An ideal coronary vasodilator for studying coronary flow reserve should rapidly produce a maximal hyperemic response, be short acting to permit repeated measurements, and not alter systemic hemodynamics. We measured with a Doppler tip balloon catheter, in 12 patients before and/or after percutaneous transluminal coronary angioplasty the hyperemic response following 12.5 mg intracoronary papaverine and following gradually incremental bolus injections of intracoronary adenosine, starting from 0.05 mg until a maximal hyperemic response or side effects. The mean dose (±SD) of adenosine needed to produce maximal hyperemia was 0.23 (±0.20 mg). Coronary blood flow velocity after adenosine increased to 1.6 ± 0.3 times resting coronary blood flow velocity, comparable in magnitude to the hyperemia following intracoronary papaverine. The time from injection to peak effect after adenosine was 7.4 (SD ± 2.2) sec and after papaverine 26 (SD ± 7) sec. Adenosine resulted in a bradyarrythmia in three patients. Intracoronary adenosine is a potent and very short acting vasodilator for studying coronary flow reserve, but the side effects and unpredictability of the dosage needed to produce maximal hyperemia may limit its applicability.
Owing to their enhanced load-carrying and serviceability performances, prestressed coldformed steel beams can potentially open up new applications within the construction industry.In the proposed concept, an eccentric prestressing force is applied to cold-formed steel beams by means of a cable that is housed within a bottom hollow flange.During prestressing, tensile stresses are induced within the top region of the beam, thus delaying the occurrence of local instabilities under subsequent vertical loading.Consequently, the moment capacity of the beam is enhanced.Furthermore, owing to the prestressing, a pre-camber is also induced along the member, thus decreasing the overall vertical deflections significantly.Following discussion of the mechanical behaviour of the proposed beams, design recommendations are developed by employing interaction equations alongside the Direct Strength Method.Subsequently, finite element (FE) analysis is employed to investigate the effects of the prestress level and the section slenderness of the steel beam on the benefits obtained from the prestressing process.The parametric FE results are then utilised to assess the design recommendations.
The phenomenon on kink banding, occurring primarily in layered structures under layer-parallel compression, has been studied extensively in a variety of different situations. Examples of physical systems which exhibit this phenomenon include the deformation of geological strata [1, 2], compressed laminated fibre composites [3, 4, 5], and internally in fibre and wire ropes [6]. In our earlier work, the focus was on the geological application of kink banding where layers are confined by pressure and therefore penalize the formation of voids in the structure. Some of the technical difficulties that are encountered in the modelling of such systems were outlined in terms of using continuum mechanics and Cosserat-type continua. The approach we adopted involved formulating a model that cut out most of the complexity, but kept large rotations—the nonlinearity that seems to govern the structural response. This simple model exhibits a path of pure squash and a path of deformation where the kink bands form and rotate. However, as the paths of equilibrium cross at infinity, i.e. there exists an infinite critical load, from the linearized viewpoint there is no such instability, a conclusion that is not confirmed by experimental evidence which clearly shows the structure deforming suddenly after a certain amount of loading. The Maxwell stability criterion [7] was used in an earlier paper to overcome this difficulty [8]. This allowed the evaluation of a robust lower bound of the displacement where the system jumped from the undeformed to the kinked state, and the evaluation of the lock-up angle of the kink band. In the current study, several enhancements of the original model are outlined such that quantitative comparisons can be made between experiments and theory away from the neighbourhood of the initial instability and significantly into the post-kinking regime. It is found that not only can the new model embrace mechanisms for band propagation, in terms of band broadening and progression, but that comparisons of the band width and orientation against experiments are excellent. 2 Model Characteristics
Steel and steel–concrete composite construction is employed in a substantial proportion of low-rise and multi-storey buildings. Design codes for these forms of structure have evolved over many years, but are currently essentially founded upon the assumption of elastic-plastic or rigid-plastic material behaviour and largely disregard the beneficial influence of strain hardening. This simplificaton can result in overly conservative predictions of capacity, particularly in the case of stocky, bare steel cross-sections and composite beams under sagging bending moment. The continuous strength method is an alternative deformation-based design approach that allows for strain hardening, provides more accurate predictions of member capacities and, thus, enables more efficient structural solutions to be achieved. In this paper, the development and application of the continuous strength method to steel structures is explained and extension of the method to steel–concrete composite design is outlined.
Small vessel size (<3 mm) has been identified as an independent predictive factor of restenosis after percutaneous coronary intervention when using bare metal stents (BMS). It remains controversial whether BMS placement in small vessels has an advantage over balloon angioplasty in terms of angiographic and clinical outcomes. The advent of drug eluting stents (DES), either paclitaxel-eluting stents (PES) or sirolimus-eluting stents (SES), has strongly impacted interventional cardiology by significantly reducing restenosis and the need for repeat revascularization. Therefore, it was also expected that DES could substantially reduce restenosis in smaller vessels. However, even in the DES era, small vessel size remains an independent predictor of angiographic and clinical restenosis. To date, only a few studies systematically investigate the clinical effect of DES placement in small vessels. In addition, some potential issues with the use of DES have been raised, such as late stent thrombosis and late restenosis. In order to (i) establish the superiority of DES over BMS; (ii) verify the efficacy and safety of DES; and (iii) critically assess the superiority of one DES over the other in patients with small coronary arteries, further multicenter, randomized clinical trials with larger sample size are warranted.
A comprehensive numerical investigation into the cross-sectional behaviour and ultimate capacity of non-slender welded I-sections, made of both normal and high strength steels (NSS and HSS), under combined compression and uniaxial bending is presented. Finite element (FE) models were initially established and validated against test results collected from the literature. Subsequently, parametric studies were conducted using the validated FE models to generate extensive numerical data considering different steel grades, cross-section geometries and loading combinations. The obtained numerical data, together with the test results collected from the literature, were utilised to assess the accuracy of the traditional European (EC3) and North American (AISC) design provisions, as well as the Continuous Strength Method (CSM), for NSS and HSS welded I-sections under combined loading. The assessment indicated that the CSM was able to provide more accurate and consistent resistance predictions than the current EC3 and AISC design provisions owing to its ability to capture the spread of plasticity and strain hardening in a systematic, mechanics-based manner. Finally, the reliability levels of the different design methods were statistically evaluated in accordance with EN 1990:2002.
