Electron beam crosslinking of rigid-rod polyesters with flexible aliphatic side chains

The crosslinking of a series of thermotropic LC polyesters, consisting of a poly(p-phenylene terephthalate) backbone and flexible aliphatic side chains, by electron beam irradiation was studied as a function of the side-chain composition, side-chain length, and irradiation temperature. For a comparison of the effect of irradiation the G(S)/G(X) ratio, as determined from sol-gel or GPC measurements, was used. Crosslinking dominates if this value is smaller than 1, which is the case for four out of five polyesters studied. Only the polyester with hexyloxy side chains shows a slight tendency to degradation. Crosslinking is stimulated by longer side chains and the introduction of hetero atoms that are more easily ionizable, like oxygen. The introduction of an unsaturation has the largest effect and boosts the crosslinking process. Raising the irradiation temperature increases the tendency to crosslinking or degradation already present. For most of the polyesters studied, irradiation slightly improves the mechanical properties of cast films. © 1996 John Wiley & Sons, Inc.     

Mobility and solubility of antioxidants and oxygen in glassy polymers. III. Influence of deformation and orientation on oxygen permeability

The mobility of small molecules in a glassy polymer is largely determined by the amount of free volume present in the material. The amount of free volume can be altered by changing the physical state of the polymer. Plastic deformation under compression reduces this amount, whereas the application of a tensile stress increases it. Furthermore, orientation of a polymer introduces an anisotropy in the free volume. The change in free volume was monitored by oxygen permeation experiments. A clear correlation was found between the draw ratio, plastic deformation and stress on the one hand and oxygen permeability on the other. Since the mobility of oxygen is an important parameter for the stabilisation of a polymer against oxidation, the physical state of the polymer can have a significant influence on the service life of the product.     

Dobutamine-atropine stress echocardiography in elderly patients unable to perform an exercise test. Hemodynamic characteristics, safety, and prognostic value

OBJECTIVE: To establish the hemodynamic effects, safety, and prognostic value of dobutamine-atropine stress echocardiography in patients 70 years of age or older. DESIGN AND SETTING: Observational study at a university hospital. PATIENTS: One hundred seventy-nine patients (mean age, 75 years; range, 70 to 90 years) referred for chest pain (n = 73) or preoperative risk assessment for major vascular noncardiac surgery (n = 106). MEASUREMENTS: All patients underwent clinical evaluation and dobutamine-atropine stress test. RESULTS: One hundred seventy-nine stress tests were performed. Test end points were the target heart rate (85% of theoretical maximum heart rate), reached in 165 tests (92%); inadequate echo images, two tests (1%); and side effects, 12 tests (7%). Side effects that caused a premature end of the test were severe chest pain (n = 5 [2.8%]), electrocardiographic changes (n = 1 [0.6%]), hypotension (n = 2 [1.1%]), chills (n = 2 [1.1%]), and cardiac arrhythmias (paroxysmal atrial fibrillation) (n = 2 [1.1%]). New wall motion abnormalities as a marker of myocardial ischemia occurred in 50 tests (28%). No death or myocardial infarction occurred during the test. Perioperative events occurred in 12 patients (four cardiac deaths, three myocardial infarctions, and five episodes of unstable angina). During 16 +/- 6 months (mean +/- SD) of follow-up of 166 patients, 22 cardiac events occurred (eight cardiac deaths, four myocardial infarctions, and 10 episodes of unstable angina pectoris). By multivariate regression analysis, only perioperative cardiac events (odds ratio, 51; 95% confidence interval, 5.8 to 454) and late cardiac events (odds ratio, 5.2; 95% confidence interval, 2.0 to 14) were correlated with new wall motion abnormalities during stress. CONCLUSION: Dobutamine-atropine stress echocardiography is a feasible and safe test for assessing elderly patients with suspected and/or proven coronary artery disease, providing useful prognostic information for perioperative and late cardiac risk with relatively few side effects.     

Time‐Resolved Quantification of Nanoparticle Uptake,Distribution, and Impact in Precision‐Cut Liver Slices

Much effort within the nanosafety field is currently focused on the use of advanced in vitro models to reduce the gap between in vitro and in vivo studies. Within this context, precision‐cut tissue slices are a unique ex vivo model to investigate nanoparticle impact using live tissue from laboratory animals and even humans. However, several aspects of the basic mechanisms of nanoparticle interactions with tissue have not yet been elucidated. To this end, liver slices are exposed to carboxylated and amino‐modified polystyrene known to have a different impact on cells. As observed in standard cell cultures, amino‐modified polystyrene nanoparticles induce apoptosis, and their impact is affected by the corona forming on their surface in biological fluids. Subsequently, a detailed time‐resolved study of nanoparticle uptake and distribution in the tissue is performed, combining fluorescence imaging and flow cytometry on cells recovered after tissue digestion. As observed in vivo, the Kupffer cells accumulate high nanoparticle amounts and, interestingly, they move within the tissue towards the slice borders. Similar observations are reproduced in liver slices from human tissue. Thus, tissue slices can be used to reproduce ex vivo important features of nanoparticle outcomes in the liver and study nanoparticle impact on real tissue.     

