A magnetic device for increasing the urethral resistance to flow: an experimental study in female dogs.

ABSTRACT

OBJECTIVE: To test a new magnetic device for increasing the urethral resistance to flow in a dog model, and thus provide a potential mechanical device for the treatment of incontinence in women. MATERIALS AND METHODS: The study comprised 12 female mongrel dogs; three dogs were used to study the effect on urethral resistance of inserting a vaginal magnet (control experiment) and five were assessed in a urodynamic study. With the animals under general anaesthesia, the bladder and the urethra were exposed by a low midline incision. One magnet, embedded in a silicon layer, was placed on the anterior side of the urethra 3 cm distal to the bladder neck and fixed with a few sutures. To increase the urethral resistance as required, a second magnet was inserted into the vagina and the device activated. Urethral pressure profiles and leak-point pressures were recorded in the anaesthetized animals under resting conditions and after the urethra was compressed between the magnets. Recordings were also made after pharmacological blockade of the urethral musculature. In four additional dogs, chronic experiments were conducted to evaluate the effect of continuous compression of the urethra and the vaginal wall for 14 days. RESULTS: Urethral compression between the magnets resulted in a doubling of the maximal pressure in the proximal urethra and in a threefold increase of the leak-point pressure. After pharmacological denervation of the urethra the differences between the control pressures and those after activating the device were even greater, although not significantly so. After 2 weeks of continuous compression of the vaginal wall and the urethra between the magnets there was no detectable tissue damage. CONCLUSION: These results suggest that the magnetic device can efficiently increase urethral pressure and that prolonged compression caused no apparent damage to the urethra or vagina. It may therefore be a useful potential method of providing urinary continence in women.