Autonomic Function Following Concussion in Youth Athletes: An Exploration of Heart Rate Variability Using 24-hour Recording Methodology

This method may provide an ecologically valid context for the collection and interpretation of physiological data following pediatric concussion along the recovery trajectory. The main advantage of this longitudinal research study is the ability to visualize fluctuations in the autonomic nervous system at multiple time points following concussive injury. Demonstrating the procedure are James Murphy, a manager, and Chris Gupta, a research student, both within the Concussion Center.

After obtaining parental and participant consent, request that the participant fill out the demographic collection form. Instruct the participant to complete the Godin Leisure-Time Exercise Questionnaire and the post-concussion symptom inventory. Then, measure and record the participant's height and weight.

Next, select an appropriate chest strap size, according to the circumference of the participant's torso and place the strap around the torso, over the participant's clothing. Adjust the strap to reflect a tight yet comfortable fit and confirm that the strap is securely fitted around the sternum on the xiphoid process. Use clip-on buttons to connect the heart rate sensor to the chest strap, and apply a modest amount of hypoallergenic electrode gel to the conductive plastic surface of the strap.

Demonstrate the location of the chest strap clasp to the participant, and give the participant access to a private area or washroom, so that the participant can place the chest strap directly on the skin with the sensor placed directly on the xiphoid process of the sternum and right-side up to ensure an optimal heart rate recording. Then, provide the participant with the watch and a troubleshooting instruction sheet, in the event the watch stops recording, instructing them not to remove the watch throughout the duration of the 24-hour recording period. On the same day or as soon as possible after a concussive injury, complete the acute concussion evaluation form to collect information on the mechanism of the injury and post-injury sequelae.

Administer the Godin Leisure-Time Exercise Questionnaire to capture changes in the physical activity repertoire and the post-concussion symptom inventory to determine the number and severity of the symptoms. Connect the watch to a computer with the provided USB transfer cable, and upload the heart rate data to the software program provided with the sensor. Transfer the HRM data file to the data analysis program, and select the appropriate high frequency and low frequency domain variable bandwidths, as indicated.

Select a 300-second window frame with a 50%overlap, an interpolation rate of four hertz, and the Fast Fourier Transform for power spectral analysis. Then, save the heart rate variability data as a new HRM file for later analysis in robust statistical software and fit the sensor to the participant's torso as just demonstrated. Here, the Kubios output of a 24-hour heart rate recording for a concussed participant is shown.

The raw recovery rate series allows the researcher to visualize changes across time, highlighting key time points of increase or decrease that are important for the interpretation of data. For example, the increased trend between the fifth and 11th hour is reflective of a state of calm and low functional activity. Conversely, the period of decrease from the 11th to 13th hour demonstrates that more functional activity was detected, but because this participant did not complete a comprehensive diary, it is uncertain as to whether this decrease in RR interval time represents physical or cognitive activity, or a combination of both.

The time and frequency domain variables represent the overall variability of the physiological signal and the branches of the autonomic nervous system, respectively. In these representative graphs, the relationship between pNN50 and the post-concussion syndrome inventory total score across days post-injury, as stratified by sex, is shown. For example, in these participants, the recovery trajectory appears to be similar within both males and females, with an initial decrease observed until day 30 in both sexes, followed by increases until day 75 for males and until day 90 for females, after which, both trajectories are followed by a plateau.

It's important to securely fit the heart rate strap and to remind the participant to wear the watch at all times. Future studies should include administering physical and cognitive diaries to answer questions like how do fluctuations in the autonomic nervous system align with varying levels of physical and cognitive activity? This protocol paved the way for researchers in the concussion field to explore heart rate variability in an understudied pediatric population.