Cerebral Hematocrit Decreases With Hemodynamic Compromise in Carotid Artery Occlusion

Abstract

Background and Purpose-This study investigated whether in patients with internal carotid artery occlusion the regional cerebral hematocrit correlates with cerebral hemodynamics or metabolic state and, if so, how the regional cerebral hematocrit changes in the hemodynamically compromised region. Methods-We used positron emission tomography to study seven patients with unilateral internal carotid artery occlusion and no cortical infarction in the chronic stage. The distributions of red blood cell and plasma volumes were assessed using oxygen-15-labeled carbon monoxide and copper-62-labeled human serum albumin-dithiosemicarbazone tracers, respectively. The calculated hematocrit value was compared with the hemodynamic and metabolic parameters measured with the oxygen-15 steady-state technique. Results-In the cerebral cortex, the value of the cerebral hematocrit varied but was correlated with the hemodynamic and metabolic status. Stepwise regression analysis revealed that the large vessel hematocrit, the cerebral metabolic rate of oxygen, and the cerebral blood flow or the oxygen extraction fraction accounted for a significant proportion of variance of the cerebral hematocrit. The oxygen extraction fraction and the cerebral metabolic rate of oxygen negatively correlated with the cerebral hematocrit, whereas the cerebral blood flow correlated positively: patients with reduced blood supply relative to metabolic demand (decreased blood flow with increased oxygen extraction fraction) showed low hematocrit values. Conclusions-In

Cerebral Oxygen Metabolism of Rats using Injectable 15O-Oxygen with a Steady-State Method

“…This significant reduction of parameters in the region of cerebral infarction was similar to a previous report (Temma et al, 2006). A single-compartment analysis used in the steady-state method may overestimate cerebral water clearance and tissue counts (Ohta et al, 1992(Ohta et al, , 1996; however, this method was established in human PET studies and many studies with CVD patients were reported (Yamauchi et al, 1996(Yamauchi et al, , 1998(Yamauchi et al, , 1999Okazawa et al, 2001;Ouchi et al, 2001). Although slightly different values were observed between the steady-state method and the bolus administration method in a previous study with CVD, the values were not significantly different (Okazawa et al, 2001).…”

Detecting Misery Perfusion in Unilateral Steno-Occlusive Disease of the Internal Carotid Artery or Middle Cerebral Artery by MR Imaging

“…Under the pathologic conditions of brain ischemia, the error may cause underestimation of OEF in the ischemic brain tissue because hematocrit in the local small vessel would decrease to some extent. 30 Another potential error comes from paramagnetic sources other than deoxyhemoglobin, which can induce an additional signal-intensity loss in MR images. Therefore, the presence of hemosiderin may lead to an unavoidable error in the measurement of OEF in the local brain.…”

Cerebral Vascular Mean Transit Time in Healthy Humans: A Comparative Study with PET and Dynamic Susceptibility Contrast-Enhanced MRI

“…Regional cerebral hematocrit may change with pathologic condition. For example, in patients with occlusive cerebrovascular disease, regional decreases in cerebral hematocrit, which may be associated with greater decreases in plasma velocity than in RBC velocity, has been reported (Yamauchi et al, 1998(Yamauchi et al, , 1999. In PET studies, the assumption of constant hematocrit ratio will cause underestimation of CBV and MTT in such brain regions.…”