The Portable Four-lead Heart Sound Acquisition System

Cardiovascular diseases have been the main threaten to the people ’s health for a long time. With the improvement of people’s living standard, cardiovascular diseases rates are still rising year by year. Nowadays, auscultation is the commonly used method to evaluate the state of the cardiovascular system. Normally, cardiovascular diseases are mixed lesions so auscultation of a single position couldn’t provide the simultaneous pathologic information of multiple valves. Only the experienced doctors can make relatively accurate judgments and the diagnosis results are vulnerable to the auscultators’ subjective experience. Obviously, the research on improving the convenience and accuracy of the auscultation is of great importance.Given the problems above, a portable four-lead heart sound acquisition system is proposed in this thesis. And the physical design is also conducted during the research.For the convenience of the auscultation and data acquisition of the heart sound, a four-lead auscultation is acquired to detect the heart signal of the aortic, pulmonary, tricuspid and mitral synchronously. Compressed sensing is utilized to analyze the heart sound simply and waveforms of the heart sound are displayed and stored via MFC modules of Visual C++.In order to achieve the goals above, the research is conducted in the following respects:(1) Introduction to the heart sound. From the point of view of clinical medicine, the generation mechanism, basic characteristic, auscultation methods and contents are introduced. Introduction and comparison of the commonly used auscultation acquisition methods are conducted. Thus, the necessity of the design of the portable four- lead heart sound acquisition system is proved.(2) The hardware design of acquisition circuit. The hardware mainly consists of heart sound sensors, amplifier circuit, filter circuit, band trap circuit, A/D converter circuit, USB communication circuit and power circuit. In this chapter, the choice of components and calculation of the key parameters of the circuits are detailedly introduced. C ircuit simulation results and practical heart sound waveforms after t he processing of the analog circuit are given in the paper. Finally, several important rules during PCB layout are summarized.(3) The software design of the heart sound acquisition instrument. Firstly, the basic function and the workflow of the software are stated. Secondly, the data sending and receiving modules, waveforms display and data storage modules are introduced. Solutions comparison and part code of the heart sound waveforms display modules are provided for reference.(4) Application research of compressed sensing in heart sound acquisition. Firstly, the principle and applicable signals’ characteristic are introduced. Secondly, the sparsity of the heart sound is proved. The compressed sensing applies to the processing of the heart sound. Finally, sub-sampling( Not satisfied the N yquist theorem) heart sound signals are restructured via OMP arithmetic. The simulation and similarity analysis of the original and restructured heart sound signal are conducted respectively.Through the analysis of the main parts above, system test shows that synchronous acquisition of the four auscultation positions is realized. The auscultation instrument is useful in clinical heart sound acquisition and auscultation. It also lays a solid foundation of the following remote smart diagnosis system.