| Heart sound is one of the most important physiological signal in human body, the history of cardiac auscultation is more than 180 years. However, the heart sound detection is still only an accessorial tool to diagnose or evaluate cardiac function, because it lacks objective and quantitative indices. Internationally, animal experiments as well as invasive and noninvasive clinical trials for studying the relationship between heart sound and cardiac contractility showed that the amplitude of first heart sound is the standard measurement of cardiac contractility, which implys that heart sound signal can be used to study myocardial inotropism; The strict synchrony between ECG signal and heart sound signal implys that heart sound signal can be used to study myocardial chronotropism. This dissertation takes heart sound as study subject. A portable heart sound signal telemetry system is developed to study the subjects' five-minute myocardial inotropism and chronotropism following phonocardiogram exercise test and under quiescent status respectively, in order to provide quantitative indices for diagnosing or evaluating cardiac function in the fields such as clinical medicine and sports medicine, aiming to further expand the application fields and values of the heart sound signal detection technique. It mainly includes the following distinctive research work and conclusions:A portable heart sound signal telemetry system is developed to satisfy the demand of studying myocardial inotropism and chronotropism in mobile places such as sports site and hospital wards. It consists of telemetry transmitter, telemetry receiver, notebook computer. This telemetry system operates at the licence-free open frequency band of 433MHz and can telemeter 10 subjects' heart sound signals simultaneously ; The telemetry transmitter is carried by subject, and transmits a cardiac cycle-long heart sound signal each time with ECG's R wave synchronous pulse as the head mark of the telemetry data packet, So the notebook computer only needs a simple algorithm to extract cardiac contractility signal and heart rate signal quickly and exactly from the received telemetry data without telemetering ECG signal; By using specific-application USB interface module, the telemetry receiver realizes high speed data transmission with the notebook computer's USB port without extra power supply. Performance test shows that this telemetry system has reached the design requirement, and can be applied to study myocardial inotropism and chronotropism in mobile sites. A combined digital filter is constructed by an one-dimension morphological filter and a wavelet filter based on Stein Unbiased Risk Estimation rule to filter out small amplitude radio frequency interference pulses and system's random noise as well as cardiac murmur respectively. Test shows that it can filter out the main noise in the telemetry heart sound signal significantly, while the main components of the heart sound signal can be kept without obvious loss.Two heart sound signal's feature extraction algorithms are designed, one uses ECG's R wave to help localization, another is based on independent heart sound signal. Compared with the classical R wave localizaton algorithm, this dissertation's algorithm has the advantage of recognizing and determining the amplitude of S1 and S2 more quickly and exactly. For the feature extraction algorithm of independent heart sound signal, according to the similarity of waveform and generation mechanism between heart sound and speech, Some mature algorithms of segmenting and extracting speech signal's feature have been used as reference, and an algorithm based on using average Shannon energy to exact heart sound signal's energy envelope is put forward to recognize and determine the feature parameters of heart sound signal, which has better recognition rate.(4) By applying the developed portable heart sound signal telemetry system, five- minute continuous cardiac contractility and heart rate signals were sampled respectively from 50 students in... |
PDF Full Text Request