Simplified Characterization of Anisotropic Yield Criteria for an Injection-Molded Polymer Material.

Injection-molded polyethylene plates exhibit highly anisotropic mechanical behavior due to, e.g., the uneven orientation of the polymer chains during the molding process and the differential cooling, especially in the thickness direction. Elastoplastic finite element modeling of these plates in particular is used with isotropic yield criteria like von Mises, trading off accuracy in favor of simpler constitutive characterization and faster solution. This article studies three different anisotropic yield criteria, namely, Hill 1948, Barlat Yld91, and Barlat Yld2004-18P, for the finite element modeling of low-density polyethylene (LDPE) at large uniaxial tensile deformation and compares the accuracy and computation time with von Mises. A simplified calibration technique is investigated to identify the constitutive parameters of the studied Barlat group yield criteria. The calibration process is simplified in the sense that only uniaxial tensile tests with digital image correlation measurements are used for the calibration of all the yield criteria studied in this article, although a standard calibration procedure for the Barlat group yield criteria requires additional material testing using more demanding test setups. It is concluded that both Barlat Yld91 and Barlat Yld2004-18P yield criteria can be calibrated with only a few tensile tests and still capture anisotropy in deformation-stress-strain at different levels of accuracy.

Unusual late presentation of asymptomatic diaphragmatic hernia following ventricular assist device explantation.

The role of left ventricular assist device (LVAD) in treatment options of congestive heart failure is becoming more important and the widespread application is imminent. There are, however, some serious complications associated with LVAD, which make patient management more challenging. We report a rare surgical case of asymptomatic diaphragmatic hernia, which was diagnosed 8.5 years after heart transplantation and LVAD explantation. A left mini (7 cm), muscle- and nerve-sparing thoracotomy was performed, and we found the splenic flexure of the colon herniated into the left pleural space through a small, circumferential defect of the diaphragm ( approximately 4 cm in diameter) created for the inflow cannula of LVAD. The hernia was reduced and the defect was repaired.

The impact of arrhythmias in acute heart failure.

BACKGROUND: Arrhythmias are common in chronic heart failure and affect outcomes. The incidence and significance of new arrhythmias in acute heart failure, however, are largely unknown. METHODS AND RESULTS: The Outcomes of a Prospective Trial of Intravenous Milrinone for Exacerbations study randomized 949 patients with decompensated heart failure to receive intravenous milrinone or placebo. In the study, patients were divided into 2 groups based on the occurrence of a new arrhythmic event during their index hospitalization and analyzed for outcome. There were 59 new arrhythmic events occurring in 6% of the population. Of these, 49% were atrial fibrillation/flutter. The primary endpoint of days hospitalized for cardiovascular causes within 60 days after randomization was 30.9+/-22.7 for those in the arrhythmia group and 11.3+/-12.7 days for those with no arrhythmias (P=.0001). Mortality during index hospitalization was 26% in the arrhythmia group and 1.8% in the no arrhythmia group (P=.001). Death or hospitalization at 60 days was also worse in the arrhythmia group (35 versus 8.2%, P=.0001; 57 versus 34%, P=.001, respectively). Cox proportional hazard analysis identified new arrhythmias as an independent risk factor for the primary endpoint and death at 60 days. CONCLUSION: New arrhythmia during an exacerbation of heart failure identifies a high-risk group with higher intrahospital and 60-day morbidity and mortality.

Pharmacologic and nonpharmacologic options to maintain sinus rhythm: guideline-based and new approaches.

Atrial fibrillation is a common arrhythmia in patients with heart failure and is responsible for substantial morbidity and mortality. Restoration and preservation of sinus rhythm, therefore, has a premium. Of the numerous treatment options available, many must be avoided because of their potential for adverse effects or because of limited proof of efficacy in defined populations. Published guidelines provide help by synthesizing clinical trial data into a recommended approach. This article summarizes current information regarding the best methods applicable to patients with left ventricular dysfunction for rate control, sinus rhythm restoration and maintenance, and stroke prevention. New and evolving therapies and how they might fit into the evolving treatment paradigm are also briefly reviewed.