Francois Charbonneau

Guidelines for the Ultrasound Assessment of Endothelial-Dependent Flow-Mediated Vasodilation of the Brachial Artery A Report of the International Brachial Artery Reactivity Task Force

Endothelial function is thought to be an important factor in the pathogenesis of atherosclerosis, hypertension and heart failure. In the 1990s, high-frequency ultrasonographic imaging of the brachial artery to assess endothelium-dependent flow-mediated vasodilation (FMD) was developed. The technique provokes the release of nitric oxide, resulting in vasodilation that can be quantitated as an index of vasomotor function. The noninvasive nature of the technique allows repeated measurements over time to study the effectiveness of various interventions that may affect vascular health. However, despite its widespread use, there are technical and interpretive limitations of this technique. State-of-the-art information is presented and insights are provided into the strengths and limitations of high-resolution ultrasonography of the brachial artery to evaluate vasomotor function, with guidelines for its research application in the study of endothelial physiology.

Systemic nature of endothelial dysfunction in atherosclerosis

Vascular endothelium plays a pivotal role in the maintenance of vasodilation and the inhibition of platelet aggregation and smooth muscle cell proliferation through the release of nitric oxide and other factors. Extensive data have demonstrated abnormalities in coronary endothelial function in the epicardial coronary arteries in patients with atherosclerosis or risk factors for atherosclerosis. This dysfunction leads to abnormal vasoconstriction and platelet aggregation, which likely play a role in producing ischemia in patients with coronary artery disease. Invasive techniques have been available to assess endothelium-dependent vasodilator responses in the coronary arteries. However, until recently little has been known about endothelial responses in the peripheral vasculature, as methods to assess this have not been readily available. The hypothesis that endothelial dysfunction is a systemic process is explored, and new noninvasive methods of assessing endothelial function are discussed.

Microvascular Function Predicts Cardiovascular Events in Primary Prevention Long-Term Results From the Firefighters and Their Endothelium (FATE) Study

Background— Biomarkers of atherosclerosis may refine clinical decision making in individuals at risk of cardiovascular disease. The purpose of the study was to determine the prognostic significance of endothelial function and other vascular markers in apparently healthy men. Methods and Results— The cohort consisted of 1574 men (age, 49.4 years) free of vascular disease. Measurements included flow-mediated dilation and its microvascular stimulus, hyperemic velocity, carotid intima-media thickness, and C-reactive protein. Cox proportional hazard models evaluated the relationship between vascular markers, Framingham risk score, and time to a first composite cardiovascular end point of vascular death, revascularization, myocardial infarction, angina, and stroke. Subjects had low median Framingham risk score (7.9%). Cardiovascular events occurred in 71 subjects (111 events) over a mean follow-up of 7.2±1.7 years. Flow-mediated dilation was not associated with subsequent cardiovascular events (hazard ratio, 0.92; P=0.54). Both hyperemic velocity (hazard ratio, 0.70; 95% confidence interval, 0.54 to 0.90; P=0.006) and carotid intima-media thickness (hazard ratio, 1.45; confidence interval, 1.15 to 1.83; P=0.002) but not C-reactive protein (P=0.35) were related to events in a multivariable analysis that included Framingham risk score (per unit SD). Furthermore, the addition of hyperemic velocity to Framingham risk score resulted in a net clinical reclassification improvement of 28.7% (P<0.001) after 5 years of follow-up in the intermediate-risk group. Overall net reclassification improvement for hyperemic velocity was 6.9% (P=0.24). Conclusions— In men, hyperemic velocity, the stimulus for flow-mediated dilation, but not flow-mediated dilation itself was a significant risk marker for adverse cardiovascular outcomes. The prognostic value was additive to traditional risk factors and carotid intima-media thickness. Hyperemic velocity, a newly described marker of microvascular function, is a novel tool that may improve risk stratification of lower-risk healthy men.

Role of Nitric Oxide in the Local Regulation of Pulmonary Vascular Resistance in Humans

