Expand the EKG time scale by clicking on <--> in the EKG plot frame and scroll to 260 seconds by clicking the right arrow (>). The EKG plot should appear as shown below with the missed beat clearly visible:
Click on the 'o' peak marker to the left or right of the missed beat to select it (turning it red). Next in the 'Peaks' frame click on the appropriate button 'Add Left' or 'Add Right' to approximately place a new 'o' peak marker over the missed peak (actually, it is placed half way between the selected peak and previous/next peak).
Select the new peak and use the Up/Down/Left/Right buttons in the Move Peak frame to move it onto the missed peak.
Increasing (-><-) and zeroing (<) the time scale reveals (below) in the IBI window that all missed beats have been found and corrected. Interbeat interval data can be saved to a text file by clicking the IBIs button in the Save frame. Ten hertz spline interpolated IBI data can be saved by clicking the IBIspline button. It is probably best to save both output files.
The HRV frame in the EkgControl window displays several important parameters: natural log power LF(0.04-0.15Hz); HF(0.15-0.40 Hz RSA); LF/HF ratio and heart rate.
Some EKG data files may not be so easy to clean. It may be necessary to raise or lower the threshold (cyan line) and click on the Find Peaks button in order to improve on the initial peak picks. For good estimates of respiratory sinus arrythmia (RSA), it's best to have several minutes of good data. UPDATE (July 2008): Added ability to read in text respiration files, select epoch of good data and get an estimate of the power spectrum of the respiration allowing for a more accurate estimate of respiratory sinus arrythmia (RSA). Also added the ability to select a peak marker and move it by clicking on a new location. Currently this update is a separate version of processHRV. In order to run it you need to remove the Matlab path to the old version and add the path to the update At Brodgen: rmpath /d1/local/matlab/HRV/processHRV addpath /d1/local/matlab/HRV/processHrvResp At Keck: rmpath /apps/brogden/matlab/HRV/processHRV addpath /apps/brogden/matlab/HRV/processHrvResp After starting processHRV the updated interface will look like: Notice that the EkgControl window now has additional buttons in the second column. These allow the user to move the lower and upper bounds of the high frequency (HF/RSA) range in order to get a better estimate of RSA if respiration data are available. Click the Plot button in the respiratory frame to open the respiration data file recorded at the same time as the EKG data. Choose the correct file from the file open dialog. The respiration data are then plotted in red above the EKG data in the top plot window. Two vertical white lines in the respiration plot can be used to select a continuous section of good data for estimating the power spectrum of the respiration data. These lines can be moved by clicking on one or the other to select it then moving the cursor to a new location and clicking the left mouse button. The respiratory power spectrum is plotted in the PSD window in red. As described above the low and high HF boundaries can be moved to match the respiratory range and thus show a better estimate of RSA in the HF window.
Click here for a detailed description of heart rate variability data processing.