A Computational Tool for the Microstructure Optimization of a Polymeric Heart Valve Prosthesis.

Styrene-based block copolymers are promising materials for the development of a polymeric heart valve prosthesis (PHV), and the mechanical properties of these polymers can be tuned via the manufacturing process, orienting the cylindrical domains to achieve material anisotropy. The aim of this work is the development of a computational tool for the optimization of the material microstructure in a new PHV intended for aortic valve replacement to enhance the mechanical performance of the device. An iterative procedure was implemented to orient the cylinders along the maximum principal stress direction of the leaflet. A numerical model of the leaflet was developed, and the polymer mechanical behavior was described by a hyperelastic anisotropic constitutive law. A custom routine was implemented to align the cylinders with the maximum principal stress direction in the leaflet for each iteration. The study was focused on valve closure, since during this phase the fibrous structure of the leaflets must bear the greatest load. The optimal microstructure obtained by our procedure is characterized by mainly circumferential orientation of the cylinders within the valve leaflet. An increase in the radial strain and a decrease in the circumferential strain due to the microstructure optimization were observed. Also, a decrease in the maximum value of the strain energy density was found in the case of optimized orientation; since the strain energy density is a widely used criterion to predict elastomer's lifetime, this result suggests a possible increase of the device durability if the polymer microstructure is optimized. The present method represents a valuable tool for the design of a new anisotropic PHV, allowing the investigation of different designs, materials, and loading conditions.

Structural changes of block copolymers with bi-modal orientation under fast cyclical stretching as observed by synchrotron SAXS.

Load-bearing tissues are composite materials that depend strongly on anisotropic fibre arrangement to maximise performance. One such tissue is the heart valve, with orthogonally arranged fibrosa and ventricularis layers. Their function is to maintain mechanical stress while being resilient. It is postulated that while one layer bears the applied stress, the orthogonal layer helps to regenerate the microstructure when the load is released. The present paper describes changes in the microstructure of a block copolymer with cylindrical morphology, having a bio-inspired microstructure of anisotropic orthogonally oriented layers, under uniaxial strain. To allow structural observations during fast deformation, equivalent to the real heart valve operation, we used a synchrotron X-ray source and recorded 2D SAXS patterns in only 1 ms per frame. The deformation behaviour of the composite microstructure has been reported for two arrangements of the cylinders in skin and core layers. The behaviour is very different to that observed either for uniaxially oriented or isotropic samples. Deformation is far from being affine. Cylinders aligned in the direction of stretch show fragmentation, but complete recovery of the spacing between cylinders on removal of the load. Those oriented perpendicular to the direction of stretch incline at an angle of approximately 25° to their original direction during load.

[Vibrio cholera (Vibrio cholerae non-01) isolated in Poland from the Bug river]. / Przecinkowce cholery (Vibrio cholerae non-01) izolowane w Polsce z wody rzeki Bug.

Non-01 cholera vibrios for the first time has been isolated from freshwater in Poland. In October 1994 during bacteriological examination of Bug water by a two-step enrichment method in alkaline peptone water at pH 8.6 and TCBS. Repeated examination in November, December and January in the same and other locations among the polish-ukrainian borderline revealed persistence of V. cholerae in the river; 22 strains were isolated. All 22 strains were identical to V. cholerae E1 Tor 01 Ogawa reference strain except to antigens 0. The strains isolated from water were no agglutinable by standard 01 serum neither by 0139 serum. Determination of their antigens 0 is under investigations. They might be pathogenic for people as it could be judged by their high resistance to bile, proteolytic and haemolytic activity. No cholera-like cases were notified on the polish side of the river.

[Further research into the formation of the "vitality and adequacy of emotion-emotional blunting" relationship in paranoid schizophrenia]. / Dalsze badania nad ksztaltowaniem sie proporcji: "zywosc i adekwatnosc emocji-stepienie emocjonalne" w schizofrenii paranoidalnej.

