Effect of internal carotid artery occlusion on middle cerebral artery blood flow at rest and in response to hypercapnia.

In patients with symptomatic cerebrovascular disease the rise in middle cerebral artery (MCA) blood-flow velocity in response to hypercapnia, recorded with a pulsed transcranial doppler velocimeter, was significantly less in MCAs above a totally occluded carotid artery than in MCAs above a patent carotid. These findings support the existence of compensatory cerebral vasodilatation above a carotid occlusion and suggest that transient ischaemic attacks in patients with carotid occlusion may be flow-related rather than embolic phenomena. These patients may therefore benefit from extracranial-intracranial surgical revascularisation. The method presented is non-invasive and therefore ideally suited for use as a screening test or in follow-up studies.