Two fluid-structure approaches for 3D simulation of St. Jude Medical bileaflet valve opening.

This paper deals with the three-dimensional (3D) numerical simulation of the opening transient for a bileaflet mechanical heart valve (St. Jude Medical Hemodynamic Plus, 27 mm characteristic size). The discussion concerns two different types of ""partitioned"" fluid-structure models, with weak and strong coupling. Both approaches are based on a moving deforming mesh method as implemented in the CFD commercial software Fluent (Fluent Inc., USA), and both yielded dynamically consistent results from a quantitative viewpoint. There is a slight improvement (peak relative difference <1%) of the numerical solution (angles vs. time) when using the strong instead of the weak coupling model. This is of utmost importance when the considerable reduction of the computational costs for the weak scheme (about 60% less) is taken into account. However, the strong coupling model provides a more consistent physical description of the interaction when looking at small-scale features like stress close to geometrical singularities. In the experiments, the differences both in terms of time-to-peak delay (15% of the opening time) and in terms of underestimation of the peak velocity (8%) seemed due to defects in the fluid inertia assessment, which depends on initial and boundary data.

Complications of diagnostic and therapeutic ERCP: a prospective multicenter study.

OBJECTIVES: Diagnostic and therapeutic endoscopic retrograde cholangiopancreatography (ERCP/ES) can be associated with unforeseeable complications, especially when involving postprocedural pancreatitis. The aim of the study was to investigate risk factors for complications of ERCP/ES in a prospective multicentric study. METHODS: One hundred fifty variables were prospectively collected at time of ERCP/ES and before hospital discharge over 2 years, in consecutive patients undergoing the procedure in nine endoscopic units in the Lombardy region of Italy. More than 150 ERCPs were performed in each center per year by a single operator or by a team of no more than three endoscopists. RESULTS: Two thousand four hundred sixty-two procedures were performed; 18 patients were discharged because the papilla of Vater was not reached (duodenal obstruction, previous gastrectomy, etc.). Two thousand four hundred forty-four procedures were considered in 2103 patients. Overall complications occurred in 121 patients (4.95% of cases): pancreatitis in 44 patients (1.8%), hemorrhage in 30 (1.13%), cholangitis in 14 (0.57%), perforation during ES in 14 (0.57%), and others in 14 (0.57%); deaths occurred in three patients (0.12%). In multivariate analysis, the following were significant risk factors: a) for pancreatitis, age (< or = 60 yr), use of precutting technique, and failed clearing of biliary stones, and b) for hemorrhage, precut sphincterotomy and obstruction of the orifice of the papilla of Vater. CONCLUSIONS: The results of our study further contribute to the assessment of risk factors for complications related to ERCP/ES. It is crucial to identify high risk patients to reduce complications of the procedures.

Original technique for small colorectal tumor localization during laparoscopic surgery.

INTRODUCTION: Small colonic tumor localization and correct extension of colonic resection is critical in laparoscopic surgery. Currently used techniques are sometimes inconclusive and may carry some morbidity. We describe an original method of small tumor localization during laparoscopic colorectal operations through the use of preoperative clip applications by colonoscopy and intraoperative ultrasound of the colon. METHODS: Eight patients with small colonic lesions necessitating preoperative marking were included into this study. A two-step technique was used. Before the operation two metal clips were endoscopically applied proximally and distally to the lesion site. At surgery an intraoperative ultrasound examination of the colon or rectum surface was performed to localize the clips. Subsequent laparoscopic colon resection was performed. RESULTS: Endoscopic metallic clips were easily applied around the lesion in all cases without complications. No dislodgement of clips was documented. At surgery laparoscopic ultrasound visualized the clips in all cases. The examination took between 5 and 17 minutes with no specific morbidity. The lesions with the surrounding clips were always found in the resected specimen. CONCLUSIONS: Endoscopic metal clipping and intraoperative laparoscopic ultrasound proved to be an easy, safe, and accurate technique in locating small colonic tumors.

A step forward in enzymatic measurement of creatinine.

We describe an improved enzymatic ultraviolet absorbance method for assaying creatinine in serum, plasma, and urine. Creatinine is hydrolyzed by creatinine iminohydrolase (EC 3.5.4.21) to ammonia and N-methylhydantoin. The ammonia produced combines with 2-oxoglutarate and NADPH in the presence of glutamate dehydrogenase to yield glutamate and NADP+. The consumption of NADPH, measured by a two-point fixed-time assay, is proportional to the amount of creatinine in the sample. The assay is carried out in two steps: The first step eliminates background absorbance in hyperlipemic samples and endogenous ammonia through a "clearing system" and an isocitrate dehydrogenase-based "ammonia scavenger system"; the second step starts creatinine measurement. The method affords a simple, rapid, and sensitive assay with good precision and extended linearity; it employs working solutions stable at least 4 months. Test results compare closely with those of the isotope dilution-mass spectrometry Definitive Method, the HPLC procedure, and the fuller's earth method. The proposed method is not subject to interference from several metabolites or from the 72 drugs tested. Because it is easily automated, the method is suitable for routine work in clinical laboratories.

Distal splenorenal shunt versus endoscopic sclerotherapy in the prevention of variceal rebleeding. First stage of a randomized, controlled trial.

In 1984 we started a prospective controlled trial comparing endoscopic sclerotherapy (ES) with the distal splenorenal shunt (DSRS) in the elective treatment of variceal hemorrhage in cirrhotic patients. The study population included 40 patients with cirrhosis and portal hypertension referred to our department from October 1984 to March 1988. These patients were drawn from a pool of 173 patients who underwent either elective surgery or endoscopic sclerotherapy during this time. Patients were assigned to one of the two groups according to a random-number table: 20 to DSRS and 20 to ES. During the postoperative period, no DSRS patient died, while one ES patient died of uncontrolled hemorrhage. One DSRS patient had mild recurrent variceal hemorrhage despite an angiographically patent DSRS. Four ES patients suffered at least one episode of gastrointestinal bleeding: two from varices and two from esophageal ulcerations. Five ES patients developed transitory dysphagia. Long-term follow-up was complete in all patients. Two-year survival rates for shunt (95%) and ES (90%) groups were similar. One DSRS patient rebled from duodenal ulcer, while three ES patients had recurrent bleeding from esophagogastric sources (two from varices and one from hypertensive gastropathy). One DSRS and two ES patients have evolved a mild chronic encephalopathy; four DSRS and two ES patients suffered at least one episode of acute encephalopathy. Two ES patients had esophageal stenoses, which were successfully dilated. Preliminary data from this trial seem to indicate that DSRS, in a subgroup of patients with good liver function and a correct portal-azygos disconnection, more effectively prevents variceal rebleeding than ES. However no significant difference in the survival of the two treatment groups was noted.