By means of a simple surgical procedure, a gauged partial obstruction of the ureter has been obtained in 15 rabbits. A newly development amplifier was used to produce electromyograms free of disturbances by cardiac current (ECG) or other electrical influences, such as alternating current and switch impulses (e.g. beepers of a paging system). Single and summary potentials were received with two different electrodes (glas-isolated gold electrodes and polarisible steel electrodes). The potentials of the obstructed and non-obstructed ureter were related to the simultaneously registered peristaltic waves of the ureter. The results give support to the theory of a myogenic release of the peristalsis proceeding from cephaled to caudad. The spreading ureteral stimulation exerted by the urinary bolus transported towards the bladder is relevant in this respect.
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The disadvantages of highly flexible endoureteral (double J) stents in the face of tumor-induced extrinsic ureteral compression are a consequence of insufficient cross-sectional stability, leading to stent compression and thus to hydronephrosis or pyonephrosis. The newly developed tumor stent, which is used in cases of tumor-induced ureteral compression, is available in sizes from 6F to 8F in diameter and 24 to 32 cm in length. The shaft consists of a combination of high-stability plastics that presents sufficient elasticity in length. Both ends are made of extremely elastic J parts, guaranteeing stable fixation. Compared with common double-J stents with the same outside diameter, the tumor stent possesses a comparable interior diameter and compared with available stents promises sufficient interior flow in the face of extrinsic diseases. The application can be undertaken using well-known endoscopic techniques, needs no special instrumentation, and entails no learning curve. To date, 49 stents were placed at our urologic departments without any problems, the latest stent remaining for 15 months. Tumor-induced compression or a higher rate of encrustation were not seen. All patients tolerated these stents well. In our opinion, the new stabilized endoureteral stent can be seen as a better solution than percutaneous nephrostomy or frequent stent changing to tumor-induced extrinsic ureteral compression.
Internal ureteral stents are widely used in urologic practice for temporary urinary diversion, but all double-J catheters to date exhibit the same disadvantage; that is, they have to be removed endoscopically, necessitating further intervention. We tested different materials (designated G100X-15×LB and G100X-20×LB) to develop a biodegradable (biodissolvable) endoureteral stent that can be held in place without functional loss yet could be dissolved by changing the environment. The principle of the biochemical background is based on the physiological milieu of the urine. The plastics tested are stable in acidic and dissolve in alkaline conditions. In a first step, specimens of two polymers were placed in artificial urine of different pH over a period of 60 days and monitored for integrity (solution trial). In a second step, artificial urine was set in motion (744 mL/24 hours) an infusion pump (Volumed μVP 5000; Fresenius AG, Bad Homburg vdH, Germany) through an infusion set in which a 30-cm piece of the materials to test had been placed (ureter model). Below the inserted specimen, the lumen of the infusion tube was minimized to make obstruction by fragments more possible. In the solution trial, all specimens remained stable under physiologic conditions (pH 5.2) over a period of at least 30 days. The specimens dissolved completely when the pH was adjusted to an alkaline one (pH 7.9). In the ureter model, with pH values of 7.9, all specimens were decomposed after 20 hours, and no occlusion of the model occurred. Using acidic artificial urine, the specimens remained stable with a smooth consistent surface. The dissolution was not a standard chemical one; the materials broke into microscopically small pieces, with fragments of G100X-20×LB being smaller than those of G100X-15×LB. Our first in vitro results show that the tested materials are suitable for further development of biodissolvable endoureteral stents, dissolution of which can be steered by changing the urinary pH.
