Heart-rate tuned comb filters for processing photoplethysmogram (PPG) signals in pulse oximetry

Figures

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  Fig. 1. a Time domain representation of a PPG signal extracted from experimental data—b Frequency domain representation of a PPG signal extracted from experimental data

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  Fig. 2. \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SpO}}_{{\text{2}}}$$\end{document}SpO2 Calculation procedure

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  Fig. 3. a Frequency domain representation of a noise contaminated experimental PPG waveform of fundamental frequency \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$f_{0}$$\end{document}f0 = 2.29 Hz—b Magnitude response of a tuned comb filter—c Frequency domain representation of the comb-filtered PPG waveform

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  Fig. 4. DST algorithm block diagram and DST plot for a noise-contaminated synthetic PPG signal of SNR of 0 dB. The \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SpO}}_{{\text{2}}}$$\end{document}SpO2 level calculated by the algorithm corresponds to the right-most peak in the DST plot (output power vs. \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SpO}}_{{\text{2}}}$$\end{document}SpO2 level)

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  Fig. 5. Calibration curves used for sensitivity study

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  Fig. 6. a DST plot on a clean synthetic PPG signal—b DST plot on noise-contaminated synthetic PPG signals (SNR = 0 dB). The red circle is the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SpO}}_{{\text{2}}}$$\end{document}SpO2 ground truth and the black ‘x’ is the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SpO}}_{{\text{2}}}$$\end{document}SpO2 level that the DST algorithm calculates. The \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SpO}}_{{\text{2}}}$$\end{document}SpO2 ground truth for both subplots was 97.5%

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  Fig. 7. Illustration of the phases of the exercise experimental profile along with Target Heart Rate (THR) intensity. Black boxes indicate the range of THR in each exercise phase

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  Fig. 8. \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SpO}}_{{\text{2}}}$$\end{document}SpO2 Root Mean Square Error using “Red over Infrared” approach and the DST-based algorithm, with and without a comb filter

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  Fig. 9. Histogram of 1000 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SpO}}_{{\text{2}}}$$\end{document}SpO2 levels calculated from red and infrared PPG signal with SNR = −10 dB using a “Red over Infrared” approach—b “Red over Infrared” approach preceded by a heart-rate tuned comb filter—c DST-based algorithm—d DST-based algorithm preceded by a heart-rate tuned comb filter

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  Fig. 10. Histogram of 1000 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SpO}}_{{\text{2}}}$$\end{document}SpO2 levels calculated from red and infrared PPG signal with SNR = 0 dB using a “Red over Infrared” approach—b “Red over Infrared” approach preceded by a heart-rate tuned comb filter—c DST-based algorithm—d DST-based algorithm preceded by a heart-rate tuned comb filter

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  Fig. 11. Histogram of 1000 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SpO}}_{{\text{2}}}$$\end{document}SpO2 levels calculated from red and infrared PPG signal with SNR = 10 dB using a “Red over Infrared” approach—b “Red over Infrared” approach preceded by a heart-rate tuned comb filter—c DST-based algorithm—d DST-based algorithm preceded by a heart-rate tuned comb filter

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  Fig. 12. \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SpO}}_{{\text{2}}}$$\end{document}SpO2 level calculations for an exercising subject on stages 1 to 8 (see Sect. 3.2 and Fig. 7). We used the “Red over Infrared” approach and DST-based algorithm with and without preprocessing of the PPG signals with the heart-rate tuned comb filter. \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SpO}}_{{\text{2}}}$$\end{document}SpO2 levels calculated using the abovementioned algorithms is compared to the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SpO}}_{{\text{2}}}$$\end{document}SpO2 levels calculated by Nonin 8000R sensor. The legends…