Effects of Changes in Carbon Dioxide Pressure and Arterial Pressure on Blood

The effect of locally induced cerebral ischemia on regional cerebral blood flow before and during elevation of Paco2 was measured qualitatively in anesthetized dogs by a thermistor probe technique and a photographic method involving cerebral angiography. The flow response to changes in systemic arterial pressure was also noted in the ischemic zone. Increased Paco2 resulted in increased flow to the ischemic zone and shrinkage of the area of ischemia, by virtue of collateral circulation from other arterial trunks. In no instance was "intracerebral steal," as previously reported, noted in response to increased Paco2, though there was no means of determining if the quantitative response in the ischemic area was similar to that in normal brain. Arteries and arterioles in the ischemic zone were seen to be constricted and irregular, rather than maximally dilated, as has been proposed. The percent decrease in pressure in the occluded arterial segment was much greater than in the patent cerebral arteries. Response to increased Paco2 occurred even though intraarterial pressures were less than 40 mm Hg. There was preservation of the response to norepinephrine in the ischemic zone, despite reduction in flow; response to changes in Paco2 persisted even after this had been lost. ADDITIONAL