The CO2 response in focal cerebral ischemia--sequential changes following recirculation

The study was undertaken to determine the effects of various levels of ischemia on the CO2 response and on the development of infarction using the canine thalamic infarction model. Three groups were studied: those with severe ischemia (rCBF below 40% of the pre-occlusion levels), moderate ischemia (between 40% and 70%) and mild ischemia (greater than 70%). The CO2 response was measured after 30 minutes, 1, 2 and 6 hours of occlusion and then for 4 hours after recirculation. The CO2 response recovered after 30 minutes of occlusion in the severely ischemic animals, but in 8 of the 9 animals with 1 or more hours of occlusion, an impaired CO2 reactivity was found during occlusion and during recirculation. Among moderately ischemic animals, many showed impaired CO2 reactivity during occlusion, but following recirculation no single trend was observed. Among mildly ischemic animals, almost no abnormalities in the CO2 response were seen either during 6 hours of occlusion or thereafter. Among the 11 animals from all 3 groups which showed impaired CO2 reactivity, 10 developed infarction, while among the 10 animals which showed no impaired CO2 reactivity, in 9 infarction did not arise.