12,097 research outputs found
Paradoxical increase in microvascular resistance during tachycardia downstream to a severe stenosis in patients with coronary artery disease
No full textBackground - The pathophysiology of microvascular response to a severe coronary stenosis has not been conclusively identified. The aim of this study was to characterize the human vasomotor response to pacing-induced ischemia of both the stenotic arterial segment and the distal microcirculation. Methods and Results - Sixteen patients with stable angina and single-vessel disease were studied. Blood flow velocity and transstenotic pressure gradient were monitored at baseline, after intracoronary adenosine (2 mg), and during ischemia induced by atrial pacing with and without adenosine. At the end of this protocol, the study was repeated after intracoronary phentolamine in 7 patients and after angioplasty in 9. Stenosis resistance was calculated as the ratio between mean pressure gradient and mean flow, and microvascular resistance as the ratio between mean distal pressure and mean flow; values were expressed as percent of baseline. Adenosine decreased (P<0.05) baseline microvascular resistance to 52 ± 17%, but not stenosis resistance. Pacing increased both stenosis and microvascular resistances (244 ± 96% and 164 ± 60% of baseline, respectively, P<0.05). Addition of adenosine to pacing decreased both stenosis (143 ± 96% of baseline, P<0.05 versus ischemia) and microvascular (51 ± 17% of baseline, P<0.05 versus baseline and ischemia) resistances. Phentolamine did not affect coronary resistance at any step of the protocol. Angioplasty and stenting restored a progressive decline in microvascular resistance during pacing (51 ± 19% of baseline, P<0.05 versus baseline). Conclusions - In patients with coronary artery disease, tachycardia-induced ischemia was associated with elevated resistance of both the stenotic segment and the microvasculature. Revascularization prevents this paradoxical behavior
DNA fragment conformations in adducts with Kiteplatin
No full textThe anticancer activity of cisplatin is triggered by its formation of intrastrand adducts involving adjacent G residues of DNA. To obtain information on the different conformers that can be formed, carrier ligands such as 2,2′-bipiperidine, which provide large steric bulk near the platinum coordination plane and decrease the dynamic motion about the Pt-N7 bonds, were introduced ("retro-modelling" approach). In the present study we investigate the effect of cis-1,4-diaminocyclohexane (cis-1,4-DACH) on the formation, stability, and stereochemistry of (cis-1,4-DACH)Pt(ss-oligo) adducts (ss-oligo = d(GpG) with 3′- and/or 5′-substituents). Interesting features of this ligand, absent in previous retro-modelling studies, include the large bite angle (expected to impede the ease of interconversion between possible conformers), the presence of two protons on each nitrogen (a characteristic associated with antitumor activity), and the absence of chiral centres. The use of cis-1,4-DACH has made it possible to detect different conformers in a system containing a primary diamine carrier ligand associated with anticancer activity and to confirm the previous hypothesis that the coexistence of different conformers established in studies of retro models having relatively bulky ligands is not an artefact resulting from carrier-ligand bulk. Moreover, the data for the (cis-1,4-DACH)Pt(d(GpG)) and (cis-1,4-DACH)Pt(d(GGTTT)) adducts indicate that at a temperature close to the physiological one (40 °C) HH1 and ΔHT1 conformers are present in comparable amounts. In contrast, at low temperature (close to 0 °C) the equilibrium shifts dramatically toward the more stable HH1 conformer (for the (cis-1,4-DACH)Pt(d(TGGT)) adduct the HH1 conformer is always dominant, even at high temperature). Notably, (cis-1,4-DACH)PtCl2 (Kiteplatin) has been recently reinvestigated and found to be particularly active against colorectal cancer (including oxaliplatin-resistant phenotypes)
Characteristics of PA cost-effectiveness studies by the first author, setting, number of PAs & design.
No full textCharacteristics of PA cost-effectiveness studies by the first author, setting, number of PAs & design.</p
South African responses to Open Access publishing: a survey of the research community
No full textOpen access publishing offers wide benefits to the scholarly community and may also afford relief to financially embattled academic libraries. The progress of the open access model rests upon the acceptance and validation of open access journals and open archives or institutional repositories by the academic mainstream, particularly by publishing researchers. To what extent are the key actors in the South African research system aware of the advantages of open access? This article reports on the findings of a recent survey undertaken to assess the current awareness, concerns and depth of support for open access amongst local researchers, research managers and policy makers in South Africa. The study focuses on issues of quality, article or author charges and the established academic reward system. It concludes that within the prevailing framework, there is little prospect that academics would choose to publish within open access
journals. Recommendations for advocacy by the library community are proposed
Global ateration in perfusion response to increasing oxygen consuption in patients with single-vessel coronary artery disease
No full textAuthor Co-Citation Analysis (ACA): a powerful tool for representing implicit knowledge of scholar knowledge workers
No full textIn the last decade, knowledge has emerged as one of the most important and valuable organizational assets. Gradually this importance caused to emergence of new discipline entitled ―knowledge management‖. However one of the major challenges of knowledge management is conversion implicit or tacit knowledge to explicit knowledge. Thus Making knowledge visible so that it can be better accessed, discussed, valued or generally managed is a long-standing objective in knowledge management. Accordingly in this paper author co- citation analysis (ACA) will be proposed as an efficient technique of knowledge visualization in academia (Scholar knowledge workers)
Coronary Microcirculatory vasoconstriction during ischemia in patients with unstable angina
No full textOBJECTIVE To verify the behavior of coronary microvascular tone during spontaneous ischemia in patients with unstable angina (UA). BACKGROUND In UA, the pathogenetic role of vasoconstriction is classically confined at the stenotic coronary
segment. However, microcirculatory vasoconstriction has been also suggested by previous experimental and clinical studies.
