Gender influences endothelial-dependent arterial dilatation via arterial size in youth

Sex differences in the vascular function and related mechanisms: role of 17β-estradiol

The incidence of cardiovascular disease (CVD) is lower in premenopausal women but increases with age and menopause compared with similarly aged men. Based on the prevalence of CVD in postmenopausal women, sex hormone-dependent mechanisms have been postulated to be the primary factors responsible for the protection from CVD in premenopausal women. Recent Women’s Health Initiative studies, Cochrane Review studies, the Early Versus Late Intervention Trial with Estradiol Study, and the Kronos Early Estrogen Prevention Study have suggested that beneficial effects of hormone replacement therapy (HRT) are seen in women of <60 yr of age and if initiated within <10 yr of menopause. In contrast, the beneficial effects of HRT are not seen in women of >60 yr of age and if commenced after 10 yr of menopause. The higher incidence of CVD and the failure of HRT in postmenopausal aged women could be partly associated with fundamental differences in the vascular structure and function between men and women and in between pre- and postmenopausal women, respectively. In this regard, previous studies from human and animal studies have identified several sex differences in vascular function and associated mechanisms. The female sex hormone 17β-estradiol regulates the majority of these mechanisms. In this review, we summarize the sex differences in vascular structure, myogenic properties, endothelium-dependent and -independent mechanisms, and the role of 17β-estradiol in the regulation of vascular function.

Peak shear and peak flow mediated dilation: a time-course relationship

PURPOSE

To explore the temporal relationship between brachial artery peak shear stress (Shear) and flow-mediated dilation (FMD) in children and adults.

METHODS

Shear and brachial artery diameter were tracked following reactive hyperemia in 122 children and 350 adults using sonographic imaging.

RESULTS

Peak Shear, Shear area under the curve (Shear(AUC)), and Peak FMD were significantly larger in children than in adults. The time to peak Shear (Shear(TTP)) and time to peak FMD (FMD(TTP)) were significantly lower in children, while there was no significant difference in time from Shear(TTP) to FMD(TTP) between children and adults.

CONCLUSIONS

Children have a lower shear stimulus and FMD response than adults, but the time interval separating these events is similar. These differences could be due to changes in vascular dynamics with age, including reduced smooth muscle cell responsiveness and other factors. Despite differences in timing, the interval from peak Shear to peak FMD was similar in children and adults.

Presence of a high-flow-mediated constriction phenomenon prior to flow-mediated dilation in normal weight, overweight, and obese children and adolescents

PURPOSE

When assessing vasomotor endothelial function by reactive hyperemia, the brachial artery, in some individuals, constricts immediately before beginning to dilate following cuff release. We call this response high-flow-mediated constriction (H-FMC). The aim of this study was to describe the rate of the H-FMC during reactive hyperemia in children and adolescents throughout a range of body mass index (BMI) values, and to investigate differences in flow-mediated dilation (FMD), cardiovascular, and anthropometric measures between subjects with and without H-FMC.

METHODS

FMD was assessed in 136 children and adolescents (61 male, 75 female; 13 ± 3 years) by sonographic imaging of the brachial artery. H-FMC was characterized as the lowest point from the baseline brachial artery diameter immediately following reactive cuff release. Independent t tests were used to compare subjects with and without H-FMC.

RESULTS

H-FMC was observed in 91 of the 136 participants (66.9%). No significant difference was found between H-FMC and non-H-FMC subjects for age (p = 0.602), gender (p = 0.767), height (p = 0.227), or weight (p = 0.171). BMI percentile was nonsignificantly higher (91.8 ± 4.9th versus 84.6 ± 22.8th percentile, p = 0.057) and FMD was significantly lower (5.43 ± 3.41% versus 8.05 ± 3.97%, p < 0.001) in H-FMC than in non-H-FMC subjects. Adding H-FMC to FMD produced no significant difference between H-FMC and non-H-FMC individuals (8.03 ± 3.27% versus 8.05 ± 3.97%, p = 0.977).

CONCLUSIONS

Approximately 67% of participants demonstrated an H-FMC during reactive hyperemia. BMI percentile was nonsignificantly higher and FMD was significantly lower in children and adolescents who displayed this phenomenon.

