Improvement of the Kolff quad-coil artificial kidney with a double-screen coil

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IN 1966 the Kolff quad-coil artificial kidney1, 2 was introduced as a pump-less, inexpensive apparatus for performing dialysis at the patient’s home. A polypropylene screen was used to separate individual coils of dialysis tubing, thereby distributing blood flow and limiting the thickness of the blood channel. This artificial kidney functions well under low pressures in the coil. Though urea clearances are high, the capacity for ultrafiltration is insufficient.3 Several methods have been tried to increase the ultrafiltration of this dialyzer. Osmotic removal of water has been achieved by adding dextrose to the dialysate bath. Kolff4 introduced the idea of using a high rate of dialysate flow through the coil to induce a negative pressure; this change increased the pressure gradient across the membrane, and ultrafiltration was improved using this technic. A simple vacuum attachment subsequently was used to create negative pressure outside the coil.3

During normal operation of the Kolff quad-coil artificial kidney, a decrease in urea clearance occurred as blood pressure increased. A similar decrease in urea clearance occurred when negative pressure was applied externally to the coil. This decrease is caused by distension of the cellophane membrane under an increasing pressure gradient. The membrane distends through the pores of the screen until it contacts the next layer of cellophane. The portions of the membranes which are in contact are blocked, and the effective dialyzing surface of the membranes is decreased. Studies showed that when the pressure across the membrane is more than 150 mm Hg, about 30 percent . . .



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