Methodological aspects of the evaluation of endothelium-dependent vasodilatation in the human forearm

Multi-site Pulse Transit Times, Beat-to-Beat Blood Pressure, and Isovolumic Contraction Time at Rest and Under Stressors

This study investigates the beat-to-beat relationships among Pulse Transit Times (PTTs) and Pulse Arrival Times (PATs) concomitantly measured from the heart to finger, ear and forehead vascular districts, and their correlations with continuous finger blood pressure. These aspects were explored in 22 young volunteers at rest and during cold pressure test (CPT, thermal stress), handgrip (HG, isometric exercise) and cyclo-ergometer pedalling (CYC, dynamic exercise). The starting point of the PTT measures was the opening of the aortic valve detected by the seismocardiogram. Results indicate that PTTs measured at the ear, forehead and finger districts are uncorrelated each other at rest, and during CPT and HG. The stressors produced district-dependent changes in the PTT variability. Only the dynamic exercise was able to induce significant changes with respect to rest in the PTTs mean values (-40%, -36% and -17%, respectively for PTTear, PTTfore, PTTfinger,), and synchronize their modulations. Similar trends were observed in the PATs. The isovolumic contraction time decreased during the stressors application with a minimum at CYC (-25%) reflecting an augmented heart contractility. The increase in blood pressure (BP) at CPT was greater than that at CYC (137 vs. 128 mmHg), but the correlations between beat-to-beat transit times and BP were maximal at CYC (PAT showed a higher correlation than PTT; correlations were greater for systolic than for diastolic BP). This suggests that pulse transit times do not always depend directly on the beat-to-beat BP values but, under specific conditions, on other factors and mechanisms that concomitantly also influence BP.

Relationship between endothelium-dependent vasodilation and fat distribution using the new "imiomics" image analysis technique

BACKGROUND AND AIMS

We investigated how vasoreactivity in the brachial artery and the forearm resistance vessels were related to fat distribution and tissue volume, using both traditional imaging analysis and a new technique, called "Imiomics", whereby vasoreactivity was related to each of the >2M 3D image elements included in the whole-body magnetic resonance imaging (MRI).

METHODS AND RESULTS

In 326 subjects in the Prospective investigation of Obesity, Energy and Metabolism (POEM) study (all aged 50 years), endothelium-dependent vasodilation was measured by acetylcholine infusion in the brachial artery (EDV) and flow-mediated vasodilation (FMD). Fat distribution was evaluated by dual-energy X-ray absorptiometry (DXA) and magnetic resonance imaging (MRI). EDV, but not FMD, was significantly related to total fat mass, liver fat, subcutaneous (SAT) and visceral (VAT) adipose tissue in a negative fashion in women, but not in men. Using Imiomics, an inverse relationship was seen between EDV and a local tissue volume of SAT in both the upper part of the body, as well as the gluteo-femoral part and the medial parts of the legs in women. Also the size of the liver, heart and VAT was inversely related to EDV. In men, less pronounced relationships were seen. FMD was also significantly related to local tissue volume of upper-body SAT and liver fat in women, but less so in men.

CONCLUSION

EDV, and to a lesser degree also FMD, were related to liver fat, SAT and VAT in women, but less so in men. Imiomics both confirmed findings from traditional methods and resulted in new, more detailed results.

Proteomic profiling of endothelium-dependent vasodilation

OBJECTIVE

As endothelial dysfunction is an early event in atherosclerosis formation, we investigated if proteins previously related to cardiovascular disease also were related to endothelial function using a novel targeted proteomics approach.

METHODS

In the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study (n = 850-970, all aged 70 years), endothelium-dependent vasodilation (EDV) in the forearm was assessed by intra-arterial infusion of acetylcholine. Flow-mediated vasodilation (FMD) was investigated in the brachial artery by ultrasound. The same investigations were carried out in the Prospective investigation of Obesity, Energy and Metabolism (POEM) study (n = 375-461, all aged 50 years). After strict quality control, 84 cardiovascular-related proteins measured by the proximity extension assay were studied in relation to EDV and FMD in PIVUS (discovery sample) and POEM (validation sample).

RESULTS

Of the 15 proteins being significantly related to EDV in PIVUS (false discovery rate <0.025), seven could be replicated in POEM at nominal significance and same effect direction when adjusted for sex and storage time. Of those, only cathepsin D remained significant following further adjustment for traditional cardiovascular risk factors (beta, -0.08; 95% confidence interval, -0.16, -0.01; P = 0.033; change in ln-transformed EDV per 1-SD increase in protein level). No protein was significantly related to FMD.

CONCLUSION

Using a discovery/validation approach in two samples, our results indicate an inverse association between plasma cathepsin D levels and endothelial-dependent vasodilation.

Impact of physical activity on cardiovascular status in obesity

BACKGROUND

We have recently shown that being physically active (PA) counteracts, but not eliminates the increased risk of future cardiovascular disease in overweight and obese subjects. To investigate this further, we studied the impact of being normal weight, overweight and obese on multiple markers of subclinical cardiovascular disease in relation to physical activity.

MATERIALS AND METHODS

At age 70, 1016 subjects were investigated in the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study. Being PA was defined as performing regular heavy exercise (self-reported). According to body mass index (BMI)/PA groups, the participants were categorized as PA/normal weight (BMI < 25 kg/m² , n = 104), non-PA/normal weight (n = 234), PA/overweight (BMI 25-29·9 kg/m² , n = 133), non-PA/overweight (n = 295), PA/obese (BMI ≥ 30 kg/m² , n = 54) and non-PA/obese (n = 169). Several different measurements of endothelial reactivity and arterial compliance (plethysmography and ultrasound), cartotid artery atherosclerosis and echocardiography were performed, and seven markers of coagulation/fibrinolysis were measured.

RESULTS

Physically active subjects with obesity showed impaired vasoreactivity in the forearm resistance vessels, increased left ventricular mass and impaired left ventricular systolic and diastolic functions, together with impaired coagulation/fibrinolysis when compared to PA/normal-weight subjects (P < 0·05 to <0·001). The majority of these disturbances were seen also in PA/overweight subjects when compared to PA/normal-weight subjects (P < 0·05 to <0·001).

CONCLUSIONS

Our data provide additional support for the notion that an increased level of self-reported physical activity does not fully eliminate the deleterious cardiovascular consequences associated with overweight and obesity.

Mental stress opposes endothelium-dependent vasodilation in young healthy individuals

Mental stress has been shown to induce myocardial ischemia in people with coronary heart disease (CHD), both in the laboratory and in daily life. In order to investigate the role of the endothelium in the regulation of blood flow during stress, the endothelium-dependent (EDV) and endothelium-independent (EIDV) vasodilation was examined in the forearms of healthy people during a mental arithmetic test (MAT), a cold pressor test (CP) and an isometric handgrip test (ISO). A total of 10 young healthy volunteers (four men and six women, aged 20-25 years) underwent measurements of forearm vascular resistance (FVR) during local intra-arterial infusions of methacholine (MCh; inducing EDV) and sodium nitroprusside (SNP; inducing EIDV) at rest and during the different forms of stress by the use of venous occlusion plethysmography. MAT induced a significant increase in FVR during MCh infusion (4 mg/min, from 3.5 6 0.7 at rest to 4.2 6 1.4 mmHg/ml per min per 100 ml tissue during MAT; p, 0.01), while FVR during SNP infusion was unchanged by MAT. CP induced a significant increase in FVR during infusions with both MCh and SNP compared to resting levels (p, 0.01 for both), while ISO induced a significant increase in FVR during MCh infusion (p, 0.05) and a smaller increase in FVR during SNP infusion. When the SNP to MCh FVR ratio was used as an index of endothelial function, only MAT impaired endothelial function significantly (p, 0.01). In conclusion, mental stress induced by an arithmetic task selectively opposed EDV in the forearms of young healthy people, while cold pressor and isometric handgrip tests induced a more general attenuation in vasodilatation.

