Systemic and Cerebral Hemodynamic Contribution to Cognitive Performance in Spinal Cord Injury

Cognitive deficits are prevalent in the spinal cord injury (SCI) population, and consensus suggests that concomitant traumatic brain injury or comorbid conditions are primarily responsible for these deficits. However, mounting evidence supports the possibility that systemic and cerebral hemodynamic dysfunction may contribute to the cognitive deficits reported in persons with SCI. We sought to determine the contribution of changes in blood pressure (BP) and changes in cerebral blood flow velocity (CBFv) to test performance on the Symbol Digit Modalities Test (SDMT) in persons with SCI compared with matched non-SCI controls. Participants included 36 non-SCI controls and 67 persons with SCI: 33 with paraplegia (T2-T12) and 34 with tetraplegia (C3-T1). Continuous beat-to-beat BP and simultaneous CBFv was monitored for 5 min during seated rest and during the SDMT, which assesses information processing speed, sustained attention, and visual working memory. The results indicate significantly lower SDMT scores in the group with tetraplegia (44 ± 10) compared to the non-SCI controls (53 ± 14; p < 0.01); however, SDMT scores did not differ significantly between the non-SCI controls and the group with paraplegia (49 ± 13). Whereas group affiliation was the most significant predictor of test performance (F = 4.84; p = 0.010, η² = 0.088), change in systolic BP (SBP) (r² = 0.047, p = 0.028) and change in diastolic CBFv (DFV) (r² = 0.047, p = 0.028) contributed significantly to SDMT scores. Further, change in SBP accounted for a significant amount of variance in change in DFV in the total study sample (r² = 0.090; p = 0.002). These results support previous findings of cognitive deficits in persons with SCI and indicate that inadequate systemic and cerebral hemodynamic responses to testing contribute to test performance. Therefore, clinical treatment of cognitive dysfunction in the SCI population should consider focusing on increasing systemic BP to improve CBFv, particularly in individuals with lesions above T1.