These results suggest a link between impaired cerebrovascular reactivity and the risk of ischemic events ipsilateral to severe asymptomatic carotid stenosis.

Background and Purpose-Evidence suggests that an alteration in cerebral hemodynamics plays a relevant role in the occurrence of stroke in patients with carotid occlusion. The purpose of the present study was to evaluate the relationships among baseline characteristics, type and number of collateral pathways, cerebral vasomotor reactivity (VMR), and outcome of patients with carotid occlusion. Methods-One hundred four patients with symptomatic or asymptomatic internal carotid artery occlusion were followed up prospectively for a median period of 24 months. Cerebral VMR to apnea was calculated with transcranial Doppler ultrasonography by means of the breath-holding index (BHI) in the middle cerebral arteries. The patency of the 3 major intracranial collateral vessels was also evaluated. Results-During the follow-up period, 18 patients experienced an ischemic stroke ipsilateral to internal carotid artery occlusion. Among factors considered, only older age, number of collateral pathways, and BHI values in the middle cerebral artery ipsilateral to the occluded side were significantly associated with the risk of ipsilateral stroke (PϽ0.001, Pϭ0.008, and PϽ0.001, respectively; multiple Cox regression analysis). A normal VMR and favorable prognosis characterized patients with full collateral development; in this group, no patient experienced an ischemic event. On the other hand, an impaired VMR and increased probability of experiencing a stroke were found in patients without collateral pathways; the annual risk of ipsilateral stroke in this group was 32.7%. Patients with 1 or 2 collateral pathways showed a different VMR ranging from normal to strongly reduced BHI values. The ipsilateral stroke event risk was 17.5% in patients with 1 collateral vessel and 2.7% in patients with 2 collateral pathways. In this case, the risk of cerebrovascular events occurring during the follow-up period was significantly related to VMR. Conclusions-These data suggest that cerebral hemodynamic status in patients with carotid occlusive disease is influenced by both individual anatomic and functional characteristics. The planning of strategies to define the risk profile and any attempt to influence patients' outcome should be based on the evaluation of the intracranial hemodynamic adaptive status, with particular attention to the number of collateral vessels and the related VMR. (Stroke. 2001;32:1552-1558.)

Background and Purpose-The purpose of this study was to investigate the possibility of obtaining prognostic indications in patients with internal carotid occlusion on the basis of intracranial hemodynamic status, presence of previous symptoms of cerebrovascular failure, and baseline characteristics. Methods-Cerebral hemodynamics were studied with transcranial Doppler ultrasonography. Cerebrovascular reactivity to apnea was calculated by means of the breath-holding index (BHI) in the middle cerebral arteries. Sixty-five patients with internal carotid artery occlusion were followed-up prospectively (median, 24 months), 23 patients were asymptomatic and 42 symptomatic (20 with transient ischemic attack and 22 with stroke). Results-During the follow-up period, 11 symptomatic patients and 1 asymptomatic patient had another ischemic event ipsilateral to carotid occlusion. Among factors considered, only lower BHI values in the middle cerebral arteries ipsilateral to carotid occlusion and older age were significantly associated with the risk of developing symptoms (Pϭ0.002 and Pϭ0.003, respectively; Cox regression multivariate analysis). Based on our data, a cut point of the BHI value for distinguishing between pathological and normal cerebrovascular reactivity was determined to be 0.69. All patients except one, who developed TIA or stroke during the follow-up period, had BHI values ipsilateral to carotid occlusion of Ͻ0.69. Conclusions-These data suggest that impaired cerebrovascular reactivity is predictive for cerebral ischemic events in patients with carotid occlusion. (Stroke. 1999;30:593-598.)

Background and Purpose-Cerebral hemodynamic and metabolic changes can compensate for the decrease in cerebral blood flow occurring in patients with carotid occlusive disease. At present, a complete assessment of the cerebral adaptive status is only possible with positron-emission tomography. Near-infrared spectroscopy (NIRS) is a noninvasive technique that, providing a real time assessment of fluctuations in cerebral hemoglobin, has been used to estimate the cerebral blood volume and to measure cerebral vasomotor reactivity (VMR). Moreover, NIRS technology, by allowing the absolute measurement of absorption and scattering coefficients of brain, can determine the oxyhemoglobin and deoxyhemoglobin concentrations in situ in the blood stream. Methods-In order to evaluate different aspects of the cerebral hemodynamic status, 27 subjects with symptomatic and asymptomatic carotid artery occlusion and 30 healthy subjects underwent a simultaneous examination by means of transcranial Doppler (TCD), able to reliably detect collateral circulation and VMR, and NIRS at rest condition and during CO 2 reactivity test. Results-The main finding of this study was the demonstration of a difference between asymptomatic and symptomatic patients in terms of mean flow velocity increase (52.4% versus 21.0%; PϽ0.001) estimated by TCD and of hemoglobin saturation increase measured by NIRS (6.8% versus 3.8%; Pϭ0.015). Conclusions-The opportunity to perform NIRS and TCD simultaneously provides useful information about both hemodynamic and metabolic cerebral adaptive status in patients with occlusive disease in a simple, noninvasive, and reliable way.

We simultaneously performed near infrared spectroscopy (NIRS) and transcranial Doppler (TCD) to evaluate the effects of hypercapnia as well as of scalp ischemia on the blood flow at two different depth levels within the brain and of the scalp vessels. A decrease in the backscattered light intensity, meaning an increment of blood volume, was detected at the end of hypercapnia in all healthy subjects. This decrement was partly masked by ischemia in the cutaneous vessels. In 2 patients with a monohemispheric lesion in the middle cerebral artery (MCA) territory, an increase in NIRS response was found in the healthy hemisphere, while in the stroke side the CO₂-induced changes were negligible. TCD data showed a similar increment of blood flow velocity to the hypercapnia in both hemispheres, with no differences between the affected and normal side in 1 patient, whereas in the second one, no increment was observed on the affected side, probably due to internal carotid artery stenosis. The two methods nicely integrate: TCD mainly tests subcortical changes in the MCA flow, while NIRS is exquisitely sensitive to cortical arterioles and capillary blood flow modifications.