Altered autonomic cardiovascular function in adults with persisting post-concussive symptoms and exercise intolerance.

Alterations in autonomic cardiovascular function may result following mild traumatic brain injury (mTBI), but there is a lack of data evaluating autonomic function in adults with persisting post-concussive symptoms (PPCS). We collected resting measures of heart rate (HR), heart rate variability (HRV), blood pressure (BP) and cardiac baroreceptor sensitivity in 50 adults with PPCS (42.8 (11.0) years; 24.5 (14.2) months post-injury; 74% female) and 50 age/sex-matched controls (43.0 (11.1) years; 74% female) with no lifetime mTBI history. HR and BP data were collected for ≥4 min when seated and standing. Between-group differences (PPCS vs. control) were analyzed using linear regression. In the seated posture, participants with PPCS had significantly lower HRV than controls, specifically RMSSD (root mean squared of successive RR interval differences) (mean difference = -10.450, p = 0.001) and SDNN (standard deviation of RR intervals) (mean difference = -12.875, p = 0.001). In the standing position, PPCS had lower SDNN. Participants with PPCS had significantly lesser change in HRV, including RMSSD (mean difference = 5.981, p = 0.007) and LF/HF (low-frequency to high-frequency ratio) (mean difference = -2.229, p = 0.016), when going from seated to standing compared to controls. Findings suggest adults with PPCS have altered autonomic function relative to controls. Physical activity level and deconditioning are potential treatment targets to improve autonomic function.