Introduction: Blunted cardiac autonomic nervous system (ANS) responses, quantified using heart rate variability (HRV), have been reported after sport-related concussion (SRC). Research suggests this persists beyond clinical recovery. This study compared cardiac parasympathetic responses in student athletes with a remote history of SRC (> 1-year ago, Concussion History: CH) with those who reported no lifetime history of SRC (Concussion Naïve: CN). Design: Retrospective nested case-control. Setting: University laboratory. Patients or Other Participants: CH (n = 9, 18.3 ± 2 years, 44% male, median 2 years since injury) were student athletes with a remote history of concussion(s) from more than 1 year ago. CN (n = 21, 16.7 ± 3 years, 67% male) were student athletes with no lifetime history of concussion. Exclusion criteria included taking medications that could affect ANS function, history of concussion within the past year, persistent concussion symptoms, lifetime history of moderate to severe brain injury, and lifetime history of more than 3 concussions. Material and Methods: Participants performed the Face Cooling (FC) test for 3-min after 10-min of supine rest while wearing a 3-lead electrocardiogram in a controlled environment. Outcome Measures: Heart rate (HR), R-R interval (RRI), root mean square of the successive differences (RMSSD) of RRI, high frequency (HF) and low frequency to HF (LF:HF) ratios. Haider et al. Persistent ANS Dysfunction After Concussion Results: At baseline, CH had a lower resting HR than CN (62.3 ± 11 bpm vs. 72.9 ± 12, p = 0.034). CH had a different HR response to FC than CN (+8.9% change from baseline in CH vs. −7.5% in CN, p = 0.010). CH also had a smaller RMSSD increase to FC than CN (+31.8% change from baseline in CH vs. +121.8% in CN, p = 0.048). There were no significant group differences over time in RRI (p = 0.106), HF (p = 0.550) or LF:HF ratio (p = 0.053). Conclusion: Asymptomatic student athletes with a remote history of concussion had a blunted cardiac parasympathetic response to FC when compared with athletes with no lifetime history of concussion. These data suggest that an impaired autonomic response to a physiological stressor persists after clinical recovery from SRC for longer than previously reported.

Context: Emerging research supports the use of mild to moderate aerobic exercise for treating sport-related concussion (SRC) and persistent postconcussive symptoms (PPCS), yet the current standard of care remains to be strict rest. The purpose of this review is to summarize the existing literature on physical activity and prescribed exercise for SRC and PPCS. Evidence Acquisition: PubMed and Embase were searched in April of 2019 for studies assessing rest or prescribed exercise for SRC and PPCS. No specific search syntax was used. Study Design: Clinical review. Level of Evidence: Level 4. Results: A majority of studies show that spontaneous physical activity is safe after SRC and that subsymptom threshold aerobic exercise safely speeds up recovery after SRC and reduces symptoms in those with PPCS. Exercise tolerance can safely be assessed using graded exertion test protocols within days of injury, and the degree of early exercise tolerance has diagnostic and prognostic value. Conclusion: Subsymptom threshold aerobic exercise is safe and effective for the treatment of SRC as well as in athletes with PPCS. Further research is warranted to establish the most effective method and dose of aerobic exercise for the active treatment of SRC and whether early exercise treatment can prevent PPCS in athletes. Strength of Recommendation Taxonomy: 2.

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To determine the number of prior concussions associated with increased incidence of persistent postconcussive symptoms (PPCS) in a cohort of acutely concussed pediatric patients. Design: Prospective observational cohort study. Setting: Three university-affiliated concussion clinics. Participants: Two hundred seventy participants (14.9 6 1.9 years, 62% male, 54% with prior concussion) were assessed within 14 days of concussion and followed to clinical recovery. Participants with a second head injury before clinical recovery were excluded. Measures: and Main Outcome: Concussion history, current injury characteristics, recovery time, and risk for prolonged recovery from current concussion. Results: There was no statistically significant change in PPCS risk for participants with 0, 1 or 2 prior concussions; however, participants with 3 or more prior concussions had a significantly greater risk of PPCS. Twelve participants sustained a subsequent concussion after clinical recovery from their first injury and were treated as a separate cohort. Our secondary analysis found that these participants took longer to recover and had a greater incidence of PPCS during recovery from their latest concussion. Conclusion: Pediatric patients with a history of 3 or more concussions are at greater risk of PPCS than those with fewer than 3 prior concussions.