Review: Clinical assessment of endothelial function — an update

Endothelial dysfunction precedes clinically detectable vascular disease, suggesting its early detection may allow the targeting of treatment to improve endothelial function and thus inhibit progression of disease.1,2 Although the evidence for a preventive strategy remains circumstantial, there is worldwide interest in the measurement of endothelial function in relation to risk factors and treatment of atherosclerotic vascular disease. Unfortunately, a widely applicable clinical measurement of endothelial function does not yet exist; those that are available remain tools for research. The ideal clinical test of endothelial function should be specific, sensitive and reproducible, as well as simple to perform, painless, and inexpensive. In this review we outline the relative merits and disadvantages of the techniques that are available.

Endothelium-dependent vasodilation predicts the development of the metabolic syndrome

BACKGROUND

Different techniques to evaluate endothelium-dependent vasodilation (EDV) in resistance and conduit arteries have been described and have been associated with the occurrence of the metabolic syndrome (MetS) in cross-sectional studies. This study aimed to evaluate whether EDV in resistance and conduit arteries could predict future development of the MetS in the Prospective Study of the Vasculature in Uppsala Seniors (PIVUS) study.

METHODS

In the population-based PIVUS study (1016 subjects all aged 70 at baseline), the invasive forearm technique with acetylcholine given in the brachial artery (resistance arteries, EDV) and the brachial artery ultrasound technique with the measurement of flow-mediated dilatation (conduit artery, FMD) were evaluated. Six hundred and twenty-four subjects free of the MetS (NCEP/ATPIII criteria) at the age of 70 were reinvestigated at the age of 75.

RESULTS

During the 5-year follow-up, 109 new subjects developed the MetS. EDV, but not FMD, predicted the development of the MetS (OR 0.78 for a 1 SD increase in EDV, 95%CI 0.62-0.97, P = 0.033). Of the five components of the MetS, EDV could significantly predict the development of the glucose (P = 0.02), waist circumference (P = 0.01) and the triglyceride components (P = 0.002), but not significantly so the HDL (P = 0.09) and blood pressure components (P = 0.92).

CONCLUSIONS

EDV in resistance arteries, but not in the brachial conduit artery (FMD), was a predictor of future development of the MetS, mainly by prediction of future impairments in fasting glucose, serum triglycerides and waist circumference in an elderly cohort.

Relationships between three different tests to evaluate endothelium-dependent vasodilation and cardiovascular risk in a middle-aged sample

OBJECTIVE

For a couple of decades, flow-mediated vasodilation in the brachial artery (FMD) and acetylcholine-mediated vasodilation in the forearm (EDV) have been used to assess endothelium-dependent vasodilation. During recent years a third technique, peripheral artery tonometry (PAT) using EndoPat, has been introduced. We now aimed to investigate the relationships between these techniques, and their relation to cardiovascular risk.

METHODS

In the population-based Prospective investigation of Obesity, Energy and Metabolism (POEM) study conducted in individuals all aged 50 years (50% women), EDV, FMD and the reactive hyperemia index were measured in the first 222 individuals. Cardiovascular risk was assessed by the Framingham risk score.

RESULTS

No significant relationships were seen between the three different tests to evaluate endothelium-dependent vasodilation. EDV (r = -0.21, P = 0.004) and FMD (r = -0.19, P = 0.004), but not PAT were significantly related to the Framingham score in an inverse way. Also sodium nitroprusside-mediated vasodilation in the forearm, reflecting endothelium-independent vasodilation (EIDV), was related to the Framingham score in an inverse way (r = -0.30, P < 0.0001).

CONCLUSION

No close relationships were seen between the three tests of endothelium-dependent vasodilation, suggesting that they each contribute with unique information on vasoreactivity. EDV, EIDV and FMD, but not PAT, were related to the Framingham score, suggesting that vasoreactivity in some vascular beds are related to cardiovascular risk in middle-aged individuals.

Flow-mediated vasodilation was found to be an independent predictor of changes in the carotid plaque status during a 5-year follow-up

AIM

It has previously been shown that flow-mediated vasodilation is a predictor of the progression of the intima-media thickness (IMT). In the present study, the degree of endothelium-dependent vasodilation in both resistance and conduit arteries was evaluated as a predictor of the IMT and plaque progression.

METHODS

In the population-based Prospective Study of the Vasculature in Uppsala Seniors(PIVUS) trial(1,016 subjects all 70 years of age), the invasive forearm technique using acetylcholine administered in the brachial artery (resistance artery, EDV) and the brachial artery ultrasound technique with measurement of flow-mediated dilatation (conduit artery, FMD) were evaluated. The IMT and number of carotid arteries with plaques (0, 1 or 2) were recorded using ultrasound at the baseline investigation and the follow-up visit conducted five years later.

RESULTS

A total of 760 subjects had valid measurements of the IMT and carotid artery plaques at both the investigations conducted at 70 and 75 years of age. Neither the FMD nor EDV significantly predicted the change in IMT over five years. However, the FMD, but not EDV, was associated with the change in carotid plaque burden during the follow-up period, independent of classical risk factors, such as gender, waist circumference, fasting blood glucose, systolic and diastolic blood pressure, HDL- and LDL-cholesterol, serum triglycerides, BMI and smoking (OR 0.81 for a 1 SD change in FMD, 95%CI 0.68 to 0.95, p=0.010).

CONCLUSIONS

The FMD was found to be a predictor of changes in the carotid plaque status, but not IMT, during the 5-year follow-up period, independent of classical cardiovascular risk factors.

Genetic variation in the dimethylarginine dimethylaminohydrolase 1 gene (DDAH1) is related to asymmetric dimethylarginine (ADMA) levels, but not to endothelium-dependent vasodilation

Objectives:

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase. The breakdown of ADMA is mainly governed by the activity of dimethylarginine dimethylaminohydrolases (DDAHs). We investigated if genetic variation in the DDAH1 and DDAH2 genes were related to ADMA and l-arginine levels, as well as measures of endothelium-dependent vasodilation.

Methods:

In 1016 70-year-old participants of the population-based Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study (50% women), we measured endothelium-dependent vasodilation (EDV) using the invasive forearm technique with acetylcholine given in the brachial artery and the brachial artery ultrasound technique with measurement of flow-mediated dilatation (FMD). Plasma l-arginine and ADMA levels were measured by high-performance liquid chromatography and 55 single nucleotide polymorphisms (SNPs) in the DDAH1 and DDAH2 genes were genotyped.

