How to use LabVIEW Biomedical Toolkit - Heart Rate Variability Analyzer

[Xuesong_Liu]

HRV Analyzer

An electrocardiogram (ECG) is commonly used in clinical applications to help doctors diagnose cardiac diseases such as tachycardia. Aside from directly analyzing an ECG, researchers and doctors also extract other indirect measurements from ECG signals. One of the most popular measurements is heart rate variability (HRV). HRV measurements analyze how RR intervals, which show the variation between consecutive heartbeats, change over time.

A normal one-cycle ECG signal is made up of several waves.

The peak with the highest amplitude is called the R wave. An RR interval is the time that elapses between two successive R waves. The lower peaks are the P wave, the T wave, and the U wave, respectively.

The HRV Analyzer is an application for extracting measurements from RR interval signals. This application includes the following features:

• Importing RR interval from text file or ECG feature file by ECG Feature Extractor.
• Synchronize RR intervals directly from ECG Feature Extractor.
• Preprocessing and analyzing RR interval signals for common time-domain and frequency-domain measurements defined by theand.
• Integrating advanced signal analysis, such as Gabor Spectrogram, Continuous Wavelet Transform Scalogram, and Recurrence Map.
• Printing analysis results or exporting as HTML file.

Importing RR Interval Signals

Complete the following steps to import an RR interval signal to the HRV Analyzer.

1. 1. In the RR source section, choose the source that you want to load RR intervals.
2. 2. Please choose the corresponding operation according to your selection in step 1.

(For Text RR file) Click Import Settings and choose the file you want to import (only .txt file supported), and click OK.

(For ECG file with annotations) Click Import Settings to display the File Settings dialog, click Browse button next to the File Path. Select file you want to import (only files generated by ECG Feature Extractor supported) and click OK. If the ECG signal contains multiple analysis results, select one from Annotation/comment list. Finally, click OK to close the dialog.

(For ECG Feature Extractor) Click Start, and wait until all RR intervals have been imported, then click Stop.

1. 3. Observe the RR interval signal in the RR interval plot.
2. 4. Right-click the location in the RR interval signal you want to begin analyzing and select Set as Start.
3. 5. Right-click the location in the RR interval signal you want to end analyzing and select Set as End.

Preprocessing RR Interval Signals

The HRV Analyzer supports preprocessing techniques, such as detrending and thresholding.

Complete the following steps to preprocess the RR interval signal you imported.

1. 1. Right-click in the RR interval plot and select Detrend? to apply detrending to the RR intervals.
2. 2. Right-click in the RR interval plot and select Threshold? to add thresholds to the RR intervals.
3. 3. Right-click in the RR interval signal you want to set as upper limit and select Set as Upper Limit.
4. 4. Right-click in the RR interval signal you want to set as lower limit and select Set as Lower Limit.
5. 5. You can click and drag the green lines to adjust the threshold values.

Analyzing RR Interval Signals

The HRV Analyzer supports the following signal analysis methods:

• Statistics
• Poincare Plot
• Fast-Fourier Transform (FFT) Spectrum
• Autoregressive (AR) Spectrum
• Short-Time Fourier Transform (STFT) Spectrogram
• Gabor Spectrogram
• Wavelet Coefficients
• Detrended Fluctuation Analysis (DFA) Plot
• Recurrence Map (RM) Plot
• You can add customized analysis method. Please refer to How to add a customized VI for Biosignal Logger and HRV Analyzer.
  

In the Signal Analysis section, select the signal analysis method you want to apply to the RR interval signal. If the method you select requires you to configure settings, click the Analysis Settings button to display the configuration dialog box of that method.

Note:  The Analysis Settings button is available only when the method you select contains settings that you can configure.

Exporting Analysis Results

The HRV Analyzer can export analysis results to HTML file. You can also print a report directly. Complete the following steps to generate a report:

1. 1. Click Report button to display the Export Report Configure dialog box.
2. 2. In the Report option section, specify whether you want to export analysis results by printing a report or by saving to an HTML file.
3. 3. Select the printer in the Printer list pull-down menu or specify the HTML file path in the File path text box.
4. 4. (Optional) Click the Options button to display the Report Options dialog box. You can customize the font and page settings of your report.
5. 5. In the Items list tree, select the measurements that you want to add to the report. You can select multiple items by using the <Shift> key or the <Control> key.
6. 6. Click the Export button to start generating report.

Following is an example of the generated report (only first page displayed):