Abstract-Auscultation is an attractive, simple, and noninvasive method for the diagnosis of cardiovascular and pulmonary disorders. However, heart sounds contaminates severely lung sound recordings. The results of our previous researches indicated that the Laplacian electrocardiographic signal (LECG) could be used as a reference for adaptive filtering to reduce heart sounds. In this paper, an integrated platform including an electronic stethoscope, an automated gain control (AGC), and an adaptive algorithm, has been developed to process the signal in real time. The AGC algorithm allows amplifying the LECG signal in different scales to solve the problem of relative weak LECG signals at right chest. The experimental result shows that the heart-noise reduction at right chest is improved from 43% reported early to 75%. The overall heart sound reduction by our new scheme ranges from 75% to 83% at different chest locations. I INTRODUCTIONIn auscultation, heart sounds is an intrusive noise source in respiratory sounds. Simply using filtering technique cannot reject the unwanted signal, i.e. interference, effectively due to the overlapping in their spectra. Adaptive filtering may be the most suitable method to reduce intelligently the unwanted heart sounds in lung sound recordings. Nevertheless, adaptive scheme requires a "noise only" reference signal. In previous research [1], electrocardiographic (ECG) signal can be the reference signal, and this technique reduces the heart sounds by 50-80 percent. However, this technique requires at least two extra sensors to pick up the reference signal such as the lead II ECG. Another approach is to extract the "noise only" reference signal by a delayed version of original signal [2]. After the complex signal processing [3], a satisfactory result can be obtained. However, this scheme requires huge computation ability. Thus, it is difficult to implement those methods in a stethoscope for the real time applications.In this work, Laplacian ECG (LECG) [4] is used for the 'noise only' reference signal rather than standard ECG. Both the electronic signal -Laplacian ECG, and the acoustic signallung sounds mixed with heart sounds can be picked up by a newly designed stethoscope. A simple adaptive filtering, leastmean-square (LMS) is used to eliminate the interference. All hardware and software designs have been integrated together to make a single device to process the signal in real time (Fig. 1). Fig. 1 Stethoscope block diagramUsing the new stethoscope, lung sounds without heart sound interference have been obtained successfully. Moreover, the LECG waveform can be observed at the same time. II. SIGNAL PRE-PROPRESSINGTwo different signals, acoustic signal and electronic signal are picked up by a new type stethoscope. Raw acoustic signal was band-pass filtered from 25Hz to 1000Hz. The operational amplifier (Linear Technology LT1013) was used with the gain factor of 40. Raw LECG was filtered by a band-pass filter with the bandwidth of 5Hz to 500Hz, and the gain factor of 1000. The high in...

Heart sounds are the acoustic vibrations produced during the systole and diastole of the cardiac cycle. The art of evaluating the acoustic properties of heart sounds is known as heart auscultation. Heart auscultation has long been the most common technique for assessing the cardiac function of a patient. Conventional medical practice uses a mechanical stethoscope for auscultation. Often, the practitioners would need to rely on their hearing ability and their subjective judgement on the interpretation of the sounds. With the introduction of electronic stethoscopes, people are now hoping to measure and analyze heart sounds in a more objective manner. The rapid development in microchip technology in the past decade has resulted in electronic stethoscopes that are portable, robust to noise, and convenient to use. The future trend of electronic stethoscope would be a multifunctional auscultatory device with graphical display, wireless data transmission, real‐time signal processing for noise removal, selectable frequency response, etc. The newly developed electronic stethoscopes allow heart sounds to be digitally recorded and downloaded to a computer for analysis. Many of the computer‐based heart sound analysis techniques adopted by researchers, for example, wavelet transform and neural network, have already provided new insight into the diagnostic value of heart sound. The exploration of further techniques in the coming years would hopefully help to realize the full potential of heart sound auscultation as a tool the early detection of heart diseases.