Aiming at the heart sound envelope burr produced by Hilbert transform in the hidden semi-Markov model(HSMM)based on logistic regression, an HSMM combining support vector machine (SVM) and Shannon energy is proposed. First, the wavelet denoising method is used to denoise the heart sound, the heart sound is labeled according to the R peak and T wave, and the Shannon energy envelope and other characteristics are extracted. Then, the HSMM related parameters are trained based on the logistic regression model (LR), and the most possible state is deduced with the help of Viterbi algorithm. Finally, the first heart sound S1 and the second heart sound S2 are identified through the SVM model. The algorithm does not need to set a hard threshold, effectively suppresses noise, and is more helpful for envelope extraction. Experimental results show that the segmentation accuracy of the proposed algorithm is significantly improved compared with the reference algorithm, with good anti-noise performance and better segmentation results.
图1 降噪前后的信号对比Fig.1 Signal comparison before and after denoising
图2 原始信号与香农能量包络Fig.2 Original signal and Shannon energy envelope
图3 提取的心音分割算法流程图Fig.3 Algorithm flowchart of processed heart sound segmentation
图4 心音分割结果Fig.4 Heart sound segmentation result
图5 3种噪声在不同信噪比时的检出正确率Fig.5 Detection accuracy of three kinds of noise at different signal-to-noise ratios
表 1 脉冲噪声下评价指标对比Table 1 Comparison of evaluation indexes under impulsive noise