Association of Hemodynamic and Cerebrovascular Responses to Exercise With Symptom Severity in Adolescents and Young...

Aerobic exercise has become a useful method to assist with postconcussion management. Exercise can exacerbate concussion symptoms even when symptoms are not apparent at rest. Few studies have examined the reasons for symptom exacerbation during exercise following a concussion. We had 2 primary objectives: (1) to delineate cardiopulmonary and cerebrovascular responses to exercise in adolescents and young adults with a concussion and healthy controls and (2) to determine the association between cerebrovascular responses and symptom burden.

We recruited participants with a recent concussion from a sport concussion clinic between September 1, 2018, and February 22, 2020. They were included if their concussion occurred <3 weeks before initial testing and if they were symptomatic at rest. Participants were excluded if they sustained a concussion in the past year (excluding index injury), reported history of neurologic disorders, or were using medications/devices that may alter neurologic function. Participants completed a progressive, symptom-limited, submaximal exercise protocol on a stationary bicycle. We assessed heart rate, blood pressure, fraction of end tidal CO₂ (FETCO₂), and middle cerebral artery blood flow velocity (CBF) and cerebrovascular function (vasoactivity and autoregulation) at seated rest and during exercise.

We conducted 107 exercise tests (40 concussed, 37 healthy participants initially; 30 concussed at follow-up). Concussed participants were tested initially (mean 17.6 ± 2.2 [SD] years of age; 55% female; mean 12.5 ± 4.7 days postconcussion) and again 8 weeks later (mean 73.3 ± 9.5 days postconcussion). Control participants (mean 18.3 ± 2.4 years; 62% female) were tested once. FETCO₂ increased throughout the exercise protocol as heart rate increased, reached a plateau, and declined at higher exercise intensities. CO₂ explained >25% of the variation in resting CBF (R > 0.25; p < 0.01) in most (73% individuals). Within the concussion group, resting symptom severity and the heart rate at which FETCO₂ reached a plateau explained ∼2/3s of variation in exercise-induced symptom exacerbation (R = 0.65; FETCO₂ β = -1.210 ± 0.517 [SE], p < 0.05). There was a moderate, statistically significant relationship between cerebrovascular responses to CO₂ at rest (cerebral vasoactivity) and cerebrovascular responses to exercise-induced changes in FETCO₂ (R = 0.13, p = 0.01).

The arterial CO₂ response and symptom exacerbation relationship during postconcussion aerobic exercise may be mediated by increased sensitivity of cerebral vasculature to exercise-related increase in CO₂.