The evolution and development of the urinary catheter

The urinary catheter is one of the most frequently used medical devices and has a long and intriguing history of development. This paper describes the catheter from its simple beginnings through the subtle but important changes it has undergone paralleling the advances in plastics technology witnessed this century. The changes have not been without controversy and the recent association of catheters with tissue toxicity, which has forced the implementation of strict guidelines for their manufacture and use, is described.     

Memory complaints in epilepsy: correlations with cognitive performance and neuroticism

Experimental results are presented to show that the adhesion force is the single most important limiting factor in high-resolution atomic force microscopy of DNA in air, prepared by the cytochrome-C-assisted spreading method. It is also shown that humidity plays a minor role in the control of probe force. Using a pure carbon film as the substrate to clean the AFM tip prior to imaging, it is demonstrated that 4-6 nm resolution on DNA can be routinely obtained by the atomic force microscope with commercial Si3N4 pyramid cantilevers. We also show that in organic solvents a resolution of up to 3 nm can be obtained under optimal conditions.     

Impact and penetration by L/D ≤ 1 projectiles

Calculations of steel target penetration by L/D ≤ 1 tungsten and tungsten alloy projectiles have been extended to L/D = 1/32 over the velocity range 1.5 to 5 km/s. The ratio of crater to projectile diameter tends to 1 as L/D decreases over this entire velocity range. For impact velocities of 1.5 and 3 km/s, penetration depth normalized by projectile length, P/L, increases with decreasing projectile L/D up to a maximum value and then decreases for still lower L/D. Experiments at impact velocities of 2 and 3 km/s confirm these results. For 5 km/s impact velocity, the calculations show P/L increasing with decreasing projectile L/D over the entire range 1/32 ≤ L/D ≤ 1. The projectile L/D for which the maximum P/L occurs appears to depend on the impact velocity. P/L generally scales with impact velocity as P/L v^f(L/D) where f(L/D) ranges from 0 for a long rod to, we believe, 2 in the limit as projectile L/D approaches zero. The calculations show for 1/8 ≤ L/D ≤ 1/2, P/L v^0.9; for L/D = 1/16, P/L v^1.5; and for L/D = 1/32, the new results give P/L v^1.9.     

Competitive inhibition by procaine of carbachol-induced stimulus-secretion coupling in rat pancreatic acini

1. Procaine (0.03-10 mM) inhibited carbachol (CCh)-induced amylase release from rat isolated pancreatic acini in a competitive manner. Kinetic analysis of the relation between CCh concentrations and the amount of amylase released in the presence of various procaine concentrations indicated that procaine caused competitive inhibition with the affinity constant (pA2) value of 5.00 +/- 0.08. 2. Receptor binding assay confirmed that procaine (0.01-10 mM) competitively inhibited [N-methyl-3H]-scopolamine chloride ([3H]-NMS) binding to its receptor with binding affinity (pKi) of 4.63 +/- 0.10. 3. Procaine transformed CCh-evoked [Ca2+]i dynamics: the initial rise in [Ca2+]i followed by a gradual decay during continuous stimulation with 3 microM CCh was transformed by 0.3 mM procaine to the oscillatory [Ca2+]i dynamics, which resembled the response to 0.3 microM CCh in the absence of procaine. The initial phase of [Ca2+]i oscillation corresponded to the initial phase of CCh-induced amylase release in isolated perfused acini. 4. Procaine (0.3-3 mM) did not inhibit the secretory response to cholecystokinin octapeptide (CCK-8) in isolated incubated acini. A higher concentration of procaine (10 mM) caused weak but significant inhibition of the response to only limited concentrations of CCK-8, 30 and 100 pM. Procaine lower than 10 mM was ineffective on [125I]-BH-CCK-8 binding, although procaine (10 mM) caused weak but significant inhibition of the binding.     

A STUDY OF SUPERIMPOSED FRACTURE MODES I, II AND III ON PMMA

A test apparatus has been developed to study the fracture behaviour of engineering materials subjected to superimposed tensile and shear (Mode I and II) loads using a single edge notch specimen. Stress intensity factors were calculated using finite element analysis. Test results for PMMA are reported. Results from circumferentially notched round bar specimens, subjected to combined tension and torsion (Mode I and III) loading are also reported. The Mode I/II results are consistent with the mixed mode fracture response of a wide range of brittle materials, although there is some evidence of non-linear behaviour. The fracture behaviour for superimposed Modes I and III indicates the strong influence of non-linear deformation which causes the mixed mode toughness to be dependent on the sequence and type of loading.     

Restenosis and arterial remodelling after coronary angioplasty

Restenosis after coronary angioplasty (PTCA) is a complex process and is still the major problem, despite improvements in equipment and technique. Thrombus formation and intimal hyperplasia have been considered to be the main causes of the development of restenosis after primary successful angioplasty. As yet, pharmacological trials to prevent restenosis have failed to prevent it, despite the fact that the therapy has been aimed at reducing thrombus formation and intimal hyperplasia. Several new angioplasty devices have been developed. Series of observations and a few controlled trials have demonstrated restenosis rates similar to those obtained with conventional balloon angioplasty, except in the case of stent implantation, which appears to be promising. Intravascular ultrasound studies have provided new insight and a more complete understanding of the process leading to restenosis. Vascular remodeling is now considered as an important pathogenetic factor. It consists of a change in the cross-sectional vessel area and may involve an actual constriction of the artery. This may lead to lumen-narrowing and finally restenosis with minimal neointimal formation. In this review we summarise the literature on the restenosis process and the current status of the clinical trials aimed at preventing restenosis.