Clare Storry

Methodological approaches to optimize reproducibility and power in clinical studies of flow-mediated dilation.

OBJECTIVES Our aim was to determine reproducibility of the flow-mediated dilation (FMD) response profile, and discriminatory ability of the components. BACKGROUND Brachial FMD is widely used to study conduit artery endothelial function. Automated B-mode image edge detection (B-ED) provides a full response profile. Reproducibility and biological relevance of these additional components have not been fully explored. METHODS Forty-two healthy adults underwent FMD using B-ED repeated at fixed time intervals up to 3 months. The FMD profile was assessed for diameter changes, area under the curve, and time course. Measures were compared in 25 adults with hypercholesterolemia, 25 subjects with diabetes, and 50 matched control subjects. RESULTS The maximum change in FMD was the most reproducible (coefficient of variation = 9.8%, 10.6%, 6.6%, and 9.2% at 4 to 6 h, 1 week, 1 month, and 3 months, respectively). Most of the variability occurred between subjects rather than within. All FMD measures except time course were significantly reduced in hypercholesterolemia and diabetes. Power curves were generated to indicate the appropriate number of subjects for parallel and crossover study designs. CONCLUSIONS Maximum FMD percentage change from baseline is the most reproducible of the response curve measures and best identifies those with risk factors. Flow-mediated dilation measured by B-ED is robust and practical to assess the effect of interventions on endothelial function in clinical trials.

Inflammation and Endothelial Function Direct Vascular Effects of Human C-Reactive Protein on Nitric Oxide Bioavailability

Background—Circulating concentrations of the sensitive inflammatory marker C-reactive protein (CRP) predict future cardiovascular events, and CRP is elevated during sepsis and inflammation, when vascular reactivity may be modulated. We therefore investigated the direct effect of CRP on vascular reactivity. Methods and Results—The effects of isolated, pure human CRP on vasoreactivity and protein expression were studied in vascular rings and cells in vitro, and effects on blood pressure were studied in rats in vivo. The temporal relationship between changes in CRP concentration and brachial flow-mediated dilation was also studied in humans after vaccination with Salmonella typhi capsular polysaccharide, a model of inflammatory endothelial dysfunction. In contrast to some previous reports, highly purified and well-characterized human CRP specifically induced hyporeactivity to phenylephrine in rings of human internal mammary artery and rat aorta that was mediated through physiological antagonism by nitric oxide (NO). CRP did not alter endothelial NO synthase protein expression but increased protein expression of GTP cyclohydrolase-1, the rate-limiting enzyme in the synthesis of tetrahydrobiopterin, the NO synthase cofactor. In the vaccine model of inflammatory endothelial dysfunction in humans, increased CRP concentration coincided with the resolution rather than the development of endothelial dysfunction, consistent with the vitro findings; however, administration of human CRP to rats had no effect on blood pressure. Conclusions—Pure human CRP has specific, direct effects on vascular function in vitro via increased NO production; however, further clarification of the effect, if any, of CRP on vascular reactivity in humans in vivo will require clinical studies using specific inhibitors of CRP.

Mineral Metabolism and Vascular Damage in Children on Dialysis

Cardiovascular disease is increasingly recognized as a life-limiting problem in young patients with chronic kidney disease, but there are few studies in children that describe its determinants. We studied the association of intact parathyroid hormone (iPTH) levels and their management on vascular structure and function in 85 children, ages 5-18 years, who had received dialysis for > or =6 months. Compared to controls, dialysis patients had increased carotid intima-media thickness and pulse-wave velocity. All vascular measures positively correlated with serum phosphorus levels, while carotid intima-media thickness and cardiac calcification score also correlated with iPTH levels. Patients with mean time-integrated iPTH levels less than twice the upper limit of normal (n = 41) had vascular measures that were comparable to age-matched controls, but those with iPTH levels greater than twice the upper limit of normal (n = 44) had greater carotid intima-media thickness, stiffer vessels, and increased cardiac calcification than controls. Patients with increased carotid intima-media thickness had stiffer vessels and a greater prevalence of cardiac calcification. There was a strong dose-dependent correlation between vitamin D and all vascular measures, and calcium intake from phosphate binders weakly correlated with carotid intima-media thickness. In conclusion, both iPTH level and dosage of vitamin D are associated with vascular damage and calcification in children on dialysis.

