Subtle changes in ADMA and l-arginine concentrations in normal pregnancies are unlikely to account for pregnancy-related increased flow-mediated dilatation

BACKGROUND: Our objective was to investigate whether serum concentrations of asymmetric dimethylarginine (ADMA) or l-arginine correlate to hyperlipidemia or endothelial function in normal pregnancy compared with the non-pregnant subjects. METHODS AND RESULTS: As a part of population-based, prospective cohort Cardiovascular Risk in Young Finns study conducted in Finland we examined 57 pregnant Finnish women throughout gestation and 62 control women matched for age and smoking. Serum glucose, triglycerides (TG), total cholesterol (TC), low-density cholesterol (LDL-C), high-density cholesterol (HDL-C) and ADMA, symmetric dimethylarginine (SDMA) and l-arginine were determined concomitantly with endothelium-dependent brachial artery flow-mediated dilation (FMD), measured by ultrasound. All serum lipid concentrations were significantly higher in pregnant women than in non-pregnant women (P < 0.001 for each). The mean serum ADMA concentration in pregnant women was significantly lower compared with the non-pregnant controls (0.513 micromol l(-1) +/- 0.0593 versus 0.577 micromol l(-1) +/- 0.0710, P < 0.001). Lowered ADMA concentrations did not correlate statistically to FMD in these healthy pregnant women but FMD was enhanced towards the end of pregnancy. CONCLUSIONS: ADMA and l-arginine concentrations fall in normal pregnancy despite marked hypercholesterolemia. Endothelium-dependent vasodilation is enhanced in normal pregnancy but is not statistically correlated to maternal serum ADMA or l-arginine concentrations.     

Simultaneous ultrasound assessment of brachial artery shear stimulus and flow-mediated dilation during reactive hyperemia

In flow-mediated dilation (FMD) studies, brachial artery diameter changes due to reactive hyperaemia are typically measured through manual or automatic analysis of high resolution B-mode images while the stimulus of diameter change, i.e., the flow change, is qualitatively estimated by measuring the mean velocity in the vessel and assuming a parabolic velocity profile. This article describes an experimental approach to simultaneously measure the wall shear rate (WSR) and the diameter variations, through multigate spectral Doppler and B-mode image processing, respectively. By using an ultrasound advanced open platform (ULA-OP), experimental results from the brachial arteries of 15 presumed healthy volunteers have been obtained. The mean increments during reflow against baseline were 105% ± 22% for the peak WSR and 8% ± 3% for the FMD. The mean time interval between the WSR peak and the beginning of plateau of diameter waveform was 38 ± 8 s. The results confirm that in young healthy subjects the postischemic vasodilation of brachial artery is largely correlated to the WSR increase.     

Pulsatility index change of brachial artery shows better reproducibility than flow-mediated vasodilation

We aim to evaluate intra- and interobserver reproducibility of brachial artery flow-mediated dilation (FMD) and of pulsatility index change (PI-C) 1 min after a 5-min forearm compression in pregnant women. Flow-mediated dilation and PI-C were assessed in 31 healthy pregnant women in 3 consecutive days, by two observers. A broader range of response to the stimulus was observed for PI-C (-58.99%-86.71%) than FMD (2.38%-27.01%). The intraclass correlation coefficients were higher for PI-C than for FMD (intra = 0.90 vs. 0.69, p = 0.047; inter = 0.94 vs. 0.61, p = 0.007). Therefore, PI-C measurements were more reliable than FMD. However, studies comprising of subjects with cardiovascular risk factors relating FMD and PI-C become necessary to validate this method for the study of endothelial dysfunction.     

How should flow‐mediated dilation be normalized to its stimulus?

The brachial artery flow‐mediated dilation test (FMD) is the non‐invasive gold‐standard used to assess endothelial function. Reduced FMD is an early event in the development of atherosclerosis and provides a marker for predicting future cardiovascular disease events. Despite its widespread popularity and proven validity, the FMD test is limited by poor reliability. There are three major limitations associated with the standard FMD methodology: (i) inappropriate expression of FMD, (ii) measurement variance associated with a short‐lived FMD response and (iii) most studies fail to account for the FMD stimulus. A series of relatively simple statistical practices can be adopted to account for these limitations. In particular, we suggest that endothelial function be estimated using shear rate–diameter dose–response curves, which can be statistically analysed using hierarchical linear modelling. The use of dose–response curves could potentially improve measurement reliability and validity.     

