Effect of Pa CO CO 2 on Hyperemia and Ischemia in Experimental Cerebral Infarction

To assess the effects of PaCO CO 2on cerebral ischemia and reactive hyperemia, the right middle cerebral artery was occluded in 18 cats. Four to six hours later, PaCO 2 was adjusted by mechanical ventilation, with or without CO2 , to less than 20 torr in four cats, 31 to 38 torr in six, and 46 to 68 torr in eight. Regional cerebral blood flow (CBF) then was measured at multiple sites in each hemisphere by autoradiography. In regions of brain tissue outside the distribution of the occluded middle cerebral artery, log10 CBF correlated positively with PaCO CO 2. In ischemic regions, CBF was higher in normocapnic cats. Reactive hyperemia occurred in two cats of the hypocapnic group, in four cats of the normocapnic group, but in only one hypercapnic cat (PaCO CO 2= 46 torr). Hyperemia also was found outside potentially ischemic regions in five cats. Multiple hyperemic foci developed in six cats. Neither hypocapnia nor hypercapnia was associated with a smaller size or higher CBF of regions of cerebral ischemia produced by occlusion of a middle cerebral artery, although hypercapnia inhibited the development of hyperemia.