The overall goal of this procedure is to non-invasively obtain measures of autonomic nervous system functioning in a large cohort of children. This is accomplished by first setting up the required hardware. The second step is to attach the measurement device VU a MS to the child and start the registration period.
Next, the registration period encompasses the child lying down and sitting up for a couple of minutes. The final step is to download the data from the VU a MS device and process it in the accompanying software. Ultimately, the VU a MS monitoring device is used to show parameters of the autonomic nervous system functioning in a quick and non-invasive manner.
The main advantage of this technique over existing methods like direct recording of action potentials, is that ambulatory measurement is non-invasive and much cheaper than invasive methods. Generally, individuals new through this method will struggle because the effect of autonomic nervous system activity on the organs is used as a proxy for actual activity. And to extract information from the Ross signals requires understanding of both the S algorithm as well as the physiology involved.
To begin collect the ambulatory recording device. Seven electrodes an empty compact flash memory card, a stopwatch, and a laptop or PC with a flashcard reader and the data analysis management software or DAM suite installed. A music player with headphones and a small air mattress are optional but helpful.
Place the memory card and full batteries in the V-U-A-M-S device and confirm that the green light flashes indicating that the unit is ready but not recording. When ready. Connect the device to the laptop using the cable provided and start the dams program.
Next, initiate communication with the device. After cleaning the skin with alcohol wipes, place the seven electrodes on the chest and back. As shown, the electrodes and lead wires are attached following the color scheme seen here.
After attaching the lead wires to the electrodes, connect the wires to the device for accurate data recording. Make sure that the time and date settings on the computer are correct. Check the battery type and voltage and fill out the identification field.
The typical sampling frequencies are shown here. Next, measure the distance between the two chest electrodes and enter it into the ICGV distance field. Click on send settings to send this information to the device, select the online option to display the ECG and other measures.
A clear QRST complex should be detectable in the ECG. The R wave should be upward, and it should be the peak with the largest absolute amplitude in either direction. The delta Z should be within negative 0.5 and positive 0.5.
Ohms instruct the child to take a slow deep breath and exhale slowly. The delta Z signal should clearly reflect the deep breathing of the subject. Confirm that the ICG has the typical upward waveform reflecting the cardiac ejection phase.
The deasy over DT should be between negative one and positive one. Ohms per second light movement of the subject should not distort this signal. If these criteria are not met, reclean the skin and reattach the electrodes until satisfactory signals are obtained.
When good signals are obtained, press the start button to begin recording a beep acknowledges the start of recording and a green light will start flashing once every three seconds. The registration has now started. Close the VU Dams program and disconnect the device from the interface cable.
Once the registration period has started, ask the child to lie down for the first experimental condition when the child has been in the supine position without head up tilt for two minutes. Briefly press the small black button on top of the device to mark a special event. This will later help identify the start of this condition in the data.
After four minutes, press the event button again. This signals the end of the lying down condition. Next, have the child sit up and repeat the procedure.
For this second condition, press the button, wait four minutes and press the button again in the configuration screen of the DAM software, stop the recording. The light will flash every 10 seconds to indicate it has stopped and is in standby mode. Once the device has stopped, disconnect the lead wire plug from the connector and the wires from the electrodes.
Remove the batteries and flashcard from the VU Dams device and save the acquired files to the appropriate directory. To begin the data processing, open the data with the VU Dams program. The data is automatically converted from a raw data format to a new data file.
When saving the file, this file is used in the following steps. The dams program automatically extracts the inter be interval time series from the ECG signal. Select the detect R peaks tab to inspect the quality of automatic R peak detector and to identify any periods with very low ECG quality.
In the upper left hand corner, yellow or red numbers show the amount of suspicious or highly suspicious beats respectively. Visually inspect each suspicious RPE and delete or add markers by hand where necessary. Next, select the label data tab panels showing the heart rate, signal and movement signal will appear along with the actual time of the recording.
The mean heart rate pre ejection period or PEP and measures of respiratory sinus arrhythmia are determined by first indicating which periods in the raw data correspond to either the experimental tasks in a laboratory setting or to situations in recordings in naturalistic settings. This process is called labeling. Each label can be given a unique identifier to signal a particular condition.
In this case, there is only one category experimental condition. This category has two values lying down and sitting up. Next, create a label configuration file to communicate the experimental design to the VU Dams program.
Load this file by clicking on the edit label configuration file under action in the menu bar. By setting this configuration file as default, future files will automatically be loaded with this configuration. Next, place the cursor near the start time of your first condition and drag the label to the end time of that condition.
Once a label has been made, a popup screen will appear. Select lying down for the first label and setting up for the second. After labeling, select the impedance scoring tab to score the PEP in the impedance cardiogram.
Place the four vertical cursors in the correct positions. ECGQ wave onset ICGB point ICG DZ over DT min and ICGX point. Next, select the respiration scoring tab to score the peak Valley RSA.
Using the respiratory and ECG signals, the detection algorithm should not classify more than 15%of the breaths as deviant. If this occurs, inspect the respiration signal and tune the parameters of the detection algorithm as needed under the settings menu. Finally, select label information to obtain the average value of a series of physiological parameters for each labeled time period.
The first column has the subject identifier, and the last column indicates the values of all categories used during labeling. This spreadsheet can be exported for further statistical analyses seen. Here are summarized data for boys and girls.
During the two experimental conditions, the heart rate was higher for both boys and girls in the sitting up condition compared to lying down and girls had a higher heart rate than boys for both conditions. The pre ejection period was hiring in girls than in boys when sitting up. While respiratory sinus arrhythmia was lower in girls than in boys for both conditions.
These data suggest a more active, sympathetic nervous system in girls paired to a less active, parasympathetic nervous system. Following this procedure, body composition and blood pressure can be assessed in order to answer additional questions about the child's cardiometabolic profile After its development. This technique paved way for researchers in the field of epidemiology to explore the effects of lifestyle on health in much larger samples.
The device allows for easy ambulatory recording and naturalistic settings yielding a much higher ecological validity in contrast to laboratory settings.
