Measuring Cardiac Autonomic Nervous System (ANS) Activity in Toddlers - Resting and Developmental Challenges

The overall goal of this protocol is to non-invasively monitor and assess cardiac measures of the parasympathetic and sympathetic nervous systems under resting and challenge conditions with 18-month-old children. Measures of the autonomic nervous system in young children under resting and challenging conditions can help answer key questions about how young children biologically respond to challenges they face in their environment. The main advantage of this technique is that provides a validated, standardized protocol for assessing parasympathetic and sympathetic nervous system responses in an understudied age group.

This technique extends our ability to study biologic reactivity in young children, as well as investigate factors that predict variation in that reactivity, and that may provide insight into later health conditions. Demonstrating the role of child assessor will be Zoe Caron, and demonstrating the role of computer operator will be Vanessa Tearnan, research assistants from my laboratory. Begin by reviewing the protocol with the child's mother.

Then, talk to the toddler in a friendly way to make the toddler comfortable before you start the protocol. Have the child assessor apply the electrodes to the child's neck and torso while the computer operator distracts the child. For this protocol, apply each electrode to the skin at least three centimeters apart from neighboring electrodes to ensure proper signal conduction.

Verify this minimum distance by measuring the length between the centers of each electrode, then press on the foam around the gel to ensure that the electrode adhered to the skin. Now, gather four impedance electrodes, of which two will be placed on the neck, and two on the trunk of the child. Place the first electrode that is attached to the red negative lead on the center of the lower back.

Then, place the second electrode that is attached to the white negative lead on the sternum just above the xyphoid process. Place the third electrode that is attached to the white positive lead to the left of the supersternal notch on the edge of the clavicle. Then, place the fourth electrode that is attached to the red positive lead on the back of the child's neck.

Locate three electrocardiogram, or ECG electrodes. Place the first ECG electrode, attached to the brown negative lead lengthwise along the right clavicle bone. Press on the foam of the electrode, and feel the clavicle bone.

Place the second ECG electrode, attached to the brown positive lead, on the left lower rib. Press on the foam of the electrode, and feel the rib bone. Then, place the third ECG grounding electrode, attached to the black negative lead, on the child's lower right rib, so that it is in line with the lower left rib electrode.

Bundle and clip the lower ends of the leads to the child's clothing to minimize movement. Have the computer operator monitor the computer. Then, engage the child, and review the activities involved in the protocol with the mother.

Turn on the autonomic nervous system, or ANS, data acquisition unit, to acquire the cardiac impedance and ECG signals. After five minutes, have the computer operator check the signals to make sure they look normal, and turn on the video camera. Offer the child a soft toy if they seem uncomfortable during this period.

Finally, show a computer image of the child's heart activity to the mother and explain what each signal represents on the ECG. Show the heartbeats and impedance signals, which indicate blood flow through the lungs and heart. During these tasks, instruct the computer operator to push F keys to mark important protocol steps in the ANS data, as seen here.

Push F11 to indicate that a task ended early, or for any major protocol problems that arise, such as an electrode falling off. Begin by opening the media player in the tablet, and playing the first one-minute lullaby. Keep the tablet out of reach of the child.

Next, hold a jack-in-the-box in front of the child, but keep it slightly out of reach. Slowly rotate the arm and play the music until the sock monkey pops up. Following that, start the lemon juice task.

Place two drops of concentrated lemon juice on the center of the child's tongue, slightly back from the front, so that the juice does not roll off the tongue. Wait quietly for ten seconds, with a friendly, neutral expression. Next, tell the child it is time to drink some water, and have the child assessor offer them a sip of water.

Have the computer operator press the F4 key when the water is offered. Then, play a 30-second recording of a sick infant crying on the tablet. Followed by the second one-minute resting lullaby.

Next, hold the tablet about 12 inches from the child's face and show the child the two-minute neutral video. This continuous monitoring of the autonomic nervous system under resting and challenge conditions with 18-month-old children is summarized in 30-second blocks within our scoring program. This software averages the child's heart rate, respiratory rate, respiratory sinus arrhythmia, and pre-ejection period during each 30-second interval.

This method successfully captured significant ANS change between calming activities and developmentally challenging tasks. Decreases in respiratory sinus arrhythmia and pre-ejection period reflect autonomic reactivity through parasympathetic withdrawal and sympathetic activation, respectively. We can also assess the variability in responses, such as with heart rate, within each task, across children.

This is critical for examining individual differences in ANS activity. Measuring children's autonomic responses to developmental challenges has paved the way for researchers in the fields of psycho-physiology, pediatrics, psychology, and child development to explore the relations between social experience, biology, and physical and mental health in young children. Once mastered, this protocol can be done in 20 minutes.

Generally, the greatest challenge to this method is learning how to apply the electrodes quickly and accurately while being respectful of the child's emotional state. When working with young children, it's important to remember to engage the child and mother before you apply the electrodes. Also, be sensitive to the child and discontinue the tasks if the child is showing signs of significant distress.

Never force a child to complete the protocol. Working with toddlers can be challenging, so you should engage children throughout the protocol. Although a child may cry when you place the electrodes on them, most 18-month-olds will shift attention to the task and stay engaged throughout the protocol.

After watching this video, you should have a good understanding of how to non-invasively monitor and assess cardiac measures of the autonomic nervous system under resting and challenge conditions with 18-month-old children.