"One-stop-shop" ultrasound diagnosis of functional, structural and physicomechanical properties of the brachial artery.

BACKGROUND: The pathogenesis of atherosclerosis comprises endothelial dysfunction, thickening as well as impaired compliance of the arterial vessel wall. Early assessment of these alterations of the vessel wall at the same site of the vascular tree has yet been hampered by the lack of highly sensitive diagnostic approaches suitable for clinical routine. We therefore aimed to develop and validate a single non-invasive examination of the brachial artery for simultaneous and highly accurate measurement of functional, structural and physicomechanical parameters of the brachial artery. PATIENTS AND METHODS: 20 healthy individuals were investigated using high resolution ultrasound. Flow-mediated dilation (FMD), fractional diameter changes (FDC) and intima-media-thickness (IMT) were measured in the same segment of the brachial artery. Coefficients of variation, day-to-day-variability, between- and within-observer-variability were investigated in 5 individuals. All measurements were performed manually and by an automated PC-based analyzing system. RESULTS: Mean values for all measured parameters were 7.65 +/- 0.8% for FMD, 0.02 +/- 0.002 for FDC, 0.351 +/- 0.007 mm for IMT and followed an even distribution throughout the study population. Automated analysis of coefficient of variation, day-to-day-, between- and within-observer variabilities were: 0. 78%, 1.3%, 0.8%, 0.8% (FMD); 4.7%, 2.8%, 4.2%, 2.7% (FDC); 1.8%, 1.1%, 1.9%, 1.1% (IMT). Coefficient of variation, day-to-day-, between- and within-observer variabilities for the manual readings were significantly higher. CONCLUSIONS: Functional, structural and physicomechanical parameters of the brachial artery can be quantified consecutively, time-saving and highly reproducibly as an "one-stop-shop" in a single session using high resolution ultrasound with digitized post-processing. This highlights the future possibility of early, sensitive and non-invasive diagnostic testing of vascular function in patients prone to vascular disease.

Serum nitrite sensitively reflects endothelial NO formation in human forearm vasculature: evidence for biochemical assessment of the endothelial L-arginine-NO pathway.

OBJECTIVE: A reduced bioactivity of endothelial nitric oxide (NO) has been implicated in the pathogenesis of atherosclerosis. In humans, the endothelial L-arginine-NO pathway has been indirectly assessed via the flow response to endothelium-dependent vasodilators locally administered into the coronary, pulmonary or forearm circulation. However, biochemical quantification of endothelial NO formation in these organ circulations has been hampered so far because of the rapid metabolism of NO. Therefore, we aimed to work out a reliable biochemical index to assess endothelial NO formation in human circulation. METHODS: In 33 healthy volunteers, forearm blood flow (FBF) was measured by standard techniques of venous occlusion plethysmography at rest, after local application of the endothelium-dependent vasodilator acetylcholine (ACH), the endothelium-independent vasodilator papaverine (PAP), the stereospecific inhibitor of endothelial NO synthase (eNOS) L-NMMA, and L-arginine (ARG), the natural substrate of eNOS. In parallel, nitrite and nitrate concentrations in blood samples taken from the antecubital vein were measured by HPLC using anion-exchange chromatography in combination with electrochemical and ultraviolet detection following a specific sample preparation method. RESULTS: ACH dose-dependently increased resting FBF (from 3.0 +/- 0.3 to 10.4 +/- 0.9 ml/min per 100 ml tissue) and serum nitrite concentration (from 402 +/- 59 to 977 +/- 82 nmol/l, both p < 0.05, n = 12). A significant correlation was observed between the changes in FBF and the serum nitrite concentration (r = 0.61, p < 0.0001). L-NMMA reduced resting FBF and endothelium-dependent vasodilation by 30% and this was paralleled by a significant reduction in serum nitrite concentration at the highest dose of ACH (n = 9, p < 0.001). PAP increased FBF more than fourfold, but did not affect serum nitrite concentration (n = 11), whereas ARG significantly increased both FBF and nitrite. Basal serum nitrate amounted to 25 +/- 4 mumol/l and remained constant during the application of ACH, PAP and L-NMMA. CONCLUSIONS: The concentration of serum nitrite sensitively reflects changes in endothelial NO formation in human forearm circulation. This biochemical measure may help to characterize the L-arginine-NO pathway in disease states associated with endothelial dysfunction and to further elucidate its pathophysiological significance for the development of atherosclerosis in humans.

