Dynamical heterogeneities and mechanical non-linearities: Modeling the onset of plasticity in polymer in the glass transition

In this paper we focus on the role of dynamical heterogeneities on the non-linear response of polymers in the glass transition domain. We start from a simple coarse-grained model that assumes a random distribution of the initial local relaxation times and that quantitatively describes the linear viscoelasticity of a polymer in the glass transition regime. We extend this model to non-linear mechanics assuming a local Eyring stress dependence of the relaxation times. Implementing the model in a finite element mechanics code, we derive the mechanical properties and the local mechanical fields at the beginning of the non-linear regime. The model predicts a narrowing of distribution of relaxation times and the storage of a part of the mechanical energy --internal stress-- transferred to the material during stretching in this temperature range. We show that the stress field is not spatially correlated under and after loading and follows a Gaussian distribution. In addition the strain field exhibits shear bands, but the strain distribution is narrow. Hence, most of the mechanical quantities can be calculated analytically, in a very good approximation, with the simple assumption that the strain rate is constant.

Role of Dynamical Heterogeneities on the Mechanical Response of Confined Polymer

Confinement induces various modifications in the dynamics of polymers as compared to bulk. We focus here on the role of dynamical heterogeneities on the mechanics of confined polymers. Using a simple model that allows computation of the mechanical response over 10 decades in frequency, we show that the local mechanical coupling controlling the macroscopic response in the bulk disappears in a confined geometry. The slowest domains significantly contribute to the mechanical response for increasing confinement. As a consequence, the apparent glass transition is broadened and shifted towards lower frequencies as confinement increases. We compare our numerical predictions with experiments performed on poly(ethylacrylate) chains in model filled elastomers. We suggest that the change of elastic coupling between domains induced by confinement should contribute significantly to the polymer mobility shift observed on filled systems.

Particles in model filled rubber: dispersion and mechanical properties

We have been able to design model filled rubbers with exactly the same chemical structure but different filler arrangements. From these model systems, we show that the particle arrangement in the elastomeric matrix controls the strain softening at small strain amplitude known as the Payne effect, as well as the elastic modulus dependence on the temperature. More precisely, we observed that the Payne effect disappears and the elastic modulus only weakly depends on the temperature when the particles are well separated. On the contrary, samples with the same interfacial physical chemistry but with aggregated particles show large amplitudes of the Payne effect and their elastic modulus decreases significantly with the temperature. We discuss these effects in terms of glassy bridge formation between filler particles. The observed effects provide evidence that glassy bridges play a key role on the mechanical properties of filled rubbers.

Mechanisms of neutrophil death in human immunodeficiency virus-infected patients: role of reactive oxygen species, caspases and map kinase pathways

Neutrophils from human immunodeficiency virus-positive (HIV+) patients have an increased susceptibility to undergo programmed cell death (PCD), which could explain neutropenia during advanced disease. In this work, key steps of PCD have been evaluated in neutrophils from HIV+ patients. The role of caspase-3, caspase-8, mitogen activated protein kinase (MAPK) and reactive oxygen species (ROS) was analysed. Spontaneous neutrophil death is dependent upon caspase-3 but independent of caspase-8, suggesting that the intrinsic pathway is involved as a pathogenic mechanism of PCD. Inhibition of ROS decreased spontaneous PCD and caspase-3 hydrolysis, connecting oxidative stress and caspase-3 activation with neutrophil PCD in HIV-infected patients. Additionally, an increased neutrophil death was observed in HIV+ patients, following inhibition of p38 MAPK, suggesting a role for p38 MAPK in cell survival during the disease. We conclude that oxidative stress secondary to HIV infection can accelerate neutrophil death.

Profiles of NK, NKT cell activation and cytokine production following vaccination against hepatitis B

Human natural killer (NK) cells (CD56+ CD3-) represent crucial components of the innate immune system especially against viral infections and because their activation can modulate the outcome of the adaptive immune response. NKT cells (CD56+CD3+), a lymphocyte T population characterized by expression of surface markers of NK cells, are known to be abundant in the liver and their activation could be associated with hepatic injury. Using three-color flow cytometry to measure surface receptors and intracellular cytokines, we have explored early activation signals and cytokine production in NK and NKT cells within a group of hepatitis B vaccinated and non-vaccinated individuals. A specific increase of the CD56bright cell population, the activation receptor CD69 and IFN-gamma, was observed in NK cells following incubation with recombinant HBsAg in responders to vaccination. Comparable results were observed in NKT cells showing an increment of CD69, CD25, IL-2 and IFN-gamma expression in responder subjects. These parameters were statistically diminished in non-responder individuals (p<0.05) in both groups of cells. These results demonstrate a diminished activation of these cells in non-responders to the vaccine, suggesting that NK and NKT cells play an important role in the immune response following hepatitis B vaccination.