Association of uric acid with obesity and endothelial dysfunction in children and early adolescents

BACKGROUND

Hyperuricemia in adults is known to be associated with hypertension, the metabolic syndrome and cardiovascular disease. The purpose of this study was to elucidate the factors associated with hyperuricemia in obese children and early adolescents and to investigate the threshold serum level of uric acid (UA) for the metabolic syndrome in children.

METHODS

We assessed anthropometric measurements, blood pressure, body composition and biochemical data in 1,559 obese children. To assess endothelial dysfunction, flow-mediated dilatation (FMD) was measured in 92 children. The correlations between serum UA levels and various parameters were examined. The threshold serum UA level for the metabolic syndrome was calculated by receiver-operating characteristic (ROC) curve analysis.

RESULTS

Serum UA levels were positively correlated with lipids in both boys and girls, and they were inversely correlated with FMD in the boys but not the girls. The threshold serum UA level for the metabolic syndrome was 5.25 mg/dl in boys and 5.05 mg/dl in girls. However, the specificity and sensitivity of ROC curve analysis are not so striking.

CONCLUSION

The correlation between UA and FMD showed gender differences and might be affected by the hormonal status. The cutoff level of serum UA as a marker of the metabolic syndrome in obese children was affected by both age and gender.

Sex differences in vascular compliance in normal-weight but not obese boys and girls: the effect of body composition

Objectives. To determine the effect of sex and obesity on vascular function in children and explore potential mechanisms that account for differences in vascular function. Methods. Participants were 61 (30 boys) normal-weight (BMI 25-75% ile for age and sex) and 62 (30 boys) obese (BMI ≥ 95% ile) children of ages 8-18 years. Measurements of large and small artery elastic index (LAEI and SAEI, resp.) and reactive hyperemia index (RHI) were obtained at rest, along with anthropometric and biochemical information. Results. In normal-weight children, LAEI was 16% higher in males than females (P = 0.04) with a similar trend for SAEI (13% higher in males, P = 0.067). In obese children, no sex-related differences in vascular measures were observed. In multivariable models, sex differences in arterial compliance were explained by higher lean mass in normal-weight boys. Fat mass predicted LAEI and SAEI in both normal-weight and obese females, but fat mass predicted arterial compliance in boys when fat mass exceeded 24 kg (37% of the sample). Conclusions. Normal-weight males have higher arterial compliance than normal-weight females due to increased lean mass, but sex-related differences were not observed among obese children due to a lack of sex-related differences in lean or fat mass.

Evaluation of gender differences in endothelium-independent dilation using peripheral arterial tonometry

BACKGROUND

A change in peripheral arterial tonometry (PAT) in response to reactive hyperaemia is often used to provide a non-invasive measure of endothelium-dependent dilation (EDD). Reactive hyperaemia does not allow one to quantify endothelium-independent dilation (EID), which is part of overall vascular function. Although most research examining vascular function and cardiovascular disease has focused on EDD, there is evidence that cardiovascular risk factors may impair EID.

PURPOSE

To examine the microvascular vasodilation response to nitroglycerin (NTG) in healthy adults using PAT.

METHODS

Microvascular responses to reactive hyperaemia and NTG were evaluated in 86 (41 female and 45 male) healthy subjects (age 37 ± 5 years). Beat-to-beat plethysmographic measurements of finger arterial pulse waves were recorded for 5 min following reactive hyperaemia. After a 10-min rest period, sublingual NTG (0.4 mg) was administered and PAT signal changes were measured for 10 min. Peak reactive hyperaemic index (RHI) and peak NTG-mediated index (NMI) were determined in all subjects.

RESULTS

There were no significant gender differences in peak RHI (females: 2.07 ± 0.56 versus males: 1.91 ± 0.58, P = 0.20). Mean peak NMI for all subjects was 2.78 (± 1.49). Peak NMI was significantly greater in females than in males (3.11 ± 1.59 versus 2.50 ± 1.34, P = 0.05). Time to peak NMI was not significantly different between genders (7 min, 28 s [± 1 min, 47 s], versus 7 min, 14 s [± 1 min, 49 s], P = 0.58).