Early Structural and Functional Changes of the Vasculature in HIV-Infected Children Impact of Disease and Antiretroviral Therapy

Background—Premature cardiovascular disease is increasingly recognized in HIV-infected patients, but the mechanisms involved are unclear. The purpose of this study was to determine the impact of HIV infection and antiretroviral therapy (ART) on markers of early vascular disease in children. Methods and Results—We studied 83 HIV-infected children (56 had taken ART, of whom 31 received a regimen containing protease inhibitors [PIs]; 27 were never treated) and a control group of 59 healthy children. Carotid intima-media thickness (IMT) and brachial artery flow-mediated dilatation (FMD) were measured. IMT was significantly greater in HIV-infected children compared with the control subjects (P<0.001). Among the HIV-infected children, age and treatment were significantly associated with increased IMT. Children exposed to PIs had greater IMT compared with both non-PI-treated children and untreated children (P=0.02). FMD was also significantly reduced in the HIV-infected children compared with control subjects (P=0.02). Pairwise comparisons of different treatment exposure groups revealed that FMD was impaired by a mean of 3.6% (95% CI, 1.8 to 5.3; P<0.001) for children exposed to PIs compared with untreated children and by a mean of 1.8% (95% CI, 0.01 to 3.5; P=0.05) compared with non-PI-treated children. HIV-infected children had lipid abnormalities, but they did not account for the observed differences in either FMD or IMT. Conclusions—HIV infection in childhood is associated with adverse structural and functional vascular changes that are most pronounced in children exposed to PI therapy. Longitudinal studies are required to differentiate the relative impact of HIV disease and ART and to assess the potential for prevention.

A dose-response study of hormone replacement in young hypogonadal women: effects on intima media thickness and metabolism.

Objective  Young hypogonadal women appear to have an increased risk of cardiovascular disease. We studied the influence of increasing doses of hormone replacement therapy (HRT) on markers of metabolism and vascular physiology.

Impact of aortic stenting on peripheral vascular function and daytime systolic blood pressure in adult coarctation

Objectives: To determine the relation of ambulatory systolic blood pressure to aortic obstruction and more extensive vascular dysfunction, assessed by central aortic, peripheral conduit arterial and resistance vessel function. Methods: 12 adults (5 native, 7 recoarctation) were studied before, and 2 weeks and 6 months after aortic stenting. Systolic blood pressure was measured during normal daily living by 24-hour ambulatory monitoring. Central aortic function was assessed by pulse wave analysis (augmentation index). Brachial artery flow-mediated dilatation and dilatation in response to 25 μg of sublingual glyceryl trinitrate was assessed by ultrasound to measure peripheral conduit arterial and resistance vessel function. Baseline vascular measures were compared with those of 12 matched controls. Results: Patients had a higher augmentation index, impaired endothelium-dependent and -independent dilatation, and forearm vascular resistance (p<0.02). After successful gradient relief by stenting, daytime ambulatory systolic blood pressure (151 (134, 166) mm Hg vs 138 (130, 150) mm Hg, p = 0.01) and the augmentation index (26 (15, 34) vs 23 (13, 30), p = 0.03) fell progressively over 6 months, but did not completely normalise. Endothelium-dependent and -independent dilatation, and forearm vascular resistance remained unchanged and impaired. Conclusion: Relief of aortic obstruction is associated with improvement in central aortic function and results in reduction of daytime ambulatory systolic blood pressure. Peripheral vascular dysfunction, however, remains unchanged and may contribute to residual hypertension.

Endothelial Dysfunction and Cytomegalovirus Replication in Pediatric Heart Transplantation

Background— Cardiac allograft vasculopathy is the major limiting factor to the long-term success of pediatric heart transplantation. Cytomegalovirus (CMV) has been shown to be a significant risk factor for the development of cardiac allograft vasculopathy. Recent work has demonstrated CMV DNA in leukocytes in the absence of direct allograft infection, suggesting that vascular changes may not be limited to the allograft. Method and Results— Systemic arterial endothelial function was assessed with high-resolution ultrasound to determine brachial artery flow-mediated dilation in 50 pediatric heart transplant recipients (8 to 17 years of age; 27 male). Patients were separated into 2 groups according to CMV status: those without evidence of CMV replication after transplantation (n=38; 19 male) and patients with evidence of viremia after transplantation (n=12; 8 male). No patient had detectable viremia at the time of study. Flow-mediated dilation was significantly impaired in patients with evidence of CMV replication after transplantation (6.64±1.12%, mean±SE) compared with those without (9.48±0.56%; P=0.02). This difference remained after adjustment for age, time since transplantation, and medication. Pretransplantation recipient and donor CMV status and traditional CMV risk were not associated with flow-mediated dilation. Conclusions— CMV replication after cardiac transplantation is associated with chronic endothelial dysfunction in the systemic circulation in children. The implication for both systemic and coronary vascular health requires prospective evaluation.

