Rationale and Objectives
In patients with severe internal carotid artery steno-occlusive lesions (ISOL), impaired cerebrovascular reactivity (CVR) is predictive of future ischemic stroke (IS) or transient ischemic attack (TIA). Therefore, the evaluation of CVR in ISOL patients may be a means to evaluate the risk for IS/TIA and decide on an intervention. Our aim was (1) to explore the feasibility of concurrent near-infrared spectroscopy (NIRS-DOS), diffuse correlation spectroscopy, and transcranial Doppler for CVR assessment in ISOL patients, and (2) to compare macrovascular and microvascular CVR in ISOL patients and explore its potential for IS/TIA risk stratification.
Materials and Methods
Twenty-seven ISOL patients were recruited. The changes in continuous microvascular and macrovascular hemodynamics upon acetazolamide injection were used to determine CVR.
Results
Oxyhemoglobin (HbO 2 , by near-infrared spectroscopy), microvascular cerebral blood flow (CBF, by diffuse correlation spectroscopy) and CBF velocity (by transcranial Doppler) showed significant increases upon acetazolamide injection in all subjects ( P < .03). Only macrovascular CVR ( P = .024) and none of the microvascular measures were significantly dependent on the presence of ISOL. In addition, while CBF was significantly correlated with HbO 2 , neither of these microvascular measures correlated with macrovascular CBF velocity.
Conclusions
We demonstrated the simultaneous, continuous, and noninvasive evaluation of CVR at both the microvasculature and macrovasculature. We found that macrovascular CVR response depends on the presence of ISOL, whereas the microvascular CVR did not significantly depend on the ISOL presence, possibly due to the role of collaterals other than those of the circle of Willis. The concurrent microvascular and macrovascular CVR measurement in the ISOL patients might improve future IS/TIA risk assessment.
Severe stenosis or occlusion of the internal carotid artery (ICA) increases the risk of subsequent ischemic stroke (IS) and transient ischemic attack (TIA) . Moreover, patients with severe internal carotid artery steno-occlusive lesions (ISOL) are found to be at a particularly higher risk of imminent stroke events when autoregulatory vasodilation capacity of the cerebral terminal arterioles in response to a reduced perfusion pressure, or cerebrovascular reactivity (CVR), is impaired . Thus, to aid in the decision of the suitable treatment, such as carotid revascularization versus drug therapy, the assessment of CVR has been proposed by several authors as a screening method to stratify ISOL patients based on their assumed risk of future IS or TIA .
CVR is normally evaluated by measuring the maximum vasodilation capacity of cerebral vasculature. The maximum vasodilation is induced by introducing a potent vasodilatory stimulus, most commonly CO 2 , inhalation or acetazolamide (ACZ) infusion. Consequent cerebrovascular changes are then followed by a method capable of measuring microvascular cerebral blood flow (CBF), blood oxygen saturation, blood volume, or macrovascular cerebral blood flow velocity (CBFV).
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Materials and methods
Subjects
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Diffuse Optics and TCD Protocol
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Analysis
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Results
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Table 1
Demographic and Clinical Characteristics of the Population Included for the Analysis
Parameter Number Total no. of subjects 20 Total no. of hemispheres 33 Male 16 (80%) Age, (mean ± STD years) 64.6 ± 9.7 Degree of ICA stenosis 0%–49% 12 (36%) 70%–99% 14 (43%) Occluded 7 (21%) Laterality of stenosis Unilateral steno-occlusion 16 (80%) Bilateral steno-occlusion 4 (20%) Presenting events Symptomatic arteries 8 (24%) Transient ischemic attack 1 Ischemic stroke 7 Asymptomatic arteries 25 (76%) Other conditions Smoker 6 (30%) Diabetic 8 (40%) Hypercholesterol 12 (60%) Hypertension 16 (80%)
Data are given as number of subjects and percentage of the total included subjects [No. (%)].
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Table 2
Median (Interquartile Range [IQR]), and P Values for Optical and Ultrasound Data
Parameter ISOL Side Normal Side Median IQR Median IQR ΔHb o 2 , μmol/L 3.7 ∗ 2.3 to 8.3 7.7 ∗ 5.4 to 12 ΔHb, μmol/L −0.4 −1.2 to 0.1 −0.5 −1.8 to 0.7 CVR DCS , % 20 ∗ 14.3 to 25.1 26.1 ∗ 13.9 to 32 CVR TCD , % 10.7 ∗ −6.8 to 27.5 27.8 ∗ 19 to 42.7
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Table 3
MCA CVR (TCD-CVR) Versus Local CVR (DCS-CVR) and ΔHbO 2
Parameter Responsive by TCD Nonresponsive by TCD Responsive by DCS 15 (45) 10 (30) Nonresponsive by DCS 5 (15) 3 (9) Responsive by NIRS-DOS, ΔHbO 2 13 (39) 4 (12) Nonresponsive by NIRS-DOS, ΔHbO 2 7 (21) 9 (27)
Data are indicated as the number of hemispheres/arteries and as percentage of the total [No. (%)].
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Discussion
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