CONCLUSION

In this population of healthy adults, peak NMI was significantly greater in females than in males. These findings suggest that gender differences exist in the microvascular vasodilation responses to NTG using PAT.

Endothelium-independent dilation in children and adolescents

Peak brachial artery dilation post-nitroglycerin (NTG) administration occurs between 3 and 5 min in adults. The purpose of this study was to identify the time to peak dilation response to sublingual NTG (0·3 mg) in youth. Endothelium-independent dilation (EID) was measured in 198 healthy (113 males, 85 females) youth (6-18 years) via ultrasound imaging of the brachial artery following NTG administration. Time to peak EID was 268 s following NTG administration, with no significant (P = 0·6) difference between males and females. There was a significant (P<0·001) difference between EID post-NTG at the 3 versus 4 min, 4 versus 5-min, and 3 versus 5 min time points. Peak EID (males: 24·8 ± 0·5 versus females: 25·3 ± 0·6%, P = 0·6) was not significantly different after accounting for baseline diameter. Peak response to NTG administration occurs between 4 and 5 min. The results demonstrate the importance of measuring EID up to 5-min post-NTG administration in youth.

Depressed mood and flow-mediated dilation: a systematic review and meta-analysis

OBJECTIVE

This systematic and quantitative review evaluates the literature on associations between depressed mood and flow-mediated dilation (FMD), a measure of endothelial function, in adults.

METHODS

Published English-language articles (through December 2010) were identified from literature searches, assessed for data extraction, and evaluated for quality.

RESULTS

The literature includes cross-sectional (n = 9) and retrospective examinations (n = 3) of how FMD correlates with clinical or subclinical depression in healthy adults and cardiovascular patients (total N across 12 studies = 1491). FMD was assessed using a variety of methodologies. Samples were predominately older white and Asian subjects with higher socioeconomic status. In eight of the 12 articles selected for this review, at least one significant inverse association was noted between depressed mood and FMD, with primarily moderate effect sizes. The overall meta-analysis (random-effects model) revealed a combined effect size of correlation coefficient r = 0.19 (95% confidence interval = 0.08-0.29, p = .001). Significant combined effects were found for subgroups of studies that a) received better quality ratings (r = 0.29), b) examined patients with cardiovascular disease or with cardiovascular disease risk factors/comorbidity (r = 0.29), c) used maximum vasodilation to quantify FMD (r = 0.27), and d) assessed samples that had a mean age of 55 years and older (r = 0.15).

CONCLUSIONS

Diverse studies support the inverse correlation between depressed mood and endothelial function, as measured by FMD. This literature would be strengthened by prospective studies, increased methodological consistency in FMD testing, and broader sampling (e.g., African Americans, younger age, lower socioeconomic status).

Gender differences in vascular function and insulin sensitivity in young adults

To examine influence of insulin resistance and other clinical risk factors for the MetS (metabolic syndrome) on vascular structure and function in young adults. This cross-sectional study was conducted in a cohort of young adults (mean age 22 years) and their siblings participating in a longitudinal study of cardiovascular risk (n=370). Insulin sensitivity was determined by euglycaemic insulin clamp. EDD (endothelium-dependent dilation) was determined by flow-mediated dilation using high-resolution ultrasound imaging of the brachial artery. EID (endothelium-independent dilation) was determined by NTG (nitroglycerine)-mediated dilation. The diameter and cIMT (intima-media thickness) of the carotid artery were also measured. There was no significant difference between males and females for age or body mass index. However, males had significantly higher glucose and triacylglycerol (triglyceride) levels, while the females had significantly higher HDL-C (high-density lipoprotein-cholesterol) and insulin sensitivity (13.00 ± 0.33 compared with 10.71 ± 0.31 mg·kg-1 of lean body mass·min-1, P<0.0001). Although peak EDD was significantly lower (6.28 ± 0.26 compared with 8.50 ± 0.28%, P<0.0001) in males than females, this difference was largely explained by adjustment for brachial artery diameter (P=0.15). Peak EID also was significantly lower in males than females (20.26 ± 0.44 compared with 28.64 ± 0.47%, P<0.0001), a difference that remained significantly lower after adjustment for brachial artery diameter. Males had a significantly greater cIMT compared with females (females 0.420 ± 0.004 compared with males 0.444 ± 0.004 mm, P=0.01), but when adjusted for carotid diameter, there was no significant difference (P=0.163). Although there were gender differences in vascular function and structure in the young adult population examined in this study, many of the differences were eliminated simply by adjusting for artery diameter. However, the lower EID observed in males could not be explained by artery diameter. Future studies need to continue to examine influence of gender on EID and other measures of vascular function.