Docosahexaenoic Acid Supplementation, Vascular Function and Risk Factors for Cardiovascular Disease: A Randomized Controlled Trial in Young Adults

Background A high consumption of omega‐3 long‐chain polyunsaturated fatty acids, and particularly docosahexaenoic acid (DHA), has been suggested to reduce the risk of cardiovascular disease (CVD). However, while DHA supplementation may have benefits for secondary prevention, few studies have investigated the role of DHA in the primary prevention of CVD. Here, we tested the hypothesis that DHA supplementation improves endothelial function and risk factors for CVD. Methods and Results Healthy volunteers (n=328), aged 18 to 37 years, were randomly assigned to 1.6 g DHA/day (from a microalgae source) together with 2.4 g/day carrier oil (index group) or to 4.0 g/day olive oil (control) (both given in eight 500‐mg capsules/day for 16 weeks). Flow‐mediated endothelium‐dependent vasodilation (FMD) of the brachial artery (primary outcome) was measured before and after the intervention (n=268) using high‐resolution vascular ultrasound. FMD was the same in both groups at randomization (mean, SD; 0.27, 0.1 mm), but postintervention was higher in the control group (0.29, 0.1 mm) compared with the DHA‐supplemented group (0.26, 0.1 mm; mean difference −0.03 mm; 95% CI −0.005 to −0.06 mm; P=0.02). Of other outcomes, only triglyceride (mean difference −28%, 95% CI −40% to −15%; P<0.0001) and very low‐density lipoprotein concentrations were significant lower in DHA‐supplemented individuals compared with controls. Conclusions DHA supplementation did not improve endothelial function in healthy, young adults. Nevertheless, lower triglyceride concentrations with DHA supplementation was consistent with previous reports and could have benefits for the prevention of CVD. Clinical Trial Registration Information URL: http://www.controlled-trials.com/ Unique identifier: ISRCTN no: 19987575.

819-1 Endothelial dysfunction in children with human immunodeficiency virus: Impact of disease and protease inhibitor therapy

Background: Only 30% of the hypertensive population is controlled. PROMPT (Palmbased Risk Outcomes Manager and Patient Tracker) is an NHLBI-sponsored randomized trial testing the effect of a point-of-care, hand-held computer collection and reminder system, coupled with regular feedback, on improving BP control. Methods: 114 physicians in a primary clinic in East Harlem, New York, were randomized to one of three groups: 1) Total intervention group (TIG) received a hand-held digital assistant (PDA) programmed to prompt entry of data for BP management. They also received regular patient-specific feedback and quarterly peer-comparison of their patient’s BP control. 2) Partial intervention group (PIG) physicians used paper charts only, had regular chart review by trained abstractors, and quarterly peer-comparison feedback. The control (zero) intervention group (ZIG) managed patients in the standard paper-chart fashion (i.e. no PDA and no quarterly feedback nor reminders). Results: 3712 patients with hypertension (HTN) were followed for an average of 434+107 days from January 2001 through September 2002.The average age of the hypertensive population was 60.7+ 13.4, average BP was 138+/80+11. 29% were African American, 43% were Caribbean Hispanic, and 28% were either white or of unknown ethnic origin. 38% had uncomplicated HTN (HTN_Only), 31% had diabetes (HTN_DM) and 31% had target organ damage (HTN_TOD). In the sub-group of patients with HTN_Only, absolute % BP control increased significantly more (14% vs. 8%, p<0.02) in patients whose physicians were in the PIG compared to the ZIG group. In HTN_Only, there was a trend toward greater improvement in the TIG group compared to the ZIG group (10% vs. 8%, p=0.12). In the HTN_TOD and HTN-DM subgroups, there was no difference in % increase in BP control between the TIG, PIG and ZIG physician groups. Conclusions: This study demonstrates that regular chart review by trained abstractors, coupled with peer-comparison feedback, effectively improves BP control. More study is required to determine if further BP control can be achieved through prompts and reminders provided to the physician at the point of care with a PDA.