Impaired cerebral autoregulation and neurovascular coupling in middle cerebral artery stroke: Influence of severity?

Abstract

We aimed to assess cerebral autoregulation (CA) and neurovascular coupling (NVC) in stroke patients of differing severity comparing responses to healthy controls and explore the association between CA and NVC with functional outcome. Patients admitted with middle cerebral artery (MCA) stroke and healthy controls were recruited. Stroke severity was defined by the National Institutes of Health Stroke Scale (NIHSS) scores: ≤4 mild, 5-15 moderate and ≥16 severe. Transcranial Doppler ultrasound and Finometer recorded MCA cerebral blood flow velocity (CBFv) and blood pressure, respectively, over 5 min baseline and 1 min passive movement of the elbow to calculate the autoregulation index (ARI) and CBFv amplitude responses to movement. All participants were followed up for three months. A total of 87 participants enrolled in the study, including 15 mild, 27 moderate and 13 severe stroke patients, and 32 control subjects. ARI was lower in the affected hemisphere (AH) of moderate and severe stroke groups. Decreased NVC was seen bilaterally in all stroke groups. CA and NVC correlated with stroke severity and functional outcome. CBFv regulation is significantly impaired in acute stroke, and further compromised with increasing stroke severity. Preserved CA and NVC in the acute period were associated with improved three-month functional outcome.

Keywords: Stroke; cerebral autoregulation; neurovascular coupling; outcome; severity.

Figure 1.

Comparison of autoregulatory index (ARI) among controls, mild, moderate and severe stroke sub-groups. Bars/whisker represents one SD. * p < 0.05 compared to controls.

Figure 2.

Cerebral and systemic hemodynamic responses to the passive paradigm (grey bar). (a) CBFv responses in the activated hemisphere of control (continuous black line + crosses), mild stroke (continuous grey line + squares), moderate stroke (continuous grey line) and severe stroke (continuous black line); (b) CBFv percentage responses in the non-activated cerebral hemispheres; (c) Variation in BP during the paradigm performance. Bars represent one SD. δ p < 0.006 between mild and the other two stroke groups *p < 0.05 between stroke and control.

Figure 3.

Scatter graphs of Spearman’s correlation analysis. Correlation coefficient (r-value) between stroke affected hemisphere ARI and severity (a) and outcome (b), and between mRS and affected (c) and unaffected hemispheres (d).