The Role of Endothelial Dysfunction on Development and Progression of Atherosclerosis and Methods to Assess Vascular Function and Structure

The endothelium was originally thought to be just a semipermeable barrier between the vessel wall and the bloodstream, but today we now realize that it is actually a highly active autocrine, paracrine, and endocrine organ. Researchers have also begun to realize that the endothelium plays a key role in the development of atherosclerosis as well as other diseases. This increased recognition has resulted in considerable effort by both researchers and clinicians to develop accurate and reliable methods to measure and track changes in both vascular structure and function. In addition, research interest has focused on various cardiovascular risk factors (eg, age, gender, obesity, physical inactivity) and the effect they have on vascular structure and function. In this review, the authors discuss different research and clinical methods to assess vascular structure and function as well as the effect of various cardiovascular risk factors on the endothelium and the vascular system. They also discuss the ability to modify vascular structure and function through various lifestyle modifications such as weight loss and exercise.

Pulse wave amplitude is associated with brachial artery diameter: implications for gender differences in microvascular function

The ratio of pulse wave amplitude (PWA) during reactive hyperemia compared to baseline as measured by peripheral arterial tonometry (PAT) is a non-invasive measure of microvascular endothelial function referred to as the pulse wave amplitude reactive hyperemia index (PWA-RHI). Whether upstream conduit vessel structure may affect downstream resistance vessel PWA has not been clearly examined. We tested the hypothesis that digital PWA is influenced by brachial artery diameter (BAD) and that this association would influence comparison of PWA-RHI between genders. Measures of vascular structure and microvascular function were carried out in 115 patients varying in cardiovascular risk profiles (average age 57 years, male n = 79, CAD n = 43). PWA was assessed using plethysmography at baseline and following 5 minutes of brachial artery occlusion. BAD was assessed using high-resolution ultrasonography. Results : There was a negative association between BAD and PWA-RHI ( r = -0.34, p < 0.05). Women had greater PWA-RHI and smaller BAD compared with men (p < 0.05). When co-varying for BAD, there were no longer gender differences in PWA-RHI. Moreover, when a sub-group of men and women without CAD (n = 40), matched for BAD, were examined, there were no gender differences in PWA-RHI. In conclusion, PWA-RHI obtained from PAT is associated with BAD. Studies examining gender differences in microvascular endothelial function with PAT may need to correct for BAD as a potential confounder.

Examining the time course of endothelium-independent dilation by nitroglycerin

Arterial smooth muscle function is commonly assessed by measuring the dilation response to sublingual nitroglycerin (NTG), and is referred to as endothelium-independent dilation (EID). The time point at which the brachial artery dilates maximally after NTG administration is generally believed to occur somewhere between three and five minutes. The aim of this study was to examine the time course of brachial artery dilation response to a single dose of sublingual NTG to identify the time point at which maximal dilation occurs and to assess factors effecting EID. Endothelial independent dilation was measured in 125 normal, healthy subjects (male = 67, female = 58) via high-resolution ultrasound on the brachial artery. Mean time to maximal EID was 279.0 +/- 26.9 s. There was a significant (p < 0.0001) difference between brachial EID at three minutes vs. five minutes post NTG. There was also a significant gender difference in EID response (p < 0.0001). The results of this study indicate that maximal EID occurs approximately five minutes after NTG administration. Measuring EID at three minutes after NTG administration likely underestimates the true dilation capacity of the artery.

