Noninvasive assessment of CO2-induced cerebral vasomotor response in normal individuals and patients with internal carotid artery occlusions.

Abstract

To evaluate the CO 2 -induced vasomotor reactivity of the cerebral vasculature, relative changes of blood flow velocity within the middle cerebral artery were measured by transcranial Doppler ultrasonography during normocapnia and various degrees of hypercapnia and hypocapnia. We studied 40 normal individuals and 40 patients with unilateral and 15 patients with bilateral internal carotid artery occlusions. When blood flow velocity changes as percent of normocapnic values were plotted against end-tidal CO 2 volume percent, a biasymptotic curve (a tangenthyperbolic function) gave the best fit of the scattergram. The distance between the upper and lower asymptotes was defined as cerebral vasomotor reactivity. In the normal individuals, mean±SD vasomotor reactivity was 85.63 ±15.96%. In patients with internal carotid artery occlusions, vasomotor reactivity was significantly lower than normal on both the occluded (mean 45.2%, median 50.4%; p<0.0001) and the nonoccluded (mean±SD 67.7 + 13.3%, /><0.01) sides in the unilateral group and on both sides (mean±SD 36.6 ±15.9% and 44.9±24.6%, p<0.0001) in the bilateral group. The difference between vasomotor reactivity for symptomatic and asymptomatic unilateral occlusions was also highly significant (mean 37.6% and 62.9%, /*<0.006). Vasomotor reactivity was also significantly lower in patients with low-flow infarctions on computed tomography than in patients with normal scans (mean ± SD 36.7 ±25% and 60.2 ± 16.9%, p<0.008). A striking association of low-flow infarctions, ischemic ophthalmopathy, and hypostatic transient ischemic attacks was found with vasomotor reactivities of <34% or even paradoxical reactions. Transcranial Doppler ultrasonographic evaluation of cerebral vasomotor reactivity is a new, feasible, noninvasive, and reproducible technique that allows selection and quantification of patients with true cerebrovascular insufficiency. (Stroke

Perfusion insufficiency in limb-shaking transient ischemic attacks.

“…This negative reactivity may indicate a steal effect, a paradoxical response that has been observed in some patients with severe carotid artery disease. 18 The normal velocity response to hypercapnia in healthy subjects without occlusive disease (2.9-3.5%/mm Hg change in PecxV 9 -20 ) appears to be constant over the physiologic range of 20-60 mm Hg. Among patients with unilateral carotid artery occlusions, Ringelstein et al 18 have shown that vasomotor reactivity measured by TCD is severely reduced, especially in patients who have distal-field infarcts, ischemic ophthalmopathy, or orthostatic TIAs.…”

Cerebral Hemodynamic Response to Generalized Spike‐Wave Discharges

“…These effects might contribute to perfusion changes during gSW and give evidence for the significance of autonomic effects in this context, but not systematic correlation between change in heart rate and course of CBFV during gSW could be established. Cerebral perfusion is known to decrease markedly with reduction of Pco, (25). Hyperventilation-induced hypocapnia during gSW would therefore result in a major decrease in CBFV.…”

Estenose de carótida extracraniana

“…Enquanto é provável que poucas formas de acidente vascular cerebral relacionado à estenose carótida extracraniana ocorram por hipoperfusão 11 , na maioria dos casos, o que ocorre é embolização de uma placa aterosclerótica ou oclusão aguda da carótida e propagação do trombo distalmente 12 .…”