In the US alone, more than half a million men a year are sterilised with a vasectomy. The operation is cheaper than female sterilisation, and has a higher success rate with fewer complications. Yet American women are still sterilised twice as often as men, says Nathaniel Fried at Johns Hopkins Medical School in Baltimore, Maryland.
In most vasectomy operations, a surgeon cuts out a 1.5-centimetre section from the vas deferens, the tubes that carry sperm from the testicles into the urethra. The cut ends of the tube are then either cauterised to seal them shut or blocked with silicone plugs. A newer method uses an implanted plastic clip to pinch the vas deferens tight enough to prevent sperm slipping through (New Scientist, 8 December 2001, p 14).
Now Fried and his colleagues say they can block the tubes without making any incisions. Fried locates the vas deferens by hand within the man's scrotum and attaches a plastic clamp to hold it in place in a pinched fold of the skin. Built into the clip is a curved plastic transducer that produces 5 watts of ultrasound. The shape of the transducer focuses the ultrasound a few millimetres beneath the surface of the skin pinched in the clip. "The intensity of the ultrasound is around a thousand times greater at its focus than on the skin surface," says Fried.
Firing a pulse of ultrasound for between 20 and 50 seconds heats the vas deferens to over 50 ¡C. This kills cells in the tube wall, which coagulate and obstruct the tube. "You are essentially cooking the tissue," says Fried. Scar tissue then forms in the tube and acts to reinforce the blockage. Fried's clip contains a water-filled latex balloon that sits between the transducer and the skin. Pumping cold water through the balloon before, during and after the operation ensures that the vas deferens can be heated without burning the skin.
The treatment has so far only been performed on dogs, but Fried claims it is so simple that it could be routinely used without calling on the skills of a surgeon. "This could be especially useful in developing countries where people don't have ready access to trained surgeons and sterile hospitals," he says.
Before the technique can be used on men, though, Fried will have to prove it can produce a permanent, effective blockage every time without causing burns to the skin. "With a vasectomy, anything less than 100 per cent success is not good enough," he says.
Author: Ian Sample
New Scientist issue: 12th January 2002
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