PC-Based ECG Monitoring and Analysis Using BioBench

National Instruments has been a leader in the field of test and measurement and PC automation for years, supplying products for instrument control, data acquisition (DAQ), and industrial automation. Besides making hardware, National Instruments has created powerful software tools including LabVIEW, the graphical programming environment. Combining programmable software and data acquisition hardware, National Instruments provides solutions leveraging off the power of the PC. From the growth of this product arena, National Instruments has become involved in creating instrumentation based on the personal computer, or computer-based instrumentation.

Computer-based instrumentation is the methodology of using programmable software and PC-based data acquisition hardware to build application-specific instrumentation solutions. A user can program the same piece of hardware to be an oscilloscope, data logger, or electrocardiograph. The software gives the hardware the desired personality. Users have created perfusion instruments that have the exact look and feel as the traditional stand-alone instrument. With the same software and hardware, users could program their system to monitor O2. There are no boundaries to what you cancreate with computer-based instrumentation. Computer-based instrumentation is very powerful because it leverages off current PC technology to provide flexible and cost-effective solutions at fractions of the cost of stand-alone devices. To showcase this power National Instruments has created turnkey packages that require no programming, such as BioBench. It uses the PC to function as a chart recorder but adds the ability to store information to disk and analyze your data.

Electrocardiograms

The recording of electrocardiograms (ECGs) has been an integral part of medicine to both doctors and researchers since its inception. Often ECG monitoring has very little flexibility in its instrumentation. Through the use of PCs, ECG data can now be recorded to disk and analyzed with greater flexibility for a more cost-effective solution. This application note explains how to use the personal computer to acquire store and analyze ECG data using National Instruments BioBench software and National Instruments data acquisition (DAQ) hardware. Using BioBench, a turnkey software package written with LabVIEW, and our data acquisition products, you can modernize your laboratory for computer-based acquisition of physiological signals. With BioBench, users can record up to 16 channels of data to disk with real-time display. One of the keys to BioBench is that a National Instruments DAQ device is used to acquire the signals from the amplifier and electrodes you are currently using in your lab. Therefore, there is no need to completely remodel your laboratory, but just consolidate experimental operations to one station. Using your current amplifier and electrode configuration with National Instruments DAQ device and BioBench will offer you the power of your current instrumentation setup with the flexibility of a PC-based system.


Step 1. Configuration and Connections
To begin setting up your experiment station, you will need to configure you National Instruments DAQ hardware. Refer to your hardware Getting Started Manual for the installation and configuration instructions. If you have problems, refer to our Technical Support site. In order to properly configure your hardware, you will need to know if your signals are single ended or differential. There is a discussion on these signal types in your hardware manual as well. After configuring and testing your hardware, you can install the BioBench software. The connection of electrodes to the subject is a very important part of an electrocardiogram measurement. In order to obtain clear signals, it is necessary to place the electrodes in certain configurations. The electrode configuration we will follow is shown in Figure 2 – three electrodes connected in a triangular representation otherwise known to as Einthoven's Triangle. Figure 2 displays the locations for each connection. Connections can be made in similar triangular configurations in different locations on the subject, but for this experiment we will use the following the configuration of Figure 2.




Once your electrode connections have been made, connect the positive, negative, and ground leads to the correct terminals on your amplifier. Using the BNC connection from your amplifier, wire it directly from the amplifier to channel 0 on the BNC-2090 Adapter. Now connect the BNC-2090 to your DAQ device using the cable supplied. You are now ready to acquire signals from your subject. See Figure 1 for more information.

