Reactivity of cerebral blood flow to carbon dioxide in various types of ischemic cerebrovascular disease: evaluation by the transcranial Doppler method.

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Abstract
The response of cerebral blood flow to changes in the arterial carbon dioxide partial pressure (i.e., carbon dioxide reactivity) has been evaluated as a parameter of cerebral perfusion reserve in patients with cerebrovascular disease. In this study, variations in this reactivity in various ischemic cerebrovascular diseases were evaluated by a newly established method, a transcranial Doppler technique. Thirty-three patients with symptomatic cerebrovascular disease, 13 patients with asymptomatic cerebral infarction, and 25 age-matched normal control subjects were investigated. The symptomatic patients were divided into three groups; those with unilateral carotid artery obstruction, those with cortical infarction, and those with lacunar infarction. The carbon dioxide reactivity of each subject was determined by simultaneously measuring the mean spatial Doppler frequency in the middle cerebral artery and the end-tidal carbon dioxide partial pressure under normocapnic, hypercapnic, and hypocapnic conditions. In the patients with carotid obstruction, the carbon dioxide reactivity of the hemisphere ipsilateral to the obstruction was more impaired than the reactivity of the symptomatic hemispheres in any other group, and was significantly less than in the contralateral asymptomatic hemisphere (p < 0.01). In patients with cortical infarction, the carbon dioxide reactivity of the symptomatic hemisphere was significantly less than in normal control subjects (p < 0.05) and was also less than that of the contralateral asymptomatic hemisphere (p < 0.05). In patients with lacunar infarction, the carbon dioxide reactivity of both hemispheres was significantly less than that in normal controls (p < 0.01), although there was no difference between the symptomatic and asymptomatic hemispheres. In patients with asymptomatic infarction, the carbon dioxide reactivity was also less than that in normal controls (p < 0.01). The carbon dioxide reactivity of cerebral blood flow measured by this transcranial Doppler technique may be useful for characterizing the hemodynamic changes that occur in various types of ischemic cerebrovascular disease.