Patterns of cerebrovascular reactivity in patients with carotid artery occlusion and severe contralateral stenosis

Cerebral hemodynamic response to upright position in acute ischemic stroke

Introduction

Concerns exist that a potential mechanism for harm from upright activity (sitting, standing, and walking) early after an acute ischaemic stroke could be the reduction of cerebral perfusion during this critical phase. We aimed to estimate the effects of upright positions (sitting and standing) on cerebral hemodynamics within 48 h and later, 3-7 days post-stroke, in patients with strokes with and without occlusive disease and in controls.

Methods

We investigated MCAv using transcranial Doppler in 0° head position, then at 30°, 70°, 90° sitting, and 90° standing, at <48 h post-stroke, and later at 3-7 days post-stroke. Mixed-effect linear regression modeling was used to estimate differences in MCAv between the 0° and other positions and to compare MCAv changes across groups.

Results

A total of 42 stroke participants (anterior and posterior circulation) (13 with occlusive disease, 29 without) and 22 controls were recruited. Affected hemisphere MCAv decreased in strokes with occlusive disease (<48 h post-stroke): from 0° to 90° sitting (-9.9 cm/s, 95% CI[-16.4, -3.4]) and from 0° to 90° standing (-7.1 cm/s, 95%CI[-14.3, -0.01]). Affected hemisphere MCAv also decreased in strokes without occlusive disease: from 0° to 90° sitting (-3.3 cm/s, 95%CI[-5.6, -1.1]) and from 0° to 90° standing (-3.6 cm/s, 95%CI [-5.9, -1.3]) (p-value interaction stroke with vs. without occlusive disease = 0.07). A decrease in MCAv when upright was also observed in controls: from 0° to 90° sitting (-3.8 cm/s, 95%CI[-6.0, -1.63]) and from 0° to 90° standing (-3 cm/s, 95%CI[-5.2, -0.81]) (p-value interaction stroke vs. controls = 0.85). Subgroup analysis of anterior circulation stroke showed similar patterns of change in MCAv in the affected hemisphere, with a significant interaction between those with occlusive disease (n = 11) and those without (n = 26) (p = 0.02). Changes in MCAv from 0° to upright at <48 h post-stroke were similar to 3-7 days. No association between changes in MCAv at <48 h and the 30-day modified Rankin Scale was found.

Discussion

Moving to more upright positions <2 days post-stroke does reduce MCAv in the affected hemisphere; however, these changes were not significantly different for stroke participants (anterior and posterior circulation) with and without occlusive disease, nor for controls. The decrease in MCAv in anterior circulation stroke with occlusive disease significantly differed from without occlusive disease. However, the sample size was small, and more research is warranted to confirm these findings.

Confounding of Cerebral Blood Flow Velocity by Blood Pressure During Breath Holding or Hyperventilation in Transient Ischemic Attack or Stroke

Background and Purpose- Breath holding (BH) and hyperventilation are used to assess abnormal cerebrovascular reactivity, often in relation to severity of small vessel disease and risk of stroke with carotid stenosis, but responses may be confounded by blood pressure (BP) changes. We compared effects of BP and end-tidal carbon dioxide (etCO₂) on middle cerebral artery mean flow velocity (MFV) in consecutive transient ischemic attack and minor stroke patients. Methods- In the population-based, prospective OXVASC (Oxford Vascular Study) phenotyped cohort, change in MFV on transcranial Doppler ultrasound (ΔMFV, DWL-DopplerBox), beat-to-beat BP (Finometer), and etCO₂ was measured during 30 seconds of BH or hyperventilation. Two blinded reviewers independently assessed recording quality. Dependence of ΔMFV on ΔBP and ΔetCO₂ was determined by general linear models, stratified by quartiles. Results- Four hundred eighty-eight of 602 (81%) patients with adequate bone windows had high-quality recordings, more often in younger participants (64.6 versus 68.7 years; P<0.01), whereas 426 had hyperventilation tests (70.7%). During BH, ΔMFV was correlated with a rise in mean blood pressure (MBP; r²=0.15, P<0.001) but not ΔCO₂ (r²=0.002, P=0.32), except in patients with ΔMBP <10% (r²=0.13, P<0.001). In contrast during hyperventilation, the fall in MFV was similarly correlated with reduction in CO₂ and reduction in MBP (ΔCO₂: r²=0.13, P<0.001; ΔMBP: r²=0.12, P<0.001), with a slightly greater effect of ΔCO₂ when ΔMBP was <10% (r²=0.15). Stratifying by quartile, MFV increased linearly during BH across quartiles of ΔMBP, with no increase with ΔetCO₂. In contrast, during hyperventilation, MFV decreased linearly with ΔetCO₂, independent of ΔMBP. Conclusions- In older patients with recent transient ischemic attack or minor stroke, cerebral blood flow responses to BH were confounded by BP changes but reflected etCO₂ change during hyperventilation. Correct interpretation of cerebrovascular reactivity responses to etCO₂, including in small vessel disease and carotid stenosis, requires concurrent BP measurement.

