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Figure 1:

A typical recorded PCG signal [1]. PCG, phonocardiogram.
A typical recorded PCG signal [1]. PCG, phonocardiogram.

Figure 1(a):

Various phases engaged in PCG analysis [2]. PCG, phonocardiogram.
Various phases engaged in PCG analysis [2]. PCG, phonocardiogram.

Figure 1(b):

Graphical representation of various steps involved in PCG signal classification [2, 14]. PCG, phonocardiogram.
Graphical representation of various steps involved in PCG signal classification [2, 14]. PCG, phonocardiogram.

Figure 2:

Characteristics of various kinds of Heart Sounds. AR, aortic regurgitation; AS, aortic stenosis; MR, mitral regurgitation; MS, mitral stenosis; MVP, mitral valve prolapse; PDA, patent ductus arteriosus; PR, pulmonary regurgitation; PS, pulmonary stenosis; TR, tricuspid regurgitation; TS, tricuspid stenosis; VSD, ventricular septal defect.
Characteristics of various kinds of Heart Sounds. AR, aortic regurgitation; AS, aortic stenosis; MR, mitral regurgitation; MS, mitral stenosis; MVP, mitral valve prolapse; PDA, patent ductus arteriosus; PR, pulmonary regurgitation; PS, pulmonary stenosis; TR, tricuspid regurgitation; TS, tricuspid stenosis; VSD, ventricular septal defect.

Figure 3(a):

Schematic diagram of sensors, pre-amplifier, and filters used in PCG signal analysis. PCG, phonocardiogram.
Schematic diagram of sensors, pre-amplifier, and filters used in PCG signal analysis. PCG, phonocardiogram.

Figure 3(b):

Schematic diagram of PCG signal acquisition system. PCG, phonocardiogram.
Schematic diagram of PCG signal acquisition system. PCG, phonocardiogram.

Figure 4:

Block diagram of ANC. ANC, adaptive noise canceller.
Block diagram of ANC. ANC, adaptive noise canceller.

Figure 5:

Block diagram of ALE. ALE, adaptive line enhancer.
Block diagram of ALE. ALE, adaptive line enhancer.

Figure 6:

Block diagram of Heart Sound preprocessing.
Block diagram of Heart Sound preprocessing.

Figure 7:

Normalization process.
Normalization process.

Figure 8:

Different segments in Heart Sound.
Different segments in Heart Sound.

Figure 9:

Reduction in data size due to feature extraction.
Reduction in data size due to feature extraction.

Figure 10(a):

PCG of a normal cardiac Heart Sound. PCG, phonocardiogram.
PCG of a normal cardiac Heart Sound. PCG, phonocardiogram.

Figure 10(b):

Shannon energy envelogram of the PCG of a normal Heart Sound. PCG, phonocardiogram.
Shannon energy envelogram of the PCG of a normal Heart Sound. PCG, phonocardiogram.

Figure 11:

Flowchart of the method used.
Flowchart of the method used.

Figure 12:

Schematic diagram of Heart Sound analysis using DWT. ANFIS, adaptive neuro fuzzy inference system; DWT, discrete wavelet transform; DT-CWT, dual tree complex wavelet transform.
Schematic diagram of Heart Sound analysis using DWT. ANFIS, adaptive neuro fuzzy inference system; DWT, discrete wavelet transform; DT-CWT, dual tree complex wavelet transform.

Figure 13:

PCG analysis of different types of Heart Sounds [41, 39, 49]. PCG, phonocardiogram.
PCG analysis of different types of Heart Sounds [41, 39, 49]. PCG, phonocardiogram.

Figure 14(a):

Different coefficients in DWT [121, 122]. DWT, discrete wavelet transform.
Different coefficients in DWT [121, 122]. DWT, discrete wavelet transform.

Figure 14(b):

Flow chart of DWT [121, 122]. DWT, discrete wavelet transform.
Flow chart of DWT [121, 122]. DWT, discrete wavelet transform.

Figure 15:

Time-domain analysis of different Heart Sounds using wavelet transform [121, 122]. AR, aortic regurgitation; MS, mitral stenosis.
Time-domain analysis of different Heart Sounds using wavelet transform [121, 122]. AR, aortic regurgitation; MS, mitral stenosis.

Figure 16:

Time (a) and frequency (b)-domain analysis of different PCG signals using DWT. AS, aortic stenosis; DWT, discrete wavelet transform; MR, mitral regurgitation; MS, mitral stenosis; MVP, mitral valve prolapse; PCG, phonocardiogram.
Time (a) and frequency (b)-domain analysis of different PCG signals using DWT. AS, aortic stenosis; DWT, discrete wavelet transform; MR, mitral regurgitation; MS, mitral stenosis; MVP, mitral valve prolapse; PCG, phonocardiogram.

Figure 17(a,b):

(a). Amplitude distribution of Normal Heart. (b). Amplitude distribution of Abnormal Heart.
(a). Amplitude distribution of Normal Heart. (b). Amplitude distribution of Abnormal Heart.

Figure 17(c):

Amplitude distribution of Murmurs.
Amplitude distribution of Murmurs.