METHODS The study included 10 patients with UA (recent worsening of anginal threshold and appearance of angina at rest) and single-vessel CAD. Blood flow velocity was monitored by
a Doppler catheter in the diseased artery. Transstenotic pressure gradient was monitored by aortic and distal coronary pressure monitoring. Stenosis resistance was calculated as the ratio
between pressure gradient and blood flow, microvascular resistance as the ratio between distal pressure and blood flow. Measurements were obtained at baseline, following intracoronary
adenosine (2 mg) and during transient ischemia. Aortic and distal coronary pressures were also measured during balloon coronary occlusion. RESULTS Adenosine did not affect stenosis resistance, while it decreased (p , 0.05) microvascular resistance to 52 6 22% of baseline. Angina and ischemic ST segment shift were associated with transient angiographic coronary occlusion in 7 of 10 patients; however, in no case was ischemia associated with interruption of flow. Despite markedly different flow values, distal
coronary pressure was similar during adenosine and during spontaneous ischemia (48 6 15 vs. 46 6 20 mm Hg, respectively, NS). During ischemia, a marked increase in the resistance of
both coronary stenosis and coronary microcirculation was observed (to 1,233% 6 1,298% and 671% 6 652% of baseline, respectively, p , 0.05). Distal coronary pressure was markedly
reduced during balloon coronary occlusion (14 6 7 mm Hg, p , 0.05 vs. both adenosine and ischemia), suggesting the absence of significant collateral circulation. CONCLUSIONS In patients with UA, transient myocardial ischemia is associated with vasoconstriction of both stenotic arterial segment and downstream microcirculation
Relative (pa,pb,pa,pa−b)-difference sets in p-subgroups of SL(n,K)
No full textAbstractIn this note, we study relative (pa,pb,pa,pa−b)-relative difference sets in certain p-subgroups of SL(n,K), K=Fq, where q is a prime power
Coronary vasoconstrinction during myocardial ischemia induced by rises in methabolic demand in patients with coronary artery disease
No full textBackground: In patients with coronary artery disease, a maximal vasodilation of the coronary microcirculation is generally assumed to occur during myocardial ischemia induced by rises in metabolic demand. However, vasoconstriction has been documented during severe prolonged ischemia in animals. The aim of this study was to investigate coronary vasomotor tone during pacing-induced ischemia in humans. Methods and Results: The study included 11 patients with exercise-induced ischemia and single vessel disease of the left anterior descending artery and 7 control subjects with normal coronary arteries. Blood flow velocity was monitored with a Doppler catheter in the left anterior descending artery. Coronary resistance index was calculated as the ratio between mean arterial pressure and flow velocity. Measurements were obtained at baseline, after intracoronary adenosine (2 mg), and during maximal atrial pacing in the absence and presence of adenosine. After adenosine administration at rest, coronary resistance decreased more in control subjects than in patients (25±7% of baseline versus 61±19%; P<.01). Coronary resistance decreased in all control subjects (P<.01) both at maximal pacing (60±17% of baseline) and after administration of adenosine during tachycardia (31±13% of baseline). By contrast, all 10 ischemic patients displayed increased coronary resistance at maximal heart rate (221 2+ 131% of baseline; P<.01 versus baseline, P<.01 versus control subjects). At this stage, adenosine decreased coronary resistance to 44±20% of values observed before injection. Additionally, it reduced ST-segment depression in 5 of 8 patients. Conclusions: In patients with coronary artery disease, transient myocardial ischemia induced by increased metabolic demand is not associated with maximal vasodilation. Rather, an inappropriate severe microvascular vasoconstriction is present that can be abolished by intracoronary adenosine
Open access self-archiving: An author study
No full textThis, our second author international, cross-disciplinary study on open access had 1296 respondents. Its focus was on self-archiving. Almost half (49%) of the respondent population have self-archived at least one article during the last three years. Use of institutional repositories for this purpose has doubled and usage has increased by almost 60% for subject-based repositories. Self-archiving activity is greatest amongst those who publish the largest number of papers. There is still a substantial proportion of authors unaware of the possibility of providing open access to their work by self-archiving. Of the authors who have not yet self-archived any articles, 71% remain unaware of the option. With 49% of the author population having self-archived in some way, this means that 36% of the total author population (71% of the remaining 51%), has not yet been appraised of this way of providing open access. Authors have frequently expressed reluctance to self-archive because of the perceived time required and possible technical difficulties in carrying out this activity, yet findings here show that only 20% of authors found some degree of difficulty with the first act of depositing an article in a repository, and that this dropped to 9% for subsequent deposits. Another author worry is about infringing agreed copyright agreements with publishers, yet only 10% of authors currently know of the SHERPA/RoMEO list of publisher permissions policies with respect to self-archiving, where clear guidance as to what a publisher permits is provided. Where it is not known if permission is required, however, authors are not seeking it and are self-archiving without it. Communicating their results to peers remains the primary reason for scholars publishing their work; in other words,
researchers publish to have an impact on their field. The vast majority of authors (81%) would willingly comply with a mandate from their employer or research funder to deposit copies of their articles in an institutional or subject-based repository. A further 13% would comply reluctantly; 5% would not comply with such a mandate
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