In Adults Who Had a Concussion, Cardiac Autonomic Function is Not Impaired Beyond Three Months from Injury

Introduction: Concussion is a form of traumatic brain injury (TBI) which temporarily disrupts normal brain function. It is well established that cardiac autonomic function is impaired immediately following concussion. However, studies investigating cardiac autonomic function as measures of spontaneous cardiac baroreflex sensitivity (BRS) and heart rate variability (HRV) beyond three months from the event are limited, and the results are inconsistent. Therefore, the purpose of this study was to investigate the lasting impact of concussion on cardiac BRS and HRV in participants who are beyond 3 months from their last concussion. We hypothesized that cardiac BRS and HRV would be impaired in adults who previously had a concussion compared to healthy controls with no known history of concussion. Methods: Five adults (3 females, 27 ± 6 years; mean ± standard error) with a diagnosed concussion prior to assessment (6.2 ± 0.5 months) and six controls (3 females, 27 ± 5 years) without a known history of concussion were studied. Heart rate (HR; ECG) and beat-to-beat blood pressure (BP; finger photoplethysmography) were recorded continuously during a five-minute supine rest period. Spontaneous cardiac BRS was estimated using the Sequence Method for overall BRS gains, then separately for up gains (increase systolic BP: increase R-R interval) and down gains (decrease systolic BP: decrease R-R interval). HRV was measured in the time-domain using the root mean square of successive differences between normal heartbeats (RMSSD), and in the frequency-domain using normalized low frequency (LF) and high frequency (HF) power, and as the LF/HF ratio. Results: There were no differences in resting BP or HR between groups (P > 0.050 for both). Overall cardiac BRS gains was also not different between controls (20.3 ± 4.3 ms/mmHg) and participants with TBI (28.6 ± 9.3 ms/mmHg, P = 0.4116). Likewise, we found no group differences for up and down gains (P > 0.050 for both). For HRV measures, no differences between groups were observed for RMSSD (control: 63 ± 20 ms; TBI: 63 ± 21 ms, P = 0.890), LF power (control: 40 ± 9 n.u.; TBI: 40 ± 14 n.u.; P > 0.999), HF power (control: 56 ± 9 n.u.; TBI: 57 ± 14 n.u.; P = 0.940), or the LF/HF ratio (control: 1.08 ± 0.50; TBI: 1.49 ± 0.85; P = 0.792). Conclusion: These preliminary findings suggest that, in contrast to our hypothesis, adults at six months post-concussion do not demonstrate impairments in any indices of cardiac autonomic function. This project was supported by the Henry M. Jackson Foundation HU0001-18-2-0016. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.