The yielding, plastic flow, and fracture behavior of ultra-high molecular weight polyethylene used in total joint replacements

The yielding, plastic flow, and fracture behavior of UHMWPE plays an important role in wear and failure mechanisms of total joint replacement components. The primary objective of this study was to compare the yielding, plastic flow, and fracture behavior of two implantable grades of UHMWPE (GUR 1120 vs 4150 HP). The first part of this work explored the hypothesis that up to the polymer yield point, the monotonic loading behavior of UHMWPE displays similar true stress strain behavior in tension and compression. Uniaxial tension and compression tests were conducted to compare the equivalent true stress vs strain response of UHMWPE up to 0.12 true strain. During monotonic loading, the equivalent true stress strain behavior was similar in tension and compression up to the yield point. However, investigation of the unloading behavior and permanent plastic deformations showed that classical deviatoric rate independent plasticity theory may dramatically overpredict the permanent strains in UHMWPE. A secondary goal of this study was to determine the ultimate true stress and strain for UHMWPE and to characterize the fracture surfaces after failure. Using a fracture mechanics approach, the critical flaw sizes were used in combination with the true ultimate stresses to predict the fracture toughness of the two resins. A custom video-based strain measurement system was developed and validated to characterize the true stress-strain behavior up to failure and to verify the accuracy of the incompressibility assumption in calculating the true stress-strains up to failure. In a detailed uncertainty analysis, theoretical expressions were derived for the relative uncertainty in digital video-based estimates of nominal strain, true strain, homogeneous stress, and true stress. Although the yielding behavior of the two UHMWPE resins was similar, the hardening and plastic flow behavior clearly discriminated between the GUR 1120 and 4150 HP. A statistically significant difference between the fracture toughness of the two resins was also evident. The long-term goal of this research is to provide detailed true stress strain data for UHMWPE under uniaxial tension and compression for future numerical simulations and comparison with more complex multiaxial loading conditions.     

The efficacy of oral appliances in the treatment of persistent sleep apnea after uvulopalatopharyngoplasty

Twenty-four patients who failed uvulopalatopharyngoplasty (UPPP) for obstructive sleep apnea (OSA) had an adjustable oral (Herbst) appliance made to treat the persistent apnea. Six patients discontinued the device prior to sleep evaluation. Eighteen patients had polysomnographic evaluations at baseline, post-UPPP, and with the Herbst appliance in place. The apnea-hypopnea index baseline (AHI) and arterial oxygen saturation (SaO2) nadir were 42.3+/-6.1 and 83.6+/-1.8%, respectively. There was no significant change in either parameter with surgery. With the oral appliance, the AHI fell to 15.3+/-4.4 (p < or = 0.01) and the SaO2 nadir increased to 87.9+/-1.2% (p < or = 0.05). Ten of the patients had control of the OSA with the Herbst appliance with a fall in the AHI to < 10. There were, in addition, two partial responders as defined by an AHI of <20 and a >50% fall in AHI compared with baseline and post-UPPP values. All but one of the responders and partial responders had complete resolution of subjective symptoms of daytime sleepiness with the appliance. An adjustable oral appliance appears to be an effective mode of therapy to control OSA after an unsuccessful UPPP.     

New Arabidopsis cue mutants suggest a close connection between plastid- and phytochrome regulation of nuclear gene expression

We searched for new components that are involved in the positive regulation of nuclear gene expression by light by extending a screen for Arabidopsis cue (chlorophyll a/b-binding [CAB] protein-underexpressed) mutants (H.-M. Li, K. Culligan, R.A. Dixon, J. Chory [1995] Plant Cell 7: 1599-1610). cue mutants display reduced expression of the CAB3 gene, which encodes light-harvesting chlorophyll protein, the main chloroplast antenna. The new mutants can be divided into (a) phytochrome-deficient mutants (hy1 and phyB), (b) virescent or delayed-greening mutants (cue3, cue6, and cue8), and (c) uniformly pale mutants (cue4 and cue9). For each of the mutants, the reduction in CAB expression correlates with the visible phenotype, defective chloroplast development, and reduced abundance of the light-harvesting chlorophyll protein. Levels of protochlorophyllide oxidoreductase (POR) were reduced to varying degrees in etiolated mutant seedlings. In the dark, whereas the virescent mutants displayed reduced CAB expression and the lowest levels of POR protein, the other mutants expressed CAB and accumulated POR at near wild-type levels. All of the mutants, with the exception of cue6, were compromised in their ability to derepress CAB expression in response to phytochrome activation. Based on these results, we propose that the previously postulated plastid-derived signal is closely involved in the pathway through which phytochrome regulates the expression of nuclear genes encoding plastid proteins.     

