Impaired Dynamic Cerebral Autoregulation to Postural Stress Following Concussive Injuries in Adolescents
The FASEB Journal
Concussions disproportionately affect adolescents and ongoing maturation places this population at increased risk for prolonged recovery and long-term impairments in neurologic functioning. Although cerebrovascular impairments are believed to contribute to concussion symptoms and recovery, little information exists regarding brain vasomotor control in adolescent concussion, particularly during rapid changes in blood pressure that demand a dynamic cerebral autoregulatory response. The current investigation tested the hypothesis that adolescent concussion is marked by impaired dynamic cerebral autoregulation (CA). Twenty-two adolescents diagnosed with a concussion (CONC; 13 females; 15 ± 1 years; 26 ± 20 days post-injury, SCAT3 symptom score = 12 ± 6) and twenty-seven healthy controls (CTRL; 15 females; 14 ± 2 years; SCAT3 symptom score = 6 ± 4) completed two repeated sit-to-stand trials. CONC were followed through their rehabilitation for up to 12-weeks. Arterial blood pressure (ABP), cerebral blood flow velocity (CBFV), end-tidal carbon dioxide partial pressure (PetCO2), and heart rate (HR) were measured continuously with finger photoplethysmography (Finapres Medical Systems BV), transcranial Doppler ultrasound (Multigon Industries), a gas analyzer (AD Instruments), and a standard 3-lead electrocardiogram (ECG), respectively. Furthermore, cardiac output (CO) was provided via the Model flow algorithm and cerebrovascular resistance (CVR) was calculated. The rate of the drop in CVR relative to the change in ABP provided the rate of regulation (RoR). The drop in ABP with standing was similar between CONC and CTRL (25 ± 8 vs. 24 ± 7 mmHg; p = 0.62) although the time to ABP nadir was longer in CONC compared with CTRL (7.2 ± 1.1 vs. 6.1 ± 1.3 sec; p = 0.002). Similarly, time to CBFV nadir was longer in CONC compared with CTRL (5.9 ± 1.4 vs. 4.4 ± 2.0 sec; p = 0.003). Compared to CTRL, RoR was reduced in CONC at study entry (0.21 ± 0.06 vs. 0.16 ± 0.04 sec−1; p = 0.005). However, at the time of CONC final visit (SCAT3 symptom score = 4 ± 5), RoR improved to levels similar to CTRL (0.20 ± 0.08 vs. 0.21 ± 0.06 sec−1; p = 0.55). During sitting and standing, CONC and CTRL had similar PetCO2. The change in heart rate with standing was similar between CONC and CTRL (30 ± 6 vs. 26 ± 9 bpm; p = 0.09) although the time to peak HR was longer in CONC compared with CTRL (10.8 ± 2.5 vs. 9.4 ± 2.0 sec; p = 0.004). Furthermore, a similar increase in CO was witnessed with standing in CONC and CTRL (1.4 ± 1.6 vs. 1.7 ± 0.7 L/min; p = 0.28). Impairments in dynamic CA are evident in adolescents following a concussive injury which recover in accordance with clinical symptoms. Therefore, RoR may aid decisions regarding diagnosis, rehabilitation, and recovery of adolescent concussion.