Increased Fas-mediated apoptosis in polymorphonuclear cells from HIV-infected patients

Neutrophils represent an important line of innate host defence against invading microorganisms and their functional detriment during HIV infection, including accelerated spontaneous cell death, has been shown to contribute to AIDS development. Neutrophils are susceptible to apoptosis via Fas and an interaction between Fas and FasL was suggested originally as a mechanism to explain constitutive neutrophil apoptosis. We have explored some intracellular pathways leading to PMN apoptosis from 28 HIV-infected patients and 24 healthy volunteers. As previously reported, accelerated spontaneous apoptosis was observed in HIV+ patients, but this did not correlate with viral load. Furthermore, an increase in the level of spontaneous apoptosis was detected in neutrophils from HIV-infected patients following inhibition of ERK, suggesting an impairment of this kinase pathway during the early stages of infection which may contribute to PMN dysfunction. An elevated susceptibility to undergo apoptosis was observed following cross-linking of Fas, which correlated both with viral load and co-expression of Fas/FasL surface molecules. Different mechanisms for spontaneous and Fas-induced apoptosis are proposed which together contribute to the neutropenia and secondary infections observed during the progression to AIDS.

Budd-Chiari syndrome caused by membranous obstruction of the inferior vena cava associated with coeliac disease

Ten cases of Budd-Chiari syndrome associated with coeliac disease have been reported in the literature, most of them in North African subjects. Supporting this association, we report a new case in a young Spanish Caucasian man in whom the cause of the syndrome was the membranous obstruction of the inferior vena cava, an infrequent cause of Budd-Chiari syndrome in Western countries. A percutaneous balloon angioplasty was performed, with satisfactory outcome.

Safety of ERCP during pregnancy

OBJECTIVES

There are few data in the literature regarding the indications, therapy, and safety of endoscopic management of pancreatico-biliary disorders during pregnancy. We report the largest single center experience with ERCP in pregnancy.

METHODS

We reviewed 15 patients that underwent ERCP during pregnancy. In all patients, the pelvis was lead-shielded and the fetus was monitored by an obstetrician. Fluoroscopy was minimized and hard copy radiographs taken only when essential.

RESULTS

The mean patient age was 28.9 yr (15-36 yr). The mean duration of gestation was 25 wk (12-33 wk); one patient was in the first, five in the second, and nine in the third trimester. The indications were gallstone pancreatitis (n = 6), choledocholithiasis on ultrasound (n = 5), elevated liver enzymes and a dilated bile duct on ultrasound (n = 2), abdominal pain and gallstones (n = 1), and chronic pancreatitis (n = 1). ERCP findings were bile duct stones (n = 6), patulous papilla (n = 1), bile duct debris (n = 1), normal bile duct and gallstones or gallbladder sludge (n = 3), dilated bile duct and gallstones (n = 1), normal bile duct and no gallstones (n = 2), and chronic pancreatitis (n = 1). Six patients underwent sphincterotomies and one a biliary stent insertion. One sphincterotomy was complicated by mild pancreatitis. All infants delivered to date have had Apgar-scores >8, and continuing pregnancies are uneventful. Mean fluorosocopy time was 3.2 min (SD +/- 1.8). An estimated fetal radiation exposure was 310 mrad (SD +/- 164) which is substantially below the accepted teratogenic dose.

CONCLUSIONS

ERCP in pregnancy seems to be safe for both mother and fetus; however, it should be restricted to therapeutic indications with additional intraprocedure safety measures.

Evaluation of a liquid urease test (LUT) for detection of Helicobacter pylori

The aim of our study was to develop a rapid diagnostic urease test to demonstrate the presence of Helicobacter pylori in the Endoscopy room.

MATERIALS AND METHODS

200 consecutive patients referred to gastroscopy for different indications, were included in this study. One antral biopsy sample was obtained to be immersed in our test. The same sample was used for histological evaluation, considered to be the gold standard method for diagnose of Helicobacter pylori infection.

