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Accelerometers spread to medical implants

Posted: 10 May 2010     Print Version  Bookmark and Share

Keywords:accelerometer  medical implant  MEMS  remote control 

More than 250,000 people use Medtronic implants for chronic pain, but to date they have relied on a remote control device to adjust the level of electrical stimulation the implants provide. The adjustments are usually required when the patient shifts from lying to standing position, changing the distance between the spinal cord and implanted electrodes. Now Medtronic has started clinical trials in the United States for a novel implant that uses an accelerometer to fine tune how it delivers electrical stimulation to nerves in the spine to reduce chronic pain and thus accelerometers move from Apple iPhones and Nintendo Wii joysticks into human medical implants

Medtronic is putting an accelerometer in its RestoreSensor neurostimulator to automatically detect the change in posture and trigger an adjustment of the electrical stimulation levels. The company's so-called AdaptiveStim technology has already been approved for use in Europe and is now in randomized trials expected to last 18 months in ten centres in the United States.

"We are using a custom three-axis accelerometer and our own algorithms, designed internally from the ground up to consume a hundredth the power of a consumer component and yet as precise," said Don Deyo, VP of development and technology at Medtronic's neural stimulation group. "Low power analogue design is something we are very familiar with," he added.

Although MEMS-based gyroscopes are starting to replace accelerometers in consumer devices, they are too large, precise and consume too much power for implants. "We need a relatively rough understanding or a person's orientation," said Devo.

The new Medtronic implant also records and stores the frequency of posture and activity changes for health care providers to analyse.

Medtronic's engineers are following developments in a broad range of electronics sectors including mechanical and chemical sensors, power sources and energy harvesting. Devo characterized energy harvesting as "still in an experimental stage and further out from commercialisation" for implants.

The Medtronic device is part of a trend towards more automated implants, acting as closed-loop systems that sense, process and adjust therapy without the need for human intervention. The implant, similar to a pacemaker in size, connects to thin, flexible wires to deliver electrical pulses to the epidural space in order to block pain signals from reaching the brain.

Implants are rapidly branching out from their base in heart therapies to a wide variety of other uses. Neural stimulators are seen as one of the fastest growing areas for a wide range of issues from overeating to depression and chronic pain.

Spinal chord stimulation is approved by the U.S. Food and Drug Administration for the treatment of chronic, intractable pain in the trunk or limbs.

- Rick Merritt
EE Times

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