SHORT blasts of ultrasound could be used to give men vasectomies without
putting them under the knife. This might encourage more squeamish men to take
responsibility for contraception, the technique鈥檚 inventors hope.
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
(快猫短视频, 8 December 2001, p 14).
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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鈥檚 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. 鈥淭he intensity of the
ultrasound is around a thousand times greater at its focus than on the skin
surface,鈥� says Fried.
Firing a pulse of ultrasound for between 20 and 50 seconds heats the vas
deferens to over 50 掳C. This kills cells in the tube wall, which coagulate
and obstruct the tube. 鈥淵ou are essentially cooking the tissue,鈥� says Fried.
Scar tissue then forms in the tube and acts to reinforce the blockage. Fried鈥檚
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. 鈥淭his could be especially useful in developing countries where people
don鈥檛 have ready access to trained surgeons and sterile hospitals,鈥� 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. 鈥淲ith a vasectomy, anything less than 100 per cent success is not good
enough,鈥� he says.