Polygenic Control of Carotid Atherosclerosis in a BALB/cJ × SM/J Intercross and a Combined Cross Involving Multiple Mouse Strains

Atherosclerosis in the carotid arteries is a major cause of ischemic stroke, which accounts for 85% of all stroke cases. Genetic factors contributing to carotid atherosclerosis remain poorly understood. The aim of this study was to identify chromosomal regions harboring genes contributing to carotid atherosclerosis in mice. From an intercross between BALB/cJ (BALB) and SM/J (SM) apolipoprotein E-deficient (Apoe^-/-) mice, 228 female F2 mice were generated and fed a "Western" diet for 12 wk. Atherosclerotic lesion sizes in the left carotid artery were quantified. Across the entire genome, 149 genetic markers were genotyped. Quantitative trait locus (QTL) analysis revealed eight loci for carotid lesion sizes, located on chromosomes 1, 5, 12, 13, 15, 16, and 18. Combined cross-linkage analysis using data from this cross, and two previous F2 crosses derived from BALB, C57BL/6J and C3H/HeJ strains, identified five significant QTL on chromosomes 5, 9, 12, and 13, and nine suggestive QTL for carotid atherosclerosis. Of them, the QTL on chromosome 12 had a high LOD score of 9.95. Bioinformatic analysis prioritized Arhgap5, Akap6, Mipol1, Clec14a, Fancm, Nin, Dact1, Rtn1, and Slc38a6 as probable candidate genes for this QTL. Atherosclerotic lesion sizes were significantly correlated with non-HDL cholesterol levels (r = 0.254; p = 0.00016) but inversely correlated with HDL cholesterol levels (r = -0.134; p = 0.049) in the current cross. Thus, we demonstrated the polygenic control of carotid atherosclerosis in mice. The correlations of carotid lesion sizes with non-HDL and HDL suggest that genetic factors exert effects on carotid atherosclerosis partially through modulation of lipoprotein homeostasis.

New quantitative trait loci for carotid atherosclerosis identified in an intercross derived from apolipoprotein E-deficient mouse strains

Carotid atherosclerosis is the primary cause of ischemic stroke. To identify genetic factors contributing to carotid atherosclerosis, we performed quantitative trait locus (QTL) analysis using female mice derived from an intercross between C57BL/6J (B6) and BALB/cJ (BALB) apolipoprotein E (Apoe^−/−) mice. We started 266 F₂ mice on a Western diet at 6 wk of age and fed them the diet for 12 wk. Atherosclerotic lesions in the left carotid bifurcation and plasma lipid levels were measured. We genotyped 130 microsatellite markers across the entire genome. Three significant QTLs, Cath1 on chromosome (Chr) 12, Cath2 on Chr5, and Cath3 on Chr13, and four suggestive QTLs on Chr6, Chr9, Chr17, and Chr18 were identified for carotid lesions. The Chr6 locus replicated a suggestive QTL and was named Cath4. Six QTLs for HDL, three QTLs for non-HDL cholesterol, and three QTLs for triglyceride were found. Of these, a significant QTL for non-HDL on Chr1 at 60.3 cM, named Nhdl13, and a suggestive QTL for HDL on ChrX were new. A significant locus for HDL (Hdlq5) was overlapping with a suggestive locus for carotid lesions on Chr9. A significant correlation between carotid lesion sizes and HDL cholesterol levels was observed in the F₂ population (R = −0.153, P = 0.0133). Thus, we have identified several new QTLs for carotid atherosclerosis and the locus on Chr9 may exert effect through interactions with HDL.