Results:

Several of the genotypes in the DDAH1 gene were highly significantly related to ADMA levels ( p = 10−7 at best), but not to the l-arginine levels. No relationships between the genotypes in the DDAH2 gene and ADMA or l-arginine levels were found. None of the DDAH1 genotypes being closely related to ADMA levels were significantly related to EDV or FMD. Neither were any of the DDAH2 genotypes closely related to any of the measurements of vasoreactivity.

Conclusion:

A close relationship was seen between SNPs in the DDAH1, but not DDAH2, gene and ADMA levels. However, variation in those genes was not related to measures of EDV in this elderly population.

Variation in genes in the endothelin pathway and endothelium-dependent and endothelium-independent vasodilation in an elderly population

AIM

Indirect evidences by blockade of the endothelin receptors have suggested a role of endothelin in endothelium-dependent vasodilation. This study aimed to investigate whether circulating levels of endotehlin-1 or genetic variations in genes in the endothelin pathway were related to endothelium-dependent vasodilation.

METHODS

In 1016 seventy-year-old participants of the population-based Prospective Study of the Vasculature in Uppsala Seniors (PIVUS) study (52% women), we measured endothelium-dependent vasodilation using the invasive forearm technique with acetylcholine given in the brachial artery (EDV) and the brachial artery ultrasound technique with measurement of flow-mediated dilatation (FMD). Plasma endothelin-1 levels were measured and 60 SNPs in genes in the endothelin pathway (ECE1, EDN1, EDNRA, EDNRB) were genotyped.

RESULTS

No significant associations were found between circulating endothelin levels and EDV or FMD. No single genotype was related to EDV or FMD following adjustment for multiple testing, but a genotype score for 3 SNPs (rs11618266 in EDNRB, rs17675063 in EDNRA, rs3026868 in ECE1) was significantly related to EDV (beta coefficient 0.070, 95% CI 0.025-0.12, P = 0.002) when adjusting for gender, systolic blood pressure, HDL and LDL cholesterol, serum triglycerides, BMI, diabetes, smoking, antihypertensive medication or statins and CRP. This score was also related to nitroprusside-induced vasodilation in the forearm.

CONCLUSION

A combination of genotypes in the endothelin pathway was related to both endothelium-dependent and endothelium-independent vasodilation in forearm resistance vessels, but not in the brachial artery in an elderly population, giving evidence for a role of the endothelin system in resistance vessel reactivity independent of major cardiovascular risk factors.

A combined test of acetylcholine-mediated vasodilation of both the forearm resistance vessels and the radial artery

OBJECTIVE

To evaluate a new combined test of endothelium-dependent vasodilation (EDV) in the forearm resistance vessel and the radial artery.

METHODS

Acetylcholine (ACh) and sodium nitroprusside (SNP) infusion in the brachial artery were used to simultaneous evaluate EDV and endothelium-independent vasodilation (EIDV) in forearm resistance vessels (plethysmography) and in the radial artery (ultrasound) in 76 healthy subjects. Brachial artery ultrasound was used to assess flow-mediated vasodilation (FMD).

RESULTS

Acetylcholine induced a 4·5% (median value, P = 0·0010) increase in the radial artery diameter, while SNP induced a 31·2% increase in diameter (P<0·0001). While no increase in radial artery blood flow was induced by ACh (P = 0·69), an increase by 181% in radial blood flow was induced by SNP (P<0·0001). When relating the radial artery diameter data to FMD, the change in radial artery diameter induced by ACh was significantly correlated with FMD (r = 0·35, P = 0·013). No such relationship was seen for the diameter change induced by SNP (r = -0·03, P = 0·81). When relating the radial artery blood flow data to EDV and EIDV, the change in radial artery blood flow induced by ACh was significantly correlated with EDV in an inverse fashion (r = -0·42, P = 0·0032). No such relationship was seen for the blood flow change induced by SNP when related to EIDV (r = -0·07, P = 0·63).

CONCLUSION

Simultaneous measurements of blood flow in forearm vessels by plethysmography and in the radial artery by ultrasound during ACh infusion is a new way to assess EDV in both resistance and conduit arteries during one investigation.

Association of anxiety with resistance vessel dysfunction in human atherosclerosis

OBJECTIVE

Anxiety predicts cardiovascular events, although the mechanism remains unclear. We hypothesized that anxiety symptoms will correlate with impaired resistance and conduit vessel function in participants aged 55 to 90 years.

METHODS

Anxiety symptoms were measured with the Symptom Checklist-90--Revised in 89 participants with clinically diagnosed atherosclerotic cardiovascular disease and 54 healthy control participants. Vascular function in conduit arteries was measured using flow-mediated dilatation, and vascular function in forearm resistance vessels (FRVs) was measured using intra-arterial drug administration and plethysmography.

RESULTS

Anxiety symptoms were not associated with flow-mediated dilatation in either group. Participants with atherosclerosis exhibited significant inverse associations of anxiety symptoms with FRV dilatation (acetylcholine: β = -.302, p = .004). Adjustment for medication, risk factors, and depression symptoms did not alter the association between anxiety and FRV dysfunction, except for body mass index (BMI; anxiety: β = -.175, p = .060; BMI: β = -.494, p < .001). Although BMI was more strongly associated with FRV function than anxiety, combined BMI and anxiety accounted for greater variance in FRV function than either separately. Control participants showed no association of anxiety with FRV function.

CONCLUSIONS

Anxiety is uniquely and substantially related to poorer resistance vessel function (both endothelial and vascular smooth muscle functions) in individuals with atherosclerosis. These relationships are independent of medication, depression, and cardiovascular risk factors, with the exception of BMI. These findings support the concept that anxiety potentially increases vascular events through worsening of vascular function in atherosclerotic disease.

Association between glomerular filtration rate and endothelial function in an elderly community cohort

BACKGROUND

Endothelial dysfunction is prevalent among individuals with chronic kidney disease. However, the association between glomerular filtration rate and endothelial function in the community is unclear and needs to be investigated in the general population.

METHODS

In the community-based Prospective Investigation of the Vasculature of Uppsala Seniors study (PIVUS, n = 952, mean age 70, women 49.3%), we investigated cross-sectional associations between estimated cystatin C-based glomerular filtration rate (eGFR), and 3 measures representing different aspects of endothelial function (endothelial-dependent vasodilation [EDV], endothelial independent vasodilatation [EIDV], and flow-mediated dilatation [FMD]). We also performed pre-specified sub-group analyses in participants with normal eGFR (>60 ml/min/1.73 m(2)).

RESULTS

In the whole cohort, 10 ml/min/1.73 m(2) higher eGFR was associated with 3% higher EDV (p = 0.001) and 2% higher EIDV (p = 0.007), adjusted for age and sex. The associations were attenuated and no longer statistically significant after adjusting for established cardiovascular risk factors. In participants with eGFR >60 ml/min/1.73 m(2), 10 ml higher eGFR was associated with 2% higher EDV (p = 0.04) after adjusting for sex and age. eGFR was not associated to FMD in any model or sub-sample.

CONCLUSION

This community-based study suggests that eGFR is associated with endothelial function also in persons with normal kidney function, but that this association is largely explained by confounding by established cardiovascular risk factors. Thus, our data do not support the notion of a direct causal interplay between renal and vascular function prior to the development of CKD.