Flow‐mediated dilation in the inactive limb following acute hypoxic exercise

The purpose of this study was to elucidate the effect of acute aerobic exercise performed under hypoxic conditions on flow‐mediated dilation (FMD) in the inactive limb. Seven males participated in the study. The subjects performed two submaximal leg cycling on a semirecumbent ergometer at the same relative intensity (60% peak oxygen uptake) in normoxia [inspired oxygen fraction (FIO₂) = 0·21] and hypoxia (FIO₂ = 0·12–0·13) for 30 min. The brachial artery diameter and blood velocity during exercise were measured via ultrasound, and the antegrade and retrograde shear rates were calculated. Before and 5, 30 and 60 min after exercise, brachial artery FMD was measured in normoxia. FMD was estimated as the percentage increase in peak diameter from the baseline diameter at prior occlusion (%FMD) and as the controlling changes in baseline diameter (the corrected‐%FMD). No difference in antegrade shear rate during exercise was detected between the normoxic and hypoxic conditions, whereas the retrograde shear rate was larger during hypoxic exercise. The %FMD decreased significantly at 5 min after exercise in both normoxia and hypoxia, and it returned to pre‐exercise levels within 60 min of recovery. Significant decreases in FMD at 5 min after exercise had disappeared when the baseline diameter was controlled using an analysis of covariance (the corrected‐%FMD). No significant differences were observed between the normoxic and hypoxic trials in the %FMD and corrected‐%FMD following exercise. These results suggest that hypoxia has no impact on endothelial function in the inactive limb following acute aerobic exercise.     

Comparison of B-mode and echo tracking methods of assessing flow-mediated dilation

The aim of this study was to compare B-mode and echo tracking methods to assess endothelium-dependent flow-mediated dilation (FMD). Baseline brachial artery diameter, 60-s post cuff release diameter and FMD percent were assessed in 17 normal, healthy individuals using both techniques. Mean values for baseline diameter, 60-s diameter and FMD for M-mode were 3.83 +/- 0.69 mm, 4.06 +/- 0.66 mm and 6.35 +/- 3.98%, respectively. Mean values for baseline diameter, 60-s diameter and FMD for B-mode were 3.75 +/- 0.65 mm, 4.00 +/- 0.63 mm and 6.91 +/- 2.85%, respectively. Results, as displayed by Bland-Altman graphs, indicate a strong agreement between B-mode and echo tracking methods of assessing brachial artery diameter changes via FMD.     

老年周围动脉闭塞性疾病内皮和非内皮依赖性舒张功能的分析(英文)

目的通过探讨老年周围动脉闭塞性疾病(peripheralarterialoc-clusivedisease,PAOD)内皮依赖性舒张功能,即血流介导的血管扩张功能(flow-mediateddilation,FMD)和硝酸甘油介导的非内皮依赖性舒张功能(nitroglycerin-mediateddilation,NMD)状况,了解其相关因素。方法采用超声多普勒检测33例已确诊为PAOD的老年患者肱动脉FMD及NMD,并分别与40例健康老人及30例具有心血管危险因素的老年非PAOD患者进行对照研究。结果老年PAOD患者FMD及NMD均显著低于对照组(t=-2.2358～2.7317,P<0.01),;肱动脉基础内径、收缩压、低密度脂蛋白胆固醇与FMD呈负相关(相关系数r分别为-0.632,-0.479,-0.608,P值分别为0.0001,0.02,0.001);FMD与NMD呈正相关(r=0.364,P=0.004),肱动脉基础内径与NMD呈负相关(r=-0.391,P=0.0006)。结论老年PAOD患者FMD及NMD均受损;肱动脉基础内径、收缩压、低密度脂蛋白胆固醇可能是FMD独立的预测因子;而FMD及肱动脉基础内径与NMD密切相关。     