Step 2. Configuring BioBench
Start BioBench by navigating to the Start Menu: Start»Programs»BioBench 1.0»BioBench. The first window that appears will prompt the user for a username. Enter a username. This username will be associated with all files recorded with BioBench until the username is changed. After entering your username, navigate to the Four-Graph Acquisition window through the View menu. Next, selectConfigure»Channels. The Channel Configuration window will appear and in the upper left-hand corner you will specify your DAQ device. For this example, we will be using the AT-MIO-16XE-10. Now we will configure our channel to record the ECG data. Select Channel 0 and type ECG in the Signal Label field. You will see the name change to ECG in the channels field. Now disconnect all of the other channels that appear by selecting them and pressing the Disconnect Signal button. Now you have configured channel zero for ECG data and the data source to be the AT-MIO-16-XE-10. The Channel Configuration window should appear as in Figure 3.



Signal voltage range should be set to the output voltages for your amplifier, and scaling will be used to set the gain on the DAQ board itself. Click on the OK button and return to the previous window.

Step 3. Timing
Select Configure»Settings»Timing tab to set up the timing configuration for the data acquisition process. Choose 200 Hz from the Sample Rate pull-down menu. The sample rate setting can be changed according to the needs of your acquisition process. In the Scan List field you should see ECG for the channel to use. The Start Time and Stop Time settings should be set to manual to employ use of the front panel manual controls. The window should appear as in Figure 4.



Click OK and return to the Four-Graph Acquisition window. Now you are ready to begin acquiring and logging data.

Step 4. Acquiring Data
Before hitting the Go button to begin acquiring data, check the Log Data box in the logging area on the right hand side of the window. After pressing the GO button, you will be prompted to name your datalog file. Choose a file name and use the extension (.bb) for a BioBench binary file. Click on OK. You should now see data appear on the first plot of your screen. This data should be similar to conventional ECG patterns if all the proper connections have been made. In order to analyze data trend characteristics, such as beats per minute (BPM), simply select the ECG channel from the trending menu and set the trend type for BPM. Clicking on the trend button displays the last set of trending data (see Figure 5).



Now that data has been acquired and logged to disk, you can use BioBench to analyze the data in detail. Press the analysis button or choose an analysis screen option from the View menu to get into analysis mode. If you have just used BioBench to record data to disk, that data file will automatically be opened in the analysis mode. If you did not just record your data to disk, simply choose File»Open and pick the BioBench data file you wish to open.

Step 5. Peak Detection
In the analysis window, highlight the data on which you would like to perform a peak detection, and press the array button located on the right side of the user interface. The array analysis window will appear with several tabs identifying different analysis options. One of the tabs is titled peak detection. Press this tab and you will see the selected data with a peak detection algorithm applied. Using the peak detection algorithm, you can locate either peaks or valleys, count the number of peaks, or measure the difference between peaks. You can also print out a list of peak/valley information, including the Y values. Figure 6 shows an example of a peak detection algorithm being applied to a data file. The data in the table to the right of the graph includes a time stamp of each peak and its Y value.



Step 6. Overlaid Analysis
With overlaid analysis, you can display several data plots on one graph to compare their characteristics. In order to perform overlaid analysis, choose Overlaid Analysis from the View pull down menu. All the signals from your data file will now be displayed on one graph. By clicking on the radio buttons to the right of each of the waveforms, you can select the waveform you would like to analyze. Overlaid analysis is ideal for comparing the results of multiple tests. Figure 7 displays an overlaid analysis graph comparing results from three different ECG files.


Any data collected with BioBench can be saved into a spreadsheet format (.txt) compatible with application software such as Microsoft Excel. Once you have selected the data you wish to export, select Export to Spreadsheet from the File pull down menu. For further analysis capabilities, you can open BioBench datalog files with LabVIEW and write your own analysis routines. To download the LabVIEW VIs for reading BioBench datalog files, see the related link below.

See Also:
LabVIEW VIs for BioBench

Summary

With these instructions, you are now ready to collect ECG signals using BioBench, National Instruments DAQ hardware, and the current amplifiers in your laboratory. With computer-based instruments, you can more effectively use the power of your PC, applying it to acquire, analyze, and present data easily. Exploit the power of your PC with computer-based instrumentation to provide flexible and powerful solutions at a fraction of the cost.

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