RESULTS

135 patients (67.5%) were found positives and 65 patients (32.5%) were negatives in our test. 128 patients (64%) showed Helicobacter pylori on histological examination. Our test showed a sensitivity of 91%, specificity of 88.1%, and positive and negative predictive values of 95% and 80% respectively. A remarkable correlation between density of Helicobacter pylori and reading time was also observed, where a high density of the bacteria reduced the reaction time in this liquid test. Furthermore, an overall accuracy of 90% was shown, which is comparable with other available commercial tests.

CONCLUSION

LUT is easy to handle, cost effective and fast, with a high positive predictive value.

Bedside scoring system to predict the risk of developing pancreatitis following ERCP

BACKGROUND AND STUDY AIMS

Pancreatitis is the most common significant complication of endoscopic retrograde cholangiopancreatography (ERCP). The aim of the present study was to develop a simple scoring system that clinicians can use to predict the risk of post-ERCP pancreatitis.

PATIENTS AND METHODS

We analyzed a prospectively assembled database of 1835 ERCP procedures at a single referral hospital. Multivariate logistic regression analysis was performed to identify risk factors for pancreatitis and determine their relative contributions. From these results, a scoring system was constructed. The performance of the scoring system was assessed on the entire procedure database and in selected subgroups.

RESULTS

Multivariate analysis yielded four risk factors: pain during the procedure, cannulation of the pancreatic duct (PD), previous post-ERCP pancreatitis, and number of cannulation attempts. Based on the regression model, the scoring system was: 4 points for pain, 3 points for PD cannulation, 2 points for a history of post-ERCP pancreatitis, and 1 - 4 points depending on the number of cannulation attempts. A total score of 1 - 4 points was associated with a low risk of pancreatitis (< 2 %), while a score of 5 - 8 points had an intermediate risk (7 %), and a score of 9 or above had a high risk (28 %).

CONCLUSIONS

This simple scoring system may enable clinicians to stratify patients into low-risk, medium-risk, and high-risk groups for the development of post-ERCP pancreatitis. In addition, when patients with suspected sphincter of Oddi dysfunction and patients who underwent minor papilla cannulation were analyzed separately, the scoring system was able to predict accurately the pancreatitis risk of these patients as well.

Cecal volvulus in pregnancy

Colonic volvulus is an important entity to consider in any pregnant patient with abdominal pain. X-ray and colonoscopy can be useful to obtain the earliest diagnosis, leading to surgical intervention if necessary. Limited use of x-rays with shielding of the fetus is of minimal risk and useful for early diagnosis of volvulus. Colonoscopy may confirm or exclude the diagnosis of colonic volvulus, detect mucosal ischemia, and avoid the requirement for emergency surgery by reducing the volvulus in cases in which ischemia is not present. If surgery is necessary for a cecal volvulus, cecostomy is a viable option because of a low rate of morbidity and subsequent volvulus recurrence.

Features that may predict hospital admission following outpatient therapeutic ERCP

BACKGROUND

Some patients are admitted following outpatient therapeutic ERCP because of adverse events. This study aimed to identify factors that may predict such admissions.

METHODS

We prospectively studied admissions for post-ERCP adverse events in 415 consecutive patients undergoing outpatient therapeutic ERCP. Potentially relevant predictors of admission were assessed by univariate analysis and in case of significance included in a multivariate analysis.

RESULTS

Admission was necessary in 41 patients (9.9%) because of complications and in 63 (15.2%) for observation of adverse events that did not progress to definable complications. Potential predictors of admission were evaluated comparing patients who required more than an overnight admission (n = 63) with those who did not (n = 352). Multivariate analysis identified three factors that were significant: pain during the procedure (odds ratio 3.8: 95% CI [1.8, 7.9]), history of pancreatitis (odds ratio 2.3: 95% CI [1.1, 4.7]) and performance of sphincterotomy (odds ratio 2.2: 95% CI [1.1, 4.3]). The presence of all these features was associated with a 66.7% likelihood of admission, whereas the absence of pain during the procedure, history of pancreatitis and performance of sphincterotomy made admission likely in only 11.0%, 9.8% and 10.7%, respectively, of the cases.

CONCLUSIONS

The occurrence of pain during the procedure, a history of pancreatitis and the performance of sphincterotomy were independent predictors of admission following outpatient therapeutic ERCP.

Accuracy and complication rate of brush cytology from bile duct versus pancreatic duct

BACKGROUND

The accuracy and complication rates of brush cytology obtained from pancreaticobiliary strictures have not been fully defined. In this study we compared the accuracy and complications of brush cytology obtained from bile versus pancreatic ducts.

