Does a relative perfusion measure predict cerebral infarct size?

Backround & Purpose: The present study tested whether or not a relative measure of cerebral blood flow is sufficient to predict irreversible tissue damage following focal cerebral ischemia and reperfusion in the rat suture model.

Methods: In rats, the middle cerebral artery was occluded (MCAO) for 1h followed by 1h reperfusion (8 animals with constant hematocrit; 7 animals with decreased hematocrit due to withdrawal of arterial reference blood without compensation). Radiolabeled microspheres were injected into the left ventricle before, 30min post-MCAO and 30min post-reperfusion, and absolute (aCBF) and relative (rCBF) cerebral blood flow then determined. RCBF was compared to baseline that is before MCAO (rCBFB) and to corresponding contralateral areas in the noninfarcted hemisphere at each time point (rCBFC). Infarct size was assessed by TTC-staining.

Results: Absolute CBF in vital tissue was 0.69±0.07ml/g/min. In partially and completely necrotic tissue aCBF was 0.39±0.05ml/g/min and 0.30±0.09ml/g/min, respectively. While there was a close inverse correlation between infarct volume and aCBF (r=0.79), the correlations between infarct volume and rCBFC (r=0.22) and rCBFB (r=0.19) were poor. In this model, a decrease in hematocrit from 41% to 27% had no effect on CBF post-MCAO and post-reperfusion or on infarct size.

Conclusion: The microspheres technique permits the measure of aCBF with good spatial resolution. A relative perfusion measurement is an unprecise predictor of infarct size.