Occlusion cuff position is an important determinant of the time course and magnitude of human brachial artery flow-mediated dilation

Non-invasive ultrasound techniques to assess flow-mediated vasodilation (FMD) are frequently used to assess arterial endothelial vasodilator function. However, the range of normal values varies considerably, possibly due to differences in methodological factors. We sought to determine the effect of occlusion cuff position on the time course and magnitude of brachial artery blood flow and flow-mediated dilation. Twelve healthy subjects underwent measurements of forearm blood flow using venous occlusion plethysmography (VOP) before and after 5 min of susprasystolic cuff inflation, using two randomly assigned occlusion cuff positions (upper arm and forearm). An additional 16 subjects underwent two brachial ultrasound studies, using the two cuff positions, to assess the extent and time course of changes in brachial artery diameter and blood flow. Maximum increase in blood flow (peak reactive hyperaemia), measured by VOP, occurred immediately upon each cuff deflation, but was greater after upper arm compared with forearm arterial occlusion (33.1+/-3.1 versus 22.8+/-2.2 ml/min per forearm tissue, P=0.001). Maximal brachial artery FMD was significantly greater following upper arm occlusion (9.0+/-1.2%, mean +/- S.E.M.) compared with forearm occlusion (5.9+/-0.7%, P=0.01). The time course of the change in brachial artery diameter was affected differently in response to each protocol. The time to peak dilation following upper arm occlusion was delayed by 22 s compared with forearm occlusion. Occlusion cuff position is thus a powerful determinant of peak reactive hyperaemia, volume repaid and the extent and time course of brachial artery FMD. Positioning the cuff on the upper arm produces a greater FMD. These results highlight the need for comparisons between FMD studies to be made with care.     

糖尿病肾病患者肱动脉与胭动脉血管内皮舒张功能对比性研究

目的：以高频超声比较糖尿病肾病Ⅴ期患者肱动脉与腘动脉血管内皮舒张功能的差异性.方法：分别选择健康志愿者（NC组）、2型糖尿病（DM组）和糖尿病肾病Ⅴ期透析前（DKD-Ⅴ组）的患者各20例. 利用高频彩色多普勒超声测量肱动脉及腘动脉血管基础状态及加压后血管内径和峰值流速,并计算血流介导的扩张值（FMD）. 比较肱动脉及腘动脉FMD及峰值流速的差异.结果：肱动脉FMD（％）、腘动脉FMD（％）,NC组、DM组、DKD-V组显著性减少（P＜0.05）;肱动脉与腘动脉FMD（％）比较,NC组、DM组、DKD-V组显著性减少（P＜0.05）;肱动脉与胭动脉FMD差值（％）,NC组、DM组、DKD-V组显著性增加（P＜0.05）.结论：DKD-V组患者血管内皮舒张功能障碍重于单纯糖尿病患者,且腘动脉血管内皮舒张功能障碍进展速度大于肱动脉.     

Velocity acceleration as a determinant of flow-mediated dilation

Shear stress is the established stimulus for flow-mediated dilation (FMD). In vivo, shear stress is typically estimated using mean blood velocity. However, mean blood velocity may not adequately characterize the shear stimulus. Pulsatile flow results in large shear gradients (velocity acceleration) at the onset of flow. The purpose of this study was to determine the importance of velocity acceleration to FMD. We define FMD as the brachial artery shear rate-diameter slope. Fourteen physically active, young (26 ± 5 years), male subjects were tested. Progressive forearm heating and handgrip exercise elicited steady-state increases in shear rate. FMD was measured prior to and following induced increases in velocity acceleration. Velocity acceleration was increased by inflating a tourniquet around the forearm to 40 mm Hg. Hierarchical linear modeling was used to estimate change in diameter with repeated measures of shear stress nested within each subject. Averaged across conditions, the 40 mm Hg cuff resulted in a 14% increase in velocity acceleration (p = 0.001). FMD was attenuated by 11.0% (p = 0.015) for the acceleration vs. control condition. However, after specifying velocity acceleration as a covariate, FMD was no longer significantly (p = 0.619) different between acceleration and control conditions. This finding suggests that mean blood velocity alone may not adequately characterize the shear stimulus.     

