Effect of 6-Month Exercise Training on Neurovascular Function in Spinal Cord Injury.

Abstract

Although previous data show exacerbated incidence of cognitive impairment after spinal cord injury (SCI), the physiology that underlies this postinjury cognitive decline is unknown. One potential culprit is impairment in the ability of cerebral vasculature to alter regional flow to sustain neural metabolism (i.e., "neurovascular coupling"). We hypothesized that cerebrovascular responses to a working memory task are impaired in individuals with SCI and can be improved by aerobic exercise training. We assessed the effect of injury and 6-month full-body aerobic exercise training on the cerebral blood flow response to cognitive demand (i.e., neurovascular coupling) in 24 individuals with SCI and 16 controls. Cognitive demand was introduced in a graded fashion using a working memory task. Reaction time tended to be higher in individuals with SCI, especially those with high-level (≥T4) injuries, possibly due to upper motor impairments. Neurovascular coupling was graded across task difficulty (P < 0.01) and followed cognitive demand, and injury itself did not have a significant effect (group effect P = 0.99, interaction P = 0.70). Individuals with low-level injuries (<T4) had higher aerobic capacity than high-level injuries (P < 0.01). Aerobic capacity increased significantly with training in both groups (P < 0.01). Although there was no overall significant improvement in neurovascular coupling with training at the group level, the degree of improvement was closely related to that in aerobic fitness in individuals with high-level injuries (R = 0.19, P = 0.03) but not low-level injuries (R = 0.04, P = 0.46). Importantly, improvement in neurovascular coupling translated to an increase in reaction time (R = 0.16, P = 0.05). Previously reported cognitive impairment after SCI may reflect a decline in neurovascular coupling primarily due to physical deconditioning rather than injury itself. The latter can be mitigated by aerobic exercise training.