Endothelial function in resistance and conduit arteries and 5-year risk of cardiovascular disease

BACKGROUND

Impaired endothelial function has been implicated as a cause of cardiovascular disease. Little is known of the relations of measures of endothelial function in resistance and conduit arteries to incident cardiovascular disease in the general population, and available techniques have not been compared.

METHODS AND RESULTS

In 1016 participants (70 years of age) of the population-based Prospective Study of the Vasculature in Uppsala Seniors (PIVUS) study (52% women), we measured endothelium-dependent vasodilation using the invasive forearm technique with acetylcholine given in the brachial artery, the brachial artery ultrasound technique with measurement of flow-mediated dilatation, and the pulse-wave analysis-based method with β-2-agonist terbutaline provocation. During 5 years of follow-up, 101 participants experienced a composite end point of myocardial infarction, stroke, or death, excluding the 85 persons with a history of myocardial infarction or stroke at baseline. In logistic regression models adjusted for several established and novel cardiovascular disease risk factors and medications, endothelium-dependent vasodilation by the invasive forearm technique with acetylcholine was associated with risk of the end point (odds ratio, 0.72 per SD; 95% confidence interval, 0.56 to 0.93; P=0.01). Endothelial function by the other 2 methods was not related to risk of the end point. Addition of endothelium-dependent vasodilation to the Framingham risk score improved discrimination of risk of the end point.

CONCLUSIONS

Endothelium-dependent vasodilation in resistance arteries, but not in the brachial conduit artery (flow-mediated dilatation), was associated with 5-year risk of a composite end point of death, myocardial infarction, or stroke independently of major cardiovascular disease risk factors. This vascular measurement improved risk discrimination when added to an established risk score in an elderly population.

Functional capillary rarefaction in mild blood pressure elevation

Capillary rarefaction is described in patients with moderate to severe hypertension. The study objective was to determine if structural and/or functional capillary rarefaction is detectable and associated with endothelial dysfunction in patients with mild blood pressure elevation (HBP: Systolic blood pressure 130 - 160 mm Hg). Capillary density was quantified by direct capillaroscopy in 110 nondiabetic black and non-black subjects. Endothelial function was quantified by plethysmographic measures of flow-mediated vasodilation. Compared to normotensives (NBP: N = 90), functional capillary rarefaction was detected in HBP (N = 20; P<0.001). Functional capillary density measures correlated with endothelial function (P<0.001). Functional, but not structural, capillary rarefaction is detectable and associated with endothelial dysfunction in both black and non-black individuals with mild blood pressure elevation.

Airway endothelial dysfunction in asthma and chronic obstructive pulmonary disease: a challenge for future research

Endothelial dysfunction in the extrapulmonary circulation has been linked to cardiovascular disease. Recent investigations have revealed that in the airway circulation, cigarette smoking, chronic obstructive pulmonary disease (COPD), and asthma are also accompanied by endothelial dysfunction. Inhaled glucocorticosteroids can partially or fully restore normal endothelium-dependent vasodilation in these conditions, thereby identifying the airway endothelium as a novel therapeutic target in the treatment of airway disease. The role of the defective endothelium-dependent vasodilation in the pathophysiology in asthma and COPD is still subject to speculation. However, there appears to be an association between COPD and extrapulmonary vascular dysfunction, and the possibility exists that the use of inhaled glucocorticosteroids has a beneficial effect on cardiovascular disease in COPD as suggested by database studies showing that inhaled glucocorticosteroids reduce the incidence of nonfatal and fatal cardiovascular events in COPD.

Parathyroid Hormone's Acute Effect on Vasodilatory Function

Parathyroid hormone (PTH) seems to affect the risk of cardiovascular disease. The aim of the present study was to investigate PTH's acute effect on endothelial vasodilatory function in forearm resistance vessels. Ten healthy subjects underwent forearm venous occlusion plethysmography. We measured forearm blood flow at baseline and at a stable, locally increased PTH level after intra-arterial infusion of metacholine and nitroprusside. The contralateral arm served as a control. Ionized calcium (Ca++) and PTH values were normal in all subjects at baseline (1.26 ± 0.02 mM/L, 3.6 ± 1.2 pM/L). After 30 minutes of PTH infusion, the PTH level increased in the active arm (13.8 ± 4.0 pM/L P < 0.01), while the Ca++ level was unchanged (1.25 ± 0.04; mM/L). Both the PTH and the Ca++ level in the contralateral arm remained unchanged, which indicates no systemic influence. The endothelial-dependent vasodilation was inversely correlated to the Ca++ level at baseline (r = -0.75, P < 0.05) and after PTH infusion (r = -0.68, P < 0.05). The vasodilatory function was not affected during PTH-infusion.

Capillary rarefaction in treated and untreated hypertensive subjects

This study aimed to determine if capillary rarefaction is detectable and associated with endothelial dysfunction in persons with mild systolic blood pressure (SBP) elevation. Capillary density and endothelial function were quantified for 150 nondiabetic participants, grouped by blood pressure (BP) as normotensive, untreated high BP, and treated high BP. Structural capillary rarefaction measures were not different between the three groups. Functional capillary rarefaction measures were significantly lower in both high BP groups compared to normotensives, and correlated inversely with endothelial function. The study findings indicate that the hypertensive vascular pathologic process is already underway at modest levels of blood pressure elevation.

Circulating fibroblast growth factor-23 is associated with vascular dysfunction in the community

OBJECTIVE

Subjects with chronic kidney disease (CKD) are at higher risk for cardiovascular (CV) disease than the general population. These patients have elevated circulating levels of FGF23, which predict for increased mortality in CKD patients on hemodialysis. Since CV disease is a major cause of death in CKD, we investigated the association between FGF23 and vascular function.

METHODS AND RESULTS

We employed a community-based cohort of subjects aged 70, the PIVUS study (n=967), to investigate the relation between serum FGF23, endothelium function and arterial stiffness. Higher FGF23 was weakly associated with both impaired endothelium-dependent (beta=-0.08, p<0.05) and endothelium-independent (beta=-0.08, p<0.01) vasodilation. The association was stronger in subjects with eGFR> or =90mL/min/1.73m(2) (beta=-0.19 and beta=-0.22, respectively, p<0.001). In addition, higher FGF23 was associated with increased arterial stiffness exclusively in subjects with an age-adjusted impaired renal function (eGFR<60mL/min/1.73m(2)) (beta=0.26, p<0.001). All associations were independent of gender, biochemical covariates and established CV risk factors.

CONCLUSIONS

Higher serum FGF23 levels, even within the normal range, are independently associated with impaired vasoreactivity and increased arterial stiffness in the community. Additional studies are required to determine possible direct vascular effects of FGF23 and whether FGF23 is a modifiable CV risk factor.

Effects of inspiratory muscle training on autonomic activity, endothelial vasodilator function, and N-terminal pro-brain natriuretic peptide levels in chronic heart failure

PURPOSE

To assess the effects of inspiratory muscle training (IMT) on autonomic activity, endothelial function, and N-terminal pro-brain natriuretic peptide (NT-proBNP) levels in patients with chronic heart failure.

