Static and impact-dynamic characterization and modeling of multiphase TRIP steels

In this paper some highlights are presented of an integrated numerical and experimental approach to obtain an in-depth understanding of the high strain rate behavior of materials. The approach is applied to TRansformation Induced Plasticity (TRIP) steels. Phenomenological and microstructurally-based models to describe the established strain rate and temperature dependent behavior are assessed. ‘Classic’ high strain rate tensile experiments using a split Hopkinson tensile bar setup are complemented with strain rate jump tests and tensile tests at elevated temperatures. High strain rate compression and three-point bending experiments are performed as well. These experiments provide additional validation data for the material models. Around room temperature the use of the Johnson-Cook model is most obvious. However, if a wider temperature range has to be covered, only the microstructurally based models give satisfying results. Advanced experimental setups using the Hopkinson principle provide excellent tools for characterizing the material and structural properties of TRIP steels

Recovery of Regional Contractile Function and Oxidative-metabolism in Stunned Myocardium Induced By 1-hour Circumflex Coronary-artery Stenosis in Chronically Instrumented Dogs

Stunned myocardium produced by 1 hour of critical coronary artery stenosis was evaluated for alteration in regional mechanical function and overall oxidative and fatty acid metabolism by positron emission tomography (PET) in chronically instrumented dogs. Twenty-seven dogs, chronically instrumented for measurements of left ventricular pressure and regional myocardial wall thickening in normal and ischemic zones, were subjected to a 1-hour period of myocardial ischemia produced by graded left circumflex coronary artery stenosis, resulting in minimal residual flow. Mean transmural myocardial flow during 1-hour coronary stenosis decreased to 0.34+/-0.04 ml/min per gram in the ischemic zones (normal zone transmural flow, 0.96+/-0.10 ml/min per gram). Systolic wall thickening in the ischemic zone was almost completely abolished (-97+/-4%). On reperfusion, systolic wall thickening immediately resumed but remained depressed. Progressive recovery was noted with time. At 24 hours, systolic wall thickening was still depressed (-20+/-6%, p < 0.01). At 1 week, wall thickening had completely recovered and was no longer significantly different from the control condition. In addition, the absence of necrosis at the site of wall thickness measurements was confirmed at autopsy in all dogs. No abnormalities were found by electron microscopy in four dogs undergoing myocardial biopsies at the time of PET studies. Dynamic PET studies using [1-C-11]acetate tracer (performed at 6 hours, 1 week, and 2 weeks after reperfusion) and [1-C-11]palmitic acid tracer (performed at 6 hours, 12 hours, 24 hours, 1 week, and 2 weeks after reperfusion) allowed the computation of regional tissue time-activity curves in different regions of interest at different times during follow-up. Despite full reperfusion, abnormal [1-C-11]acetate and [1-C-11]palmitic acid kinetics were observed in the posterior segments, previously subjected to ischemia, as evidenced by a significant decrease in the slope of the early C-11 clearance curve component. Repeat PET studies revealed progressive normalization of overall oxidative metabolism and fatty acid metabolism, which paralleled the time course of recovery of mechanical function. Thus, myocardial ischemia, produced by 1-hour coronary artery stenosis, followed by full reperfusion is associated with a prolonged period of postischemic mechanical and metabolic dysfunction. This transient reduction in oxygen delivery induced a prolonged impairment in fatty acid beta-oxidation as well as a reduction in overall oxidative metabolism despite full reoxygenation. A similar time course for recovery of function and metabolism was observed

Should minimally invasive aortic valve replacement be restricted to primary interventions?

Background: The role of minimally invasive aortic valve replacement in cardiac reoperations has not yet been defined. The purpose of this study is to report our experience with this technique

Minimally invasive versus standard approach aortic valve replacement: A study in 506 patients

Background. Minimally invasive aortic valve replacement through partial upper sternotomy has been shown to reduce surgical trauma, and, supposedly, decrease postoperative pain, blood loss, and hospital stay

Minimally invasive aortic root replacement: a bridge too far?

Aim Minimally invasive aortic valve surgery has been studied widely with outcomes comparable or better than standard sternotomy. We recently reported on decreased blood loss, cross clamp time and length of hospital stay when compared to conventional full sternotomy. We expanded the indication to aortic root surgery and report here our 8 years experience

Robotically enhanced minimally invasive direct coronary artery bypass surgery: a winning strategy?

Aim. Minimally invasive direct coronary artery bypass (MMCAB) through a small anterolateral thoracotomy on the beating heart can be considered as the better approach for treating isolated lesions on the left anterior descending (LAD) artery. This original MIDCAB procedure, however, involves a larger and often painful thoracotomy due to rib spreading. We describe our experience with robotically enhanced harvesting of one or both internal mammary arteries (IMAs), and with anastomosis performed under direct vision on a beating heart through a very small thoracotomy without rib retraction. Methods. Between February 2001 and January 2006,146 consecutive patients underwent robotically enhanced MIDCAB surgery. Perioperative and early follow-up data were analyzed. Results. In all, 144 left and 13 right IMAs were harvested. The mean extubation time was 11.3 h, the mean intensive care (ICU) stay was 30.3 h, the mean hospital stay 8 days. There were no in-hospital deaths, postoperative myocardial infarctions or renal failures. Systematic control angiograms; performed in the first 64 patients showed a 96.3% patency rate of the investigated anastomoses. Conclusion. Robotically assisted takedown of the IMA and direct off-pump anastomosis through a small anterolateral thoracotomy with no rib retraction appears to be safe, with minimal morbidity, little blood loss, and a reasonable ventilation time, ICU and hospital stay. It is recommended as the preferred method of revascularization for a growing number of indications and certainly an acceptable alternative to percutaneous transluminal coronary angioplasty

Surgical treatment of atrial fibrillation.

Atrial fibrillation is a very common arrhythmia that carries a considerable risk of thromboembolic complications. Surgical treatment is an effective way to convert atrial fibrillation into sinus rhythm and significantly prevents thromboembolism postoperatively. In this review we describe recent advancements in the surgical options and detail our strategy for the surgical treatment of atrial fibrillation.Journal ArticleReviewinfo:eu-repo/semantics/publishe