PET studies of changes in cerebral blood flow and oxygen metabolism after unilateral microembolization of the brain in anesthetized dogs.

Abstract

Cerebral blood flow and oxygen metabolism have been measured with the steady-state oxygen-15 technique and positron emission tomography in anesthetized dogs. Regional microembolization was induced by infusing Sephadex particles (diameter, 40 /am) into one of the common carotid arteries. In the first series of experiments, 2.5 mg Sephadex was infused, and the dogs were examined within 3-4 hours after embolization. In a second series 0.55 mg Sephadex was infused, and the dogs were examined either in the first 3-4 hours or 24-48 hours after embolization. Cerebral blood flow, oxygen extraction ratio, and cerebral oxygen utilization were measured at 3 Pco 2 levels. In the acute experiments, cerebral oxygen utilization in the embolized hemisphere was 6 (0.55 mg Sephadex) and 25% (2.5 mg Sephadex) lower than on the contralateral side. While cerebral blood flow was symmetrically distributed in normocapnia and hypocapnia, it was 9 (0.55 mg Sephadex) and 35% (2.5 mg Sephadex) lower in the embolized hemisphere during hypercapnia. In normocapnia and hypocapnia the lower oxygen utilization in the embolized hemisphere was characterized by a lower oxygen extraction ratio, and in hypercapnia by an unchanged (0.55 mg Sephadex) or by a higher (2.5 mg Sephadex) extraction ratio. The different effect on oxygen extraction ratio in the control and embolized hemispheres resulted in images of uncoupling between perfusion and oxygen demand that varied according to the Pco 2 . The experiments also showed a fall in cerebral blood flow in the embolized hemisphere after 3-4 hours, indicating delayed hypoperfusion. After 24-48 hours, blood flow was about 10% higher in the embolized hemisphere, and this was observed at the 3 Pco 2 levels, while the oxygen extraction ratio was systematically lower. Oxygen utilization in the embolized hemisphere was depressed to practically the same extent as in acute experiments. It can be concluded that between 4 and 24 hours after microembolization the cerebral microcirculation shows important changes, with installation of luxury perfusion in the face of an unchanging decreased oxygen metabolism. (Stroke 1987;18:128-137)

Cerebral Blood Flow and Oxygen Metabolism in Leuko-Araiosis

“…The measurement of the radioactivity in the blood samples and the rCBF, rOER and rCMRO: determinations were calculated according to the methods described by Weyne et al [27], Three slide reconstructions were obtained 3, 19 and 35 mm above the orbitomeatal line, respectively. The different cortical and subcortical regions were defined by superposition on corresponding CT scan slides, thus avoiding measurements in the ventricular sys tem.…”

Parkinsonism in Patients with Vascular Dementia: Clinical, Computed- and Positron Emission-Tomographic Findings

“…For measuring rCMRO 2 , 15 O 2 was inhaled at 1.5 GBq/min, and after 10 min of equilibration, scan times were extended to 400 s. Two samples of arterialized blood were taken anaerobically at the procedural beginning and end. Methods for measuring radioactivity in blood samples, and rCBF, rOER and rCMRO 2 were calculated as described previously [52]. rOER and rCMRO 2 values were not corrected for cerebral blood volumes, probably leading to a relative overestimation of rOER and rCMRO 2 due to the signal from the nonextracted intravascular 15 O [53].…”

Significance of White Matter Lucencies in Posthypoxic-Ischemic Encephalopathy: Comparison of Clinical Status and of Computed and Positron Emission Tomographic Findings

“…[18]. Values of rOER were not corrected by those of regional cerebral blood volume, as the latter have not been measured.…”