METHODS

We identified 148 consecutive patients for whom brush cytology was done during an ERCP from a database with prospectively collected data. We compared cytology results with the final diagnosis as determined by surgical pathologic examination or long-term clinical follow-up. We followed all patients and recorded ERCP-related complications.

RESULTS

Forty-two pancreatic brush cytology samples and 101 biliary brush cytology samples were obtained. The accuracy rate of biliary cytology was 65 of 101 (64.3%) and the accuracy rate of pancreatic cytology was 30 of 42 (71.4%). Overall sensitivity was 50% for biliary cytology and 58.3% for pancreatic cytology. Of 67 patients with pancreatic adenocarcinoma, sensitivity for biliary cytology was 50% versus 66% for pancreatic cytology. Concurrent pancreatic and biliary cytology during the same procedure increased the sensitivity in only 1 of 10 (10%) patients. Pancreatitis occurred in 11 (11%) patients (9 mild cases, 2 moderate cases) after biliary cytology and in 9 (21%) patients (6 mild cases, 3 moderate cases) after pancreatic cytology (p = 0.22). In 10 patients who had pancreatic brush cytology, a pancreatic stent was placed. None of these patients developed pancreatitis versus 9 of 32 (28%) patients in whom a stent was not placed (p = 0.08). Pancreatic cytology samples obtained from the head of the pancreas were correct in 13 of 18 (72%) cases, from the genu in 7 of 7 (100%) cases, from the body in 5 of 9 (55%) cases, and from the tail in 4 of 7 (57%) cases.

CONCLUSION

The accuracy of biliary brush cytology is similar to the accuracy of pancreatic brush cytology. The yield of the latter for pancreatic adenocarcinoma is similar to that of the former. Complication rates for pancreatic cytology are not significantly higher than the rates for biliary cytology. The placement of a pancreatic stent after pancreatic brushing appears to reduce the risk of postprocedure pancreatitis.

Endoscopic management of choledocholithiasis

The first description of endoscopic sphincterotomy 25 years ago spearheaded the widespread use of endoscopic treatment of choledocholithiasis. It is largely accepted that common bile duct stone removal should be endoscopic rather than surgical in patients who have undergone previous cholecystectomy, in the high-risk surgical patient when the gallbladder is still present, in patients with severe acute cholangitis, in selected patients with acute biliary pancreatitis, and in special circumstances for the average risk surgical patient with suspected choledocholithiasis before laparoscopic cholecystectomy. We have summarized a number of endoscopic techniques that are used in the management of bile duct stone disease.

Palliation of malignant gastric outlet obstruction using an endoscopically placed Wallstent

BACKGROUND

Treatment options for malignant gastric outlet obstruction are limited. Surgical gastrojejunostomy, commonly performed, has significant morbidity and mortality.

METHODS

Over 2 years, we prospectively studied the safety, feasibility, and outcomes for use of a newly designed expandable metal stent (Wallstent Enteral; Schneider, Minneapolis, Minn.) to treat malignant gastric outlet obstruction. Stents 16 to 22 mm in diameter and 60 to 90 mm in length were deployed directly through the endoscope.

RESULTS

Twelve patients (ten women, two men; mean age 59.7 years) underwent stenting. Thereafter, six patients were able to eat a regular diet; three could eat pureed food. In three patients, the procedure was unsuccessful because of multiple obstructions not recognized before stenting (one) and stents deployed too proximally (one) or too distally (one).

CONCLUSIONS

Placement of a newly designed stent through the endoscope is safe and effective palliation for various types of malignant gastric outlet obstruction and significantly improves many aspects of patient quality of life.

Portal vein absence and nodular regenerative hyperplasia of the liver with giant inferior mesenteric vein

We present a patient with nodular regenerative hyperplasia of the liver (NRH) and portal vein absence studied with CT, MR imaging, and MR angiography. The most striking feature was exuberant hemorrhoids due to a giant hepatofugal inferior mesenteric vein. A relationship between unbalanced portal blood flow and nodular regenerative transformation of the liver is suggested in this patient.

