acquiring photoplethysmogram (PPG) and motion data. Moreover, the performance of AF detectors, initially developed to detect AF in electrocardiogram (ECG) signals, is evaluated on PPG. The study population consisted of 12 patients undergoing cardiac rehabilitation. Based on accelerometer data, 65% of recording time was considered as motion-free, which resulted in 86.8 hours of data with AF and 85.4 hours without. The performance of AF detectors was found to be comparable when both ECG and PPG are used for constructing heart rhythm series. Considering that 2/3 of monitoring time PPG was of satisfactory quality, the wrist-worn device has potential to be applied for long-term mass screening of target population.

General Data Format Security Extensions for Biomedical Signals

Biosignals recorded using personal health devices and stored in General Data Format (GDF) are vulnerable when the data is transferred, processed and stored to the external servers. The aforementioned vulnerabilities influence data security and user’s privacy. In this paper, we propose modifications of GDF format that enables the encryption both - personal data and biosignals. These modifications do not corrupt the intrinsic structure of the GDF format and allow to encrypt independently the header with personal data and the section of biosignals. The proposed modifications were implemented, embedded and tested in a personal health device – multiparametric scale. The header data and biosignals are encrypted directly in the scale, and saved in the micro-SD card using our modified GDF format. Finally, we present the required resources needed for encryption process.

Video and inertial sensors based estimation of kinematical parameters in swimming sport

The purpose of this study was to investigate if tracking of kinematical parameters (longitudinal acceleration, velocity and pitch angle) in swimming sport is feasible using data acquired with inertial sensors: accelerometer and gyroscope. Video data analysis combined “video + inertial sensor” and “inertial sensors only” methods are presented for estimation of kinematical parameters. The equation for estimation of longitudinal acceleration from inertial sensors data is derived and complementary filter for estimation of pitch angle variation is proposed. The inertial sensor based kinematical parameters are compared with video data analysis and electromagnetic tracking system derived parameters.

Digital filter in hardware loop for on line ECG signal baseline wander reduction

This paper presents the method for the ECG signal baseline wander reduction and prevention the analog to digital converter from saturation. The method is based on digital low pass filter in feedback loop. The digital filter estimates the ECG signal low pas variation (<0,5Hz) and via digital to analog converter feeds back the signal to reference input of instrumentation amplifier. The change of the signal voltage at the reference input is opposite in sign to the change of the signal at instrumentation amplifier input. Thus the baseline wander is significantly reduced. The method is suitable for on line processing of ECG signals, is resistant to high motion intensities and can be implemented using low power mixed signal microcontrollers.

Simplified approach investigating non-linear transformations of ultrasound diagnostics signals

Progress of medical ultrasonic diagnostics systems and methods is strongly dependent on new research findings in non-linear interaction of waves and tissues. Advanced and complex solutions of non-linear ultrasound signals transformations in tissues are developed. Developments are based on derivation of second order differential equations, their calculations using finite elements or finite difference methods. These methods we found very complex to study and explaining separately diffraction, attenuation and non-linear interaction effects. The paper aims to discuss simplified method for analysis of non-linear transformations. Solution is based with few assumptions on ultrasound elementary waves superposition and aperture impulse spatial response calculation.