Figure 18:

Comparison of different Heart Sounds.
Comparison of different Heart Sounds.

Figure 19:

Earlier studies on deep-learning-based methods for cardiac sound classification.
Earlier studies on deep-learning-based methods for cardiac sound classification.

Figure 20:

Convolution operation [131, 132].
Convolution operation [131, 132].

Figure 21:

Comparison of machine-learning and deep-learning architectures.
Comparison of machine-learning and deep-learning architectures.

Figure 22:

Architecture of CNN model [137] for Heart Sound classification.
Architecture of CNN model [137] for Heart Sound classification.

Figure 23:

PCG signal classification based on deep-learning models [138, 139]. PCG, phonocardiogram.
PCG signal classification based on deep-learning models [138, 139]. PCG, phonocardiogram.

Figure 24:

Application of Heart Sound classification method adopted by a medical practitioner [140, 141].
Application of Heart Sound classification method adopted by a medical practitioner [140, 141].

Figure 25:

Study of machine-learning vs. deep-learning methods for cardiac sound classification [148, 149, 150].
Study of machine-learning vs. deep-learning methods for cardiac sound classification [148, 149, 150].

Figure 26:

Schematic block diagram of Le Net.
Schematic block diagram of Le Net.

Figure 27:

Schematic block diagram of Alex Network.
Schematic block diagram of Alex Network.

Figure 28:

Schematic block diagram of VGG 16.
Schematic block diagram of VGG 16.

Figure 29:

Schematic block diagram of VGG 19.
Schematic block diagram of VGG 19.

Figure 30:

Schematic block diagram of Dense Net 121.
Schematic block diagram of Dense Net 121.

Figure 31:

Schematic block diagram of Squeeze Net.
Schematic block diagram of Squeeze Net.

Figure 32:

Schematic block diagram of Mobile Net 5.9 Inception Net Model.
Schematic block diagram of Mobile Net 5.9 Inception Net Model.

Figure 33:

Schematic block diagram of Inception Net 5.10 Residual Net Model.
Schematic block diagram of Inception Net 5.10 Residual Net Model.

Figure 34:

Schematic block diagram of Residual Net.
Schematic block diagram of Residual Net.

Figure 35:

Study of all CNN-based deep-learning models [142, 143].
Study of all CNN-based deep-learning models [142, 143].

Figure 36:

Deep neural network based model architecture [144, 145].
Deep neural network based model architecture [144, 145].

Figure 37:

Architecture of a machine-learning algorithm like Random Forest [146, 147].
Architecture of a machine-learning algorithm like Random Forest [146, 147].

Heart Sound frequencies found in various abnormal Heart Sounds.

Heart Sound Lowest frequency (Hz) Highest frequency (Hz)
First Heart Sound 100 200
Second Heart Sound 50 250
AR 60 380
PR 90 150
AS 100 450
PS 150 400
ASD 60 200
VSD 50 180
MR 60 400
TR 90 400
MS 45 90
TS 90 400
MVP 45 90
PDA 90 140
Flow murmur 85 300

Comparison of training and validation performance metrics of CNN-based deep-learning models.

System Training loss Training accuracy Validation loss Validation accuracy
LENET-5 0.4352 0.7089 0.4757 0.6799
Alex Net 0.3476 0.7379 0.3837 0.7199
VGG16 0.2979 0.8102 0.3134 0.7978
VGG19 0.2692 0.8709 0.2899 0.8469
DENSENET121 0.2476 0.9087 0.2665 0.8876
Squeeze Network 0.2097 0.9265 0.2098 0.8906
Mobile Network 0.1576 0.9435 0.1376 0.9073
Inception Network 0.0472 0.9843 0.0654 0.9863
Residual Network 0.0432 0.9856 0.0533 0.9892
Xception Network 0.0320 0.9951 0.0325 0.9926

