Sintered silicon nitride/nano-silicon carbide materials based on preceramic polymers and ceramic powder

A flexible method is presented, which enables the fabrication of porous as well as dense Si₃N₄/nano-SiC components by using Si₃N₄ powder and a preceramic polymer (polycarbosilazane) as alternative ceramic forming binder. The SiCN polymer benefits consolidation as well as shaping of the green body and partially fills the interstices between the Si₃N₄ particles. Cross-linking of the precursor at 300 °C increases the mechanical stability of the green bodies and facilitates near net shape machining. At first, pyrolysis leads to porous ceramic bodies. Finally, subsequent gas pressure sintering results in dense Si₃N₄/nano-SiC ceramics. Due to the high ceramic yield of the polycarbosilazane binder, the shrinkage during sintering is significantly reduced from 20 to 15 lin.%. Investigations of the sintered ceramics reveal, that the microstructure of the Si₃N₄ ceramic contains approx. 6 vol.% nano-scaled SiC segregations, which are located both at the grain boundaries and as inclusions in the Si₃N₄ grains.     

S-nitrosylation and S-glutathiolation of protein sulfhydryls by S-nitroso glutathione

The modification of reactive protein sulfhydryls by S-nitrosoglutathione and other NO donors has been studied by gel isoelectric focusing. S-nitrosylated, unmodified, and S-glutathiolated protein forms are differentiated by this method. With specific antibodies for the protein of interest, both S-nitrosylation and S-glutathiolation of the protein were analyzed in mixtures obtained as soluble tissue or cell extracts. The effect of S-nitrosoglutathione (GSNO) on purified phosphorylase b, on carbonic anhydrase III in an extract from rat liver, and on H-ras expressed in Escherichia coli was examined. When fresh GSNO reacted with pure phosphorylase b, only S-nitrosylated forms of the protein were observed. Likewise the NO donors, amyl nitrite, spermine NONOate, and diethylamine NONOate, all generated S-nitrosylated phosphorylase b. When crude mixtures of proteins from rat liver (containing carbonic anhydrase III) or from E. coli (containing an overexpressed form of H-ras) were exposed to fresh GSNO, both the S-nitrosylated and the S-glutathiolated forms of the proteins were observed. It is suggested that reactive intermediates from the breakdown of GSNO are responsible for the observed S-glutathiolation. These experiments show that both S-nitrosylated and S-glutathiolated forms of proteins may be generated by the addition of GSNO to mixtures containing proteins with reactive sulfhydryls. These protein modifications may exhibit metabolic consequences independent of the release of nitric oxide.     

The effect of exercise and rehabilitation on anterior-posterior knee displacements after anterior cruciate ligament autograft reconstruction

We studied the effect of rehabilitation strength training and return to activities on anterior-posterior knee displacements after patellar tendon autogenous anterior cruciate ligament reconstruction. A total of 938 measurements were sequentially collected for 142 patients with the KT-2000 arthrometer. Rehabilitation included immediate knee motion and early weightbearing, light sports at 6 months, and competitive sports at 8 months or later. At a minimum of 2 years after surgery, 121 patients (85%) had normal displacements (less than 3 mm of increase at 134 N), 14 (10%) had 3 to 5.5 mm of increase (partial function), and 7 (5%) had more than 5.5 mm of increase (failed). There was no association found between the initial onset of the abnormal displacements in the 21 knees and either the amount of time after surgery or the rehabilitation program. Six of the seven grafts that failed did so in the 1st postoperative year. Serial displacement measurements allow early detection of graft stretching and subsequent modification of rehabilitation or delay in return to strenuous activities. These measurements showed that the rehabilitation program used in this study was not itself injurious and resulted in an acceptable failure rate of 5%.     

The Millimeter Wave Atmospheric Sounder (MAS): a shuttle-basedremote sensing experiment

The Millimeter Wave Atmospheric Sounder (MAS) will be launched in the spring of 1992 as part of the ATLAS 1 (Atmospheric Laboratory for Application and Science) mission. Using passive limb-scanning millimeter-wave radiometry, it will sense the thermal emission produced by ozone at 184 GHz, water vapor at 183 GHz, chlorine monoxide at 204 GHz, and oxygen (for retrieval of temperature and pressure) at 60 GHz. From these observations, concentration profiles of these gases throughout the middle atmosphere will be made. The fundamentals of the measurements, the design of the radiometers, and the approaches used for the data analysis are described     

Is it possible to predict limb viability in complex Gustilo IIIB and IIIC tibial fractures? A comparison of two predictive indices