BACKGROUND Endothelium-derived nitric oxide (NO) may be an important mediator of vascular resistance in the pulmonary circulation. We tested the hypotheses that in conscious adults the endothelium, through NO production, is important in maintaining basal pulmonary vascular resistance and that it can increase NO production further in response to receptor-mediated stimulation, leading to further vasodilation. METHODS AND RESULTS Pulmonary arterial resistance vessel function was studied within the distribution of a segmental lower lobe pulmonary artery in eight conscious adults 37 to 76 years old who were undergoing cardiac catheterization. Segmental blood flow was determined with use of a Doppler-tip guide wire and quantitative angiography. Drugs were administered locally within the segmental artery through an infusion catheter. NG-Monomethyl-L-arginine (L-NMMA) was used as a specific inhibitor of NO production, whereas acetylcholine (ACh) was used to test receptor-mediated vasodilation. To demonstrate that vasodilation to ACh was NO dependent, ACh response was tested alone, in the presence of L-NMMA, and in the presence of a control constrictor phenylephrine. Basal pulmonary vascular resistance was NO dependent because L-NMMA infusion resulted in a dose-dependent decrease in local flow velocity (P < .005), with flow decreasing 33% at the highest dose of L-NMMA. ACh infusion resulted in a dose-dependent increase in flow velocity (P = .001). The ACh response was at least in part NO dependent because it was diminished by the presence of L-NMMA (P < .05). The effect of L-NMMA on the ACh response was not due to nonspecific preconstriction because L-NMMA diminished the ACh response significantly more than did the endothelium-independent constrictor phenylephrine (P < .05) despite comparable preconstriction. CONCLUSIONS In healthy conscious adults, (1) normal basal pulmonary resistance is maintained in part by continuous local production of NO and (2) the local NO production is responsive to receptor-mediated stimulation, leading to further vasodilation, and can be tested with ACh.

The T-786→C Mutation in Endothelial Nitric Oxide Synthase Is Associated With Hypertension

Although the pathogenic mechanisms involved in predisposing individuals to hypertension are not well defined, evidence is accumulating that suggests a strong genetic transmission. Animal studies and some clinical investigations have revealed that aberrant NO production may be an important contributing factor. Indeed, a missense mutation in the endothelial NO gene caused by a Glu298Asp alteration has been strongly associated with essential hypertension, coronary artery spasm, and myocardial infarction. Recently, another point mutation caused by a T-786→C transition in the 5′-flanking region of the endothelial NO synthase gene has been identified and, like the Glu298Asp mutation, is associated with coronary artery spasm. The present study was conducted to determine the effect of the T-786→C point mutation on hypertension. We investigated the interaction between the endothelial NO synthase T-786→C polymorphism and blood pressure in a large (n=705) clinically healthy population. Allele frequencies for the T and C alleles were 62% and 38%, translating into 39%, 46% and 15% of the population having the T/T, T/C, and C/C genotypes, respectively, for the T-786→C point mutation. Subjects with the C/C genotype had significantly higher systolic blood pressures and were 2.16(95% confidence interval, 1.3 to 3.7) more likely to be hypertensive. Therefore, the −786 C/C genotype in NO synthase is a significant contributing factor for increasing the risk of essential hypertension.

Comparison of New Measures of Vascular Function to Flow Mediated Dilatation as a Measure of Cardiovascular Risk Factors

Although flow-mediated dilatation (FMD) is widely used, the ideal vascular parameter for the measurement of cardiovascular risk is not clear. Recently, it has been proposed that shear stress and blood velocity during hyperemia (VRH) may provide stronger correlations with cardiovascular risk factors than FMD. The aim of this study was to evaluate the relations of VRH and shear stress during reactive hyperemia (SSRH) to FMD and the association of these measures to cardiovascular risk factors in 1,477 men without cardiovascular disease. SSRH and VRH showed weak correlations with FMD in bivariate analysis (r = 0.239, p <0.001, and r = 0.108, p <0.001, respectively). The only cardiovascular risk factor independently associated with FMD was systolic blood pressure (beta = -0.073, p <0.01). In contrast, as the dependent variable, SSRH (R2 for model = 0.107) was independently associated with age, systolic blood pressure, low-density lipoprotein cholesterol, and body mass index. As the dependent variable, VRH was associated with the same risk factors with a slightly weaker R2 value of 0.095. In conclusion, SSRH and simply calculated VRH have stronger associations with cardiovascular risk factors than FMD. This may reflect greater sensitivity of these measures to detect early abnormalities associated with risk factors in a relatively young and healthy population.

Relationship between brachial artery flow-mediated dilatation, hyperemic shear stress, and the metabolic syndrome

Abstract Metabolic syndrome (MetSyn) may predispose to cardiovascular disease (CVD) by causing vascular dysfunction. This study aimed to determine the association of MetSyn with vascular function, as assessed by brachial artery flow-mediated dilatation (FMD) and hyperemic shear stress (HSS). A total of 1,417 male firefighters without established diabetes and CVD were classified for MetSyn, according to the National Cholesterol Education Program Adult Treatment Panel III (NCEP) definition. MetSyn was present in 267 individuals (19%). Although FMD was lower in those with versus without MetSyn (8.1 ± 4.1 vs 8.7 ± 4.0%; p = 0.02), this was not significant after adjusting for baseline differences (age, smoking, and brachial artery diameter) (p = 0.2). However, HSS was significantly lower in those with versus without MetSyn (72.0 ± 27.8 vs 80.9 ± 24.8 dyne/cm2; p < 0.001), and there was a significant inverse graded relationship with the number of NCEP criteria present (mean HSS for those with 0, 1, 2, 3, 4, and 5 criteria: 83.2 ± 22.5, 82.2 ± 24.7, 76.5 ± 27.2, 74.3 ± 27.4, 66.5 ± 28.4, 67.1 ± 27.6 dyne/cm2; p < 0.001 for trend). The individual NCEP criteria of abdominal obesity, systolic hypertension, and impaired fasting glucose were independent predictors for HSS. In conclusion, MetSyn was not associated with impaired FMD. Alternatively, HSS, a measure of microvascular function, was significantly lower in those with MetSyn. Thus, MetSyn may contribute to CVD by causing microvascular dysfunction.

