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The hemodynamic effects of nisoldipine were investigated in 16 patients with suspected coronary artery disease who underwent routine cardiac catheterization. Nisoldipine was given intravenously in a dose of 6 μg/kg over 3 minutes and measurements made before and after drug administration during spontaneous and matched atrial paced heart rate. During sinus rhythm, nisoldipine produced a significant increase in heart rate (19%, p < 10−5). Left ventricular systolic pressure decreased 28% (p < 10−6) and left ventricular end-diastolic pressure did not change significantly (5%, difference not significant). Coronary sinus and great cardiac vein blood flow increased by 21% (p < 0.02) and 25% (p < 0.005), respectively, after nisoldipine administration. Simultaneously, mean aortic pressure decreased 33% (p < 10−6); consequently, the global and regional coronary vascular resistances decreased by 50% (p < 10−4). The decreases in global (−8%) and regional (−4%) myocardial oxygen consumption did not reach statistical significance. A 6% (not significant) increase in end-diastolic volume and an 11% (p < 0.002) decrease in end-systolic volume resulted in an increase of 21% in stroke volume (p < 10−4) with a consistent increase in ejection fraction (+16%, p < 10−5). Total systemic vascular resistance was reduced by 30% (p < 0.0002). During spontaneous heart rate and matched atrial pacing, the time constant of isovolumic relaxation as assessed by a biexponential model, was significantly shortened. The maximal velocity of isovolumic contraction after nisoldipine was administered remained higher (+12%, p < 0.02) at an identical paced heart rate. Thus, nisoldipine is a potent coronary and peripheral vasodilator. No negative inotropic effects were observed in the dosage used.
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No abstract is provided for this article.
Formulae for determining the elastic buckling loads of structural steel rectangular hollow sections (RHS) subjected to concentrated transverse forces are presented herein. The predicted elastic buckling load is bounded by a theoretical lower bound, where only the material within the bearing length is mobilised, and a practical upper bound, where the adjacent material is mobilised to its maximum extent. The lower bound is the elastic buckling load of a wide plate with a width equal to the bearing length and a length equal to the web depth, while the upper bound is determined from finite element (FE) analyses of various representative loading scenarios. The level of mobilisation of adjacent material is quantified by introducing a coefficient ζ that is calibrated through FE analyses in the commercial package ABAQUS, with the rotational stiffness afforded to the webs by the flanges also being captured. The four loading scenarios defined in the North American Specification (NAS) and Australian/New Zealand Standard (AS/NZS) for the design of cold-formed steel structures, namely the Interior-Two-Flange (ITF), End-Two-Flange (ETF), Interior-One-Flange (IOF) and End-One-Flange (EOF) loading conditions, alongside their transitional cases, are considered. Rectangular hollow sections with a broad spectrum of cross-sectional geometric proportions and bearing lengths encompassing the aforementioned loading conditions are considered. It is found that the developed formulae for predicting the elastic buckling loads under concentrated transverse forces provide accurate results that are typically within 5% of the numerical values. Hence, the developed formulae can be employed as a convenient alternative to numerical methods in advanced structural design methodologies, such as the Direct Strength Method (DSM) and the Continuous Strength Method (CSM).
No abstract is provided for this article.
No abstract is provided for this article.
The EN 1993-1-4 (2015) design approach for stainless steel CHS beam-column members has been observed from prior experimental studies to provide capacity predictions that can be either overly conservative or unconservative depending upon the ratio of axial load to bending moment. Hence, a numerical parametric study has been undertaken to explore the buckling response of stainless steel CHS beam-columns, covering austenitic, duplex and ferritic grades with a wide range of local and global slendernesses and applied loading eccentricities. Over 2000 numerical results have been generated and used to assess new design proposals for stainless steel beam-columns, featuring improved compression and bending end points and new interaction factors. The new proposals are more consistent and, on average, 4% more accurate in their resistance predictions than the current EN 1993-1-4 (2015) design approach. The reliability of the existing and new proposals has been verified by means of statistical analyses according to EN 1990 (2005).