A quantitative framework for analyzing epicardial activation patterns during ventricular fibrillation

We have developed a method for quantifying the complexity of activation patterns observed during ventricular fibrillation (VF) that is based on our previously reported methodology for decomposing epicardial mapping data into a set of isolated wavefronts. One-half second datasets are acquired from a 21 x 24 array of unipolar electrodes (1 mm spacing), and the wavefronts are isolated. A correlation technique is used to compute the similarity between all possible pairs of the isolated wavefronts. From these data, the wavefronts are sorted into clusters, each of which represents a recurring wavefront morphology. We define multiplicity (M) as the number of clusters needed to account for 90% of the total activations in the VF episode. M measures the complexity of the rhythm. In repetitive patterns (e.g., sinus rhythm), M = 1, indicating that the same morphology repeatedly activates the mapped region. Typically, in VF, M > 1, with larger numbers representing more complex, disorganized patterns. As an example, we computed M at 5, 10, 15, and 20 sec after electrical induction of VF in six pigs. M decreased significantly (p < 0.001), suggesting increasing organization during this period.     

Influence of water on crack propagation in poly methyl methacrylate: craze stress and craze fibril lifetime

Polymethylmethacrylate (PMMA) is often used as a material in submarine applications. Therefore, the fracture properties of dry and wet PMMA in water and/or under hydrostatic pressure are of great importance. Previous work has shown that water strongly increases fracture toughness, and leads to a complicated figure of K ₁ versus crack speed, and stable-unstable crack and craze propagation, depending on external loading rate. In this study, compact tension specimens immersed in water have been tested on a tensile machine and crack tips have been observed during propagation by means of optical interferometry. Fracture stress intensity factors, and craze-zone shapes and sizes have been measured as a function of loading time and crack speed in water. The results have been rationalized in terms of craze fibril stress versus fibril extraction velocity and craze fibril lifetime versus fibril stress. Both may be expressed in terms of a stress-activated process governing fracture. It is found that, when expressed in these terms, the complicated influence of the external loading rate becomes irrelevant for describing local intrinsic material properties and K ₁ values. It is shown that there is no contradiction between the fact that water increases the fracture toughness, and the fact that the microscopic craze stress and craze fibril lifetime decrease at the crack tip.     

Decalcified, lyophilized, sterile heterotopic porcine ossicular xenografts. Experimental evaluation in the guinea pig

Using the guinea pig middle ear model, we assessed decalcified, lyophylized, sterile heterotopic porcine ossicular xeno-implants based on a histology (optic and electron scan microscope) and immunologic (immunofluorscence) methods. Implants were placed in the middle ear and others in the dorsal subcutaneous area. Allo-implants were compared as controls. Implants were placed in the middle ear in 54 animals and skin implants in 14. Under the influence of BMP, the implant ossified in all cases in the middle ear. Intense immune recruitment was not observed. Inversely, there was a mononuclear infiltration reaction to the skin implants with formation of a fibrous capsule, immunoglobulin and complement influx and consequently sequestration. The allo-implants were partially reossified. These findings confirm the value of decalcification with hydrochloric acid for BMP induction, independent of species and the failure of attempted immune despecification. Implant outcome is not dependent on its antigen load, which is high compared with its weight, but on the site of implantation. The middle ear appears to be a privileged site of implantation.     

