Fatigue life assessment of cardiovascular balloon-expandable stents: a two-scale plasticity-damage model approach.

Cardiovascular disease has become a major global health care problem in the present decade. To tackle this problem, the use of cardiovascular stents has been considered a promising and effective approach. Numerical simulations to evaluate the in vivo behavior of stents are becoming more and more important to assess potential failures. As the material failure of a stent device has been often associated with fatigue issues, as a result of the high number of cyclic loads these devices are subjected to in vivo, numerical approaches for fatigue life assessment of stents has gained special interest in the engineering community. Numerical fatigue predictions can be used to modify the design and prevent failure, without making and testing numerous physical devices, thus preventing from undesired fatigue failures. This work presents a fatigue life numerical method for the analysis of cardiovascular balloon-expandable stainless steel stents. The method is based on a two-scale continuum damage mechanics model in which both plasticity and damage mechanisms are assumed to take place at a scale smaller than the scale of the representative volume element. The fatigue failure criterion is based on the Soderberg relation. The method is applied to the fatigue life assessment of both PalmazShatz and Cypher stent designs. Validation of the method is performed through comparison of the obtained numerical results with some experimental results available for the PalmazShatz stent design. The present study gives also possible directions for future research developments in the framework of the numerical fatigue life assessment of real balloon-expandable stents.

Diagnosis of primary cancer of the liver.

The diagnosis of primary cancer of the liver was reviewed in 75 patients. A definitive diagnosis was made during life in 63% and in a further 20% this condition was suspected though histological confirmation was obtained only at necropsy. The most common presenting complaints were abdominal pain and weight loss and the most frequent findings hepatomegaly and ascites. Less than one-half of the patients were jaundiced and when present it was usually mild. An arterial bruit was heard over the liver in 25% of the patients. A sudden and unexplained deterioration in a patient known to have cirrhosis or haemochromatosis should raise the possibility of a primary hepatic tumour; this occurred in 24% of our patients.Alpha-fetoprotein was found in the serum of 11 out of 18 cases. The presence of a mass in the liver was frequently confirmed by liver scan, portal venography, or hepatic arteriography, but these showed no features diagnostic of a primary tumour. Liver scan also proved useful in localizing the lesion for biopsy purposes. Definitive diagnosis is dependent on the histological demonstration of the features of the tumour. This can frequently be achieved by percutaneous needle biopsy, which was positive in 38 out of 57 patients. Wedge biopsies were positive in a further nine patients.

Portal hypertension in primary biliary cirrhosis.

Evidence of portal hypertension was found in 50 out of 109 patients (47%) with primary biliary cirrhosis, and of these 32 bled from oesophageal varices. In four patients portal hypertension was the initial manifestation of the disease and this complication was recognized in a further 17 within two years of the first symptom of primary biliary cirrhosis. The development of portal hypertension was associated with a poor prognosis and death could frequently be attributed to variceal bleeding; the mean duration of survival from the time that portal hypertension was recognized was 14.9 months. Portal decompression operations may have improved the immediate prognosis in some patients but did not otherwise influence the progression of the disease. In 47 patients the histological findings in wedge biopsy or necropsy material were correlated with the presence or absence of varices. An association between nodular regeneration of the liver and varices was confirmed, but, in the absence of nodules, no other histological cause for portal venous obstruction could be found.

[Perianal manifestations in Crohn's disease]. / Manifestações perianais na doença de Crohn.

UNLABELLED: A total of 114 of 195 patients with Crohn's disease had perianal involvement. The average age at the beginning of symptomatology was 30.3 years. The interval between symptoms and diagnosis was 3.1 years. PAC was associated with colonic disease and in these patients, was multiple. PAC preceded intestinal disease in 11 percent, was coincident in 66 percent and appeared later in 23 percent. Sixty one patients (53.5%) were operated on 104 times (1.7 operations per patient). None of these patients developed faecal incontinence. Two patients were treated with hyperbaric oxygenation. The association of perianal disease and extra-intestinal manifestation occurred in 76 patients. There was no association in 38 patients. Forty patients had extra-intestinal manifestation without perianal disease. Twenty two patients had panproctocolectomy because of perianal disease. Twenty one had a stoma, with or without intestinal resection. The stoma improved perianal symptoms, but all remain defunctioned. After mean follow-up of 8.8 years, 45 patients present some kind of perianal complication. CONCLUSION: the surgical treatment of perianal disease well indicated and performed don't result in incontinence; PAC combined with colonic or rectal disease is associated with higher need of performing a proctocolectomy or a defunctioning stoma. Only 22.8 percent presented resolution of perianal disease maintaining anal sphincter function.