METHODS

Using age- and sex-matched controlled study, 23 patients (mean left ventricular ejection fraction 29 +/- 2%) were assigned to either a high-intensity training group (n = 14), New York Heart Association (NYHA) class II (n = 9)/III (n = 5), or a low-intensity training group (n = 9), NYHA class II (n = 6)/III (n = 3), exercising at 60% and 15% of sustained maximum inspiratory pressure (SPImax), respectively, 3 times per week for 10 weeks. Before and following IMT, patients underwent cardiopulmonary exercise testing and dyspnea evaluation on exertion. Sympathovagal balance was assessed by heart rate variability (HRV) from 24-hour electrocardiogram and endothelial function, using venous occlusion plethysmography. Serum levels of NT-proBNP were determined.

RESULTS

High-intensity training group improved maximum inspiratory pressure (PImax, 105.4 +/- 5.3 vs 79.1 +/- 5 cm H2O, P = .001), SPImax (511 +/- 42 vs 308 +/- 28 cm H2O/sec/10, P = .001), peak oxygen consumption (19 +/- 1.2 vs 17.1 +/- 0.7 mL.kgmin, P = .01) and dyspnea (17.6 +/- 0.2 vs 18.1 +/- 0.1, P = .02). Endothelium-dependent vasodilation, HRV, and NT-proBNP levels were not altered. Low-intensity training group increased only the PImax (97.6 +/- 11.3 vs 84.2 +/- 8.7 cm H2O, P = .03).

CONCLUSIONS

Improvement in dyspnea and exercise tolerance after IMT were not associated with changes in markers of HRV, endothelial function, and NT-proBNP in patients with mild to moderate chronic heart failure. Further studies on the effects of IMT in advanced heart failure would be worthwhile.

Endothelium-dependent vasodilation, insulin resistance and the metabolic syndrome in an elderly cohort

BACKGROUND

Only a few previous studies have investigated endothelium-dependent vasodilation in the metabolic syndrome (MetS). In the Prospective Study of the Vasculature in Uppsala Seniors (PIVUS) study, different techniques to assess vasodilation in conduit and resistance arteries were evaluated in relation to the MetS and insulin resistance.

METHODS

In this population-based study, 1016 subjects aged 70 were evaluated by the invasive forearm technique with acetylcholine (EDV), brachial artery ultrasound to assess flow-mediated vasodilation (FMD) and pulse wave analysis with a beta-2 receptor agonist challenge, terbutaline.

RESULTS

EDV was lower in subjects with the MetS (NECP/ATP III-criteria, prevalence 23%) compared to those without (p<0.0001), and declined with increasing number of MetS criteria (p<0.0001), after adjustment for coronary heart disease, stroke and cardiovascular medication. Also a reduced pulse wave response (p=0.015), but not FMD (p=0.64), was seen in those with the MetS. EDV and the pulse wave response, but not FMD, were inversely related to insulin resistance evaluated by the HOMA index. Also endothelium-independent vasodilation (EIDV) induced by intra-brachial infusion of sodium nitroprusside was impaired in subjects with MetS and in insulin resistance.

CONCLUSIONS

Vasodilation evaluated with the invasive forearm technique and pulse wave analysis with a beta-2 agonist, but not FMD, was reduced in elderly subjects with the MetS and was related to insulin resistance. Also EIDV showed the same pattern, suggesting a general deterioration in vasoreactivity mainly in resistance arteries in elderly subjects with the MetS.

The new oral immunomodulating drug DiNAC induces brachial artery vasodilatation at rest and during hyperemia in hypercholesterolemic subjects, likely by a nitric oxide-dependent mechanism

OBJECTIVES

To investigate if the immunomodulator drug DINAC (1) affects arterial dimensions in asymptomatic patients with hypercholesterolemia, (2) has effects on leucocyte markers of inflammation and (3) has in vitro effects on nitric oxide synthase (NOS) in human umbilical vein endothelial cells (HUVEC).

METHODS AND RESULTS

One hundred and fifty-three patients with asymptomatic hypercholesterolemia were randomized to either 100 or 500 mg of DINAC or placebo in a double-blind, parallel-group fashion for 24 weeks. Treatment at the highest dose induced a significant increase in resting brachial artery diameter measured by ultrasound and also induced a significant increase in vessel diameter during hyperemia. However, flow-mediated vasodilation (FMD) and the vasodilatory response to nitroglycerin, lipid levels or leukocyte count were unaltered. Expression of several cell surface markers of inflammation, like CD11b and CD25, were reduced by treatment. In vitro, DINAC counteracted TNF-alpha induced reductions in NO levels and in NOS protein and mRNA levels.

CONCLUSION

The immunomodulator drug DINAC increased brachial artery diameter at rest and during hyperemia in asymptomatic subjects with hypercholesterolemia without affecting blood lipid levels. Based on parallel in vitro studies this effect is likely due to an enhancement of NOS activity.

Endothelial function, arterial stiffness and lipid lowering drugs

The endothelium is a dynamic organ that plays a pivotal role in cardiovascular homeostasis. Alteration in endothelial function precedes the development of atherosclerosis and contributes to its initiation, perpetuation and clinical manifestations. It has been suggested that the assessment of endothelial function could represent a barometer of vascular health that could be used to gauge cardiovascular risk. This review summarises the various methods used to assess endothelium-dependent vasodilatation and their potential prognostic implications. In addition, the techniques used to evaluate arterial stiffness are discussed. The latter is to some extent controlled by the endothelium and has been the subject of considerable research in recent years. This paper also discusses the effects of lipid lowering treatment on both endothelial function and arterial stiffness.

Mental stress impairs endothelial vasodilatory function by a beta-adrenergic mechanism

Mental stress has been shown to impair endothelium-dependent vasodilation (EDV) in the human forearm. The aim of this study was to investigate if this response could be blunted by local infusions of beta-blockade (propranolol), alpha-blockade (phentolamine), or neurogenic blockade. Thirty-one young healthy volunteers underwent forearm blood flow (FBF) measurements, using venous occlusion plethysmography, during local intra-arterial infusions of metacholine (MCh; inducing EDV) and sodium nitroprussid (SNP; inducing endothelial-independent vasodilation [EIDV]), respectively. These measurements were repeated during a 5-min mental arithmetic stress test without (n = 8) or with concomitant local infusion of propranolol (n = 7) or phentolamine (n = 8) in the forearm or during axillary plexus blockade (n = 8). An index of endothelial vasodilatory function (EFI) was calculated as the EDV to EIDV ratio. Mental stress impaired EDV significantly (p < .05), and as a result, EFI was significantly reduced (p = .02). This effect on EFI could be blocked by propranolol and neurogenic blockade but not by phentolamine (p < .05). Thus, impairment of endothelial vasodilatory function induced by mental stress could be blocked by beta-adrenergic, but not alpha-adrenergic, receptor blockade.

