Development of a magnetically operated artificial urethral sphincter : chronic effects of compression on the skin structure and blood flow

The artificial urethral sphincter (AUS) has been in clinical use for more than 20 years. Currently available AUS devices, however, are difficult to use and not entirely reliable. A magnetically operated AUS is currently under the development. Although the skin between the magnets will be compressed all day long, little information exists on the effects of chronic pressure on the skin structure and blood flow. In five miniature pigs, two internal magnets and one control metal disk were implanted subcutaneously at three different positions, and external magnets with differing magnetic forces were applied to the skin overlying the internal magnets for six weeks. In four pigs, the skin blood flow was measured by a laser Doppler flow meter applying different pressures. Compression of 10 mmHg preserved normal skin morphology in all but one animal where blood flow had not recovered 2 weeks after surgery. Compression of 20 mmHg for 6 weeks, however, produced pressure ulcers in all five cases (p < 0.05 vs. 10 mmHg group). The skin blood flow declined for pressures exceeding 20 mmHg (0 mmHg: 4.3 +/- 1.2, 10 mmHg: 4.3 +/- 3.3, 20 mmHg: 2.6 +/- 2.7 ml/min/100 g). We concluded that the magnetically operated AUS should use a magnetic coupling with a pressure less than 10 mmHg exerted on the interposing skin.