Instytut Podstawowych Problemów Techniki

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The presented paper concerns the technological aspects of the interface evolution in the nickel-silicon carbide composite during the sintering process. The goal of our investigation was to analyse the material changes occurring due to the violent reaction between nickel and silicon carbide at elevated temperatures. The nickel matrix composite with 20 vol pct SiC particles as the reinforcing phase was fabricated by the spark plasma sintering technique. The sintering tests were conducted with variable process conditions (temperature, time, and pressure). It was revealed that the strong interaction between the individual components and the scale of the observed changes depends on the sintering parameters. To identify the microstructural evolution, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy were used. The silicon carbide decomposition process progresses with the extension of the sintering time. As the final product of the observed reaction, new phases from the Ni-Si system and free carbon were detected. The step-by-step materials evolution allowed us to reveal the course of the reaction and the creation of the new structure, especially in the reaction zone. The detailed analysis of the SiC decomposition and formation of new components was the main achievement of the presented paper.

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Pulse wave velocity (PWV) is commonly used for assessing arterial stiffness and it is a useful and accurate cardiovascular mortality predictor. Currently, many techniques and devices for PWV measurement are known, but they are usually expensive and require operator experience. One possible solution for PWV measurement is photoplethysmography (PPG), which is convenient, inexpensive and provides continuous PWV results. The aim of this paper is validation of a new device for PPG sensor-based measurement of multi-site arterial PWV using a SphygmoCor XCEL (as the reference device) according to the recommendations of the Artery Society Guidelines (ASG). In this study, 108 subjects (56 men and 52 women, 20–91 years in 3 required age groups) were enrolled. The multi-site PWV was simultaneous measured by 7 PPG sensors commonly used in pulse oximetry in clinical settings. These sensors were placed on the forehead, and right and left earlobes, fingers and toes. Pulse transit time (PTT) was measured offline as the difference of time delay between two onsets of the pulse wave determined by the intersecting tangent method. The PWV was calculated by dividing the distance between PPG sensors by PTT. During PPG signals measurement, reference carotid to femoral PWV (cfPWV) was performed with a SphygmoCor XCEL system. The Pearson correlation coefficient (r) between the obtained PWV results was calculated. The Bland-Altman method was used to establish the level of agreement between the two devices. Mean difference (md) and standard deviation (SD) were also calculated. The multi-site PWV was highly correlated with accuracy at the ASG-defined level of “Acceptable” (md < 1.0 m/s and SD ≤ 1.5 m/s) with cfPWV: forehead - right toe (r = 0.75, md = 0.20, SD = 0.97), forehead - left toe (r = 0.79, md = 0.18, SD = 0.91), right ear - right toe (r = 0.79, md = 0.11, SD = 0.96), left ear - left toe (r = 0.75, md = 0.43, SD = 0.99), right ear - left toe (r = 0.78, md = 0.40, SD = 0.93), left ear - right toe (r = 0.78, md = 0.11, SD = 0.96), right finger - right toe (r = 0.66, md = 0.95, SD = 1.29), left finger - left toe (r = 0.67, md = 0.68, SD = 1.35). This study showed that PWV measured with the multi-site PPG system, in relation to the obtained numerical values, correlated very well with that measured using the commonly known applanation tonometry method. However, it should be noted, that the measured PWV concerns the central and muscular part of the arterial tree while the cfPWV is only for the central one. The best results were obtained when the proximal PPG sensor was placed on the head (ear or forehead) and the distal PPG sensor on the toe. PPG sensors can be placed in many sites at the same time, which provides greater freedom of their configuration. Multi-site photoplethysmography is an alternative method for PWV measurement and creates new possibilities for the diagnostics of cardiovascular diseases.