Successful treatment of hepatic veno-occlusive disease in a peripheral blood progenitor cell transplant patient with a transjugular intrahepatic portosystemic stent-shunt (TIPS)

Hepatic veno-occlusive disease (VOD) is a common cause of morbidity and mortality after BMT. Although treatment of VOD is primarily supportive, some success has been obtained recently with fibrinolytic therapy. However, for critically ill patients liver transplantation may be the only therapeutic option. Nevertheless, this procedure is associated with high mortality and can only be performed in a minority of cases. The transjugular intrahepatic portosystemic stent-shunt (TIPS) is a non-surgical, side-to-side shunt consisting of an intraparenchymal duct between a main branch of the portal vein and a hepatic vein. In this report we describe a patient who underwent TIPS placement for severe VOD following autologous PBPC transplant. No complications developed and gradual improvement in clinical status and liver function was observed early after this therapy. Nine months after TIPS, the patient is asymptomatic with normal liver function. TIPS provides an interesting alternative to invasive therapies for patients with severe VOD after bone marrow or PBPC transplants.

[Prevalence of antibodies against hepatitis C virus in multitransfused patients]

We have done a study in order two know the prevalence of anti-hepatitis C virus antibodies in polytransfused patients with hemophilia, leukemia and hemolytic anemia, along with 17 healthy donors, without previous history of transfusions. We analyzed samples from 10 hemophilic patients and 12 from leukemia, lymphoma and hemolytic anemia, all of them had received blood or blood products, at least six months before the study. Using a second generation ELISA, 4 positive sample (3 hemophilic and 1 lymphoma) were detected (10.26%), which represent a prevalence of 30% in the hemophilic group, in contrast with the prevalence detected in other countries. A very significant statistic association was demonstrated, between the positive ELISA, the amount of the transfused product (P < 0.0004) and the type of blood product used for transfusion (crioprecipited, P = 0.000, plasma P = 0.000).

A system for the simultaneous delivery of intraoperative radiation and ultrasound hyperthermia

A multi-element ultrasonic applicator, utilizing an ultrasound reflector, is presented which enables the controlled delivery of ultrasonic energy for the induction of hyperthermia while allowing the simultaneous application of orthovoltage ionizing radiation. A temperature-controlled water circulating system allows for acoustic coupling, additional control over the tumour surface temperature and depth of maximum temperature into the tissue. In vitro and in vivo testing supported the applicators objective of effectively controlling temperature elevation. Therapeutic target temperatures of 42 degrees C can be achieved within a 5-min period and maintained for a 60-min treatment time. The depth of heat penetration could be varied as a function of surface temperature and ultrasound frequency. Heating was achieved to at least a depth of 3 cm. Radiation measurement methods verified the expected radiation dose uniformity and distribution.

Patterns of cigarette smoking among Hispanics in the United States: results from HHANES 1982-84

In the 1982-84 Hispanic Health and Nutrition Examination Survey, the prevalence of cigarette smoking was examined among Mexican Americans, Puerto Ricans, and Cuban Americans in the United States. Among 20-74 years olds, the age-adjusted smoking rates for Mexican American, Puerto Rican, and Cuban American men were high--42.5, 39.8, and 41.6 percent, respectively. Quite striking among Cuban American men was the high smoking rate among 20-34 year olds (50.1 percent), the highest smoking rate in the three Hispanic groups compared. The age-adjusted smoking rates for Mexican American, Puerto Rican, and Cuban American women were much lower than those for men-23.8, 30.3, and 24.4 percent, respectively. Both Puerto Rican and Cuban American men were more likely to be heavy smokers (52.3 and 64.1 percent, respectively, smoking a pack or more a day) as compared to the Mexican Americans (33.8 percent smoking a pack or more a day). The pattern was the same for women, with Mexican American women being lighter smokers (18.8 percent smoking a pack or more a day) as compared to heavy smoking among Puerto Rican and Cuban American women (35.1 and 48.6 percent, respectively, smoking a pack or more a day). Given the health hazards of smoking, future research and intervention are required for those groups with high exposure to cigarette smoking.

CT diagnosis of primary mediastinal hydatid cyst rupture into the aorta: a case report

Primary hydatid cyst of the mediastinum is rare. We report a patient with a primary mediastinal hydatid cyst which ruptured into the aorta, resulting in bilateral popliteal embolism. The contrast-enhanced computed tomographic features represent a pathognomonic sign of a communicating rupture of an echinococcal cyst into the aorta. Comparison is made with ultrasonography and aortography.

Absorption coefficient at 10.6 microm in CdTe modulator crystals

The bulk and surface absorption coefficients of CdTe modulator crystals at 10.6 microm were compared with those of single-crystal KC1 and NaCl which served to calibrate the laser calorimeter. High-resistivity (>10(7) ohm/cm) CdTe crystals exhibited a bulk absorption coefficient of 0.0014 cm(-1).