Evidence for a multifactorial process involved in the impaired flow response to nitric oxide in hypertensive patients with endothelial dysfunction.

The assessment of endothelial function in hypertensive patients receiving acetylcholine has revealed conflicting results. Whether an impaired flow response to acetylcholine is explained solely by a diminished endothelial synthesis of nitric oxide (NO) remains unclear as yet. In the present study, we tested the hypothesis that mechanisms other than reduced NO synthesis contribute to the hypertension-associated impairment of endothelium-dependent vasodilation. Therefore, the dilatory response to endogenous and exogenous NO was measured in resistance arteries and cutaneous microvessels in the forearm circulation of 12 normotensive individuals and 17 hypertensive patients. In addition, the overall dilatory capacity was assessed by peak flow during reactive hyperemia after 3 minutes of ischemia. Forearm blood flow was quantified by venous occlusion plethysmography at rest, during application of the NO donor sodium nitroprusside, and during stimulation of endogenous NO synthesis by acetylcholine and bradykinin. Blood flow velocity in the cutaneous microvasculature was measured with laser-Doppler flowmetry in parallel. Resting forearm flow was comparable in both groups (3.1 +/- 0.2 and 3.4 +/- 0.2 mL.min-1.100mL-1 tissue), whereas blood pressure and thus peripheral vascular resistance was significantly elevated in hypertensive compared with normotensive subjects. Hyperemic peak flow was significantly blunted in hypertensive patients. Sodium nitroprusside, acetylcholine, and bradykinin increased flow in a dose-dependent manner to a comparable extent in the control group (13.3 +/- 0.8, 13.6 +/- 1.3, and 14.6 +/- 0.7 mL.min-1.100mL-1 tissue, respectively). In contrast, in hypertensive patients maximum increase in resting flow was significantly reduced (sodium nitroprusside, -36%; acetylcholine, -44%; and bradykinin, -56%). The flow response after stimulation of endogenous NO synthesis by bradykinin was significantly more blunted compared with that of exogenous NO after application of sodium nitroprusside. In the cutaneous microvasculature, bradykinin-induced increases in blood flow velocity were selectively impaired in hypertensive patients, whereas flow response to acetylcholine was preserved. Thus, we conclude that in arterial hypertension endothelium-dependent, NO-mediated dilation of resistance arteries and cutaneous microvessels of the forearm vasculature is heterogeneously impaired, depending on the type of endothelial receptor stimulated. Furthermore, the present data suggest that in hypertensive patients the impairment of NO-dependent dilation of resistance arteries is caused by at least three different mechanisms: (1) a reduced endothelial synthesis of NO due to either a disturbed signal-transduction pathway and/or a reduced activity of NO synthase, (2) an accelerated NO degradation within the vessel wall, and (3) alterations in the vessel architecture resulting in an overall reduced dilatory capacity of resistance arteries.

Impaired effectiveness of nitric oxide-donors in resistance arteries of patients with arterial hypertension.

