Resting and hypercapnic rCBF in patients with unilateral occlusive disease of the internal carotid artery

Regional cerebral blood flow was measured by the 133Xe inhalation technique in 15 patients with severe unilateral internal carotid artery stenosis (75%) or occlusion, and in the absence of evidence of any sign of occlusive disease in other main afferent cerebral arteries. A comparison with normal subjects showed that lowered resting flow in both hemispheres was a common finding in all patients. Interhemispheric asymmetry was present only in patients with occlusion and the precentral, posterior temporal, and occipital regions were the most seriously affected. The CO2 reactivity was substantially reduced in both hemispheres of all stenotic and occluded patients, but occluded patients showed an increased reduction of CO2 reactivity only in the ipsilateral hemisphere. In addition to an hypothetical age effect, the atherosclerotic involvement of the cerebral vascular system leads to a reduction of flow and loss of CO2 reactivity in both hemispheres. In this context, the collateral supply capacity is not overloaded in case of a unilateral severe stenosis but fails in case of a unilateral occlusion of the internal carotid artery. A suitable estimate of the blood flow reduction as a result of occlusion is made by the hemispheric and regional laterality indices applied in resting and hypercapnia conditions. These indices could be used as indicators for endarterectomy or bypass surgery as well as a sensitive means for appreciating cerebral blood flow response to treatment.