Prosthetics Prosthetics: Electronic Arm

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From space labs to hospital operating rooms, American technologists pride themselves on being able to miniaturize the most delicate equipment. But last week it was a Russian achievement that stirred their admiration. Soviet scientists have turned out a highly sophisticated and dexterous artificial arm that weighs less than 3 lbs., and is driven by the minuscule electrical impulses of the wearer's own nerves.

Prosthetics experts from the U.S. learned six years ago that the Russians were working on such an arm, but then the gadget needed a 500-lb. electrical-power unit to drive it. Now, Charles E Yesalis, an executive of Michigan's S. H. Camp & Co. (surgical appliances), has returned from a trip to Moscow carrying pictures and information about a far-advanced model that is completely portable and self-contained.

Wires up the Sleeve. Most artificial limbs use the mechanical power of the stump muscles to actuate parts of the hand. But all body movements are controlled from the brain by electrical impulses that pass along the nerves to work the muscles. After an amputation, especially below the elbow, the nerve-muscle system still works as far as the stump of the limb. With this in mind, Moscow Scientists A. E. Kobrinsky and V. S. Gurfinkel decided to use these muscular contractions to make electric currents. In effect, they set about reversing nature's process. The resulting currents are so minute that they have to be enormously amplified to work an artificial limb.

In the Russian model that Yesalis saw, a hard leather cylinder attaches the artificial hand and forearm to the patient's upper arm. The plastic strap secured to the stump below the elbow contains two electrodes, each attached to two wires that proceed up the sleeve of coat or dress in a single cable. They lead to a transistorized power pack the size of a cigarette case, which may be worn under a man's shirt or a woman's blouse. Another wire leads back from the power pack, down the arm, to the artificial hand. Inside this hand are "the works": an amplifier to magnify the body's muscle currents about 20,000 times, a storage cell, an electric motor and some gears.

Make a Fist. When the patient contracts a muscle in his arm, just as if he intended to make a fist, the servo-electric system relays the signals and his artificial hand clenches in a fist. The lightweight arm is so versatile that the wearer can unscrew a light bulb, lift weights up to 9 lbs., and bend every knuckle on every finger.

The basic scientific principle underlying the Russian development is so valid, and potentially so valuable, that American researchers have been trying for years to perfect what they call a Myoelectric Control system (from the Greek mys, for muscle). Such a system would enable a man in space to guide his swiftly moving vehicle even if heavy g. forces prevented him from moving a single muscle: his electronically amplified impulses would still be capable of carrying out his commands.