OBJECTIVE: To assess the dilatory effectiveness of nitric oxide donors in resistance arteries of patients with arterial hypertension in comparison with that in those of normotensive controls. BACKGROUND: Endothelium-dependent vasodilation has been demonstrated to be impaired in arterial hypertension. Besides disturbances in endothelial nitric oxide production a reduced vasodilatory effectiveness of nitric oxide might contribute to this phenomenon of endothelial dysfunction. We therefore investigated the dilatory responsiveness of resistance arteries to exogenous nitric oxide by means of administration of the nitric oxide donors glycerol trinitrate (GTN), isosorbide dinitrate (ISDN) and sodium nitroprusside (SNP) in hypertensive patients. METHODS: Forearm blood flow was measured by venous occlusion plethysmography at rest and during intra-arterial infusion of nitric oxide donors at increasing doses in 11 patients with arterial hypertension and in 10 age-matched normotensive controls. RESULTS: Forearm blood flow at rest was comparable in the two groups and was dose-dependently increased by administration of either nitric oxide donor. In patients with arterial hypertension, blood flow responses to infusions of organic nitrates were significantly impaired over the entire dose-response curve compared with those of normotensive controls (220 nmol/min GTN 13.1 +/- 1.3 and 8.6 +/- 0.3 ml/min per 100 ml tissue; 212 nmol/min ISDN 9.9 +/- 0.7 and 5.8 +/- 1.0 ml/min per 100 ml tissue). Blood flow responses to infusion of the nitric oxide donor SNP were also profoundly impaired in the hypertensive patients, the extent of which impairment equalled that found with the organic nitrates. Within the entire set of normotensive and hypertensive subjects, maximal flow responses to either nitric oxide donor were inversely correlated with mean arterial blood pressure. CONCLUSIONS: Dilation of resistance arteries in response to infusion of nitric oxide donors is impaired in hypertensive patients and the degree of this impairment depends critically on the severity of arterial hypertension. The reduced effectiveness of nitric oxide appears to be independent of the class of nitric oxide donor and thus of the mode of intravascular nitric oxide generation. These findings are likely to have important implications not only for our understanding of the pathophysiological mechanisms of endothelial dysfunction but also for nitric oxide donor therapy in arterial hypertension.

Additive effect of coexistent type 2 diabetes and arterial hypertension on endothelial dysfunction in resistance arteries of human forearm vasculature.

Population studies suggest that vascular complications accumulate when arterial hypertension supervenes on diabetes mellitus. Although it has been demonstrated that endothelial function is impaired in patients with either diabetes mellitus or arterial hypertension it is unknown whether or not both diseases exert additive effects on endothelial dysfunction. The authors therefore investigated endothelium-dependent and endothelium-independent vasodilation in the forearm vasculature of 44 individuals: in 10 type 2 diabetic patients (DM), in 12 patients with arterial hypertension (HT), in 10 patients with both DM and HT (DM+HT), and in 12 healthy control subjects (C). Forearm blood flow (FBF) was measured by venous occlusion plethysmography at rest and following intraarterial infusion of acetylcholine (ACh) and the NO-donor sodium nitroprusside (SNP) at increasing doses. FBF at rest was significantly lower in diabetic patients: 2.2 +/- 0.1 (DM) and 2.6 +/- 0.2 (DM+HT) versus 3.1 +/- 0.1 (HT) and 3.4 +/- 0.2 (C) mL/min per 100 mL of tissue. ACh and SNP both increased FBF dose-dependently in each group. The maximum response to ACh was progressively decreased in DM and HT: 13.7 (C) > 8.1 (DM) > 7.6 (HT) > and 5.7 (DM+HT) mL/min per 100 mL of tissue. Reduction of the endothelium-dependent flow reserve assessed as percent increase in maximum FBF was also impaired following the same rank order: 349 (C) > 268 (DM) > 160 (HT) > 126 (DM+HT)%. The flow response to the NO-donor SNP amounted to: 327 (C), 306 (DM), 200 (HT), and 194% (DM+HT). In DM+HT the reduction of endothelium-dependent flow response was more pronounced compared with the endothelium-independent flow response. The present data provide evidence that type 2 diabetes and arterial hypertension impair endothelium-dependent dilation of resistance arteries in an additive manner suggesting that this progressive endothelial dysfunction might contribute to the increased incidence of cardiovascular complications when both diseases are coexistent.

Impairment of adenosine-induced dilation of forearm resistance arteries in patients with arterial hypertension.

