Effect of MCA occlusion on brain O₂ supply and consumption determined microspectrophotometrically

This study compared oxygen extraction, oxygen consumption, and cerebral blood flow (CBF) in the ischemic and contralateral cortex of middle cerebral artery (MCA)-occluded feline brain using a microspectrophotometric technique. This technique was further validated in several experiments. A transorbital approach exposed the right MCA. After preocclusion blood pressure, heart rate, and blood gas values were determined, radioactively labeled microspheres (15 ± 3 μm diam) were injected intra-artrially. The right MCA was then occluded. These same measurements were taken 1 h later. Arterial and venous oxygen saturations were determined in the center and surrounding area of the occluded ischemic cortex and other brain regions. Regional cerebral oxygen consumption was determined as the product of CBF and oxygen extraction. CBF decreased significantly from 54.0 ± 5.0 to 26.6 ± 4.8 (means ± SE) ml·min^-1·100 g^-1 in the center of the ischemic cortex and from 49.6 ± 7.0 to 30.6 ± 5.0 ml·min^-1·100 g^-1 in the surrounding ischemic cortex. Oxygen extraction was significantly increased from 3.7 ± 0.4 ml O₂/100 ml blood to 4.6 ± 0.6 ml O₂/100 ml blood in the center of the occluded cortex but was not significantly altered in the surrounding moderately ischemic cortex. Oxygen consumption was not significantly altered in either ischemic cortex region when compared with the contralateral cortices. Unilateral MCA occlusion caused a decreased regional CBF associated with increased brain oxygen extraction in the cortical region directly supplied by the MCA. The feline brain appears to maintain oxygen consumption in the occluded cortex by increasing oxygen extraction.