Measuring FMD in the brachial artery: how important is QRS gating?

Recommendations for the measurement of brachial flow-mediated dilation (FMD) typically suggest images be obtained at identical times in the cardiac cycle, usually end diastole (QRS complex onset). This recommendation presumes that inter-individual differences in arterial compliance are minimized. However, published evidence is conflicting. Furthermore, ECG gating is not available on many ultrasound systems; it requires an expensive software upgrade or increased image processing time. We tested whether analysis of images acquired with QRS gating or with the more simplified method of image averaging would yield similar results. We analyzed FMD and nitroglycerin-mediated dilation (NMD) in 29 adults with type 2 diabetes mellitus and in 31 older adults and 12 young adults without diabetes, yielding a range of brachial artery distensibility. FMD and NMD were measured using recommended QRS-gated brachial artery diameter measurements and, alternatively, the average brachial diameters over the entire R-R interval. We found strong agreement between both methods for FMD and NMD (intraclass correlation coefficients = 0.88-0.99). Measuring FMD and NMD using average diameter measurements significantly reduced post-image-processing time (658.9 ± 71.6 vs. 1,024.1 ± 167.6 s for QRS-gated analysis, P < 0.001). FMD and NMD measurements based on average diameter measurements can be performed without reducing accuracy. This finding may allow for simplification of FMD measurement and aid in the development of FMD as a potentially useful clinical tool.

Folic acid supplementation improves vascular function in amenorrheic runners.

OBJECTIVE: The purpose of this study was to determine if folic acid supplementation improves endothelial vascular function (brachial artery flow-mediated dilation; FMD) in amenorrheic runners. DESIGN: Prospective cross-sectional study. SETTING: Academic medical center in the Midwest. PARTICIPANTS: Ten amenorrheic and 10 eumenorrheic women runners from the community volunteered for this study. INTERVENTIONS: Each participant was treated with folic acid (10 mg/d) for 4 weeks. MAIN OUTCOME MEASURES: Brachial artery FMD was measured before and after folic acid supplementation with standard techniques. RESULTS: The brachial artery FMD response to reactive hyperemia improved after folic acid supplementation in amenorrheic women (3.0% +/- 2.3% vs. 7.7% +/- 4.5%; P = 0.02). In the eumenorrheic control group, there was no change in brachial artery FMD (6.7% +/- 2.0% vs. 5.9% +/- 2.6%; P = 0.52). CONCLUSIONS: This study demonstrates that brachial artery FMD, an indicator of vascular endothelial function, improves in amenorrheic female runners after short-term supplementation with folic acid.

Usefulness of two-dimensional strain echocardiography to predict segmental viability following acute myocardial infarction and optimization using bayesian logistic spatial modeling.

Viability assessment after acute myocardial infarction (MI) is important to guide revascularization. Two-dimensional strain echocardiography was shown to predict viability, but the method assumed that strain in each segment is independent of contiguous segments. The aim of this study was to test the hypotheses that segmental strain after MI is spatially correlated and that using a Bayesian approach improves the prediction of nonviable myocardium. Twenty-one subjects (mean age 58 +/- 12 years, 6 women) with MI >or=2 weeks before recruitment underwent 2-dimensional strain echocardiography and late gadolinium enhancement (LGE) cardiac magnetic resonance imaging within 48 hours of each other. The heart was divided into 16 segments, and longitudinal, radial, and circumferential strains were measured using software. Using similar segmentation, LGE was measured, and segments with >50% LGE were considered nonviable. Spearman's analyses were used to assess the spatial correlation of strain, and receiver-operating characteristic curve analysis was used to determine the prediction of nonviable myocardium without and with a Bayesian logistic spatial conditionally autoregressive (CAR) model. There was a significant spatial correlation in strain and LGE among segments, especially in the apex. Longitudinal strain was the best predictor of nonviability and was impaired in nonviable myocardium (-12.1 +/- 0.6%, -8.0 +/- 0.6%, and -4.6 +/- 1% for 0%, 1% to 50%, and >50% LGE, respectively, p <0.001). Use of the CAR model improved the area under the curve for the detection of nonviable myocardium (from 0.7 to 0.94). A CAR probabilistic score of 0.17 had 88% sensitivity and 86% specificity for detecting nonviable myocardium. In conclusion, longitudinal strain from 2-dimensional strain echocardiography can predict myocardial viability after MI, and exploiting spatial correlations in segmental strain using Bayesian CAR modeling enhances the ability of 2-dimensional strain to predict nonviable myocardium.

Benefit of low-fat over low-carbohydrate diet on endothelial health in obesity.

Obesity is associated with impaired endothelial-dependent flow-mediated dilation, a precursor to hypertension and atherosclerosis. Although dieting generally improves cardiovascular risk factors, the direct effect of different dietary strategies on vascular endothelial function is not known. The purpose of this study was to test the hypothesis that a low-fat (LF) diet improves endothelial function compared with an isocaloric low-carbohydrate (LC) diet. Obese (n=20; body mass index: 29 to 39; mean systolic blood pressure: 107 to 125 mm Hg) and otherwise healthy volunteers were randomly assigned to either the American Heart Association modeled LF (30% fat calories) diet or an isocaloric LC Atkins' style diet (20 g of carbohydrates) for 6 weeks (4-week weight loss and 2-week maintenance phase). Brachial flow-mediated dilation and dilation to nitroglycerin were measured with ultrasound using automated edge detection technology (baseline, week 2, and week 6). Blood pressure, weight loss, and cholesterol profiles were measured throughout the study. Weight loss was similar in LF (100+/-4 to 96.1+/-4 kg; P<0.001) and LC (95.4+/-4 to 89.7+/-4 kg; P<0.001) diets. Blood pressure decreased similarly in both groups (LF: 8/5 mm Hg; LC: 12/6 mm Hg) at 6 weeks. After 6 weeks, the percentage of flow-mediated dilation improved (1.9+/-0.8; P<0.05) in the LF diet but was reduced in the LC diet (-1.4+/-0.6; P<0.05) versus baseline. Dilation to nitroglycerin and lipid panels was similar at 0, 2, and 6 weeks. Despite similar degrees of weight loss and changes blood pressure, LF diets improved brachial artery flow-mediated dilation over LC diets. LF diets may confer greater cardiovascular protection than LC diets.

