CEREBRAL HEMATOCRIT DECREASES WITH HEMODYNAMIC COMPROMISE IN CAROTID-ARTERY OCCLUSION - A PET STUDY

Background and Purpose-This study investigated whether in patients wit h internal carotid artery occlusion the regional cerebral hematocrit c orrelates with cerebral hemodynamics or metabolic state and, ii so, ho w the regional cerebral hematocrit changes in the hemodynamically comp romised region, Methods-We used positron emission tomography to study seven patients with unilateral internal carotid artery occlusion and n o cortical infarction in the chronic stage. The distributions oi red b lood cell and plasma volumes were assessed using oxygen-15-labeled car bon monoxide and copper-62-labeled human serum albumin-dithiosemicarba zone tracers, respectively. The calculated hematocrit value was compar ed with the hemodynamic and metabolic parameters measured with the oxy gen-15 steady-state technique, Results-In the cerebral cortex, the val ue of the cerebral hematocrit varied but was correlated with tile hemo dynamic and metabolic status, Stepwise regression analysis revealed ch at the large vessel hematocrit, the cerebral metabolic rate of oxygen, and the cerebral blood flow or the oxygen extraction fraction account ed for a significant proportion of variance of the the cerebral hemato crit, The oxygen extraction fraction and the cerebral metabolic rate o xygen negatively correlated with the cerebral hematocrit, whereas the cerebral blood flow correlated positively: patients with reduced blood supply relative to metabolic demand (decreased blood now with increas ed oxygen extraction fraction) showed low hematocrit values. Conclusio ns-In carotid artery occlusion in the chronic stage, regional cerebral hematocrit may vary according to cerebral hemodynamics and metabolic status, Regional cerebral hematocrit may decrease with hemodynamic com promise unless oxygen metabolism concomitantly decreases.