Assessment of endothelial function in normal twin pregnancy.

OBJECTIVE: To assess the maternal endothelial function in normal twin pregnancy. DESIGN: Cross-sectional study. SUBJECTS: Endothelial function was investigated in 74 women with normal twin pregnancy at 11-30 weeks of gestation and the results were compared to previous reported findings in 98 women with normal singleton pregnancy and 19 non-pregnant controls. METHODS: Endothelial function was assessed by measuring the changes of the brachial artery diameter in response to reactive hyperemia (flow-mediated dilatation) using external high resolution ultrasound. RESULTS: Flow-mediated dilatation of the brachial artery in both twin and singleton pregnancies was significantly higher than in non-pregnant women (P = 0.002 and P = 0.02, respectively). However, there was no significant difference in flow-mediated dilatation between women with twin and singleton pregnancy (9.61 +/- 4.36 vs. 8.84 +/- 3.18, P = 0.38). Resting vessel size, baseline flow and reactive hyperemia did not change significantly with gestation in twin pregnancy and were similar to values in singleton pregnancies and controls. CONCLUSION: Our findings indicate that although in pregnancy endothelial function is enhanced, this change may not be affected by the number of fetoplacental units present.     

Non-invasive assessment of endothelial function in normal pregnancy.

OBJECTIVE: To assess endothelial function in normal pregnancy by non-invasive methods. METHODS: Flow-mediated dilatation of the brachial artery was measured by ultrasonography in 157 women with normal singleton pregnancies between 10 and 40 weeks' gestation and 19 non-pregnant controls. RESULTS: Flow-mediated dilatation in the non-pregnant controls was 6.42 +/- 2.45%. In pregnant women, between 10 and 30 weeks, the mean flow-mediated dilatation (8.84 +/- 3.18%) was significantly higher than the non-pregnant controls (P = 0.002), but after 30 weeks of gestation there was a decrease to prepregnancy levels. Resting vessel diameter and blood flow were significantly increased in pregnancy, mainly after 30 weeks' gestation (P < 0.001, P < 0.001, respectively). Flow-mediated dilatation was significantly correlated to resting vessel diameter and reactive hyperemia. CONCLUSION: Normal pregnancy is associated with enhanced endothelial function which is apparent from at least 10 weeks' gestation.     

Sustained hyperaemia stimulus is necessary to induce flow-mediated dilation of the human brachial artery

We studied the relative importance of the magnitude and duration of the shear stimulus to induce flow‐mediated dilation (FMD) in the brachial artery of 10 healthy men by ultrasound imaging. The shear stress stimulus was induced by different durations of reactive hyperaemia following 15‐min forearm occlusion. The control condition of continuous postocclusion hyperaemia was compared to 20, 40 and 60 s of reactive hyperaemia followed by reapplication of circulatory arrest for 2 min and a second cuff release. In response to the first cuff release, peak shear rate was not different between conditions; total shear during the first minute was reduced in the 40 s and further reduced in the 20 s conditions. FMD in control (10·0 ± 3·0%), 60 s (10·5 ± 3·2%) and 40 s (7·8 ± 3·6%) were greater than the 20‐s condition (2·9 ± 2·8%). At second cuff release, peak shear of the 20‐s condition was slightly reduced from the first release, but 40 and 60‐s conditions were progressively reduced. Total shear to peak dilation was reduced after the second cuff release for the 20 and 40‐s conditions and further after the 60‐s condition. FMD was maintained in the 20‐s condition (8·3 ± 3·7%) but reduced in the 40‐s (3·7 ± 1·7%) and 60‐s conditions (1·5 ± 2·6%). FMD was not related to peak shear rate after the first occlusion (r = 0·003) but was after the second cuff release (r = 0·32, P = 0·004). The FMD response was correlated with the total shear to time of peak diameter after the first (r = 0·35, P<0·001) and the second (r = 0·25, P = 0·009) cuff release.     