Słowa kluczowe:

photoplethysmography, pulse wave velocity, multi-site pulse wave velocity, pulse transmit time, arterial stiffness, cardiovascular diseases

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Cardiovascular disease (CVD) is one of the major causes of perioperative complications. Screening of patients referred to major surgery is a costly and time and resources- consuming process. The study aimed to assess the usefulness of an electronic stethoscope with dedicated analytical software operated by a nurse for detecting heart disease in patients prepared for major orthopedic surgery. The study group consisted of 137 patients aged (46 – 91) with defined cardiovascular diseases qualified for hip or knee replacement surgery and 94 healthy age-matched volunteers. Heart auscultation with Littmann lectronic stethoscope using Littmann® StethAssist™ Heart and Lung Sound Visualization Software software was conducted and analyzed by a trained nurse. The signal recorded was analyzed by the blinded researcher using dedicated custom- made algorithm. Finally, 91 signals (52 CVD (+) patients, 39 CVD (-) patients) were analyzed. Eventually a classifier with a sensitivity of 92% and a specificity of 97% was obtained in a group. The global accuracy of the classifier was 95%. Heart auscultation by nursing staff using Littmann® StethAssist™ Heart and Lung Sound Visualization Software with dedicated custom- made can be cheap and noninvasive method of identifying patients with cardiovascular disease made algorithm for arthroplasty.

Słowa kluczowe:

electronic stethoscope, heart auscultation, nurse, arthroplasty, cardiovascular disease

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A precise, multi-track system for the simultaneous, real-time measurement of electrocardiographic (ECG) and many photopletysmographic (PPG) signals is described. This system allows the calculation of pulse wave delay parameters such as pulse arrival time (PAT) and pulse transit time (PTT). The measurement system was built on a custom, real-time embedded system with multiple specific analogue-front-end devices. Signals were recorded on-line and data were processed off-line in the Matlab software. Testing of human subjects was carried out on a group of 16 volunteers. The system was capable of taking a measurement of one 24-bit ECG and eight 22-bit PPG tracks with high precision (input-referred noise 1.4 μV for ECG and about 20 pA for PPG). All signals are sampled simultaneously (phase shift between ECG and PPG is only 1.5 ms for 250 Hz frequency sampling). Significant differences in pulse wave delays were found for the 16 subjects studied (e.g. about 100 ms for PAT on a right toe, 40 ms for differential PAT on left-right toes and about 100 ms for PTT calculated for forehead-right toe pulse wave). The proposed system provides a simultaneous and continuous evaluation of pulse wave delays for the entire arterial bed. The proposed measurement methods are comfortable and can be used for a long time. Simultaneous measurements of pulse wave delays at various sites increase the reliability of measurement and create new possibilities for medical diagnosis.

Słowa kluczowe:

biomedical monitoring, cardiovascular diseases, pulse arrival time, pulse transit time, pulse wave delay, simultaneous measurement

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Układ oddechowy pacjenta jest początkowo diagnozowany przy zastosowaniu stetoskopu. Osłuchowa interpretacja zjawisk fizycznych jest skomplikowana i wymaga od lekarza doświadczenia oraz predyspozycji. W niniejszym artykule zaprezentowano system pomiarowy i oprogramowanie badawcze, a także proces generacji cech dystynktywnych szmerów oddechowych różnicujących przypadki chorobowe od zdrowych. Wybrane reprezentacje stanowią obiecującą podstawę do opracowania systemu klasyfikującego wspierającego proces diagnostyczny

Słowa kluczowe:

szmery oddechowe, klasyfikacja, cyfrowe przetwarzanie sygnałów

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W artykule przedstawiono koncepcję analizy spektralnej sygnałów fonokardiograficznych. Zaprezentowano wyniki analizy sygnałów zawierających od kilku do kilkunastu uderzeń serca oraz sygnałów krótkich zawierających pojedyncze uderzenie serca. Przedstawiono propozycje kilkudziesięciu widmowych cech dystynktywnych oraz ocenę ich przydatności w diagnostyce schorzeń kardiologicznych. (Multifaceted Spectral Analysis of Phonocardiographic Signals)

Słowa kluczowe:

fonokardiografia, elektrokardiografia, metrologia medyczna, tony serca, analiza spektralna

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