A histomorphological study in age related changes in the elastic fiber system of the basilar artery

The aim of the study was to quantify the distribution of elastic fibers within the wall of the basilar artery. Three age groups were studied: 1) 0-1 yr.; 2) 20-50 yr. 3) > 50 yr. A histomorphometrical study was undertaken using an estimation of the linear density of the components of the fibrous elastic tissue system: the full length in the proximal and distal segments of the basilar artery was evaluated. Our results showed that: The elastic tissue of the basilar artery is not evenly distributed throughout the tunica media. Compared to the 0 to 1-year age group, mature elastic, elauninic and oxytalan fibers decreased with age. In all age groups the linear density of the mature elastic fibers was more evident in the proximal than in the distal segment of the artery.     

Tuberculosis of the larynx

Laryngeal tuberculosis was diagnosed in two men, a 73-year-old man Dutch by birth and a 40-year-old one Turkish by birth. In the former patient it was probably primary tuberculosis, in the latter secondary (he had lung tuberculosis as well). The clinical picture was highly suggestive of laryngeal carcinoma in both patients. They both recovered with chemotherapy. Laryngeal tuberculosis may mimic laryngeal carcinoma. The diagnosis is based on Ziehl-Neelsen staining, culture and polymerase chain reaction (PCR) on Mycobacterium tuberculosis. Because laryngeal tuberculosis is highly infectious, the patient has to be nursed in isolation and people in his or her environment have to be screened. The response of laryngeal tuberculosis to chemotherapy is good.     

Exogenous norepinephrine induces an enhanced microproteinuric response in microalbuminuric insulin-dependent diabetes mellitus

Exogenous norepinephrine (NE) increases intraglomerular pressure in animal experiments, but it is unknown whether NE induces a microproteinuric response in humans. Moreover, it has not been studied whether possible microproteinuric and renal hemodynamic changes induced by NE are altered in insulin-dependent diabetes mellitus (IDDM) complicated by microalbuminuria. Therefore, the microproteinuric and renal hemodynamic responses to exogenous NE infusions were measured in eight matched normoalbuminuric IDDM patients (group D1), microalbuminuric IDDM patients (group D2), and control subjects (group C). As anticipated, mean arterial pressure (MAP)-NE dose-response curves were significantly shifted leftward in groups D1 and D2 compared with group C (P < 0.05), indicating a higher systemic NE responsiveness in IDDM. On separate days, NE or placebo was infused at individually determined NE threshold doses (T; delta MAP = 0 mmHg), 20% pressor doses (20% P; delta MAP = 4 mmHg), and pressor doses (P; delta MAP = 20 mmHg), with measurement of urinary albumin (UalbV), IgG excretion (UIgGV), GFR (by 125I-iothalamate), and effective renal plasma flow (by 131I-hippurate). At NE pressor dose, UalbV and UIgGV rose in all groups (P < 0.05 to 0.01), whereas urinary beta 2-microglobulin was unchanged. The increases in UalbV and UIgGV were more pronounced in the microalbuminuric group than in the other groups (P < 0.05). An NE dose-dependent fall in effective renal plasma flow and rise in filtration fraction were found in all groups (P < 0.05 to 0.001 for all), whereas GFR did not change significantly. The renal hemodynamic dose-response relationship was similar in the groups. In conclusion, exogenous NE acutely promotes glomerular protein leakage, and it is plausible that intraglomerular NE effects contribute to this phenomenon. The microproteinuric response is enhanced in microalbuminuric IDDM despite unaltered renal hemodynamic responsiveness, which may reflect a specific NE response or a general effect of vasopressor stimuli to promote glomerular protein leakage in patients with a preexistent defect in glomerular permselectivity.     

