Predictive Value of Cerebrovascular Reserve in Patients with Carotid Artery Stenosis for Choosing Treatment Strategy

Va, Aliev; Vb, Semenyutin; Panuntsev, GK

doi:10.23937/2469-5807/1510086

Cited by 1 publication

(3 citation statements)

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“…Clinically measured ratios of reserve Qr/Qn and reactivity Vmax/Vn for patients considered to have adequate-normal reserve are 1.2 to 1.3 (1,2, 11). At 70.7% stenosis and 20% reserve and Pa = 120, 100, and 80 mmHg the Rw are 0.14, 1.0 and 1.3 respectively.…”

Section: Resultsmentioning

confidence: 99%

“…Missing from this analysis and the majority of publications is consideration of systemic arterial pressure or of the precise degree of carotid stenosis between 70% and 100%. Many studies and a recent review (1) conclude that collateral circulation is the major determinant of reserve/reactivity but provide little objective evidence for this. While published reserve or reactivity results support the hypothesis that patients with significant carotid stenosis and little or no reserve blood flow are at a significantly higher risk of stroke than those with “adequate” reserve, it is not possible to reach this conclusion in specific patients.…”

Section: Resultsmentioning

confidence: 99%

“…While carotid plaque stability-embologeneity, degree of carotid stenosis and estimates of cerebrovascular blood flow reserve have been extensively studied, there remains no scientifically acceptable criteria for recommending reconstructive carotid surgery in these patients. A recent review and meta analysis (1, 2) of studies reporting cerebrovascular reserve blood flow or cerebrovascular reactivity in patients with greater than 70% carotid artery stenosis found on that those with impaired reserve or reactivity had a significantly higher stroke/TIA rate than those with measurable reserve/reactivity deemed adequate over a three year follow-up. This was independent of carotid stenosis or occlusion, with or without symptoms and method of measuring reserve and reactivity.…”

Section: Introductionmentioning

confidence: 99%

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Determinants of Cerebrovascular Reserve in Patients with Significant Carotid Stenosis

2020

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IntroductionIn patients with 70% to 99% diameter carotid artery stenosis cerebral blood flow reserve may be protective of future ischemic cerebral events. Reserve cerebral blood flow is created by brain auto-regulation. Both cerebral blood flow reserve and cerebrovascular reactivity can be measured non-invasively. However, the factors and variables that determine the availability and magnitude and of reserve blood flow remain poorly understood. The availability of reserve cerebral blood flow is a predictor of stroke risk. The aim of this study is to employ a hemodynamic model to predict the variables and functional relationships that determine cerebral blood flow reserve in patients with significant carotid stenosis.MethodsA basic one-dimensional, three-unit (carotid, collateral and brain) energy conservation fluid mechanics blood flow model is employed. It has two distinct but adjacent blood flow components with normal cerebral blood flow at the interface. In the brain auto-regulated blood flow component cerebral blood flow is maintained normal by reserve flow. In the brain pressure dependent blood flow component cerebral blood flow is below normal because cerebral perfusion pressure is below the lower threshold value for auto-regulation. Patient specific values of collateral vascular resistance are determined from a model solution using clinically measured systemic and carotid arterial stump pressures. Collateral vascular resistance curves illustrate the model solutions for reserve and actual cerebral blood flow as a function of percent diameter carotid artery stenosis and mean systemic arterial pressure. The threshold cerebral perfusion pressure value for auto-regulation is assumed to be 50 mmHg. Normal auto-regulated regional cerebral blood flow is assumed to be 50 ml/min/100g. Cerebral blood flow and reserve blood flow solutions are given for systemic arterial pressures of 80, 90, 100, 110 and 120 mmHg and for three patient specific collateral vascular resistance values, Rw = 1.0 (mean patient value), Rw = 0.5 (lower 1 SD) and Rd = 3.0 (upper 1 SD).ResultsReserve cerebral blood flow is only available when a patients cerebral perfusion pressure is in the normal auto-regulatory range. Both actual and reserve cerebral blood flows are primarily from the carotid circulation when carotid stenosis is less than 60% diameter. Between 60% and 75% stenosis the remaining carotid blood flow reserve is utilized and at higher degrees of stenosis all reserve flow is from the collateral circulation. The primary independent variables that determine actual and reserve cerebral blood flow are mean systemic arterial pressure, degree of carotid stenosis and patient specific collateral vascular resistance. Approximate 16% of patients have collateral vascular resistance greater than 5.0 and are predicted to be at high risk of cerebral ischemia or infarction with progression to severe carotid stenosis or occlusion. The approximate 50% of patients with a collateral vascular resistance less than 1.0 are predicted to have adequate cerebral blood flow with progression to carotid occlusion, and most maintain some reserve. Clinically measured values of cerebral blood flow reserve or cerebrovascular reactivity are predicted to be unreliable without consideration of systemic arterial pressure and degree of carotid stenosis. Reserve cerebral blood flow values measured in patients with only moderate 60% to 70% carotid stenosis are in general too high and variable to be of clinical value, but are most reliable when measured near 80% diameter stenosis and considered as percent of the maximum reserve blood flow. Patient specific measured reserve blood flow values can be inserted into the model to calculate the collateral vascular resistance.ConclusionsPredicting cerebral blood flow reserve in patients with significant carotid stenosis is complex and multifactorial. A simple cerebrovascular model predicts that patient specific collateral vascular resistance is an excellent predictor of reserve cerebral blood flow in patients with significant carotid stenosis. Cerebral blood flow reserve measurements are of limited value without accounting for systemic pressure and actual percent carotid stenosis. Asymptomatic patients with severe carotid artery stenosis and a collateral vascular resistance greater than 1.0 are at increased risk of cerebral ischemia and may benefit from carotid endarterectomy.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%