A sample of 100 paranoidal schizophrenic patients were assessed. Scales of "vitality and the adequacy of emotion" and "emotional blunting" which are described in a separate paper were used. At the beginning attention was focused on the fact that several synonimous terms are used to describe the blunting of emotion (flatness of affect, blunted or inappropriate affect, presence of affect as opposed to flatness). The results indicate that in only a very few cases the intensity of both studied qualities was negligible, however in the majority of the cases it appeared that the quality of "vitality" and its opposite is present. In 62 patients the emotional blunting was moderate. Emotional vitality in these cases remained in the wide range from moderate to significant. Both factors may be considered to be additional factors on the basis of the size and type of correlation. The coefficient of both Scales is expressed by r = -0.77. The correlation between the studied proportion and the syntonic-autistic proportion is expressed by r = 0.69. The cases of emotional blunting which occurred at different levels of intensity were generally accompanied by relative vitality and adequate emotional reaction. The formation of the studied proportion and in particular the high correlation coefficient between this proportion and the syntonic-autistic proportion suggests that autistic schizophrenia and syntonic schizophrenia form two basic subgroups of paranoidal schizophrenia.

[Post-traumatic posterior cranial fossa hematomas from material of the Department of Neurosurgery, Silesian Medical Academy in Katowice]. / Pourazowe krwiaki tylnego dolu czaszkowego w materiale Kliniki Neurochirurgii SL. AM w Katowicach.

The location of posttraumatic haematomas in the posterior cranial fossa is rare and the correct diagnosis was difficult before the advent of CT. In the years 1976-1989 in the group of 2450 cases of craniocerebellar injuries treated in the Department of Neurosurgery, Silesian Medical Academy 24 patients had posterior fossa haematomas, but only one of them (out of 550 cases of injuries) was diagnosed without CT. In 20 cases surgical treatment was carried out with good and satisfactory results in 16 cases (80%). The authors stress the importance of early CT and surgical intervention.

Aspirin, heparin, or both to treat acute unstable angina.

We tested the usefulness of aspirin (325 mg twice daily), heparin (1000 units per hour by intravenous infusion), and a combination of the two in the early management of acute unstable angina pectoris in a double-blind, randomized, placebo-controlled trial involving 479 patients. The patients entered the study as soon as possible after hospital admission (at a mean [+/- SD] of 7.9 +/- 8.0 hours after the last episode of pain), and the study was ended after 6 +/- 3 days, when definitive therapy had been selected. Major end points--refractory angina, myocardial infarction, and death--occurred in 23, 12, and 1.7 percent of the 118 patients receiving placebo, respectively. Heparin was associated with a decrease in the occurrence of refractory angina (P = 0.002). The incidence of myocardial infarction was significantly reduced in the groups receiving aspirin (3 percent; P = 0.01), heparin (0.8 percent; P less than 0.001), and aspirin plus heparin (1.6 percent, P = 0.003), and no deaths occurred in these groups. There were too few deaths overall to permit evaluation of the effect of treatment on this end point. The combination of aspirin and heparin had no greater protective effect than heparin alone but was associated with slightly more serious bleeding (3.3 vs. 1.7 percent). We conclude that in the acute phase of unstable angina, either aspirin or heparin treatment is associated with a reduced incidence of myocardial infarction, and there is a trend favoring heparin over aspirin. Heparin treatment is also associated with a reduced incidence of refractory angina.

[Brain glioma complicated by subdural hematoma]. / Powiklanie glejaka mózgu krwiakiem podtwardówkowym.

A case is reported in which chronic subdural haematoma developed in association with a glioma of the left temporal lobe. The stroke-like onset of symptoms one month before surgical intervention, encapsulated liquid subdural haematoma, necrotic cerebral cortex over the tumour and easily bleeding peripheral parts of the tumour suggested a primary haemorrhage into the peripheral part of the tumour followed by penetration of the haematoma into the subdural space.