Endothelial dysfunction in trauma patients: a preliminary communication

Global ischemia, followed by reperfusion during resuscitation, leads to cellular damage by generating toxic reactive metabolites that includes, but is not exclusive to, superoxide radical. Superoxide decreases the bioavailability of nitric oxide (NO) via its reaction that yields peroxynitrite. The observation of decreased bioavailability of NO, and attenuated endothelium-dependent relaxation have been observed in animal models of trauma and resuscitation. However, it remains unknown whether endothelium-mediated vasodilation is impaired in humans after traumatic hemorrhage followed by crystalloid resuscitation. Based on these previously established precepts, we hypothesized that endothelium-dependent relaxation is impaired in trauma patients despite adequate fluid resuscitation with crystalloid solutions. Baseline characteristics such as age, body mass index, and blood pressure being similar in both groups, NO-mediated, endothelium-dependent flow-mediated dilation (FMD) of the brachial artery was examined in resuscitated trauma victims (n = 13) and compared in normal controls (n = 12). Baseline brachial artery diameter, endothelium-dependent FMD induced by reactive hyperemia and endothelium-independent dilation induced by administration of sublingual nitroglycerin were measured. Brachial artery diameter measured at baseline in trauma patients and in control subjects were not dissimilar. In conclusion, brachial artery FMD, a surrogate for NO-mediated endothelial function, was significantly impaired in trauma patients despite fluid resuscitation resulting in stable hemodynamics (0.8 +/- 1.7 mm vs. 5.7 +/- 0.8 mm, respectively; P < 0.05) However, endothelium-independent dilation induced by nitroglycerin was not significantly different between trauma patients and controls.     

Physical Activity and Vascular Dilation Function in Healthy Middle-aged Individuals

Objective: Vascular dilation dysfunction has been linked with risk of cardiovascular disease. This study was undertaken to investigate the relationship between physical activity and vascular dilation function in healthy middle-aged adults to help explaining the effect of physical activity on preventing cardiovascular disease. Method: We recruited 91 healthy middle-aged adults to complete a self-report 7-day physical activity recall questionnaire and an exam of brachial artery flow-mediated dilation(FMD) and Nitroglycerin-mediated dilation (NMD) detected by ultrasound. The relationship between physical activity level (PAL) and FMD and NMD were explored. Result: Physical activity showed a significant and positive relationship with the brachial artery FMD, even after adjustment for possible confounding factors (r=0.363, P<0.01). The group of high physical activity level had the highest FMD. The means of FMD (%) in low, moderate and high PAL groups were respectively 8.70%±3.93％,9.01%±3.22％ and 12.38±5.67％ with significant difference between individuals of low and high PAL and between moderate and high PAL group(P<0.01). The means of NMD (%) is 25.13%±6.52%,24.38%±5.44% and 29.50%±7.25% respectively (P>0.05) and there was no significant difference among three groups. There was no positive relation between PAL and FMD in premenopausal females but in men and postmenopausal females. Although individuals of high PAL have the best FMD, the moderate PAL can also retard FMD decrease with ageing. Conclusion: Maintaining high physical activity level can enhance endothelial-dependent vascular dilation, and moderate or high physical activity level can prevent endothelial-dependent vascular dilation declining with aging, which may contribute to decrease risk of cardiovascular disease in healthy middle-aged adults.     

妊娠期糖尿病对孕妇产前及产后血管内皮功能影响的纵向研究

目的 探讨妊娠期糖尿病对孕妇产前及产后血管内皮功能的影响。 方法 2016年11月至2019年6月期间在我院产检并分娩,并分别在孕前、孕24-28周和产后12周后进行右侧肱动脉内皮依赖性血流介导血管扩张(flow-mediated dilation,FMD)检测的34名正常妊娠孕妇(对照组)和29名妊娠期糖尿病(Gestational diabetes mellitus,GDM)孕妇(研究组)纳入本次研究。对不同组间或同一组内不同时间点的FMD值差异性比较采用重复测量方差分析；不同组间相关指标的差异性比较采用独立样本T检验；对研究组FMD值变化趋势影响因素进行主成分分析。结果 两个组别组内不同时间点FMD值差异有统计学意义(P<0.05),呈先降后升趋势。两个组别间三个时间点FMD值总体水平差异有统计学意义(P<0.001)。不同组别各时间点患者的FMD值组间比较孕前基线水平差异无统计学意义(P>0.05),在晚孕期和产后12周两个时间点,对照组的FMD值和研究组的FMD值差异有统计学意义(P<0.05)。主成分分析显示,空腹血糖、服糖后2h血糖和舒张压对研究组FMD值变化趋势影响因素最大。 结论 妊娠期糖尿病对于血管内皮功能损伤很可能是不可逆性的；妊娠期糖尿病孕妇产后定期评估FMD值的变化可以作为筛查心脑血管病高危人群的重要手段。     