Mobility and solubility of antioxidants and oxygen in glassy polymers. I. Concentration and temperature dependence of antioxidant sorption

Sorption experiments have been conducted at temperatures between 65 and 135°C using five phenolic antioxidants in polycarbonate at different antioxidant concentrations. A model based on the free volume was used to predict the mobility of the additives. In this model, the ratio of the specific volume of a jumping unit to the free volume available in the polymer determines the diffusion behavior of the additives. It was found that the mobility of the antioxidant was predicted accurately using literature and experimental data on the free volume in polycarbonate. Furthermore, the solubility of the antioxidants was predicted very well, based on thermodynamic considerations. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2163–2178, 2003     

Cardiac depression after experimental air embolism in pigs: role of addition of a surface-active agent

OBJECTIVE: Air bubbles entering the coronary artery may have harmful effects on cardiac function. From the physical point of view it is the relatively high surface tension of the blood-air interface which causes bubbles to trap in small vessels. The aim of the present study was to reduce depression of myocardial function from air embolism by lowering the surface tension of air bubbles. METHODS: The effect of using antifoam as a surface-tension-reducing agent on air bubble entrapment and cardiac function was investigated in 6 anesthetized pigs (27 +/- 1 kg) and analyzed using a two-compartment diffusion model. Air bubbles with a diameter of 150 microns were selectively injected into the left anterior descending coronary artery (LADCA) in a carrying fluid in the presence or absence of antifoam. Myocardial systolic segment shortening in the LADCA region (SS-LADCA) was measured by sonomicrometry. Presence of emboli was detected by measuring the amount of reverberation of ultrasound scattered by trapped air bubbles. RESULTS: SS-LADCA transiently decreased after injections of air bubbles in both the absence and presence of antifoam. However, in the presence of antifoam the regional depression recovered to normal sooner, the average depth of the depression was reduced, and bubbles from the embolized area cleared faster. These observations can be explained by a model derived from Laplace's law.     

Function of the hypothalamic-pituitary-adrenal axis in patients with fibromyalgia and low back pain

OBJECTIVE: We suggested fibromyalgia (FM) is a disorder associated with an altered functioning of the stress-response system. This was concluded from hyperreactive pituitary adrenocorticotropic hormone (ACTH) release in response to corticotropin-releasing hormone (CRH) and to insulin induced hypoglycemia in patients with FM. In this study, we tested the validity and specificity of this observation compared to another painful condition, low back pain. METHODS: We recruited 40 patients with primary FM (F:M 36:4), 28 patients (25:3) with chronic noninflammatory low back pain (LBP), and 14 (12:2) healthy, sedentary controls. A standard 100 microg CRH challenge test was performed with measurement of ACTH and cortisol levels at 9 time points. They were also subjected to an overnight dexamethasone suppression test, followed by injection of synthetic ACTH1-24. At 9 AM, the patients divided in 2 groups, received either 0.025 or 0.100 microg ACTH/kg body weight to test for adrenocortical sensitivity. Basal adrenocortical function was assessed mainly by measurement of 24 h urinary excretion of free cortisol. RESULTS: Compared to the controls, the patients with FM displayed a hyperreactive ACTH release in response to CRH challenge (ANOVA interaction effect p = 0.001). The mean ACTH response of the patients with low back pain appeared enhanced also, but to a significantly lesser extent (p = 0.02 at maximum level) than observed in the patients with FM. The cortisol response was the same in the 3 groups. Following dexamethasone intake there were 2 and 4 nonsuppressors in the FM and LBP groups, respectively. The very low and low dose of exogenous ACTH1-24 evoked a dose and time dependent cortisol response, which, however, was not significantly different between the 3 groups. The 24 h urinary free cortisol levels were significantly lower (p = 0.02) than controls in both patient groups; patients with FM also displayed significantly lower (p < 0.05) basal total plasma cortisol than controls. CONCLUSION: The present data validate and substantiate our preliminary evidence for a dysregulation of the HPA axis in patients with FM, marked by mild hypocortisolemia, hyperreactivity of pituitary ACTH release to CRH, and glucocorticoid feedback resistance. Patients with LBP also display hypocortisolemia, but only a tendency toward the disrupted HPA features observed in the patients with FM. We propose that a reduced containment of the stress-response system by corticosteroid hormones is associated with the symptoms of FM.     

A note on eye movements as a measure of emotional reactivity to chromatic elements in Rorschach stimuli.

Measured s reactivity to colored stimuli by recording the eye movements of 24 impulsive and 24 inhibited undergraduates while they were shown rorschach cards. Analysis of eye-movement variables indicating the location of ss' visual inspection on cards ii and iii revealed that inhibited ss, compared with impulsive ss, spent more total time looking at chromatic elements. Inhibited ss tended to look at chromatic areas more frequently during the recording period. In contrast, impulsive ss mentioned color more often in verbal reports. It is suggested that eye movements may serve as a measure of the difficulty an s has in "handling" a particular stimulus element. (PsycINFO Database Record (c) 2010 APA, all rights reserved)