The implant, the size of a grain of rice, is one of a new breed of medical devices that requires no batteries. A radio transmitter and receiver held near the body provides the power and interrogates the implant.
The device is designed for people with congestive heart failure, where fluid builds up in organs and limbs because the heart fails to pump enough blood around the body. There are now more than half a million new cases each year in the US alone. The condition is usually treated with drugs, and to ensure they are working doctors sometimes have to measure the pressure inside the left atrium of the heart.
At the moment, this can only be done by temporarily inserting a catheter into the heart, via an artery in the arm or leg. In some patients this unpleasant and costly operation has to be done three times a year.
But with the new implant a similar operation would only have to be done once, to place the sensor inside the left atrium, says Nader Najafi, head of Integrated Sensing Systems (ISSYS) in Ypsilanti, Michigan, the company developing the implant. Results from trials in dogs (Biomedical Microdevices, vol 6, p 61) are very encouraging, he says. "It's extremely accurate and extremely fast." One major problem with implanted devices is that they can become clogged by cells or proteins. But because this device measures pressure mechanically, by the flexing of a membrane, it is not such a problem. Najafi says that tests show it can still measure pressure accurately even when coated in cell-like layers. Another drawback is that, being batteryless, the device cannot monitor the heart continuously, says Tim Bowker of the British Heart Foundation. "You would only get a snapshot of what was going on at the time," he says. But it would still allow more frequent checking than doctors can do now.
The greatest risk is that the device could become detached and be swept into the brain, causing a stroke. Najafi insists the company has a sound method for anchoring the implant, but he refuses to reveal any details.
Author: Duncan Graham-Rowe
New Scientist issue: 28 February 2004
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