超声对2型糖尿病上下肢动脉内皮功能损伤的对比研究

目的 应用高频超声分别检测并比较2型糖尿病(2DM)患者肱动脉和腘动脉血流介导的内皮舒张功能(Flow-mediated vasodilation,FMD),为临床提供其内皮功能障碍的可靠依据.方法 对50例2DM患者和65例正常人,应用高频超声分别检测肱动脉和腘动脉基础内径、基础状态峰值流速、反应性充血后最大血管内径、峰值流速,分别计算FMD并进行比较.结果 (1)2DM组肱动脉及腘动脉FMD均明显小于正常对照组[(肱动脉:(4.03±1.12)% vs (8.90±2.02)%,P<0.01];腘动脉:[(3.64±1.30)% vs (5.91±1.05)%,P<0.01)];(2)2DM患者腘动脉FMD明显小于肱动脉FMD[(3.64±1.30)% vs (4.03±1.12)%,P<0.01)].结论 2DM时内皮依赖性血管舒张功能明显受损,尤以下肢FMD受损更明显.     

老年心力衰竭患者血管内皮舒张功能变化及临床意义

目的：通过对慢性心力衰竭（CHF）病人血流介导性肱动脉内皮舒张功能（FMD）的测定,探讨心衰病人FMD的变化及其与心力衰竭的关系和临床意义。方法：随机选择心衰患者50例,健康人20例。采用美国菲利普7500型超声心动图仪检测肱动脉基础状态下、反应性充血时（内皮依赖性舒张）及含服硝酸甘油后（非内皮依赖性舒张）的内径。计算反应性充血时肱动脉内径舒张百分比及含服硝酸甘油后肱动脉内径舒张百分比。结果：与正常组比较,心衰组FMD均显著降低（P〈0.05）,心功能越差,FMD降低越明显。结论：老年慢性心衰患者存在内皮功能障碍,改善内皮功能对于心力衰竭的防治具有重要临床意义。     

Noninvasive assessment of brachial artery endothelial function with digital ultrasound and 13-MHz scanning frequency: feasibility of measuring the true inner luminal diameter using the intima-lumen interface

Previous studies assessing endothelial function as flow-mediated changes in the brachial artery diameter have not been able to measure the true inner luminal diameter. This is due to the lack of image quality, which has hampered the visualisation of the lumen-intimal interface. Because increases in resolution and scanning frequency have recently led to improved ultrasound (US) image quality, we assessed the feasibility of measuring the true brachial artery diameter using digital US and 13-MHz scanning frequency. Satisfactory true inner diameter measurements were obtained in all subjects (n = 148, middle-aged men, mean age 54 +/- 7 y) participating in a risk factor study. At baseline flow, the intima to intima diameter was 4.03 +/- 0.49 and 4.67 +/- 0.52 mm measured conventionally from the anterior to the posterior media-adventitia interface (difference 0.64 +/- 0.10 mm). After hyperaemia, the intima to intima diameter was 4.23 +/- 0.46 mm and the adventitia to adventitia diameter 4.86 +/- 0.50 mm. Flow-mediated dilation (FMD) expressed as the percentage change from the baseline diameter measured 5.3 +/- 4.3% using the true inner diameters and 4.3 +/- 3.7% using the conventional outer diameters. The difference in FMD values was systematic, and there was a good linear correlation between them (r = 0.93, p < 0.0001). If FMD is presented as the percentage change from baseline to hyperaemia, this new method gives values that are approximately 1% unit higher, compared with values when brachial luminal diameter is measured in the conventional way between the adventitia-media interfaces.     

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.