Biomechanical characterization of needle piercing into peripheral nervous tissue

Several neural interfaces have been developed to control neuroprostheses and hybrid bionic systems. Among them, intraneural electrodes are very promising because they represent an interesting trade-off between the needs for high selectivity and for reduced invasiveness. However, in most of the cases, no particular attention has been devoted so far to the design of these systems starting from the mechanical properties of the system to be interfaced. The aim of this paper was to study and characterize in a quantitative way the piercing of peripheral nervous tissue in order to gather useful information to design intraneural interfaces able to reduce (as much as possible) the damages provoked by this task. In particular, attention has been paid to determine the values of force and pressure to carry out the piercing task in different velocity conditions. From the experimental data it was possible to characterize indirectly the tissue sinking under the needle tip. For each experimental velocity (ranging from 1 to 2000 mm/min) a threshold, under which the tissue cannot be pierced, has been calculated. The force magnitude required for piercing was shown to be in the range 0.3-25 mN for the different velocities. Moreover, differences between piercing carried out at very low velocity (multi-piercing) and at low velocity (mono-piercing) have been characterized and correlated with the physical characteristics of the nervous tissue. Experimental data have been integrated with a theoretical analysis of the neural interfaces piercing structures. The problem of buckling, representing for these structures the main cause of tissue piercing impossibility, has been analyzed. The nonlinear theoretical model allows to compare different needle geometries and materials with regard to piercing possibility at different velocities. Moreover, an optimization of piercing elements geometry with regard to amount of used material and space has been provided.     

The contribution of Rayleigh waves to the acoustic field arising from internal-defect growth

Karpenko Physicomechanics Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 2, pp. 12–19, March–April, 1993.     

Simultaneous analysis of production and investment performance of Canadian life and health insurance companies using data envelopment analysis

A new data envelopment analysis (DEA) model is created to provide valuable managerial insights when assessing the dual impacts of operating and business strategies for Canadian life and health (L&H) insurance industry. This problem-oriented new DEA model can simultaneously assess the production and investment performance of insurers, differing from classical DEA models appropriate for independent performance evaluation. The mathematical solution is provided for this new model and the results show that the Canadian L&H insurance companies operated very efficiently for the examined 3-year period (1996–1998). In addition, no scale efficiency in the Canadian L&H insurance industry is found in this study.     

A dysfunctional desmin mutation in a patient with severe generalized myopathy

Mice lacking desmin produce muscle fibers with Z disks and normal sarcomeric organization. However, the muscles are mechanically fragile and degenerate upon repeated contractions. We report here a human patient with severe generalized myopathy and aberrant intrasarcoplasmic accumulation of desmin intermediate filaments. Muscle tissue from this patient lacks the wild-type desmin allele and has a desmin gene mutation encoding a 7-aa deletion within the coiled-coil segment of the protein. We show that recombinant desmin harboring this deletion cannot form proper desmin intermediate filament networks in cultured cells, nor is it able to assemble into 10-nm filaments in vitro. These findings provide direct evidence that a mutation in desmin can cause human myopathies.     

Utilization of magnetic resonance imaging in autopsy planning with specimen preservation for thoraco-omphalopagus symmetricus conjoined twins

Conjoined twinning is a rare obstetric event that has fascinated physicians and laypersons alike for centuries. When this event occurs, early diagnosis, close prenatal management, and the proper route of delivery will assure the best possible outcome for mother and affected infants. Magnetic resonance imaging (MRI) is used both as an ancillary technique to the sonography for the antepartum diagnosis and in the preoperative planning for the surgical separation of conjoined twins. This report describes the MRI findings in conjoined twins of the thoraco-omphalopagus symmetricus type, a condition incompatible with extrauterine life. The twins were delivered at 21 weeks gestation. The MRI was used to evaluate the anatomic nature of the internal anomalies. These findings were then used to develop an autopsy approach plan that preserved the external phenotype. After dissection, the specimen was preserved by using polyethylene glycol and ultimately prepared for use as a teaching specimen.     

Oxidative stress and lipid abnormalities in renal transplant recipients with or without chronic rejection

BACKGROUND: The histological picture of chronic rejection with endothelial lesions and vascular hyperplasia resembles the early arteriosclerotic lesions. As increasing evidence suggests a role for oxidative stress in arteriosclerosis, we examined whether chronic rejection in renal transplant recipients was associated with increased oxidative stress markers. METHODS: We investigated lipid metabolism and oxidative stress in 77 renal transplant recipients. Group I patients (n=34; 48+/-2 years old, 12 women, 22 men) had no clinical or histological signs of chronic rejection, whereas group II patients (n=43; 47+/-3 years old, 15 women, 28 men) had histologically proven chronic rejection. All patients were treated with cyclosporine and steroids. Lipid metabolism was evaluated by determining total cholesterol, triglycerides, high-density lipoprotein cholesterol, apolipoproteins AI and B, and lipoprotein (a). Oxidative stress was evaluated by determining: (i) the end product of lipid peroxidation, malonyldialdehyde (MDA), and erythrocyte polyunsaturated fatty acids; (ii) the nonenzymatic antioxidant system: erythrocyte alpha-tocopherol and glutathione; and (iii) the enzymatic antioxidant system: erythrocyte superoxide dismutase and plasma glutathione peroxidase. Results were compared with those of a control group (38 healthy volunteers). RESULTS: Compared with controls, renal transplant recipients had significantly increased total cholesterol, triglyceride, and apolipoprotein B levels; they also had, in association with these lipid abnormalities, a significant increase in MDA and a significant decrease in erythrocyte polyunsaturated fatty acids, as well as a significant decrease in enzymatic and nonenzymatic antioxidant defense mechanisms. In contrast to lipid disturbances, where no difference was observed between groups I and II, markers of oxidative stress were significantly higher in group II compared with group I (MDA: 1.87+/-0.43 and 1.62+/-0.31 nmol/ml, respectively, P<0.05). The red blood cell antioxidative defense mechanisms were significantly decreased in group II compared with controls (erythrocyte alpha-tocopherol: 0.61+/-0.38 and 1.08+/-0.31 mg/L, respectively, P<0.01; superoxide dismutase: 1.08+/-0.2 and 1.32+/-0.31 U/mg Hb, respectively, P<0.01). CONCLUSION: Our data show that oxidative stress with a decrease in antioxidant defenses is associated with kidney transplantation. In addition, oxidative stress markers are particularly increased in transplant recipients with chronic rejection, which suggests that oxidative stress may participate in the development and/or progression of vascular lesions observed in these patients.