Regional cerebral blood flow response to hypocapnia in the contralateral hemisphere of patients with acute cerebral infarction.

The rCBF response to hypocapnia induced by active short-term hyperventilation was determined in the contralateral hemispheres of ten patients with acute unilateral cerebral infarction. Overall rCBF reduction occurred in only two patients. Regional or widespread abnormal responses to Paco2 reduction manifested as either no change or a paradoxical increase in the rCBF were observed in eight patients. The hemispheric mean rCBF reduction following hypocapnia was diminished as compared with control subjects. Our findings suggest that an impairment of the chemical control of rCBF may occur in the non-infarcted hemisphere during the early period following the onset of cerebral infarction. The pathophysiological mechanisms which may underlie this abnormal rCBF reactivity to Paco2 reduction are considered.