1,721,024 research outputs found
Heterogeneity of resting and hyperemic myocardial blood flow in healthy humans
No full textObjective: Absolute myocardial blood flow (MBF) is not well-defined in large normal populations, and appears to be heterogeneous in both humans and animals. These factors contribute to the difficulties in defining resting MBF to hibernating myocardium. We therefore assessed absolute baseline and hyperemic MBF in a large population of normal humans. Methods: MBF was quantified by positron emission tomography with oxygen-15-labeled water at baseline and during hyperemia induced by either adenosine or dipyridamole in 131 men and 38 women, aged 21-86 (mean 46+/-12) years. MBF was corrected for workload using the rate-pressure product (RPP). Results: Uncorrected baseline MBF ranged from 0.590 to 2.050 (mean 0.985+/-0.230) ml/min/g (coefficient of variation=27%), and corrected MBF from 0.736 to 2.428 (mean 1.330+/-0.316) ml/min/g (coefficient of variation=24%). MBF in the inferior region was significantly (P<0.0001) lower than either the anterior or lateral regions. Baseline MBF in females was significantly (P<0.001) higher than in males. Conclusions: These results confirm the heterogeneity of MBF in normals and highlight the difficulty in establishing the lower limit of normal MBF. (C) 2001 Elsevier Science B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Systemic nitric oxide synthase inhibition improves coronary flow reserve to adenosine in patients with significant stenoses
No full textCoronary heart disease in smokers - Vitamin C restores coronary microcirculatory function
No full textBackground-Coronary endothelial function and vasomotion are impaired in smokers without coronary disease, and this is thought to be due to increased oxidative stress. Methods and Results-We used positron emission tomography to measure the coronary flow reserve, an integrated measure of coronary flow, through both the large epicardial coronary arteries and the microcirculation in 11 smokers and 8 control subjects before and after administration of the antioxidant vitamin C, At baseline, coronary flow reserve was reduced by 21% in smokers compared with control subjects (P < 0.05) but was normalized after vitamin C, whereas the drug had no effect in control subjects. Conclusions-The present study is the first to demonstrate that the noxious prooxidant effects of smoking extend beyond the epicardial arteries to the coronary microcirculation and affect the regulation of myocardial blood flow. Vitamin C restores coronary microcirculatory responsiveness and impaired coronary flow reserve in smokers, which provides evidence that the damaging effect of smoking is at least in part accounted for by an increased oxidative stress
Low density lipoprotein cholesterol and coronary microvascular dysfunction in hypercholesterolemia
No full textOBJECTIVES The present study evaluates the impact of total cholesterol (TC) and its subfractions on coronary flow reserve (CFR), an index of the integrated function of the coronary circulation, in asymptomatic subjects. BACKGROUND Endothelial dysfunction of the coronary microcirculation has been reported in asymptomatic subjects with hypercholesterolemia. METHODS Using oxygen-15-labeled water and positron emission tomography, myocardial blood flow (MBF, in ml/min per g) was measured at rest and during intravenous adenosine (140 mu g/kg body weight per min) in 80 asymptomatic nonsmoking men: group 1 (n = 61; age 45 +/- 7 years) had normal TC (less than or equal to 6.5 mmol/liter or less than or equal to 250 mg/dl) and group 2 (n = 19; age 48 +/- 10 years) had elevated TC. RESULTS Total cholesterol were 5.1 +/- 0.8 and 7.2 +/- 0.7 mmol/liter in groups 1 and 2 (p < 0.0005), respectively; low density lipoprotein (LDL) cholesterol levels were 3.2 +/- 0.8 and 4.9 +/- 0.7 mmol/liter (p < 0.0005); high density lipoprotein (HDL) cholesterol levels were 1.1 +/- 0.3 and 1.0 +/- 0.4 mmol/liter (p = NS); and triglyceride levels were 1.8 +/- 1.3 and 3.0 +/- 1.8 mmol/liter (p < 0.005). Groups 1 and 2 did not differ with regard to MBF at rest (0.87 +/- 0.14 vs. 0.84 +/- 0.14), MBF during adenosine (3.63 +/- 1.02 vs. 3.30 +/- 0.86) or CFR (4.23 +/- 1.29 vs. 3.95 +/- 0.93). A significant but weak correlation was found between CFR and HDL in group 1 (r = 0.29, p < 0.05), but not in group 2. In contrast, a significant inverse correlation between LDL and CFR was found in group 2 (r = -0.61, p < 0.05), but not in group 1. CONCLUSION Low density lipoprotein cholesterol but not TC correlated inversely with CFR in hypercholesterolemic subjects. Thus, LDL-induced coronary microvascular dysfunction could play an important role in the pathogenesis of coronary artery disease and its complications. (J Am Coil Cardiol 2000;36:103-9) (C) 2000 by the American College of Cardiology
Tetrahydrobiopterin restores impaired coronary microvascular dysfunction in hypercholesterolaemia
No full textPurpose: Tetrahydrobiopterin (BH4) is an essential co-factor for the synthesis of nitric oxide (NO), and BH4 deficiency may cause impaired NO synthase (NOS) activity. We studied whether BH4 deficiency contributes to the coronary microcirculatory dysfunction observed in patients with hypercholesterolaemia. Methods: Myocardial blood flow (MBF; ml min(-1) g(-1)) was measured at rest, during adenosine-induced (140 mug kg(-1) min(-1) over 7 min) hyperaemia (mainly non-endothelium dependent) and immediately after supine bicycle exercise (endothelium-dependent) stress in ten healthy volunteers and in nine hypercholesterolaemic subjects using O-15-labelled water and positron emission tomography. Measurements were repeated 60 min later, after intravenous infusion of BH4 (10 mg k(g)-(1) body weight over 30 min). Adenosine-induced hyperaemic MBF is considered to represent (near) maximal flow. Flow reserve utilisation was calculated as the ratio of exercise-induced to adenosine-induced hyperaemic MBF and expressed as percent to indicate how much of the maximal (adenosine-induced) hyperaemia can be achieved by bicycle stress. Results: BH4 increased exercise-induced hyperaemia in controls (2.96 +/- 0.58 vs 3.41 +/- 0.73 ml min(-1) g(-1), p<0.05) and hypercholesterolaemic subjects (2.47 +/- 0.78 vs 2.70 +/- 0.72 ml min(-1) g(-1), p<0.01) but had no influence on MBF at rest or during adenosine-induced hyperaemia in controls (4.52 +/- 1.10 vs 4.85 +/- 0.45 ml min(-1) g(-1), p=NS) or hypercholesterolaemic subjects (4.86 +/- 1.18 vs 4.53 +/- 0.93 ml min(-1) g(-1), p=NS). Flow reserve utilisation remained unchanged in controls (70 +/- 17% vs 71 +/- 19%, p=NS) but increased significantly in hypercholesterolaemic subjects (53 +/- 15% vs 66 +/- 14%, p<0.05). Conclusion: BH4 restores flow reserve utilisation of the coronary microcirculation in hypercholesterolaemic subjects, suggesting that BH4 deficiency may contribute to coronary microcirculatory dysfunction in hypercholesterolaemia
Myocardial perfusion scintigraphy for risk stratification of patients with coronary artery disease: the AMICO registry
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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