Early markers of cardiovascular disease

Vascular endothelium function plays a pivotal role in cardiovascular pre-clinical markers. Nitric oxide secreted by the vascular endothelium has a vasodilatory effect that reduces blood pressure which, in turn, prevents increases of left ventricular mass and intima-media thickness and improves left ventricular relaxation. Modern ultrasound technique allows noninvasive assessment of endothelial function and permits identification of functional alteration prior to manifestation of anatomical changes in the cardiovascular system. However, effort is needed to improve the reliability and reproducibility of ultrasound derived measure of endothelial function. This article provides an overview of challenges of clinical determination of endothelium-dependent arterial dilatation. In addition, we highlight the necessity of targeting the pediatric population in studies aimed at preventing and treating cardiovascular disease.

Noninvasive Arterial Measurements of Vascular Damage in Healthy Young Adults: Relation to Coronary Heart Disease Risk

PURPOSE

There is an increasing interest in noninvasive measurements of early structural or functional changes in large arteries such as pulse wave velocity (PWV), carotid intima-media thickness (CIMT), and augmentation index (AIx). These measurements may be applied in etiologic or prognostic research. The role of the AIx as a marker of cardiovascular risk has not fully been established. Our aim was to study whether AIx is related to coronary heart disease (CHD) risk and to compare the strength of the relations of AIx, PWV, and CIMT with cardiovascular risk in healthy young adults.

METHODS

Our study included 224 men and 273 women (mean age 28 years, range 27-30 years) from the Atherosclerosis Risk in Young Adults (ARYA) study. Cardiovascular risk profile was determined and CHD risk was estimated using the Framingham risk score. AIx, PWV and CIMT were measured using standard methods. Data were analyzed in strata of gender using linear regression models.

RESULTS

In men, PWV and CIMT were most strongly related to CHD risk. The increase in CHD risk per standard deviation increase in measurement was 0.24%/m/s, 95% CI (0.01;0.33) and 0.32%/mm, 95% CI (0.08;0.55), whereas the AIx was not significantly related to CHD risk (0.09 %/% 95% CI [-0.15;0.33]). In women, AIx, PWV, and CIMT were weakly but significantly related to CHD risk; there was no clear difference between the measurements.

CONCLUSION

In young men, PWV and CIMT are better measures of CHD risk than AIx. In women, AIx, PWV and CIMT estimate CHD risk equally well.

Common carotid arterial interadventitial distance (diameter) as an indicator of the damaging effects of age and atherosclerosis, a cross-sectional study of the Atherosclerosis Risk in Community Cohort Limited Access Data (ARICLAD), 1987-89

Background

The effect of age on common carotid artery diameter is unclear for varying atherosclerosis risk levels.

Methods

Cross-sectional data from the Atherosclerosis Risk in Communities Limited Access Data set were used to estimate the association of age with B-mode ultrasound common carotid artery diameter for three atherosclerosis risk levels. Based on information from clinical examinations, B-mode ultrasounds, questionnaires, blood and other tests, participants were categorized into three groups: pre-existing disease (prevalent stroke and/or coronary heart disease), high risk group (no pre-existing disease, but prevalent diabetes, hypertension, plaques/shadowing, body mass index >= 30, current smoking, or hyperlipidemia), and a low risk group (no pre-existing disease, no plaques/shadowing, and no major elevated risk factors). Multivariable linear regression analyses modeled the common carotid artery diameter relationship with age.

Results

Age was positively and significantly associated with common carotid artery diameter after risk factor adjustment in the overall sample, but age had a larger effect among persons with evidence of atherosclerosis (interaction p < 0.05). Each year of older age was associated with 0.03 mm larger diameter/year among persons with pre-existing disease, with 0.027 mm larger diameter/year in the high risk group, but only 0.017 mm/year among the low risk group. Results were qualitatively similar using plaques/shadowing status to indicate atherosclerosis severity.

Conclusion

The significant impact of age on common carotid artery diameter among low risk, middle-aged, black and white men and women suggests arterial remodelling may occur in the absence of identified risk factors. The significantly larger impact of age among persons with, compared to persons without identified atherosclerosis or its risk factors, suggests that arterial remodelling may be an indicator of exposure duration.