BACKGROUND: Adenosine is a potent mediator of arteriolar tone in particular during ischemia, hypoxia, and exercise. Functional disturbance of this dilatory pathway may be highly significant for the pathophysiology and pathogenesis of arterial hypertension. PATIENTS AND METHODS: Forearm blood flow (FBF) was quantified by venous occlusion plethysmography following intra-arterial infusion of adenosine at increasing doses in 13 patients with arterial hypertension (HT) and 12 age-matched normotensive controls (NT). Hyperemic peak flow was measured following 3 minutes of non-flow ischemia. RESULTS: FBF at rest was comparable in both groups and was dose-dependently increased by adenosine in both groups. In patients with HT adenosine-induced vasodilation was significantly impaired over the entire dose-response curve compared with NT (6.0 mumol/min: 14.5 +/- 1.0 versus 8.6 +/- 0.9 ml.min-1.100 ml-1 of tissue, p < 0.01). Maximum forearm blood flow during reactive hyperemia was also profoundly impaired in the hypertensive patients (-38%, p < 0.01). In the overall group of normotensive and hypertensive subjects, flow responses to adenosine were i) significantly correlated with peak flow (adenosine 2.0 mumol/min: r = 0.79, p < 0.001), and total flow during reactive hyperemia and ii) inversely related to the magnitude of arterial blood pressure. CONCLUSIONS: The study reported presents first evidence that adenosine-dependent dilation of forearm resistance arteries is impaired in patients with arterial hypertension. This vascular dysfunction is associated with the impairment of ischemia-induced reactive hyperemia which in turn may contribute to progressive end-organ damage in arterial hypertension.

Automated ultrasonic measurement of human arteries for the determination of endothelial function.

AIM: Brachial artery ultrasonography is used to measure flow-mediated dilatation (FMD) as a marker of endothelial function in patients at risk for atherosclerosis. Major disadvantages are the time-consuming manual readings and the high within- and between-observer variability. The authors hypothesize that the ultrasound-based determination of endothelial function can be simplified and refined by an automated analysis system. METHODS AND RESULTS: FMD was quantified by a 7.5 MHz linear transducer following 5 minutes of ischemia of the proximal forearm in 8 healthy volunteers on two occasions. Brachial artery diameter was comparatively assessed 1. manually from the video signal and 2. by a PC-based analyzing system. For the manual readings the mean differences for the FMD were 2.5 +/- 2.3% between-reader, 2.0 +/- 0.9% within-reader and 2.1 +/- 1.5% for scans on different days in contrast to 0.8 +/- 0.4 (between-reader), 0.8 +/- 0.6 (within-reader) and 1.3 +/- 0.9% (day-to-day) for the computerized system. The coefficient of variability for the measurement of arterial diameter was 1.34% for manual readings and 0.78% for the automated analysis system. The mean time for manual readings from S-VHS tapes was 35 minutes in contrast to 9 minutes for the PC-based analysis system. CONCLUSIONS: The new automated analysis system for the boundary detection of the vascular wall reduces the variability and greatly increases the speed of the measurements to determine endothelial function. In future, these advantages will help to screen larger numbers of individuals for endothelial dysfunction, particularly for follow-up and intervention trials, and to reduce the variability between different laboratories.

Selective impairment of nitric oxide dependent vasodilation in young adults with hypercholesterolaemia.

OBJECTIVE: To investigate comparatively flow response of resistance arteries to exogenous and endogenous nitric oxide in young adults with high serum cholesterol. BACKGROUND: Impaired vascular effectiveness of endogenous and exogenous nitric oxide may be considered to unmask impairment of its anti-atherogenic properties. It may thus represent a valuable early diagnostic index for these young adults at high risk for developing atherosclerosis. METHODS: In 10 patients with elevated plasma levels of low-density lipoprotein (high cholesterol group, age 34 +/- 5 year; (mean +/- SEM) level of low-density lipoprotein 5.2 +/- 0.5 mmol/l) and 12 age-matched control individuals (control group, 34 +/- 3 years; level of low-density lipoprotein < 3.9 mmol/l), forearm blood flow was measured by venous occlusion plethysmography at rest, during reactive hyperaemia after 3 min no-flow ischaemia, and during local intra-arterial infusions of acetylcholine, bradykinin, sodium nitroprusside and adenosine in increasing doses. RESULTS: In both groups resting forearm blood flow was similar and was dose-dependently increased by each vasodilator. In the hypercholesterolaemic patients compared with control subjects maximal forearm blood flow was significantly impaired after stimulation of endogenous nitric oxide synthesis by acetylcholine and bradykinin and during infusion of the nitric oxide donor sodium nitroprusside (acetylcholine: -19%, bradykinin: -29%, sodium nitroprusside: -24% versus control individuals; P < 0.05). In contrast, adenosine-dependent vasodilation and peak flow during reactive hyperaemia were similar in both groups. CONCLUSION: Excess of low-density lipoprotein cholesterol leads to selective impairment of nitric oxide-dependent vasodilation even in young adults, whereas adenylylcyclase-dependent vasodilation of vascular smooth muscle and maximal dilatory capacity are preserved. In view of the anti-atherogenic properties of nitric oxide, it appears highly desirable to detect this selective vascular dysfunction early in these young adults at high risk of developing atherosclerotic lesions.

