Transcranial doppler CO2 test for the detection of hemodynamically critical carotid artery stenoses and occlusions

Abstract

Cerebral CO2-reactivity was tested by transcranial Doppler sonography (Doppler CO2 test) in 232 patients. Time averaged flow velocity in the middle cerebral artery at the 40 mm Hg blood pCO2 level was taken as a reference point, and the relative increase of flow in hypercapnia of 46.5 mm Hg pCO2 was defined as "Normalized Autoregulatory Response" (NAR). A total of 82 patients with no evidence of cerebrovascular disease gave "normal" values for NAR (23.2 +/- 5.2 SD). In 150 patients with 233 stenoses and occlusions of the internal carotid artery NAR was significantly decreased in higher-grade stenoses (P = 0.01 for 80% diameter reduction, P less than 10(-6) for 90% or more). In such stenoses, patients with NAR less than 14 had suffered more frequently (P less than 0.01) from ipsilateral transient ischemic attacks and/or stroke during the previous 6 months than patients with "normal" NAR. Preoperative NAR less than 14 always improved to "normal" values following carotid surgery, while preoperative NAR greater than 19 remained unchanged (60 cases). The transcranial Doppler CO2 test is thought to be a reliable noninvasive method to detect hemodynamically critical carotid stenoses and occlusions. This may be of interest in selecting patients for superficial temporal artery-middle cerebral artery bypass and carotid surgery. For practical use 4 categories of NAR are suggested.

Effect of carotid endarterectomy on patterns of cerebrovascular reactivity in patients with unilateral carotid artery stenosis.

“…They found that surgery improved intracerebral hemodynamics ipsilateral to ICA stenosis only in patients who preoperatively had a reduced cerebral perfusion pressure at the side of ICA stenosis of at least 20% (indicating inadequate intracerebral collateralization) compared with the pressure in the common carotid artery. Halsey et al, 24 Widder et al, 25 and our group 26 reported a significant inverse correlation between the preoperative CBF reactivity, flow velocity reactivity, or CR, reactivity ipsilateral to ICA occlusion or stenosis and the change in reactivity after surgery. Correspondingly, Vorstrup et al, 27 Russel et al, 28 and Karnik et al 29 found that surgery significantly improved CBF or flow velocity reactivity (as evaluated by the acetazolamide test) only in patients who had an abnormal side-to-side asymmetry in reactivity before surgery.…”

“…1 It was suggested that abnormal intracerebral hemodynamics (as indicated by increased oxygen extraction fraction, pathological reserve capacity testing, or ocular pneumoplethysmography) are associated with a significantly higher incidence in ischemic hemispheric events. 25 Recently we were able to show that the compensatory hemodynamic response to significant unilateral carotid artery stenosis varies and that specific subgroups of carotid artery patients exist who may have, despite an identical degree of stenosis, a greater risk of stroke or cerebral ischemia and thus require different treatment.…”

Course of carotid artery occlusions with impaired cerebrovascular reactivity.

“…89 Another simple and noninvasive technique is the Doppler CO 2 test. 10 It is based on transcranial Doppler sonography that gives information about changes of blood flow velocity in the basal cerebral arteries.…”

Simultaneous Assessment of Vasoreactivity Using Transcranial Doppler Ultrasound and Cerebral Blood Flow in Healthy Subjects

“…Two methods are commonly used for this purpose: mea surement of rCBF with dynamic single-photon emission computerized tomography (SPECT) and measurement of blood flow velocities in the basal intracranial arteries using trans cranial Doppler ul trasound (TCD). The measurements are performed before and after the application of a potent vasodila tory stimulus, such as carbon dioxide or acetazol-amide (Brown et al, 1986;Vorstrup et al, 1986;Widder et al, 1986;Russell et al, 1990). Recent studies have shown an increased risk of ischemic episodes in the hemisphere ipsilateral to an oc cluded or stenotic carotid artery when its distribu tion territory had a reduced cerebrovascular va soreactivity (Kleiser and Widder, 1992;Y onas et ai, 1993).…”