Improving a Patient's Quality of Life


Sensitive Implants Help You Adjust Your Grip

Source: New Scientist

NERVE implants can help paralysed people perform simple tasks, such as gripping a cup. But the lack of feedback means they can drop the cup or even crush it. Now Danish scientists say they have found a way to help people grip more effectively. They hope eventually to help restore sensation to those with spinal injuries.

Without sensation, patients using neural prostheses have to rely upon their eyes and experience: grip an object too forcefully and they risk muscle fatigue, too gently and they drop it. This is one of the biggest problems with bionic implants, says Morten Haugland at the Center for Sensory-Motor Interaction at Aalborg University.

Haugland and his colleague Andreas Inmann have developed a portable system that monitors bundles of nerves from the index finger of a patient to detect overexertion and compensate by adjusting their grip. The system has been designed to work with commercial neural prostheses such as the Freehand muscle stimulator, which helps quadriplegics. Such systems work by electrically stimulating particular muscles, causing them to contract and making it possible to achieve coordinated movements. This, says Haugland, can help patients carry out everyday tasks that would otherwise be impossible, such as eating with a fork.

But while such devices can help to improve a patient's quality of life, Haugland says they can be frustrating as well. Anyone who has tried drinking after a mouth-numbing visit to the dentist knows how hard it is to use muscles when there is no sensation to tell you what they are doing.

Haugland's add-on device consists of three electrodes wrapped around a nerve bundle implanted into the palm of the hand. Information on the strength of grip is fed back to the muscle stimulator, located externally on a wrist cuff.

The stimulator is controlled by two buttons pressed by a head-mounted prodder: one turns the system on and increases the power, the other decreases the power and turns it off. There are systems that do this using artificial sensors embedded in gloves, but it makes far more sense to use the sensors in your own fingers, says Haugland.

Patients tend to crank the system up to full power all the time, says Haugland. But this isn't necessary: prodding a potato with a fork may require a strong grip, but carrying it to your mouth does not. "Our system makes sure you use the right amount of force," he says.

His team's ultimate goal is to restore a patient's sensation, but for now they are planning to exploit the new approach. Haugland is using similar electrodes to help paraplegics balance when standing.

Haugland's system uses the hand as an extension to a machine--with muscles instead of motors, and nerves replacing touch sensors. But this is effectively what is going on normally when we grasp objects, says Gerald Loeb, a biomedical engineer and expert in neural prosthetics at the University of Southern California in Los Angeles. "When you grasp an object you do not think about the details of what muscles to contract," he says.

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