Chronic ethanol inhibits inositol metabolism in specific brain regions

Many neurotransmitters and hormones in the nervous system transmit signals through receptors coupled to the poly-phosphoinositide (PI) signaling pathway. In this study, an in vivo protocol with [3H]inositol was used to examine the effect of chronic ethanol administration on inositol metabolism and poly-PI turnover in the cerebral cortex, hippocampus, and cerebellum of mouse brain. C57BL/6 mice were given a nutritionally complete liquid diet containing either ethanol (5%, w/v) or isocaloric sucrose for 2 months. Mice were injected intracerebrally with [3H]inositol; after 16 or 24 hr, they were injected intraperitoneally with lithium (8 mEq/kg body weight) to inhibit the inositol monophosphatase (IP1) activity. All mice were decapitated 4 hr after lithium injection. Labeled inositol phospholipids accounted for 16 to 23% of total labeled inositol in different regions of control mouse brain, and the percentages in the hippocampus were consistently higher than the cerebral cortex and cerebellum. In control mice, the percentages of labeled IP1 after a 4-hr lithium treatment were 11.5%, 9.9%, and 3.7% for cerebral cortex, hippocampus, and cerebellum, respectively. Chronic ethanol feeding resulted in a significant (p < 0.05) decrease in the percent of labeled IP1 and inositol phospholipids, and this effect was observed in the cerebral cortex and, to a lesser extent, hippocampus but not cerebellum. When ratios of labeled IP1 were expressed against labeled inositol phospholipids as an index of the poly-PI turnover activity, significant decreases in IP/lipid ratios were observed in the cerebral cortex, but not the hippocampus or cerebellum. Although mice killed 24 + 4 hr after the last ethanol feeding would have experienced an 8-hr period of ethanol withdrawal, compared with the 16 + 4-hr group, no differences in IP/lipid ratios were observed between the two time groups. These results illustrate regional differences in the effect of chronic ethanol on inositol metabolism in the brain, but no difference in poly-PI turnover in brain due to ethanol withdrawal.     

Ligand-induced translocation of epidermal growth factor receptor to the nucleus of NR6/HER fibroblasts is serum dependent

Ligand-induced translocation of epidermal growth factor receptors (EGF-R) to the nucleus of NR6/HER fibroblasts has been studied by immunoelectron microscopy. Following treatment of NR6/HER cells with epidermal growth factor (EGF) for 1 h, there was a decrease in EGF-R labeling at the plasma membrane and a corresponding increase in EGF-R in the nucleus. This was preceded by a rapid and sustained increase in nuclear phosphotyrosine content, detectable within 2 min of EGF treatment. EGF-R translocation into the nucleus was completely prevented by 18 h serum starvation prior to treatment with EGF. These results indicate that translocation of EGF-R to the nucleus is a controlled process and they suggest that EGF-R may directly influence nuclear function.     

Effects of dietary manipulations and glucose infusion on glucagon response during exercise in rats

OBJECTIVE: To describe our initial experience with a computerized telecommunication system, termed the interactive voice-response system, to record resident performance of laparoscopic surgery. METHODS: After completing a laparoscopic procedure, the surgeon and resident telephone a toll-free number independently and respond to three prerecorded statements using a Likert scale of 1 to 5. The caller then is asked to describe the resident's response to critical incidents or elements of surprise that arose during the surgery. The ratings and verbal comments are compiled, transcribed, and forwarded to the respective resident. The resident (and program director) can hear the verbal comments by entering a four-digit code. RESULTS: Between May 1, 1995, and May 31, 1996, 430 cases were reported by 11 surgeons and 16 residents using the interactive voice-response system. One hundred ninety-five (45%) procedures were entered by both the resident and surgeon. A survey undertaken during the introductory phase of the project revealed that five of the seven residents exposed to the system found that it provided useful feedback and preferred the system to traditional in-service reporting methods. In addition, five residents thought that the system complemented the personal feedback they received in the operating room. CONCLUSION: The system has been accepted by both residents and surgeons and has addressed the important components of resident in-training evaluation, namely, evaluation on a case-by-case basis, timely feedback, and self-assessment of resident performance.     

Electrostatic and non-electrostatic contributions to the binding free energies of anthracycline antibiotics to DNA

The knowledge about molecular factors driving simple ligand-DNA interactions is still limited. The aim of the present study was to investigate the electrostatic and non-electrostatic contributions to the binding free energies of anthracycline compounds with DNA. Theoretical calculations based on continuum methods (Poisson-Boltzmann and solvent accessible surface area) were performed to estimate the binding free energies of five selected anthracycline ligands (daunomycin, adriamycin, 9-deoxyadriamycin, hydroxyrubicin, and adriamycinone) to DNA. The free energy calculations also took into account the conformational change that DNA undergoes upon ligand binding. This conformational change appeared to be very important for estimating absolute free energies of binding. Our studies revealed that the absolute values of all computed contributions to the binding free energy were quite large compared to the total free energy of binding. However, the sum of these large positive and negative values produced a small negative value of the free energy around -10 kcal/mol. This value is in good agreement with experimental data. Experimental values for relative binding free energies were also reproduced for charged ligands by our calculations. Together, it was found that the driving force for ligand-DNA complex formation is the non-polar interaction between the ligand and DNA even if the ligand is positively charged.