[Coronary vasomotion in coronary heart disease--significance of epicardial and microcirculatory vessels for myocardial perfusion]. / Koronare Vasomotion bei der koronaren Herzerkrankung--Bedeutung epikardialer und mikrozirkulatorischer Gefässe für die Myokardperfusion.

The most important function of the coronary vasculature is the effective regulation of coronary blood flow according to the metabolic needs of the myocardium. Under physiological conditions, coronary blood flow is regulated by a balance of vasoconstricting and -dilating components which can be differentiated with regard to the site (macro- vs. microcirculation), compartment (endothelium vs. vascular smooth muscle), and mechanism of action (receptor dependent vs. independent). This balance includes on the one hand the ability of the coronary circulation to maintain a relatively constant blood flow at any given oxygen demand irrespective of perfusion pressure (coronary autoregulation). On the other hand, coronary blood flow can be increased rapidly and effectively several-fold when myocardial oxygen demand increases. Previous investigations have demonstrated that the coronary endothelium plays a key role in the development of arteriosclerotic vascular lesions. In the time course of arteriosclerosis, functional alterations in endothelium dependent vasodilatation alterations are already present before angiographically demonstrable morphologic lesions. In the present manuscript, the diagnostic methods used to assess clinically the coronary macro- and microcirculation with regard to endothelium and smooth muscle dependent vasomotion are reviewed. In addition, present pharmacotherapeutic strategies to improve myocardial perfusion in coronary artery disease are discussed.

Plasma nitrite rather than nitrate reflects regional endothelial nitric oxide synthase activity but lacks intrinsic vasodilator action.

The plasma level of NO(x), i.e., the sum of NO(2)- and NO(3)-, is frequently used to assess NO bioavailability in vivo. However, little is known about the kinetics of NO conversion to these metabolites under physiological conditions. Moreover, plasma nitrite recently has been proposed to represent a delivery source for intravascular NO. We therefore sought to investigate in humans whether changes in NO(x) concentration are a reliable marker for endothelial NO production and whether physiological concentrations of nitrite are vasoactive. NO(2)- and NO(3)- concentrations were measured in blood sampled from the antecubital vein and brachial artery of 24 healthy volunteers. No significant arterial-venous gradient was observed for either NO(2)- or NO(3)-. Endothelial NO synthase (eNOS) stimulation with acetylcholine (1-10 microg/min) dose-dependently augmented venous NO(2)- levels by maximally 71%. This effect was paralleled by an almost 4-fold increase in forearm blood flow (FBF), whereas an equieffective dose of papaverine produced no change in venous NO(2)-. Intraarterial infusion of NO(2)- had no effect on FBF. NOS inhibition (N(G)-monomethyl-l-arginine; 4-12 micromol/min) dose-dependently reduced basal NO(2)- and FBF and blunted acetylcholine-induced vasodilation and NO release by more than 80% and 90%, respectively. In contrast, venous NO(3)- and total NO(x) remained unchanged as did systemic arterial NO(2)- and NO(3)- levels during all these interventions. FBF and NO release showed a positive association (r = 0.85; P < 0.001). These results contradict the current paradigm that plasma NO(3)- and/or total NO(x) are generally useful markers of endogenous NO production and demonstrate that only NO(2)- reflects acute changes in regional eNOS activity. Our results further demonstrate that physiological levels of nitrite are vasodilator-inactive.