Cerebral blood flow velocity : does it play a role in symptom exacerbation during exercise in concussed athletes?

Exercise frequently results in exacerbation of symptoms following a sports-related concussion (SRC). However, the mechanism(s) behind this phenomenon has yet to be determined. It is possible that an inability to regulate cerebral blood flow (CBF) may lead to over-perfusion, and thus cause the exacerbation of symptoms seen during exercise. It was hypothesized that: 1) CBF velocity during exercise will be greater in SRC. 2) Severity of symptoms will be correlated with CBF velocity during exercise and 3) day-to-day variability in CBF velocity will be greater in SRC compared to control subjects. Subjects refrained from caffeine, alcohol and exercise 24hrs prior to testing. Blood velocity was monitored using transcranial Doppler targeting both the middle and posterior cerebral artery (MCAv and PCAv). Exercise was performed on a stationary bike at 30% and 70% predicted heart rate reserve (HRR) for 2-3 minutes and changes in MCAv and PCAv were compared to baseline at rest. Symptoms were evaluated using SCAT2 pre and post-exercise. Subjects included 6 subjects (5 males and 1 female) diagnosed with sport-related concussion (mean ± standard deviation; age: 17.5±2 years, BMI: 24±1 kg/m²) and 6 healthy control-subjects (5 males and 1 female; age: 20±2 years, BMI: 22±2 kg/m²). Concussed subjects were tested at the same time of day on Day 4±1, Day 8±1, Day 17±3 and Day 29±1 following injury. Assessment of day-to-day variability also conducted using the test-retest method with the inclusion of a subgroup of control subjects (n=12). Results demonstrated that 1) there was no effect of concussion on resting MCAv or PCAv over the month post-injury. In addition, no effect of concussion was seen on the relative changes in MCAv or PCAv at either 30% or 70% HRR. 2) A linear regression revealed a relationship between the increase in both number and severity of symptoms and MCA velocity response to 70% HRR (R² = 0.37). 3) Concussion did not significantly change day-to-day variability over the course of testing. Taken together, these results demonstrate that SRC does not significantly impact CBF responses during mild to moderate exercise; however, MCAv response may play a role in symptom exacerbation during exercise.Graduate Studies, College of (Okanagan)Graduat