Richard Jackson, MD
Nai-Fang Chi et al. published a study on the evaluation of autoregulation in ischemic stroke. The purpose of this study was to investigate whether dynamic cerebral autoregulation (dCA) indices constitute an independent functional outcome predictor of acute ischemic stroke.
Cerebral autoregulation (CA) regulates vascular tone to compensate hypoperfusion after during ischemia but no concrete guidelines for blood pressure targets are currently known. The impact of cerebral autoregulation is associated with infarct volume but outcome is currently confounded by other comorbid variables. Dynamic cerebral autoregulation (dCA) is a way to quantify CA by analyzing the relationship between transient changes in cerebral blood flow and blood pressure. This study attempted to assess whether resting state dCA was a functional predictor of outcome.
The study was performed at Taipei Medical University. 100 stroke patients were assessed with NIHSS, MRI and mRS within 7 days after stroke onset and compared with 40 control patients. Pure sensory impairment, carotid occlusions, and atrial fibrillation were excluded. dCA was assessed between 3 and 7 days post-event. CA was calculated using the transfer function analysis recommended by the International Cerebral Autoregulation Research Network. Very Low Frequency (VLF) bands are the frequencies at which CA is active. The phase shift and gain between blood pressure and cerebral blood flow velocity were studied. In impaired CA larger gains and smaller phase shifts are found in comparison to normal CA. Demographics and dCA indices were compared using ANOVA, Kruskal-Wallis test, or the χ2 test and post hoc analysis.
Hypertension, diabetes, hyperlipidemia, MAP, and CBF velocity were not found to be significant, but the patients with non-favorable outcomes were older, male, with higher MAPs, rates of hypertension, diabetes, and dyslipidemia, larger stroke volumes, higher rates of large artery atherosclerosis, lesions in the corticospinal tract, and lower TCD mean CBF velocity. The autoregulation indices have very wide confidence intervals which overlap and the scatter plot does not show a clear pattern. In the regression analysis there are 15 variables for only 86 total patients possibly causing overfitting bias.
Bilateral cerebral autoregulation has been documented to occur in lacunar strokes per the study. However, there are many limitations which could be evaluated in future and repeated studies including overfitting of the regression model, lack of pre-specified endpoints for regression, lack of attention to hemispheric lateralization and the subsequent effects of NIHSS evaluation, imaging evaluation of infarct size, and lack of clarity as to whether the evaluators were blinded to the TCD data.