Impaired cerebral blood flow regulation in chronic traumatic brain injury.

Baroreflex sensitivity (BRS) and cerebral autoregulation (CA) play an important role in maintaining constant cerebral blood flow (CBF) during systemic changes in blood pressure (BP). Impaired BRS and CA have been reported in acute traumatic brain injury (TBI) which may also contribute to secondary injury and poorer recovery after acute TBI; however, their status during chronic stages remains elusive. Thus, the goal of this study is to determine whether cardiac BRS and dynamic CA (dCA) were impaired during the chronic stage in patients with single TBI and persistent neurological symptoms. Twenty-two subjects with blunt head TBI ≥ 6 months prior to the study (13 mild and 9 moderate to severe TBI) and persistent symptoms on Rivermead Post-Concussion Symptoms Questionnaire at enrollment were compared to 22 age/sex/fitness level-matched healthy control subjects. Beat-to-beat changes in heart rate, BP, and CBF velocity were measured at rest and during a repeated sit-stand maneuver. Hemodynamic variability, dCA, and cardiac BRS were calculated using spectral and transfer function analyses. We found dCA phase in low frequency (LF) range of 0.07-0.20 Hz was lower in subjects with TBI than in control subjects (0.51 ± 0.19 vs. 0.63 ± 0.26, p = 0.043) during the resting condition. Among subjects with TBI, the lower dCA phase in LF was correlated with poorer performance on measures of cognitive function (all p < 0.05). These findings suggested that subjects with chronic TBI showed impaired dCA which may contribute to persistent cognitive impairment. Cerebrovascular measures may provide a physiological measure to evaluate interventions for chronic TBI and accompanying functional deficits.