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In a single optical fibre transducer, light is injected into a fibre through a fibre optic coupler, located at some distance from the distal end of the fibre. Injected light travels toward the front face of the fibre, where it exits in the shape of a cone. then, after reflection from a reflective surface, it is readmitted into the same fibre. The reflected beam of light travels back through the coupler, exits through the distal end of the fibre and illuminates the photosensitive area of a photo diode, where it is converted to an electrical current. Depending on which one of the parameters is allowed to vary the amount of the returning light, one can build a variety of different sensors. Among them are: linear/angular displacement sensors and their derivatives such as pressure or force sensors; transmittance sensors such as turbidity and chemical sensors; reflectance sensors such as temperature sensors, optical encoders and scanners, colourometric and other types of chemical sensors. In the case of the single optic fibre transducer (SOFT) made by Pearl Instruments (Chicago, II, USA), the reflective surface is made of a thin metal foil with 6 microns thickness and 1.25 mm diameter. Optical fibres are pf the multimode type with 55 microns diameter. Their numerical aperture is equal to 0.66. The SOFT head is 1.25 mm in diameter and has an overall length of 50 cm. The disposable part of the system contains the head, fibre, protective sheathing and plug. Its operating range is -15 to +300 mmHg, and +25 to +45 degrees C, and its resolution is +/- 1 mmHg.

Clinical urodynamics is the present standard for diagnosing voiding dysfunction. The nonphysiological nature of this exam often hinders symptom reproduction in the laboratory. Currently, a small intrabladder device is being developed to conduct ambulatory urodynamics. This study investigates the feasibility of using fluid volume conductance for the realtime intravesical volume measurement needed in urodynamics. Prototype devices are polymer bodies having 4 electrodes. Electrode configurations and probe geometries were tested in bladder-like latex vessels using saline having conductivity similar to urine. Sensitivity to temperature and fluid concentration were determined using fresh pig bladders in vitro. The voltage across the fluid volume was found to be inversely related to volume. The ideal probe configuration was found to be an ellipsoid having strip electrodes spaced at 25deg. Increasing fluid temperature and concentration increased solution conductivity, significantly decreasing the measured voltage. Urine's dynamic chemical properties therefore necessitate real-time compensation of conductivity in clinical application; which could be accomplished with another smaller electrode array.

The mechanical and metallurgical properties of carotid artery clamps were evaluated. The pressure plate retreat propensity, metallurgical composition, surface morphology, magnetic properties, and corrosion resistance of the Crutchfield, Selverstone, Salibi, and Kindt clamps were tested. None of the clamps showed evidence of pressure plate retreat. The clamps differed significantly in their composition, surface cleanliness, magnetic properties, and corrosion resistance. The Crutchfield clamp was the only one manufactured from an ASTM-ANSI-approved implantable stainless steel (AISI 316) and the only clamp in which the surfaces were clean and free of debris. The Selverstone clamp was made principally from AISI 304 stainless steel, as was one Salibi clamp. The pressure plate on another Salibi clamp was made from a 1% chromium and 1% manganese steel. Machining and surface debris consisting principally of aluminum, silicon, and sulfur was abundant on the Selverstone and Salibi clamps. The Kindt clamp was manufactured from AISI 301 stainless steel with a silicate-aluminized outer coating. The Crutchfield and Selverstone clamps were essentially nonferromagnetic, whereas the Salibi and Kindt clamps were sensitive to magnetic flux. In the pitting potential corrosion test, the Crutchfield clamp demonstrated good corrosion resistance with a pitting potential of 310 mV and no surface corrosion or pitting by scanning electron microscopy examination. The Selverstone clamp had lower pitting potentials and showed various degrees of corrosion and surface pitting by scanning electron microscopy. The Salibi pressure plate had a very low pitting potential of -525 mV and showed severe corrosion. By metallurgical criteria, only the Crutchfield clamp is suitable for long term implantation.

The fluid flow and particle motion in a tube are solved numerically by coupling the Navier-Stokes equations with the dynamic equation of a particle. The particulate flow is simulated from rest under a prescribed pressure drop. The symptotic steady state solution is in good agreement with the analytical solution of creeping flow and with the experimental data reported in the literature. The present computational analysis explores the Reynolds numbers effects on the flow processes and gives some insight into qualitative similarities of the kinematics and dynamics of particulate flows. The resistant coefficient, the apparent viscosity, the tube hemotocrit, and the distribution of viscous stresses and pressure on the particle and on the capillary wall are considered along with the curvilinear flow patterns.

A properly functioning aneurysm clip is of paramount importance in the surgical ablation of intracranial aneurysms. An appropriate match between the closing force needed to ablate an aneurysm and the force exerted by the aneurysm clip must be achieved. In this study, the opening and closing forces exerted by several commonly used aneurysm clips were tested. There was a strong correlation between the classification of the clips, according to the Dujovny system, and their mechanical behavior. Minimal variability among different lots of the same clip type and minimal hysteresis were generally exhibited by the alpha mobile fulcrum class clips, such as the Yasargil, Vari-Angle McFadden, Scoville, and Mayfield clips. Significant exceptions included several types of Mayfield and Drake clips. In contrast, pivot class clips generally showed twice as much lot variability among different lots, as well as a significant amount of hysteresis. Clips of this class include the Vari-Angle, Heifetz, and Pivot clips. Because significant variations in clip force exist and because several other factors can compound these differences, it is suggested that aneurysm clips be individually tested for their closing forces before they are used in an operation.

An easily adjustable, variable-force microvascular clip is described. This clip is superior to other clips currently available because it is essentially three clips in one. Its advantages are that it can reduce the amount of table area needed to store clips during surgery and it offers the surgeon greater flexibility in the selection of clips with different closing forces. This clip was developed by modifying the segments of a basic alpha-type clip, designing a computer program to analyze the force contributions made by each segment of the clip, constructing several clips with different blade lengths, and testing them in a microvascular surgery research program. The clip we have developed is easy to use, reduces clutter on the instrument table, aand offers the surgeon a wide choice of closing forces with a minimal number of clips.

✓ Microsurgical clips and tourniquets were used to occlude middle cerebral arteries of dogs for 45-minute periods. Scanning electron microscopy and light microscopy studies revealed significant endothelial damage in many of these arteries. Less traumatic microsurgical clips are needed for temporary small vessel occlusion.

Six commonly used surgical clips (Kleinert-Kutz, PivotTM Vari-Angle, Yasargil, Biemer, and Acland) that have been designated by their manufacturer as being suitable for temporary occlusion were studied in terms of their mechanical and metallurgical properties. Opening and closing forces were determined for all of the clips. Significant variations in clip force with respect to blade gap were found in all of the pivot-type clips. Metallurgical testing showed that all six clips exhibited properties that contraindicate long-term implantation.

Selected commercially designated temporary clips (Acland, Biemer, Kleinert-Kutz, Variangle, and Yasargil) were applied for 1 hour to rat common carotid arteries. Scanning electron and light microscopic studies revealed varying degrees of endothelial damage. The authors believe that further improvements are needed in the design of temporary clips.