Impact of mild traumatic brain injury on cerebrovascular function

Introduction: The majority of research into the assessment of mild traumatic brain injury (mTBI) has been focussed on the neuropsychological aspect of the injury, with neuropsychological tests forming the cornerstone of concussion management (Ross et al., 1987). The impact that a mTBI has on the cerebrovascular system still remains relatively unclear (Wilberger et al., 2006, McCrory et al., 2009). With advancing techniques such as transcranical Doppler (TCD) assessing the impact on the cerebrovascular system has become a key aspect of recent research into the injury (Len and Neary, 2011). In the current study we tested the hypothesis that cerebral function would show the greatest impaired i.e. reduced vasomotor reacivity in those individuals who had the highest exposure to repetitive impact of head trauma. Methods: Twelve currently active professional boxers aged 27 (mean) ± 4 (SD) years and 10 physically trained concussed individuals (28 ± 8 years), with a history of knockouts 2 ± 3 and 4 ± 5 (respectively) were compared to 13 physically trained non-concussed individuals (22 ± 3 years) and 11 sedentary individuals (25 ± 5 years). Haemodynamic function was assessed following a 3-minute hypocapnea challenge, with contemporaneously measured the middle cerebral artery velocity (MCAv) via transcranical Doppler ultrasound, mean arterial pressure (MAP) via finger photoplethysmography and continuous end-tidal carbon dioxide (PETCO2) measurements. Cerebrovascular resistance (CVR) was calculated as MAP/MCAv and cerebrovascular conductance (CVC) as MCAv/MAP. Vasomotor reactivity (VMR) was calculated as the percentage change in MCAv from hypocapnea to baseline/ delta change in PETCO2. Following confirmation of normality using Shapiro-Wilks W tests, data were analysed using a two-way repeated measures ANOVA and Bonferonni corrected independent samples t-test. Significance was established as Pandlt;0.05. Results: There was no visible impairment of cerebrovascular function following a hypocapnea challenge across all groups. Conclusion: The findings demonstrate that cerebrovascular function remains preserved following a mTBI. This indicates that incorporating techniques such as TCD to assess cerebral function with neuropsychological tests it will help further the understanding of the injury. Acknowledgements: The study was supported by JPR Williams Research Fellowship.