A study of PCG signal and their gap analysis reported in the literature

Ref. Author Year Methodological problem and research gap analysis Features
[15] Dewangan et al. 2018 Basic features used in the time domain only Heart Sound analysis using the DWT method
[16] Thomas Schanze 2017 Biomedical heart signal analysis not using latest machine-learning and deep-learning methods Singular value decomposition
[17] Othman and Khaleel 2017 Only time-domain analysis has been made PCG signal analysis using Shannon Energy Envelop and DWT method
[18] Martinek et al. 2017 PCG signal analysis applicable to fetal heart only, not real-time human subjects Adaptive filtering based fetal heart rate monitoring
[19] Abhijay Rao 2017 It is a survey paper only, not a research paper Biomedical signal processing
[20] Sh-Hussain et al. 2016 Frequency domain and statistical domain features need to be analyzed Heart Sound monitoring system using wavelet transformation
[21] Prasad and Kumar 2015 Real-time PCG signal analysis was not applied Analysis of various DWT methods for feature extracted PCG signals
[22] Pan et al. 2015 Real-time analysis not done Categorization of PCG signals using multimodal features
[23] Lubaib and Muneer 2015 More features need to be considered for this analysis Using pattern recognition techniques
[24] Roy et al. 2014 No proper experimentation has been done A survey on classification of PCG signals
[25] Mishra et al. 2013 It deals with PCG signal noise removal only, not classification Denoising of Heart Sound signal using DWT
[26] Zhao et al. 2013 PCG signal/Heart Sound biometric Marginal Spectrum Analysis
[27] Singh and Cheema 2013 Limited application of deep-learning algorithms has been used Classification using Feature Extraction
[28] Safara et al. 2013 Only time-domain analysis has been made Multi-level basis selection of wavelet
[29] Salleh et al. 2012 PCG signal analysis using Kalman filter, not using any standard deep-learning method Heart Sound analysis: a Kalman filter-based approach
[30] Misal and Sinha 2012 It deals with PCG signal noise removal only, not classification Denoising of PCG signal using DWT
[31] Kasturiwale 2012 Biomedical signal analysis, limited features. Analysis using component extraction
[32] McNames and Aboy 2008 It deals with the modeling part of PCG signals, not the classification and analysis Techniques, statistical modeling of PCG signals
[33] Ahmad et al. 2009 More feature extraction needs to be done for the PCG signal analysis Classification of PCG signal using an Adaptive Fuzzy Inference System.
[34] Debbal and Bereksi-Reguig 2006 Time-domain analysis in time domain only PCG signal analysis using the CWT
[35] Gupta et al. 2005 A real-time PCG signal analysis was not done Segmentation and categorization of Heart Sound for analysis purpose.
[36] Muthuswamy 2004 It is a survey paper only, not a research paper Biomedical signal analysis

Comparison of performance metrics in various CNN-based deep-learning models.

System Accuracy (%) Precision (%) Recall (%) F1 Score (%) Train time (s) Test time (s)
LeNet-5 68.97 69.75 67.44 66.68 1086 1135
Alex Net 72.34 70.74 73.88 71.24 1233 1337
VGG16 74.08 75.29 75.08 75.13 1352 1011
VGG19 82.17 83.33 82.19 84.21 1343 947
DenseNet121 92.47 93.55 93.47 94.48 1201 937
Squeeze Network 93.57 92.65 94.79 93.56 1098 1012
Mobile Network 95.09 94.35 95.68 93.46 890 987
Inception Network 96.96 98.17 98.96 97.02 710 974
Residual Network 97.32 98.42 98.32 98.35 783 1056
Xception Network 99.13 98.18 98.43 99.19 750 865
Efficient Network-B3 99.49 98.62 98.72 99.37 786 854

Different sensors used in real-time Heart Sound analysis methods.

Denoising domain Type of sensors used Number of sensors Algorithm adopted
Time Electret condenser microphone 1 LMS-ANC
Time Electronic stethoscope 1 Single input ANC
Time Microphone 1 LMS-ALE, RLS-ALE
Frequency Electronic stethoscope with an electret microphone 1 DWT, Hilbert transform
Frequency Microphone 1 DWT, LMS-ALE, RLS-ALE
Frequency NM NM EMD

A summary of CNN and RNN based methods used in PCG signal analysis [108, 109].

S. No. References Methods Features used Segmentation optimizer Types of PCG signal
1 Maknickas and Maknickas 2017 [55] 2D-CNN MFSC No RMSprop N, A
2 Alafif et al. 2020 [56] 2D-CNN + transfer learning MFCC No SGD N, A
3 Deng et al. 2020 [54] CNN + RNN Improved MFCC No Adam N, A
4 Abduh et al. 2019 [57] 2D-DNN MFSC No Adam N, A
5 Chen et al. 2018 [58] 2D-CNN Wavelet transform + Hilbert–Huang features No Adam N, M, EXT
6 Rubin et al. 2016 [59] 2D-CNN MFCC Yes Adam N, A
7 Nilanon et al. 2016 [60] 2D-CNN Spectrograms No SGD N, A
8 Dominguez-Morales et al. 2018 [61] 2D-CNN Spectrograms No Adam N, A
9 Bozkurt et al. 2018 [62] 2D-CNN MFCC + MFSC Yes Adam N, A
10 Chen et al. 2019 [63] 2D-CNN MFSC No Adam N, A
11 Cheng et al. 2019 [64] 2D-CNN Spectrograms No Adam N, A
12 Demir et al. 2019 [65] 2D-CNN Spectrograms No Adam N, M, EXT
13 Ryu et al. 2016 [66] 1D-CNN 1D time-series signals No SGD N, A
14 Xu et al. 2018 [67] 1D-CNN 1D time-series signals No SGD N, A
15 Xiao et al. 2020 [68] 1D-CNN 1D time-series signals No SGD N, A
16 Oh et al. 2020 [69] 1D-CNN WaveNet 1D time-series signals NO Adam N, AS, MS, MR, MVP
17 Khan et al. 2020 [70] LSTM MFCC No Adam N, A
18 Yang et al. 2016 [71] RNN. 1D time-series signals No Adam N, A
19 Raza et al. 2018 [72] LSTM 1D time-series signals No Adam N, A
20 Tschannen et al. 2016 [73] 2D-CNN + SVM Deep features Yes Adam N, A
eISSN:
1178-5608
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Calendario de la edición:
Volume Open
Temas de la revista:
Engineering, Introductions and Overviews, other