Quantitative trait locus analysis of carotid atherosclerosis in an intercross between C57BL/6 and C3H apolipoprotein E-deficient mice

BACKGROUND AND PURPOSE

Inbred mouse strains C57BL/6J (B6) and C3H/HeJ (C3H) exhibit marked differences in atherosclerotic lesion formation in the carotid arteries on the apolipoprotein E-deficient (apoE(-/-)) background when fed a Western diet. Quantitative trait locus analysis was performed on an intercross between B6.apoE(-/-) and C3H.apoE(-/-) mice to determine genetic factors contributing to variation in the phenotype.

METHODS

Female B6.apoE(-/-) mice were crossed with male C3H.apoE(-/-) mice to generate F(1) hybrids, which were intercrossed to generate 241 female F(2) progeny. At 6 weeks of age, F(2) mice were started on a Western diet. After being fed the diet for 12 weeks, F(2) mice were analyzed for phenotypes such as lesion size in the left carotid arteries and plasma lipid levels and typed for 154 genetic markers spanning the mouse genome.

RESULTS

One significant quantitative trait locus, named CAth1 (25 cM, log of the odds score: 4.5), on chromosome 12 and 4 suggestive quantitative trait loci, on chromosomes 1, 5, 6, and 11, respectively, were identified to influence carotid lesion size. One significant quantitative trait locus on distal chromosome 1 accounted for major variations in plasma low-density lipoprotein/very-low-density lipoprotein, high-density lipoprotein cholesterol, and triglyceride levels. Carotid lesion size was not significantly correlated with plasma low-density lipoprotein/very-low-density lipoprotein or high-density lipoprotein cholesterol levels.

CONCLUSIONS

These data indicate that the loci for carotid lesions do not overlap with those for aortic lesions as identified in a previous cross derived from the same parental strains, and carotid atherosclerosis and plasma lipids are controlled by separate genetic factors in the B6 and C3H mouse model.

Cerebral vasomotor reactivity of bilateral severe carotid stenosis: is stroke unavoidable?

We evaluated the cerebral hemodynamic features of severe bilateral carotid stenosis by assessing and comparing cerebral vasomotor reactivity (VMR) in the middle cerebral (MCA) and vertebral arteries (VA) by transcranial Doppler and the Diamox (1 g acetazolamide i.v.) test. VMR was evaluated by recording the percentage differences in peak systolic blood flow velocity in each MCA and VA at baseline and by the Diamox test. Twenty-eight symptomatic (SCAS) and 31 asymptomatic (ACAS) patients with bilateral severe (>70%) internal carotid artery stenosis were studied. The mean MCA VMR% was 29 +/- 26.9% in SCAS and 43.2 +/- 26.8% in ACAS patients (P < 0.01). Their respective mean VA VMR% was 30.2 +/- 36.5% and 39.6 +/- 24.4% (P = NS). VMR% of the symptomatic MCA side in SCAS patients was significantly lower than the opposite side (20.5 +/- 31.1% and 39.2 +/- 37.9% respectively; P < 0.03). In contrast, the VA VMR% of both sides in SCAS patients remained similar (28.1 +/- 39.3% and 34.6 +/- 47.9% respectively; P = NS). VMR% of the MCA and VA in ACAS patients was also similar for both sides of bilateral carotid stenosis. The cerebral hemodynamic features differ between SCAS and ACAS patients with bilateral carotid occlusive disease in the anterior part of the circle of Willis. An independent cerebral vascular reserve capacity of the posterior circulation is proposed.