CBF/CBV maps in normal volunteers studied with ^(15)O PET:a possible index of cerebral perfusion pressure

Local cerebral perfusion pressure （CPP） is a primary factor controlling cerebral circulation and previous studies have indicated that the ratio of cerebral blood flow （CBF） to cerebral blood volume （CBV） can be used as an index of the local CPP. In this study, we investigated whether the CBF/CBV ratio differs among different brain structures under physiological conditions, by means of （15）O positron emission tomography. Nine healthy volunteers （5 men and 4 women; mean age, 47.0 ± 1.2 years） were studied by H2（15）O bolus injection for CBF measurement and by C（15）O inhalation for CBV measurement. The CBF/CBV ratio maps were created by dividing the CBF images by the CBV images after anatomical normalization. Regions of interest were placed on the CBF/CBV maps and comparing the regions. The mean CBF/ CBV ratio was highest in the cerebellum （19.3 ＋ 5.2/ min）, followed by the putamen （18.2 ± 3.9）, pons （16.4 ±4.6）, thalamus （14.5：1： 3.3）, cerebral cortices （13.2 ±2.4）, and centrum semiovale （1115 ± 2.1）. The cerebellum and putamen showed significantly higher CBF/CBV ratios than the cerebral cortices and centrum semiovale. We created maps of the CBF/ CBV ratio in normal volunteers and demonstrated higher CBF/CBV ratios in the cerebellum and putamen than in the cerebral cortices and deep cerebral white matter. The CBF/CBV may reflect the local CPP and should be studied in hemodynamicallycompromised patients and in patients with risk factors for small-artery diseases of the brain. Keywords： cerebral perfusion pressure; cerebra blood flow; cerebral blood volume; H2（15）O; C（15）O

Hypoperfusion assessed by pressure reactivity index is associated with delayed cerebral ischemia after subarachnoid hemorrhage:an observational study

Background:Dysfunction of cerebral autoregulation is one of the pathophysiological mechanisms that causes delayed cerebral ischemia(DCI)after subarachnoid hemorrhage(SAH).Pressure reactivity index(PRx)have been confirmed to reflect the level of cerebral autoregulation and used to derive optimal cerebral perfusion pressure(CPPopt).The goal of this study is to explore the associations between autoregulation,CPPopt,PRx,and DCI.Methods:Continuous intracranial pressure(ICP),arterial blood pressure(ABP),and cerebral perfusion pressure(CPP)signals acquired from 61 aSAH patients were retrospectively analyzed.PRx was calculated and collected by Pneumatic computer system.The CPP at the lowest PRx was determined as the CPPopt.The duration of a hypoperfusion event(dHP)was defined as the cumulative time that the PRx was>0.3 and the CPP was<CPPopt.The duration of CPP more than 10 mmHg below CPPopt(ΔCPPopt<−10 mmHg)was also used to assess hypoperfusion.The percent of the time of hypoperfusion by dHP andΔCPPopt<−10 mmHg(%dHP and%ΔCPPopt)were compared between DCI group and control group,utilizing univariate and multivariable logistic regression.It was the clinical prognosis at 3 months after hemorrhage that was assessed with the modified Rankin Scale,and logistic regression and ROC analysis were used for predictive power for unfavorable outcomes(mRs 3–5).Results:Data from 52 patients were included in the final analysis of 61 patients.The mean%dHP in DCI was 29.23%and 10.66%in control.The mean%ΔCPPopt<−10 mmHg was 22.28%,and 5.90%in control.The%dHP(p<0.001)and the%ΔCPPopt<−10mmHg(p<0.001)was significantly longer in the DCI group.In multivariate logistic regression model,%ΔCPPopt<−10 mmHg(p<0.001)and%dHP(p<0.001)were independent risk factor for predicting DCI,and%ΔCPPopt<−10 mmHg(p=0.010)and%dHP(p=0.026)were independent risk factor for predicting unfavorable outcomes.Conclusions:The increase of duration of hypoperfusion events and duration of CPP below CPPopt over 10 mmHg,evaluated as time of lowered CPP,is highly indicative of DCI and unfavorable outcomes.