Athletic amenorrhea and endothelial dysfunction.

OBJECTIVES: To determine if menstrual status changed in amenorrheic college runners over a 2-year period and what effect this had on brachial artery flow-mediated dilation. PARTICIPANTS: Eighteen athletes first studied in our laboratory 2 years prior were available for follow-up. Nine of the 10 original women with athletic amenorrhea (mean +/- SE, age 21.3 +/- 1.2 yrs), and 9 of the 11 eumenorrheics/controls (age 20.1 +/- 0.5 yrs) were studied 2 years after baseline measurements. METHODS: Questionnaires/personal interviews and blood draws were performed to determine menstrual status. A non-invasive ultrasound technique was used to determine brachial artery flow-mediated dilation (endothelium-dependent). RESULTS: Menstrual status changed in 7 of 9 original amenorrheic subjects (2 were taking hormone replacement, 2 were taking oral contraceptives, 3 had a natural menstrual period prior to testing, and 2 remained amenorrheic). Endothelium-dependent brachial artery dilation, measured as the percent change in maximal brachial artery diameter from baseline during reactive hyperemia, was improved in the original amenorrheic subjects (a 1.1% +/- 1.0 increase in the original study versus 5.6% + 1.1 increase in the current study, P=0.01) while in the eumenorrheic/control group there was no change (6.3% +/- 1.7 versus 8.0% +/- 1.3, P=0.42). CONCLUSIONS: Menstrual status changed in 7 of the 9 original amenorrheic athletes, and this change was associated with an improvement in brachial artery flow-mediated dilation.

The female athlete triad and cardiovascular dysfunction.

In the past 35 years, a significant increase has occurred in sports participation by women. An estimated 3 million girls and young women compete in American high school sports. Women who participate in sports and fitness programs are generally healthier and have higher self-esteem. However, an increase has also been seen in gender-specific injuries and medical problems. The female athlete triad is a syndrome of separate but interrelated conditions of disordered eating, amenorrhea, and osteoporosis. Athletic amenorrhea is known to have a hormonal profile similar to menopause characterized by decreased circulating estrogens. Menopause is known to be associated with osteoporosis and accelerated cardiovascular disease. Although enhanced risk for cardiovascular disease is theoretically possible, it has not been explored in the young athletic population. Premature cardiovascular disease first manifests as endothelial dysfunction, which can be examined noninvasively with ultrasound. This article discusses disordered eating, amenorrhea, osteoporosis, and the potential for heightened cardiovascular risk in young athletic women.

The influence of lipoproteins on whole-blood viscosity at multiple shear rates.

Whole-blood viscosity appears to be an independent predictor of stroke, carotid intima-media thickening, and carotid atherosclerosis. The purpose of this study was to examine for relationships between whole-blood viscosity and blood lipids in young healthy subjects over a range of shear rates. Twenty-seven healthy men and women aged 10 to 25 years having a range of low-density lipoprotein (LDL) cholesterol values 88 to 258 mg/dL and body mass index z scores -1.18 to 2.64 SDs were studied. Whole-blood viscosity at shear rates from 1 to 1000 per second was measured using an automated capillary viscometer. Blood lipids were measured using standard techniques. Triglyceride-rich lipoproteins were isolated by ultracentrifugation at density of <1.020 g/mL, and a high ratio of cholesterol to triglyceride was used as an indicator of lipoprotein remnants. Whole-blood viscosity at shear rates of 100 to 1000 per second showed significant negative correlations with apolipoprotein A-1, but not with high-density lipoprotein cholesterol. Whole-blood viscosity at a shear rate of 1000 per second correlated with LDL cholesterol and inversely with LDL size. On stepwise multivariate analysis, apolipoprotein A-1 accounted for 14.7% of the variation in whole-blood viscosity at a shear rate of 150 per second. This study points to the importance of high-density lipoprotein particle number on whole-blood viscosity at physiological shear rates. The physiological significance of the relationships between whole-blood viscosity and LDL cholesterol and LDL particle size at a very high shear rate remains to be determined.

Influence of glycemic load on HDL cholesterol in youth.

BACKGROUND: The influence of dietary carbohydrate glycemic index on blood lipids has not been well studied. Assessment of glycemic load is not usually included in a standard dietary analysis. OBJECTIVE: The purpose of the present study was to examine relations between diet and blood lipids in youth with a broad range of cholesterol values and carbohydrate, fat, and protein intakes. DESIGN: Relations between blood lipids and dietary constituents were examined in 32 healthy males and females aged 11-25 y. Subjects exhibited a range of LDL-cholesterol values (1.71-6.67 mmol/L) and body mass index z scores (-1.18 to 2.64). Dietary constituents were assessed from 3-d food diaries. RESULTS: The only significant correlations evident were negative correlations between HDL cholesterol and glycemic load (in relation to white bread), percentage carbohydrate, total dietary sugar, total carbohydrate, and fructose. On stepwise multiple regression analysis, glycemic load accounted for 21.1% of the variation in HDL cholesterol. CONCLUSIONS: Glycemic load appears to be an important independent predictor of HDL cholesterol in youth. This relation is of concern and suggests that dietary restrictions without attention to a possible resulting increase in glycemic load may result in an unfavorable influence on blood lipids.