David S. Celermajer

Non-invasive detection of endothelial dysfunction in children and adults at risk of atherosclerosis

Endothelial dysfunction is an early event in experimental studies of atherogenesis, preceding formation of plaques. We have devised a non-invasive method for testing endothelial function, to find out whether abnormalities are present in symptom-free children and young adults at high risk of atherosclerosis. With high-resolution ultrasound, we measured the diameter of the superficial femoral and brachial arteries at rest, during reactive hyperaemia (with increased flow causing endothelium-dependent dilatation), and after sublingual glyceryl trinitrate (GTN; causing endothelium-independent dilatation) in 100 subjects--50 controls without vascular risk factors (aged 8-57 years), 20 cigarette smokers (aged 17-62 years), 10 children with familial hypercholesterolaemia (FH; aged 8-16 years), and 20 patients with established coronary artery disease (CAD). Adequate scans were obtained in all but 6 cases. Flow-mediated dilatation was observed in arteries from all control subjects. Dilatation was inversely related to baseline vessel diameter (r = -0.81, p < 0.0001); in arteries of 6.0 mm or less, mean dilatation was 10 (SE 2)%. In smokers, FH children, and adults with CAD, flow-mediated dilatation was much reduced or absent (p < 0.001 for comparison with each relevant control group). Dilatation in response to GTN was present in all groups. Endothelial dysfunction is present in children and adults with risk factors for atherosclerosis, such as smoking and hypercholesterolaemia, before anatomical evidence of plaque formation in the arteries studied. This may be an important early event in atherogenesis.

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.

Cigarette smoking is associated with dose-related and potentially reversible impairment of endothelium-dependent dilation in healthy young adults.

BackgroundCigarette smoking is the most important modifiable risk factor for atherosclerosis. Endothelial dysfunction is an early event in atherogenesis, and we hypothesized that smoking might be associated with endothelial damage in the systemic arteries of otherwise healthy young adults. Methods and ResultsWe studied noninvasively the brachial arteries of 200 subjects aged 15 to 57 years, all normotensive, nondiabetic with cholesterol level 5240 mg/dL and no family history of premature vascular disease: 80 control subjects aged 16 to 56 years (mean, 35), 80 current smokers aged 15 to 55 years (mean, 33), and 40 former smokers aged 25 to 57 years (mean, 38). Total lifetime amount smoked varied from 1 to 75 pack years in the smokers. Using high-resolution ultrasound, vessel diameter was measured at rest, during reactive hyperemia (with flow increase causing endothelium-dependent dilation), and after sublingual glyceryl trinitrate (GTN, an endothelium-independent vasodilator). Flow-mediated dilation (FMD) was observed in all the control subjects (10±33%; range, 4% to 22%) but was impaired or absent in the smokers (4±3.9%vo; range, 0% to 17%; P<.0001). FMD in the smokers was inversely related to lifetime dose smoked (6.6±4.0%o in very light smokers, 4.0±3.1% in light smokers, 3.2±3.2% in moderate smokers, and 2.6±1.2% in heavy smokers; P<.01). FMD for the former smokers was 5.1±4.1% (range, 0%/ to 15%). In a multivariate model adjusting for age, sex, cholesterol, smoking history, and vessel size, former smoking was associated with a higher FMD than current smoking (P=.07); when only male former and current smokers were considered, the higher FMD was significant (P=.0001) but not for female smokers (P=.24). GTN caused dilation in all subjects (control subjects, 20±5.2%; smokers, 17±5.8%; former smokers, 17.4±5.4%). Vessel diameter, baseline flow, and degree of reactive hyperemia (Doppler estimated) were similar in all groups. ConclusionsCigarette smoking is associated with dose-related and potentially reversible impairment of endothelium-dependent arterial dilation in asymptomatic young adults, consistent with endothelial dysfunction.

Endothelium-dependent dilation in the systemic arteries of asymptomatic subjects relates to coronary risk factors and their interaction.

OBJECTIVES This study attempted to assess whether coronary risk factors are associated with endothelial dysfunction in the systemic arteries of asymptomatic men and women. BACKGROUND Endothelial dysfunction is present in adults with established atherosclerosis. It is not known whether risk factors interact to produce endothelial dysfunction in clinically well subjects early in the natural history. METHODS Using high resolution ultrasound, we measured arterial diameter at rest, after reactive hyperemia (with increased flow causing endothelium-dependent dilation) and after sublingual nitroglycerin (an endothelium-independent dilator). Arterial responses were studied noninvasively in 500 clinically well, nonhypertensive subjects (252 men, 248 women; mean [+/- SD] age 36 +/- 15 years, range 5 to 73), including 179 current and former smokers. The superficial femoral artery was studied in 46 subjects and the brachial artery in 454. RESULTS Flow-mediated dilation ranged from -1% to +17%. All arteries dilated in response to administration of nitroglycerin (17 +/- 6%), suggesting an abnormality of endothelial function in subjects with impaired flow-mediated dilation. On univariate analysis, reduced flow-mediated dilation was significantly related to hypercholesterolemia, cigarette smoking, higher blood pressure, male gender, older age, family history of premature vascular disease and larger vessel size (p < 0.01). By multiple stepwise regression analysis, reduced flow-mediated dilation was independently associated with cigarette smoking, older age, male gender and larger vessel size (p < 0.005) but not with total cholesterol level, blood pressure or family history. A composite risk factor score was independently related to flow-mediated dilation (r = -0.30, p < 0.0001), suggesting risk factor interaction. CONCLUSIONS Loss of endothelium-dependent dilation in the systemic arteries occurs in the preclinical phase of vascular disease and is associated with interaction of the same risk factors known to predispose to atherosclerosis and its complications in later life.

