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To preserve sterility of body fluids (e.g. blood) during pumping they can be pumped inside soft rubber tubes squeezed between rollers. The rollers move forward keeping a part of the tube closed. This produces a pulsatile or peristaltic form of flow which is suitable for many applications such as pumping during haemodialysis and open-heart surgery. The usual form has two or three rollers on a rotating arm which presses the tubing into a shoe so that one of the rollers is always occluding the tube (thus preventing back flow). The tubing must be relatively soft. It may be part of a long silicon-rubber tube or it may be a short section within a stiffer tube. This type of pump produces relatively little damage to blood.
A modified form of roller pump is used in many automatic infusion pumps. A set of cams drive a row of fingers which squeeze the tube in turn, so that the closed point moves forward. As the last finger closes on the tube the first one will seal the tube to prevent back flow, and the process is repeated. See also Blood pump, and Heart-lung machine.
Content and Design Copyright 2000 Dr. Malcolm C Brown. See Title Page for more details