Effect of the administration of fish oil by gavage on activities of antioxidant enzymes of rat lymphoid organs

Expression of retinoblastoma (Rb) protein was immunohistochemically examined in laryngeal squamous cell neoplasias from 72 patients. Staining patterns were considered with reference to such prognostic factors as patient's age, histologic grade, tumour size and lymph node status, and 5-year survival rate. Rb protein negativity, either partial or complete, was noted in 28.8% of cases and was associated with a significantly lower 5-year survival rate, as well as with a higher likelihood of lymph node metastasis. This suggests that Rb alteration may be a prognostic indicator in patients with laryngeal carcinoma.     

Prognostic value of plasma fibrinogen concentration in patients with unstable angina and non-Q-wave myocardial infarction (TIMI IIIB Trial)

The records of 60 patients with gallbladder carcinoma (GBC) operatively treated between 1966 and 1993 at Belen Hospital, Trujillo, Perú, were retrospectively reviewed. The ratio of men to women was 1:7.5 and the average of age was 61 years. The accuracy of ultrasonography and oral cholecystograms for the specific diagnosis was 21% and 0% respectively. The surgical procedures employed were simple cholecystectomy (n = 56), right hepatectomy (n = 2). Whipple operation (n = 1) and extended cholecystectomy (n = 1), and our resectability rate for GBC is currently 50%. Simple cholecystectomy was a potentially curative surgical procedure in patients with in situ cancer (stage O) and early GBC (stage 1). In hospital mortality was 11.6% and 5-year survival rate for the total series was 15%. Gallstones were present in 95% of patients and most tumors (58%) had grown by diffuse infiltration or were associated with empyema (38%). Tumor stage, depth of invasion, tumor grade histologic type were all predictive of patient outcome. This report reinforces the difficulty in diagnosis and the poor prognosis for patients with GBC. We hold the view that more radical approaches for invasive cancers will enhance the operative results.     

Expression of multiple apoptosis-regulatory genes in human breast cancer cell lines and primary tumors

Low molecular mass polypeptides (LMP) 2 and LMP7 and transporter associated with antigen processing (TAP) subunits TAP1 and TAP2 play a crucial role in antigen processing and cell surface expression of HLA class I molecules. Since monoclonal antibodies (mAb) to these molecules will facilitate the analysis of their expression, structure and function in normal and transformed cells, in the present study we have developed these reagents. Specifically anti-LMP2 and LMP7 mAb were generated from BALB/c mice immunized with specific peptides, and anti-TAP1 and TAP2 mAb from BALB/c mice immunized with respective recombinant proteins. mAb VF101-39F7 and VF101-39G5 were shown to be specific for LMP2, mAb VF103-5D5 and VF103-8C2 for LMP7, mAb VF108-1B3 and VF108-12D6 for TAP1 and mAb VF118-1E4 and VF118-2C5 for TAP2, since they reacted specifically with the corresponding immunogens in ELISA and with the corresponding LMP and TAP subunits when tested in Western blotting with human lymphoid cell extracts. Furthermore, the mAb immunoprecipitated components with the characteristic electrophoretic mobility from lymphoid cells. Both anti-LMP and anti-TAP mAb stained keratinocytes and infiltrating lymphocytes in frozen and formalin-fixed, paraffin embedded sections of normal skin in indirect immunoperoxidase reactions. Furthermore, all the mAb except mAb VF103-5D5 stained the cytoplasm of lymphoid cells in an intracytoplasmic staining reaction. The specificity and reactivity pattern of the mAb we have characterized indicate that they will be valuable reagents to analyze the cellular expression and tissue distribution of LMP and TAP subunits.