Interactions among higher trait anxiety, sympathetic activity, and endothelial function in the elderly

Negative psychological characteristics have been recognized as independent risk factors of cardiovascular disease (CVD). The purpose of this study was to evaluate the influence of depression and anxiety on cardiac autonomic function and endothelial function in healthy elderly subjects. Forty-six healthy elderly volunteers (mean age 60.8 years) were enrolled in this study. Cardiac autonomic function was assessed by spectral analysis of heart rate variability (HRV) with the head-up tilt test. Brachial artery endothelium-dependent flow-mediated dilation (FMD) was measured using high-resolution ultrasound. A significant positive correlation was observed between the State and Trait Anxiety Inventory (STAI)-trait score as a parameter of anxiety and HRV sympathetic modulation in the supine position (baseline), and a significant negative correlation between this score and the head-up-induced HRV sympathetic response from the baseline. The STAI-trait score also showed a significant negative correlation with the percent change of FMD (%FMD). Analysis using structural equation modeling showed that higher trait anxiety reduced %FMD via abnormalities of sympathetic activity. On the other hand, psychometric parameters of depression were not associated with any HRV component or %FMD. These results suggest that there are specific interactions among higher trait anxiety, abnormalities of sympathetic activity, and endothelial dysfunction. This finding may be useful in clarifying the pathophysiological mechanism by which anxiety is associated with increased risks for atherosclerosis and CVD.

Vasodilation in resistance arteries is related to the apolipoprotein B/A1 ratio in the elderly – The Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study

BACKGROUND

Recent studies have shown the apolipoprotein B to apolipoprotein A1 ratio (apoB/A1) to be superior to LDL-cholesterol measurements to predict cardiovascular events. The present study aims to relate apoB/A1 to endothelium-dependent vasodilation, an early marker of atherosclerosis, in the Prospective Study of the Vasculature in Uppsala Seniors (PIVUS) study.

METHODS AND RESULTS

In this population-based study, 1016 subjects aged 70 years were evaluated by the invasive forearm technique with acetylcholine (EDV), brachial artery ultrasound to assess flow-mediated vasodilation (FMD) and pulse wave analysis with a beta-2 receptor agonist challenge, terbutaline. EDV and the pulse wave response, but not FMD, were related to apoB/A1 levels (r=-0.11, p=0.0038 for EDV, r=-0.16, p<0.0001 for the pulse wave analysis and r=0.01, p=0.65 for FMD). Neither LDL-cholesterol, nor non-HDL-cholesterol, was significantly related to the measurements of endothelium-dependent vasodilation. Also endothelium-independent vasodilation (EIDV) evaluated by the invasive forearm technique with sodium nitroprusside was related to apoB/A1 levels (r=-0.12, p<0.0016).

CONCLUSION

The apoB/A1 levels, but not LDL-cholesterol, were inversely related to endothelium-dependent vasodilation evaluated by EDV and pulse wave analysis, but not by FMD. Also EIDV showed the same pattern, suggesting a general deterioration in vasoreactivity mainly in resistance arteries in elderly subjects with high apoB/A1 levels.

Vasodilation and visceral fat in elderly subjects: the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study

BACKGROUND

Although obesity has long been recognised as a cardiovascular risk factor, only in recent years has the role of visceral adipose tissue (VAT) been evaluated. In the Prospective Study of the Vasculature in Uppsala Seniors (PIVUS) study, we related VAT and other obesity indices to endothelium-dependent vasodilation in both capacitance and resistance arteries.

METHODS AND RESULTS

In this population-based study, 1016 subjects aged 70 were evaluated by the invasive forearm technique with acetylcholine (EDV) and brachial artery ultrasound to assess flow-mediated vasodilation (FMD). Intra-abdominal visceral (VAT) and subcutaneous adipose tissue (SAT) were determined by magnetic resonance imaging in a random sample of 287 subjects. EDV, but not FMD, was inversely related to VAT, SAT, BMI and the waist/hip ratio (r=-0.23, -0.16, -0.21 and -0.11, respectively, p=0.05-0.001 after adjustment for gender). In multiple regression analysis however, only VAT was an independent predictor of EDV. Similar results were obtained for endothelium-independent vasodilation (EIDV, infusion of sodium nitroprusside in the brachial artery).

CONCLUSIONS

Both endothelium-dependent and independent vasodilation in the forearm resistance arteries, but not FMD in the brachial artery, was reduced in elderly subjects with increased intra-abdominal adipose tissue mass. This finding suggests deterioration in general vasoreactivity mainly in resistance arteries in elderly subjects with intra-abdominal obesity.

Systolic and diastolic hypertension impair endothelial vasodilatory function in different types of vessels in the elderly: the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study

BACKGROUND

Endothelium-dependent vasodilation (EDV) is known to be impaired in middle-aged hypertensive individuals, but less is known regarding hypertension in the elderly.

OBJECTIVE

In the Prospective Study of the Vasculature in Uppsala Seniors (PIVUS) study, different techniques to evaluate EDV in resistance and conduit arteries were applied in elderly subjects and were related to the type of hypertension.

DESIGN AND METHODS

In this population-based study, 1016 subjects aged 70 years were evaluated by the invasive forearm technique with acetylcholine (EDV), brachial artery ultrasound to assess flow-mediated dilatation (FMD) and pulse wave analysis with a beta-2 receptor agonist challenge, terbutaline. Those without antihypertensive treatment were divided into three groups: normotensive individuals (n = 256), and those with isolated systolic hypertension (n = 309) or combined systolic/diastolic hypertension (n = 79).

RESULTS

Compared with normotensive individuals, EDV was reduced in those with combined systolic/diastolic hypertension only (P = 0.0019), whereas FMD was mainly reduced in those with isolated systolic hypertension (P = 0.013). Furthermore, in regression analysis, EDV was related to diastolic blood pressure only (r = -0.10, P = 0.017), whereas FMD was mainly related to systolic blood pressure (r = -0.13, P = 0.0023). The pulse wave-based method to analyse vasoreactivity was not consistently affected by hypertension.

CONCLUSIONS

In elderly subjects, systolic hypertension mainly impairs conduit artery endothelial vasodilatory function, whereas diastolic hypertension mainly induces dysfunction in resistance arteries.

Effects of aging and atherosclerosis on endothelial and vascular smooth muscle function in humans

BACKGROUND

Nitric oxide is an endothelium dependent dilator, which may protect against atherosclerosis. Several studies have shown a decrease in nitric oxide activity with aging, however none have assessed aging and atherosclerosis separately. We tested the hypothesis that aging blunts both basal and receptor-mediated endothelial nitric oxide release in humans.

METHODS

We examined whether forearm blood flow responses to intra-arterial acetylcholine, and nitroprusside, were altered with aging, with and without co-infusion of an inhibitor of nitric oxide synthase (N(G)-mono-methyl-L-arginine) in three groups of human subjects; a group with clinical atherosclerotic vascular disease (n = 31, 21 M), otherwise healthy elderly (n = 17, 13 M), and healthy young controls (n = 15, 8 M).

RESULTS

There was no difference in basal flows between the three groups. There was also no difference in the dilatation to either acetylcholine or nitroprusside responses between the AVD and the healthy elderly group; however, aging significantly decreased acetylcholine or nitroprusside responses when compared to the young controls (p < 0.02). Furthermore, the ratio between acetylcholine and nitroprusside, a marker of endothelial NO synthase activity, was significantly greater in the young volunteers (0.816 +/- 0.094% vs. 0.892 +/- 0.146 % vs. 1.389 +/- 0.2%, in atherosclerotic vascular disease, healthy elderly group, and young controls respectively).