Aging is associated with endothelial dysfunction in healthy men years before the age-related decline in women

OBJECTIVES This study assessed whether aging is associated with progressive endothelial dysfunction, whether the pattern of any age-related decline in vascular health is different in men and women and whether any gender difference is consistent with known changes in hormonal status. BACKGROUND Coronary and cerebrovascular disease are much less common in young and middle-aged women compared with men, although the gender difference in death from atherosclerosis is less marked after the menopause. Endothelial dysfunction is an early event in atherogenesis and is important in dynamic plaque stenosis in later life. The effect of aging on endothelial function in men and women, however, is not well known. METHODS We used high resolution ultrasound to study endothelium-dependent and endothelium-independent vascular responses. Brachial artery physiology was investigated in 238 subjects (103 men, 135 women; mean [+/- SD] age 38 +/- 17 years, range 15 to 72) with no known risk factors for atherosclerosis. The responses to reactive hyperemia (flow-mediated dilation, which is endothelium dependent) and to glyceryl trinitrate (an endothelium-independent dilator) were assessed for all the subjects and then for men and women separately. RESULTS On multivariate analysis for the whole group, reduced flow-mediated dilation was related to older age (r = -0.34, p < 0.0001). In men, flow-mediated dilation was preserved in subjects aged < or = 40 years but declined thereafter at 0.21%/year. In women, flow-mediated dilation was stable until the early 50s, after which it declined at 0.49%/year (p = 0.002 compared with men). In contrast, there was no significant change in the glyceryl trinitrate response with aging in either gender. CONCLUSIONS Aging is associated with progressive endothelial dysfunction in normal humans, and this appears to occur earlier in men than in women. In women, however, a steep decline commences at around the time of the menopause. This is consistent with a protective effect of estrogens on the arterial wall.

Passive smoking and impaired endothelium-dependent arterial dilatation in healthy young adults.

BACKGROUND Passive smoking has been linked to an increased risk of dying from atherosclerotic heart disease. Since endothelial dysfunction is an early feature of atherogenesis and occurs in young adults who actively smoke cigarettes, we hypothesized that passive smoking might also be associated with endothelial damage in healthy young-adult nonsmokers. METHODS We studied 78 healthy subjects (39 men and 39 women) 15 to 30 years of age (mean +/- SD, 22 +/- 4): 26 control subjects who had never smoked or had regular exposure to environmental tobacco smoke, 26 who had never smoked but had been exposed to environmental tobacco smoke for at least one hour daily for three or more years, and 26 active smokers. Using ultrasonography, we measured the brachial-artery diameter under base-line conditions, during reactive hyperemia (with flow increase causing endothelium-dependent dilatation), and after sublingual administration of nitroglycerin (an endothelium-independent dilator). RESULTS Flow-mediated dilatation was observed in all control subjects (8.2 +/- 3.1 percent; range, 2.1 to 16.7) but was significantly impaired in the passive smokers (3.1 +/- 2.7 percent; range, 0 to 9; P < 0.001 for the comparison with the controls) and in the active smokers (4.4 +/- 3.1 percent; range, 0 to 10; P < 0.001 for the comparison with the controls; P = 0.48 for the comparison with the passive smokers). In the passive smokers, there was an inverse relation between the intensity of exposure to tobacco smoke and flow-mediated dilatation (r = -0.67, P < 0.001). In contrast, dilatation induced by nitroglycerin was similar in all groups. CONCLUSIONS Passive smoking is associated with dose-related impairment of endothelium-dependent dilatation in healthy young adults, suggesting early arterial damage.

Endothelial Dysfunction: Does It Matter? Is It Reversible?☆

Until recently, the endothelium was regarded as a relatively inert cell layer. However, over the past 20 years, research has revealed an extraordinary array of endothelial functions, including control over coagulation, fibrinolysis, arterial tone and vascular growth. Importantly, endothelial dysfunction has been implicated as a key event in the pathogenesis of atherosclerosis, coronary vasoconstriction and, probably, myocardial ischemia. The recent demonstration that endothelial dysfunction may be reversible raises the possibility of slowing the progression of atherosclerosis or modifying arterial function, or both, to decrease the risk of acute cardiovascular events.

Impairment of endothelium-dependent dilation is an early event in children with familial hypercholesterolemia and is related to the lipoprotein(a) level.

