Pathophysiology of unilateral high-grade carotid artery stenosis: evaluation of intracranial haemodynamics by analysis of velocity waveforms from the middle cerebral artery

Abstract

1. Transcranial flow velocity waves were measured via Doppler sonography of the middle cerebral artery during hypo-, hyper- and normo-capnia. Applying the principle of vascular impedance, flow velocity waves were analysed in 30 young subjects, 37 elderly subjects and 18 patients with high-grade unilateral internal carotid artery disease. 2. There was evidence that the relative peak-to-peak velocity in the middle cerebral artery could serve as an index of peripheral wave reflection and cerebral resistance (CRi). The response of CRi to changes in arterial CO2 concentration (CRi reactivity) showed a clear age-dependency. However, the absolute side-to-side asymmetry of CRi reactivity (delta R) did not vary with age and could be used to define a normal range (0-4%CRi/vol.%CO2). 3. Selective angiography demonstrated no cerebral cross-flow through the anterior part of the circle of Willis in nine patients with carotid artery stenosis whose absolute delta R was above the normal range and whose CRi reactivity of the affected hemisphere was lower than that of the healthy opposite hemisphere. Conversely, another group of nine patients, whose ipsilateral CRi reactivity was higher than the contralateral CRi reactivity, demonstrated cross-flow through the anterior part of the circle of Willis. 4. delta R may be used to identify patients who have high-grade internal carotid artery stenosis and present with low cerebral vascular resistance owing to poor intracerebral collaterals.

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

“…This subgroup has been identified by various other techniques (positron emission tomography, single-photon emission computed tomography) in the past, 23141617 -2021 and is characterized by a critical reduction of ipsilateral perfusion pressure caused by insufficient collaterals. 7 All patients were scheduled for CEA. Indication for surgery in patients with unilateral high-grade to threadlike symptomatic ICA stenosis is no longer controversial.…”

“…7 In brief, a 2-MHz TCD sonography transducer (VingMed SD 50, Sonotron) was placed on the "skull window" above the zygomatic arch, and the MCA was studied at the depth of 50 to 60 mm. Average blood flow velocity at peak systole and diastole was transferred to a personal computer (Macintosh II CI, Apple) for further off-line data processing.…”

“…Details of this group were published recently. 7 To determine the normal absolute side-to-side asymmetry, we subtracted arbitrarily right CR, reactivity from left CR, reactivity in control subjects and ignored the signs. Normal absolute sideto-side asymmetry amounted to 1.6+0.2 [1.2] %CR,/vol%CO 2 (mean±SEM [SD]).…”

“…the control group, 7 allowed differentiation of our patients into three subgroups that did not differ with respect to age or localization of carotid artery stenosis. Also, the percentage of symptomatic and asymptomatic patients was comparable between these subgroups.…”

Patterns of cerebrovascular reactivity in patients with unilateral asymptomatic carotid artery stenosis.

“…14 There is evidence that the relative peak-to-peak velocity of the flow velocity curve may be used as an indicator of peripheral resistance. Relative peak-to-peak velocity (also known as Pourcelot's index) is, furthermore, superior to the pulsatility index with regard to resistance measurement.…”