Pneumatic Arm

Most artificial arms are based on a simple principle: mechanical linkage carries muscle power to the artificial limb, from either the shoulder or the stump muscles. Convinced that mechanically transmitted muscle power was not the best solution, Professor Siegmund Weil and Technician Otto Haefner of Heidelberg University set out to develop a light, small and more efficient substitute. This week, after seven years of research, they were busy teaching amputees how to use their invention: an artificial arm operated by pressurized gas.

Made of wood, metal and rubber, the arm is powered by a flat, easily hidden carbon-dioxide container linked by rubber tubes to a system of tiny valves. The valves can be opened or closed by the slightest movement of the muscles over which they are placed. The opening of each valve causes carbon dioxide to spurt from the container through a corresponding tube to tiny air bellows that move part of the limb. The carbon gases escape through a special exhaust.

In tests on 50 patients, the pneumatic arm enabled amputees to make up to a dozen different movements. They are able to eat and drink with normal utensils, grasp an object firmly or gently. Some can type, use keys, write with a pen. The new arm costs between $357 and $600, including the cost of a three-to four-week course in adjustment at the Heidelberg University Clinic. Chief disadvantage: depending on how often the limb is used, the supply of carbon dioxide has to be renewed every two days to two weeks.

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