Concussion is often followed by headache, brain fog, and dizziness. These symptoms are often clinically attributed to changes in autonomic function and cerebral blood flow. Thus, understanding arterial baroreflex and related physiological responses in concussion is key to understanding the pathophysiology of this condition.

Participants with acute (<14 days of injury) concussion and age/sex-matched healthy controls completed a symptom assessment (Rivermead Post-Concussion Questionnaire; RPQ) and standardized autonomic testing with continuous beat-to-beat heart rate (HR) and blood pressure (BP) monitoring, which included HR response to deep breathing (HRDB), HR and mean BP response to Valsalva, and HR and BP response to 10-minute head-up tilt (HUT) testing. In addition to calculation of standard autonomic metrics (HRDB, Valsalva ratio, HR/BP changes to HUT), the data was analyzed for variability via standard deviation (SD of HR/BP) and continuous wavelet transform (to identify very low, low, and high frequency domains). Between-group comparisons were made using Mann-Whitney U tests, and reported as median and interquartile range. Spearman’s rho correlation coefficients were calculated between autonomic measures and symptom assessment scores.

Forty-six mTBI and 17 control participants completed the study. LF measures of HR and BP during HUT were significantly lower in mTBI participants, compared to controls. HR and BP variability (SD) also trended lower in mTBI participants. Baseline symptom burden (RPQ) was positively, though weakly, correlated with LF power and variability (SD) during HUT (Spearman’s rho 0.32, p=0.03).

These data suggest a blunted sympathetic response to orthostatic challenge (HUT) in concussion participants, with the potential to explain some of the clinical features of activity (orthostatic activity) intolerance and other common symptoms after mTBI. However, this finding does not fully explain corresponding symptom report and require further confirmation with direct cerebral blood flow evaluation.