Oxygen extraction efficiency and white matter lesion burden in older adults exhibiting radiological evidence of capillary shunting

Impact of leukoaraiosis on the infarct growth rate and clinical outcome in acute large vessel occlusion stroke after endovascular thrombectomy

INTRODUCTION

As a marker of chronic cerebral small vessel disease, leukoaraiosis (LA) was reported to impact the recruitment of collaterals in acute ischemic stroke (AIS). We intended to explore the impact of LA on the infarct growth rate (IGR) and clinical outcome by impaired collateral development in AIS patients with large vessel occlusion (LVO) who underwent endovascular thrombectomy (EVT).

PATIENTS AND METHODS

Two hundred thirty-six AIS patients who underwent EVT were retrospectively reviewed. The severity of LA was graded using the Fazekas scale with non-contrast CT. IGR was calculated by the acute core volume on CT perfusion divided by the time from stroke onset to imaging. The collateral status after LVO was assessed using the ASITN/SIR collateral scale. The clinical outcomes after EVT were evaluated using a modified Rankin Scale (mRS). The Alberta stroke program early CT score (ASPECTS), the National Institutes of Health Stroke Scale (NIHSS) score at admission, and the modified treatment in cerebral infarction (mTICI) score after EVT were also included. Correlations between those factors were analyzed.

RESULTS

Patients with severe LA had significantly larger core volume on CTP (p = 0.022) and lower collateral grade (p < 0.001). Faster IGR was significantly associated with higher LA severity (adjusted odds ratio [aOR]: 1.53; 95% CI: 1.02-2.33; p = 0.046), higher NIHSS (aOR: 1.04; 95% CI: 1.00-1.09; p = 0.032) and impaired collaterals (aOR: 2.26; 95% CI: 1.27-4.03; p = 0.005). In mediation analysis, collaterals explained 33% of the effect of LA on fast IGR. There was correlation between the severity of LA and mRS (p = 0.007).

DISCUSSION AND CONCLUSION

The increasing severity of LA is associated with impaired collateral status and fast infarct growth. These findings suggest that LA may become a predictive imaging biomarker for the likelihood of progression of tissue injury and clinical outcome after EVT in acute large vessel occlusion stroke.

Red cell exchange transfusions increase cerebral capillary transit times and may alter oxygen extraction in sickle cell disease

Persons with sickle cell disease (SCD) suffer from chronic hemolytic anemia, reduced blood oxygen content, and lifelong risk of silent and overt stroke. Major conventional stroke risk factors are absent in most individuals with SCD, yet nearly 50% have evidence of brain infarcts by the age of 30 years, indicating alternative etiologies for ischemia. We investigated whether radiological evidence of accelerated blood water transit through capillaries, visible on arterial spin labeling (ASL) magnetic resonance imaging, reduces following transfusion-induced increases in hemoglobin and relates to oxygen extraction fraction (OEF). Neurological evaluation along with anatomical and hemodynamic imaging with cerebral blood flow (CBF)-weighted pseudocontinuous ASL and OEF imaging with T2 -relaxation-under-spin-tagging were applied in sequence before and after blood transfusion therapy (n = 32) and in a comparator cohort of nontransfused SCD participants on hydroxyurea therapy scanned at two time points to assess stability without interim intervention (n = 13). OEF was calculated separately using models derived from human hemoglobin-F, hemoglobin-A, and hemoglobin-S. Gray matter CBF and dural sinus signal, indicative of rapid blood transit, were evaluated at each time point and compared with OEF using paired statistical tests (significance: two-sided p < 0.05). No significant change in sinus signal was observed in nontransfused participants (p = 0.650), but a reduction was observed in transfused participants (p = 0.034), consistent with slower red cell transit following transfusion. The dural sinus signal intensity was inversely associated with OEF pretransfusion (p = 0.011), but not posttransfusion. Study findings suggest that transfusion-induced increases in total hemoglobin may lengthen blood transit times through cerebral capillaries and alter cerebral OEF in SCD.

Impaired oxygen extraction and adaptation of intracellular energy metabolism in cerebral small vessel disease

BACKGROUND

We aimed to investigate whether combined phosphorous (³¹P) magnetic resonance spectroscopic imaging (MRSI) and quantitative T 2 ' mapping are able to detect alterations of the cerebral oxygen extraction fraction (OEF) and intracellular pH (pH_i) as markers the of cellular energy metabolism in cerebral small vessel disease (SVD).

MATERIALS AND METHODS

32 patients with SVD and 17 age-matched healthy control subjects were examined with 3-dimensional ³¹P MRSI and oxygenation-sensitive quantitative T 2 ' mapping (1/ T 2 '  = 1/T₂* - 1/T₂) at 3 Tesla (T). PH_i was measured within the white matter hyperintensities (WMH) in SVD patients. Quantitative T 2 ' values were averaged across the entire white matter (WM). Furthermore, T 2 ' values were extracted from normal-appearing WM (NAWM) and the WMH and compared between patients and controls.

RESULTS

Quantitative T 2 ' values were significantly increased across the entire WM and in the NAWM in patients compared to control subjects (149.51 ± 16.94 vs. 138.19 ± 12.66 ms and 147.45 ± 18.14 vs. 137.99 ± 12.19 ms, p < 0.05). WM T 2 ' values correlated significantly with the WMH load (ρ=0.441, p = 0.006). Increased T 2 ' was significantly associated with more alkaline pH_i (ρ=0.299, p < 0.05). Both T 2 ' and pH_i were significantly positively correlated with vascular pulsatility in the distal carotid arteries (ρ=0.596, p = 0.001 and ρ=0.452, p = 0.016).

CONCLUSIONS

This exploratory study found evidence of impaired cerebral OEF in SVD, which is associated with intracellular alkalosis as an adaptive mechanism. The employed techniques provide new insights into the pathophysiology of SVD with regard to disease-related consequences on the cellular metabolic state.