ecgdemo.m

MATLAB Program:

%   We are processing two data samples to demonstrate two different situations

for demo = 1:2:3

    %   Clear our variables

    clear ecg samplingrate corrected filtered1 peaks1 filtered2 peaks2 fresult

   

    %   Load data sample

    switch(demo)

        case 1,

            plotname = 'Sample 1';

            load ecgdemodata1;

        case 3,

            plotname = 'Sample 2';

            load ecgdemodata2;

    end

   

    %   Remove lower frequencies

    fresult=fft(ecg);

    fresult(1 : round(length(fresult)*5/samplingrate))=0;

    fresult(end - round(length(fresult)*5/samplingrate) : end)=0;

    corrected=real(ifft(fresult));

   

    %   Filter - first pass

    WinSize = floor(samplingrate * 571 / 1000);

    if rem(WinSize,2)==0

        WinSize = WinSize+1;

    end

    filtered1=ecgdemowinmax(corrected, WinSize);

   

    %   Scale ecg

    peaks1=filtered1/(max(filtered1)/7);

    %   Filter by threshold filter

    for data = 1:1:length(peaks1)

        if peaks1(data) < 4

            peaks1(data) = 0;

        else

            peaks1(data)=1;

        end

    end

    positions=find(peaks1);

    distance=positions(2)-positions(1);

    %   Returns minimum distance between two peaks

    for data=1:1:length(positions)-1

        if positions(data+1)-positions(data)<distance

            distance=positions(data+1)-positions(data);

        end

    end

    % Optimize filter window size

    QRdistance=floor(0.04*samplingrate);

    if rem(QRdistance,2)==0

        QRdistance=QRdistance+1;

    end

    WinSize=2*distance-QRdistance;

   

    % Filter - second pass

    filtered2=ecgdemowinmax(corrected, WinSize);

    peaks2=filtered2;

    for data=1:1:length(peaks2)

        if peaks2(data)<4

            peaks2(data)=0;

        else

            peaks2(data)=1;

        end

    end

%% This part of the code between the double comments is added by Surya Penmetsa

    positions2=find(peaks2);

    distanceBetweenFirstAndLastPeaks = positions2(length(positions2))-positions2(1);

    averageDistanceBetweenPeaks = distanceBetweenFirstAndLastPeaks/length(positions2);

   

    averageHeartRate = 60 * samplingrate/averageDistanceBetweenPeaks;

   

    disp('Average Heart Rate = ');

    disp(averageHeartRate);

% The code written by Surya Penmetsa Ends here.

%%

   

    %   Create figure - stages of processing

    figure(demo); set(demo, 'Name', strcat(plotname, ' - Processing Stages'));

    %   Original input ECG data

    subplot(3, 2, 1); plot((ecg-min(ecg))/(max(ecg)-min(ecg)));

    title('\bf1. Original ECG'); ylim([-0.2 1.2]);

    %   ECG with removed low-frequency component

    subplot(3, 2, 2); plot((corrected-min(corrected))/(max(corrected)-min(corrected)));

    title('\bf2. FFT Filtered ECG'); ylim([-0.2 1.2]);

    %   Filtered ECG (1-st pass) - filter has default window size

    subplot(3, 2, 3); stem((filtered1-min(filtered1))/(max(filtered1)-min(filtered1)));

    title('\bf3. Filtered ECG - 1^{st} Pass'); ylim([0 1.4]);

    %   Detected peaks in filtered ECG

    subplot(3, 2, 4); stem(peaks1);

    title('\bf4. Detected Peaks'); ylim([0 1.4]);

    %   Filtered ECG (2-d pass) - now filter has optimized window size

    subplot(3, 2, 5); stem((filtered2-min(filtered2))/(max(filtered2)-min(filtered2)));

    title('\bf5. Filtered ECG - 2^d Pass'); ylim([0 1.4]);

    %   Detected peaks - final result

    subplot(3, 2, 6); stem(peaks2);

    title('\bf6. Detected Peaks - Finally'); ylim([0 1.4]);

    %   Create figure - result

    figure(demo+1); set(demo+1, 'Name', strcat(plotname, ' - Result'));

    %   Plotting ECG in green

    plot((ecg-min(ecg))/(max(ecg)-min(ecg)), '-g'); title('\bf Comparative ECG R-Peak Detection Plot');

    %   Show peaks in the same picture

    hold on

    %   Stemming peaks in dashed black

    stem(peaks2'.*((ecg-min(ecg))/(max(ecg)-min(ecg)))', ':k');

    %   Hold off the figure

    hold off

end