The differential association between various anthropometric indices of obesity and subclinical atherosclerosis

BACKGROUND Recent observational studies have reported differential quantitative relationships between the different anthropometric indices of obesity and risk for cardiovascular (CV) events. Specifically, waist circumference and waist-to-hip ratio (WHR) as crude measures of abdominal obesity were shown to be more predictive of CV events than body mass index (BMI). However, it remains undetermined whether indices of abdominal obesity are also more strongly associated with early subclinical atherosclerosis in asymptomatic individuals. METHODS The associations between carotid intimal-medial thickness (cIMT) as a validated marker of subclinical atherosclerosis and each of BMI, waist circumference and WHR were compared among 1578 middle-aged men free of clinical CV disease enrolled in the Fire Fighter and Their Endothelium (FATE) study. RESULTS In univariate analyses, the correlation with cIMT as well as the ability to predict substantially increased atherosclerotic burden (cIMT>75% percentile of the cohort) was strongest for WHR, intermediate for waist circumference, and weakest for BMI (Pearsons coefficient of 0.21, 0.18 and 0.12, respectively; area under the receiver operating characteristics curve [AUC] of 0.65, 0.62 and 0.58, respectively, P<0.01 for differences). Within each traditional BMI category, WHR uniformly outperformed waist circumference in further refining discrimination for increased atherosclerotic burden. In multivariable analyses, WHR consistently demonstrated the strongest graded independent relationship with cIMT, beyond most of the established risk factors of atherosclerosis, and superseded both waist circumference and BMI. CONCLUSION Our findings support the use of WHR for estimating adiposity-related atherosclerotic burden in clinical practice and in obesity research. Moreover, our study suggests that the increased CV risk associated with abdominal obesity may be mediated in part by the increased anatomic extent of atherosclerotic vascular disease.

Nitroglycerin-induced coronary vasodilation is not enhanced in patients with impaired endothelium-dependent dilation

OBJECTIVES This study was designed to determine whether enhanced sensitivity to exogenous nitrovasodilators is present in the coronary arteries of patients with impaired endothelium-dependent dilation. BACKGROUND Animal studies have demonstrated that the dilator response to exogenous nitrovasodilators is exaggerated in the setting of endothelial dysfunction (diminished nitric oxide activity). Whether such relative hyperresponsiveness to exogenous nitrates occurs and is important in humans is unknown. METHODS We assessed coronary vasomotion in 110 patients (mean [+/- SD] age 56 +/- 10 years) by serial intracoronary infusions of acetylcholine (10(-8) to 10(-6) mol/liter) to test endogenous nitric oxide and nitroglycerin (40 micrograms) to test responses to exogenous nitrovasodilators. RESULTS The vasomotor response to 10(-6) mol/liter of acetylcholine differed between patients with (n = 95) and those without (n = 15) normal endothelial dysfunction (-21 +/- 14% vs. 12 +/- 8%, respectively, p < 0.001). However, neither the dilator response to nitroglycerin (21 +/- 14% vs. 18 +/- 13%) nor the baseline diameter differed between those with endothelial dysfunction and normal function, respectively. There was no correlation between the magnitude of the dilator response to nitroglycerin and acetylcholine. The response to nitroglycerin was decreased with increasing age (r = -0.21, p = 0.03) but was not related to any other demographic factors or to the angiographic appearance of the vessel. CONCLUSIONS The coronary vasodilator response to nitroglycerin is not significantly enhanced in patients with impaired endothelium-dependent dilation but decreases with increasing age. This finding provides indirect evidence that basal coronary tone is not increased in patients with endothelial dysfunction and that supersensitivity to exogenous nitrates is not clinically important in humans.

The relationship between anthropometric indexes of adiposity and vascular function in the FATE cohort

Numerous indexes of adiposity have been proposed and are currently in use in clinical practice and research. However, the correlation of these indexes with measures of vascular health remain poorly defined. This study investigated which measure of adiposity is most strongly associated with endothelial function.