Familial hypercholesterolemia is associated with premature atherosclerosis. Since endothelial dysfunction is an early event in atherogenesis, we used a noninvasive method to assess endothelial function in the systemic arteries of 30 children aged 7-17 yr (median 11) with familial hypercholesterolemia (2 homozygotes, 28 heterozygotes, total cholesterol 240-696 mg/dl) and 30 healthy age- and sex-matched controls. Using high resolution ultrasound, the diameter of the superficial femoral artery was measured at rest, in response to reactive hyperemia (with increased flow causing endothelium-dependent dilation), and after sublingual glyceryltrinitrate (causing endothelium-independent vasodilation). Flow-mediated dilation was present in the controls (7.5 +/- 0.7%) but was impaired or absent in the hypercholesterolemic children (1.2 +/- 0.4%, P < 0.0001). Total cholesterol was inversely correlated with flow-mediated dilation (r = -0.61, P < 0.0001). In the hypercholesterolemic children, flow-mediated dilation was inversely related to the lipoprotein(a) level (r = -0.61, P = 0.027) but not to other lipid fractions. Glyceryltrinitrate-induced dilation was present in all subjects but was lower in the hypercholesterolemia group (10.0 +/- 0.6% vs 12.4 +/- 0.8%, P = 0.023). Thus, impaired endothelium-dependent dilation is present in children with familial hypercholesterolemia as young as 7 yr of age and the degree of impairment is related to the lipoprotein(a) level.

The Assessment of Endothelial Function From Research Into Clinical Practice

The discovery of nitric oxide (NO) as a crucial endothelium-derived molecule for vascular relaxation and the recognition of the endothelium as more than a passive interface between blood and the vessel wall led to substantial progress in the field of vascular research.1 Endothelial dysfunction is a pathological condition characterized mainly by an imbalance between substances with vasodilating, antimitogenic, and antithrombogenic properties (endothelium-derived relaxing factors)2 and substances with vasoconstricting, prothrombotic, and proliferative characteristics (endothelium-derived contracting factors).3 Among the most important vasodilator molecules, particularly in muscular arteries, is NO, which also inhibits other key events in the development of atherosclerosis such as platelet adhesion and aggregation, leukocyte adhesion and migration, and smooth muscle cell proliferation. Particularly in the microcirculation, prostacyclin and endothelium-derived hyperpolarization factors (an umbrella term for substances and signals hyperpolarizing vascular myocytes by opening voltage channels4) also play an important role. Generally, loss of NO bioavailability indicates a broadly dysfunctional phenotype across many properties of the endothelium. Thus, the assessment of its vasodilator properties resulting from NO and other molecules may provide information on the integrity and function of the endothelium. Interestingly, most, if not all, cardiovascular risk factors are associated with endothelial dysfunction,5 and risk factor modification leads to improvement in vascular function. Endothelial dysfunction has been detected in the coronary epicardial and resistance vasculature and in peripheral arteries, so endothelial dysfunction can be regarded as a systemic condition.6 Importantly, the process of atherosclerosis begins early in life, and endothelial dysfunction contributes to atherogenesis and precedes the development of morphological vascular changes.7 Over the past 25 years, many methodological approaches have been developed to measure the (patho)physiological function of the endothelium in humans.8 Although the ability to measure endothelial function has boosted clinical research in this field, its use as a …

Hyperhomocyst(e)inemia Is a Risk Factor for Arterial Endothelial Dysfunction in Humans

BACKGROUND Hyperhomocyst(e)inemia is associated with premature peripheral vascular, cerebrovascular, and coronary artery disease. Because homocysteine has been found to be damaging to endothelial cells in animal and cell culture studies, we evaluated the association between hyperhomocysteinemia and arterial endothelial dysfunction (a marker of early atherosclerosis) in asymptomatic adult subjects. METHODS AND RESULTS Using high-resolution ultrasound, we measured endothelium-dependent flow-mediated dilation (EDD) and endothelium-independent nitroglycerin-induced dilation (GTN) of the brachial artery in 14 prospectively defined hyperhomocysteinemic (mean plasma homocysteine, 34.8+/-8.5 micromol/L), nonsmoking, healthy subjects aged 53+/-9 years and 14 control subjects with low plasma homocysteine levels (9.9+/-3.2 micromol/L). The two groups were well matched for age; sex; body mass index; blood pressure, blood cholesterol, folate, and vitamin B12 levels; and vessel diameter. EDD was significantly lower in hyperhomocysteinemic subjects (6.5+/-1.7%) than in subjects with low homocysteine levels (10.8+/-1.7%) (P<.001). GTN responses were similar in the two subject groups (P=.90). Multivariate analysis confirmed homocysteine level as the strongest predictor for impaired EDD, independent of age, sex, body mass index, or blood pressure, folate, vitamin B12, and cholesterol levels. CONCLUSIONS Hyperhomocysteinemia is an independent risk factor for arterial endothelial dysfunction in healthy middle-aged adults.