The patient with severe lower limb trauma presents a management dilemma; whether to amputate primarily or to attempt limb salvage. In recent years, many predictive indices have been published which purport to identify limbs which are non-viable. We retrospectively applied two recently described indices, the Mangled Extremity Severity Score (MESS) and the Limb Salvage Index (LSI), to 54 limbs in 50 patients with either Gustilo IIIB or IIIC complex tibial fractures. There were 22 amputations (40.7 per cent) in the series. The mean MESS score in the limb salvage group was 3.8 (range 2-10), and the mean MESS score in the amputation group was 7.7 (range 4-13) (P < 0.0001). The mean LSI score in the limb salvage group was 3.6 (range 3-8), and the mean LSI score in the amputation group was 6.9 (P < 0.01). However, in the group with MESS scores > 7 (which recommends amputation), there were three limbs which were salvaged with acceptable functional outcome. Similarly, in those with LSI scores > 6 (which recommends amputation), there were seven limbs successfully salvaged. A MESS > 7 offered a greater relative risk of amputation (9.2) than a LSI score > 6 (5.3). We found both indices of use in predicting limb salvage and functional outcome. However, neither is sufficiently accurate to be considered absolutely reliable in clinical practice.     

Joint loading with valgus bracing in patients with varus gonarthrosis

The purpose of this study was to determine whether a brace designed to unload varus degenerative knees actually alters medial compartment loads by decreasing the adduction moment. Eleven patients who had arthrosis confined to the medial compartment were fitted with a valgus brace and tested before and after brace wear with pain and function scoring instruments and by automated gait analysis. The biomechanical data from these patients were compared with those from 11 healthy control subjects. Scores from an analog pain scale decreased 48% with brace wear, and function with activities of daily living increased 79%. Mean adduction moment without the brace measured 4.0 +/- 0.8% body weight times height versus 3.6 +/- 0.8% body weight times height when wearing the brace (10% decrease). The mean adduction moment for control subjects was 3.5 +/- 0.6% body weight times height. Thus, the mean adduction moment decreased from approximately one standard deviation from the normal mean to a value that is similar to the control value. Nine of 11 patients had a decrease in the adduction moment with the brace, five of 11 patients had a reduction higher than 10%, and decreases in this moment were as high as 32%. This study shows that pain, function, and biomechanical knee loading can be altered by a brace designed to unload the medial compartment of the knee.     

Long-term intravesical oxybutynin chloride therapy in children with myelodysplasia

PURPOSE: We evaluated the clinical use of long-term intravesical oxybutynin chloride in the treatment of neurogenic bladder dysfunction in children with myelodysplasia who could not tolerate oral anticholinergics. MATERIALS AND METHODS: We retrospectively reviewed the records of all patients recommended for intravesical oxybutynin chloride therapy. A total of 12 girls and 18 boys 1 to 17 years old was recruited for study. Oxybutynin chloride (5 mg.) was instilled 2 times daily and pretreatment cystograms were compared to followup urodynamic studies. Duration of therapy was 2 to 26 months (mean 13, median 12). RESULTS: Mean total capacity plus or minus standard deviation increased from 209 +/- 103 to 282 +/- 148 ml. (p < 0.01), mean safe capacity increased from 157 +/- 105 to 234 +/- 147 ml. (p < 0.01) and mean age adjusted safe capacity increased from 76 +/- 36 to 115 +/- 62%. Of the 29 patients who were incontinent 3 (10%) achieved continence and 19 (65%) reported a decreased use of sanitary pads. None of the patients had systemic side effects related to intravesical treatment. CONCLUSIONS: We believe that intravesical oxybutynin chloride is a viable treatment option for patients with myelodysplasia in whom oral therapy fails.     

Headache in intracerebral hematomas

OBJECTIVES: We sought to describe the frequency and location of headache in intracerebral hematoma (ICH) and to analyze its clinical and CT predictors by means of multivariate analysis. BACKGROUND: Headache is more common in intracerebral hemorrhage than in ischemic stroke, and its frequency varies with hematoma location, but the pathophysiologic mechanisms of headache associated with ICH are not fully known. METHODS: We examined a cohort of 289 patients with ICH during a 14-month period in a university hospital. Clinical, including the presence and location of headache, and CT features were collected by two neurologists. RESULTS: One hundred and sixty-five (57%) patients with ICH had a headache at the onset of their stroke. Headache was more common in cerebellar and lobar hemorrhages than in deep ones (thalamic, caudate, capsuloputaminal, brainstem). Headache was also more common in women, patients younger than 70 years, those who vomited, and those with meningeal signs, a Glasgow Coma Scale score < 10, a hematoma volume > 10 ml or CT evidence of intraventricular or subarachnoid bleeding, moderate to severe hydrocephalus, or transtentorial herniation or midline shift. In multiple logistic regression analysis, only meningeal signs (odds ratio [OR] = 2.3), cerebellar or lobar location (OR = 2.1), transtentorial herniation (OR = 1.8), and female gender (OR = 1.6) were significant predictors of headache at the onset of ICH. CONCLUSIONS: Hematoma location, meningeal signs, and gender are more predictive of headache than hematoma volume, suggesting that headache is more often related to the activation of an anatomically distributed system in susceptible individuals and to subarachnoid bleeding than to intracranial hypertension.