CONCLUSIONS

Forearm blood flow responses to endothelium dependent and independent stimuli are blunted with aging, independent of the presence of atherosclerotic disease. Moreover, the normal aging process may induce significant global vascular dysfunction (involving the endothelium and the vascular smooth muscle); to as great a degree as clinically manifest atherosclerosis.

Uric acid and endothelial dysfunction in essential hypertension

Recent epidemiologic and experimental evidence suggests that serum uric acid (UA) is an independent risk factor for cardiovascular and renal diseases. However, endothelial dysfunction is an early predictor of cardiovascular events, particularly in hypertensive patients. For assessment of the association between UA and endothelial function, 217 (108 men, 109 women; aged 48.0 +/- 10.6 yr) white never-treated hypertensive patients were studied. All patients underwent the following procedures: BP measurements, laboratory tests (C-reactive protein [CRP], insulin resistance by homeostasis model assessment, serum creatinine, and UA), and endothelial function evaluated by intra-arterial infusion of acetylcholine (ACh). Serum creatinine, CRP, and maximal vasodilatory response to ACh were related to the UA (all P < 0.0001). In the multiple regression analysis, serum UA ranked as the third correlate of peak of forearm blood flow predictor, after homeostasis model assessment and CRP. The data show an independent link between UA and endothelial function, also in a statistical model that included CRP. In conclusion, the data demonstrate an inverse and significant relationship between UA and ACh-stimulated vasodilation in patients with uncomplicated, untreated essential hypertension, independent of traditional cardiovascular risk factors. Probably, the chronic inflammation that was documented in these patients may be considered the mechanistic link between serum UA and vascular damage.

Airway blood flow reactivity in smokers

Cigarette smoking has been associated with impaired endothelium-dependent relaxation responses in the brachial and coronary arteries (endothelial dysfunction). The aim of the present study was to determine if the airway circulation is also affected and if airway treatment has an effect on endothelial function. Airway blood flow (Q(aw)) responses to inhaled albuterol as an index of endothelial function were measured in age-matched healthy current smokers, healthy ex-smokers, ex-smokers with COPD and healthy lifetime non-smokers; in the ex-smokers with COPD, the albuterol responsiveness was repeated after a 4-week treatment with an inhaled glucocorticoid/beta(2)-adrenergic agonist combination drug. Mean baseline Q(aw) was similar in the four groups. Albuterol inhalation increased mean Q(aw) in lifetime non-smokers (50.1+/-8.3%; p<0.05) and in healthy ex-smokers (37.2+/-3.4%; p<0.05) but not in healthy current smokers (13.9+/-3.2%; p=NS) and ex-smokers with COPD (9.7+/-4.5%; p=NS). While drug treatment per se did not change Q(aw) significantly, it restored albuterol responsiveness (+67.6+/-11.1%; p<0.05) in the ex-smokers with COPD. Thus, cigarette smoking is associated with endothelial dysfunction in the airway, with a partial recovery of endothelial function after smoking cessation in healthy ex-smokers but not in ex-smokers with COPD. In the latter, combined glucocorticoid/beta(2)-adrenergic agonist treatment restores albuterol responsiveness.

A Comparison of Three Different Methods to Evaluate Endothelium-Dependent Vasodilation in the Elderly

Background— Three different techniques to evaluate endothelium-dependent vasodilation in the peripheral circulation have been described but not simultaneously tested in a large-scale population-based setting. This study aimed to evaluate the feasibility and usefulness of these techniques in the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study.

Methods and Results— In the population-based PIVUS study (1016 subjects aged 70 years), the invasive forearm technique with acetylcholine given in the brachial artery (EDV), the brachial artery ultrasound technique with measurement of flow-mediated dilatation (FMD), and the pulse wave analysis method with β-2-agonist (terbutaline) provocation were successfully used in 87%, 97%, and 86% of the sample, respectively. The results of EDV and pulse wave analysis were interrelated ( r =0.12, P =0.0013), but no relationships were found with FMD measurements. All 3 techniques were correlated to the Framingham risk score ( r =0.10 to 0.12, P =0.0007 to 0.001). In multiple regression analysis, however, only EDV and FMD were independently associated with the Framingham score.

Conclusions— All 3 evaluated techniques were feasible to perform in a general elderly population. Both the invasive forearm technique and FMD were independently associated with increased coronary risk, suggesting that information on conduit artery and resistance artery endothelial function carry different, but important, information in the elderly. If the invasive technique cannot be used, the pulse wave based technique is an alternative.

Physical exercise capacity is associated with coronary and peripheral vascular function in healthy young adults

Short-term exercise training has been shown to improve cardiovascular function, whereas long-term effects of a physically active lifestyle, on coronary artery function in particular, are still not well studied. We explored possible relationships between physical exercise capacity and coronary and peripheral vascular function in healthy young adults. Twenty-nine healthy young male and female volunteers participated in the study. They underwent 1) basic clinical and echocardiographic characterization, 2) coronary flow velocity reserve (CFVR) measurement of the left anterior descending coronary artery (LAD), 3) common carotid artery (CCA) intima-media thickness (IMT) measurement, 4) assessment of CCA stiffness index (SI), 5) forearm flow-mediated vasodilation (FMD), and 6) submaximal exercise test. The calculated weight-adjusted maximal oxygen uptake capacity (V̇o2 maxc) was positively correlated to LAD CFVR and inversely correlated to IMT and SI. Also, subjects with high compared with moderate exercise capacity had higher FMD. In addition, subjects with LAD CFVR in the upper median had greater ratios between endothelium-dependent and -independent vasodilation in the forearm and lower SI in CCA. High exercise capacity due to a physically active lifestyle is associated with high coronary and peripheral artery function, indicating an early protective role of physical exercise for cardiovascular health.

Erythropoietin Impairs Endothelial Vasodilatory Function in Patients with Renal Anemia and in Healthy Subjects

BACKGROUND/AIM

The mechanisms underlying the aggravation or development of hypertension frequently seen during treatment of renal anemia with epoetins are not fully elucidated. The aim of the present study was to investigate the effects of epoetin alfa on endothelial vasodilatory function in patients with renal anemia and in healthy subjects.

METHODS

Eighteen preuremic patients with anemia (GFR 23.4 +/- 11 SD ml/min, Hb 101 +/- 8 g/l) and 10 healthy subjects underwent evaluation of endothelium-dependent vasodilation (EDV) and endothelium-independent vasodilation (EIDV) by means of forearm blood flow (FBF) measurements with venous occlusion plethysmography during local intra-arterial infusions of methacholine (MCh, evaluating EDV) and sodium nitroprusside (SNP, evaluating EIDV). These investigations were performed before and 30 min after an intravenous injection of epoetin alfa (10,000 IU). Ten healthy subjects underwent the same procedure with the exception that saline were given instead of epoetin. The patients were treated with epoetin alfa subcutaneously for 12-19 weeks and reevaluated when Hb exceeded 120 g/l.

RESULTS

EDV was attenuated after the epoetin injection in both renal patients and healthy subjects. This impairment persisted after anemia had been treated. EDIV and blood pressure remained constant. Saline had no effect on the variables measured.

CONCLUSION

Our results indicate that epoetin alfa impairs endothelial function in renal patients and healthy subjects which may have an impact on vascular complications.

