Restenosis following coronary stent implantation remains an important and costly therapeutic problem. Since intimal smooth muscle cell (SMC) proliferation is largely the culprit,1-4 various attempts to inhibit this process have been studied.5-10 Modulation of the stimuli for neointimal hyperplasia by appropriate pharmacologic agents would, in theory, permit vessel wall healing after coronary stent implantation without an exaggerated, obstructive proliferative response. Until recently, local drug delivery, using various agents and different methods of administration, has failed to affect restenosis rate after stenting (see further the discussion in Chapter 29).11,12 This may be related to the agent studied, and the design of the delivery device, as well as the timing of drug delivery with respect to stenting. Arterial injury triggers thrombus formation with release of growth factors known to stimulate neointimal proliferation: platelet-derived growth factor (PDGF), transforming growth factor (TGF)-β, fibroblast growth factor (FGF) and others.13-15STUDIESEnoxaparin has been shown to inhibit smooth muscle cell proliferation at high tissue concentrations.16-18 However, it has not reduced the incidence of angiographic restenosis or clinical events after successful coronary angioplasty when administered systemically.19 In a baboon angioplasty model low molecular weight heparin (LMWH) blocked seruminduced but not PDGF-induced SMC proliferation and migration, suggesting heparin sensitive and insensitive pathways. If the assumption that human SMC are less sensitive to growth inhibition by heparin is true, one may consider the possibility that in-stent restenosis may be reduced by local prevention of early prothrombotic events. Enoxaparin is a potent inhibitor of factor Xa and thrombin.20,21 The strategy of local delivery of enoxaparin during predilation was specifically designed to modulate the magnitude of thrombin-mediated and thrombus-mediated stimuli for neointimal proliferation. The purpose of enoxaparin delivery during predilation is to have an antithrombotic agent in place at the time of the initial balloon deflation, when the injured vessel wall was first exposed to circulating prothrombotic elements. This hypothesis was tested in an atherosclerotic rabbit model where 10 mg of enoxaparin delivered during iliacangioplasty reduced neointimal proliferation as evidenced by reduced BRDU uptake compared with conventional angioplasty.18
No abstract is provided for this article.
No abstract is provided for this article.
The effect of thrombolysis in acute myocardial infarction on infarct size, left ventricular function, clinical course and patient survival was studied in a randomized trial comparing thrombolysis (269 patients) with conventional treatment (264 control patients). All 533 patients were admitted to the coronary care unit within 4 hours after the onset of symptoms related to the infarction. Baseline characteristics were similar in both groups. Informed consent was requested only of patients allocated to thrombolysis; no angiography was performed in 35. The infarct-related artery was patent in 65 patients and occluded in 169. Recanalization was achieved in 133 patients. The median time to angiographic documentation of vessel patency was 200 minutes after the onset of symptoms. The clinical course in the coronary care unit was more favorable after thrombolysis. Infarct size, estimated from myocardial enzyme release, was 30% lower after thrombolysis. In patients admitted within 1 hour after the onset of symptoms the reduction of infarct size was 51%, in those admitted between 1 and 2 hours it was 31% and in those admitted later than 2 hours it was 13%. Left Myocardial infarction in most patients results from a thrombotic occlusion of a major coronary artery. Recently, Rentrop and other investigators (1-4) have demonstrated that rapid recanalization can be achieved by intracoronary inventricular function measured by radionuclide angiography before hospital discharge was better after thrombolysis (ejection fraction 48 ± 15%) than in control patients (44 ± 15%). Similar improvement was observed in patients with a first infarct only (thrombolysis 50 ± 14%, control subjects 46 ± 15%), in patients with anterior infarction (thrombolysis 44 ± 16%, control subjects 35 ± 14%) and in those with inferior infarction (thrombolysis 52 ± 12%, control subjects 49 ± 12%). Similar results were obtained by contrast angiography. Mortality was lower after thrombolysis. After 28 days 16 patients allocated to thrombolysis and 31 control patients had died. One year survival rates were 91 and 84%, respectively. On the other hand, nonfatal reinfarction occurred more frequently after thrombolysis (36 patients) than in control subjects (16 patients). Early thrombolysis by intracoronary streptokinase leads to a smaller infarct size estimated by enzyine release, preserves left ventricular function at the second week and leads to improved 1 year survival.
Aluminium alloys are nonlinear metallic materials with continuous stress-strain curves that are not well represented by the simplified elastic, perfectly plastic material model used in many current design specifications. Departing from current practice, the continuous strength method (CSM) is a recently proposed design approach for non-slender aluminium alloy structures with consideration of strain hardening. The CSM is deformation based and employs a base curve to define a continuous relationship between cross-section slenderness and deformation capacity. This paper explains the background and the two key components - (1) the base curve and (2) the strain hardening material model of the continuous strength method. More than 500 test results are used to verify the continuous strength methodas an accurate and consistent design method for aluminium alloy structures.
No abstract is provided for this article.
No abstract is provided for this article.
While the number of galactic supernova remnants (SNRs) now known is fairly large (>150), the subset among these that are known to resemble the Crab Nebula is still distressingly small, about 15 or so (Green, 1984). Thus any object that can be unambiguously included in this exclusive club forms a valuable addition to our knowledge of this class. We report here observations of a newly recognised nonthermal galactic object, G18.94-l.06, having all the hallmarks of the classical shell-type SNRs, while also appearing to have a filled-centre component located inside the shell. Among the known Crab-like remnants, about one third show this dual nature (Green, 1984). This diagnosis of G18.94-1.06 is supported mainly by the variations in spectral index α (S ν ∝ ν α ) across the source, as seen between the two observation frequencies, 408 MHz and 5.0 GHz.