Reproducibility of forearm vasodilator response to intra-arterial infusion of calcitonin gene-related peptide assessed by venous occlusion plethysmography

AIMS

To assess the reproducibility of the forearm blood flow (FBF) response to intra-arterial infusion of calcitonin-gene related peptide (CGRP), measured by venous occlusion plethysmography. In addition, to compare different ways of expressing the FBF response and perform sample size calculations.

METHODS

On two separate visits, CGRP (10 ng min(-1) dl(-1) forearm) was infused for 45 min into the brachial artery of six healthy subjects. Reproducibility was assessed by calculating mean difference, repeatability coefficient, within-subject coefficient of variation (WCV) and intraclass correlation coefficient.

RESULTS

CGRP increased FBF from 2.8 +/- 0.4 and 3.2 +/- 0.7 (at baseline) to 15.4 +/- 1.4 and 15.2 +/- 1.5 ml min(-1) dl(-1) forearm (at 45 min) on visits 1 and 2, respectively (P < 0.0001 for both visits). Mean difference in FBF at 45 min between both visits was 0.3 ml min(-1) dl(-1) forearm (repeatability coefficient: 4.1 ml min(-1) dl(-1) forearm). This FBF response appeared to be more reproducible when expressed as absolute FBF in the infused arm (WCV 11%) compared with absolute FBF-ratio between both arms (WCV 37%), percentage change from baseline in FBF in the infused arm (WCV 29%) and percentage change from baseline in FBF-ratio (WCV 40%). When expressed as absolute FBF, a sample size of five (95% confidence interval: 2-12) subjects gives 90% power at a type I error probability of 0.05 to detect a 25% shift in FBF response.

CONCLUSIONS

Intra-arterial infusion of CGRP results in a forearm vasodilator response which is reproducible between days. This response is most reproducible when expressed as absolute FBF. The presented methodology provides a suitable pharmacodynamic model to assess the in vivo activity of CGRP-receptor antagonists in a small number of subjects.

Limitations of non-invasive endothelial function assessment by brachial artery flow-mediated dilatation

A non-invasive technique using high-frequency ultrasound brachial artery imaging to assess endothelium-dependent flow-mediated vasodilatation is a widely used test, but interpretation of results is not consistent. This study was designed to assess the method of non-invasive endothelial function determination of a brachial artery. Endothelial function was assessed by two physicians in 18 young, healthy volunteers. Each volunteer was examined by both physicians on the same day using an identical protocol; a second assessment was carried out at an interval of 6-7 days. When comparing arterial dilatation at first and second measurements by one physician, there were no statistically significant differences (first physician: 5.95 +/- 2.93% versus 7.63 +/- 4.3%; P = 0.21; second physician: 4.23 +/- 1.6% versus 4.94 +/- 2.69%; P = 0.22). Further, we found statistically significant differences in artery dilatation when comparing measurements made separately by both physicians on the same day (5.95 +/- 2.93% versus 4.23 +/- 1.6%; P = 0.03, and 7.63 +/- 4.3% versus 4.94 +/- 2.69%; P = 0.003). Our results suggest a large inter-individual variability of measurements within the whole group, if made on the same day and at the same time by two physicians. On the contrary, no significant differences were noted when comparing measurements of the whole group by the one physician at an interval of 1 week. It can be concluded that the degree of brachial artery flow-mediated dilatation is difficult to evaluate on the basis of a predefined cut-off point as a single-measurement screening test.

PRETREATMENT WITH INTRAVENOUS ASCORBIC ACID PRESERVES ENDOTHELIAL FUNCTION DURING ACUTE HYPERGLYCAEMIA (R1)

1. Acute hyperglycaemia may impair endothelial function. Ascorbic acid (AA), administered intra-arterially, has been reported to improve endothelium-dependent vasodilatation during a forearm hyperglycaemic clamp. Using a randomized, double-blind, placebo-controlled, cross-over study, we investigated the potential for intravenous ascorbic acid to modify the endothelial response to acute systemic hyperglycaemia in humans. 2. Nine healthy male volunteers were recruited from the hospital staff. Endothelial function was determined by measuring the forearm blood flow responses to intrabrachial infusions of endothelium-dependent (ED) and endothelium-independent (EID) vasodilators. The endothelial function index (EFI) was derived from the ratio of ED and EID vasodilatation. Haemodynamic and endothelial function measurements were performed at baseline and then repeated 2 h after a systemic hyperglycaemic clamp (14 mmol/L). The subjects, studied on two separate occasions, were randomized to placebo or 2 g intravenous ascorbic acid prior to the initiation of hyperglycaemia. 3. After systemic hyperglycaemia with placebo pretreatment, the EFI fell from 1.08 +/- 0.21 to 0.74 +/- 0.13 (difference (95% confidence interval): 0.34 (0.20, 0.47); P < 0.001). When subjects were pretreated with ascorbic acid, the EFI was not affected by hyperglycaemia (1.11 +/- 0.21 to 1.12 +/- 0.17; P = 0.938). This difference between placebo and ascorbic acid was significant (P < 0.001). Plasma ascorbate concentrations decreased during hyperglycaemia and correlated directly with the reduction in the EFI (r = 0.798; P < 0.001). 4. Pretreatment with an intravenous bolus of ascorbic acid can prevent endothelial dysfunction during acute systemic hyperglycaemia. Therefore, ascorbic acid may have potential therapeutic use in clinical situations where acute hyperglycaemia may be a complication.

Neuromuscular electric stimulation enhances endothelial vascular control and hemodynamic function in paretic upper extremities of patients with stroke

OBJECTIVE

To investigate the effects of neuromuscular electric stimulation (NMES) on endothelial vascular control and hemodynamic function in patients in rehabilitation after acute stroke.

DESIGN

Before-after trial.

SETTING

Inpatients in a tertiary hospital.

PARTICIPANTS

Sixteen stroke patients (11 women, 5 men) with a mean age of 60.6+/-19.5 years.

INTERVENTIONS

All patients received NMES for paretic wrist extensor and flexor muscles 30 minutes daily, 5 days a week, for 4 weeks. The nonparetic upper extremities, which served as controls, did not receive NMES.

MAIN OUTCOME MEASURES

Laser Doppler perfusion testing was conducted to measure cutaneous microcirculatory responses to transdermal iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP), as specific endothelium-dependent and -independent vasodilators, respectively. Arterial and venous hemodynamic function was also measured by impedance plethysmography.

RESULTS

Before NMES treatment, the venous capacity and compliance of the paretic extremities did not differ significantly from those of the nonparetic extremities. However, hyperemic arterial inflow, ACh-induced cutaneous perfusion, and the ratio of ACh- to SNP-induced cutaneous perfusion were lower in the paretic than in the nonparetic extremities. After NMES treatment, hyperemic arterial inflow and venous outflow increased by 21.5% and 57.2%, respectively, in the paretic extremities (P<.05). ACh-induced cutaneous perfusion and the ratio of ACh- to SNP-induced cutaneous perfusion were also significantly enhanced in the paretic extremities. In contrast, hyperemic arterial inflow decreased by 39.6% in the nonparetic extremities (P<.05), and endothelium-dependent cutaneous vasodilation also decreased significantly.

CONCLUSIONS

NMES therapy may enhance the hyperemic arterial response and endothelium-dependent dilation in skin vasculature in the paretic upper extremities of patients with stroke.