Method and apparatus for determining the amount of ultrafiltration during dialysis

Claim 1

In a dialysis system which includes dialysis solution conduit means for passing dialysis solution through a membrane dialyzer, the improvement comprising: means for supplying and means for withdrawing essentially identical volumes of dialysis solution to and from a portion of said dialysis solution conduit means and a dialyzer connected to said conduit means, to precisely and positively control the input and output of dialysis solution to and from said conduit portion and connected dialyzer; container means capable of holding a variable liquid volume and connected to said portion of the dialysis solution conduit means which is under precise positive control of the input and output of dialysis solution; and means for measuring the total liquid volume of dialysis solution in said precisely, positively controlled conduit portion and connected dialyzer, said total liquid volume being less than the entire liquid volume of dialysis solution in said dialysis system, whereby changes in said total liquid volume indicate the amount of ultrafiltration during dialysis; in which said means for supplying and means for withdrawing identical liquid volumes comprises double-faced piston means, reciprocable in a chamber, and defining a first, variable volume chamber portion adjacent one face of said piston, and a second, variable volume chamber portion adjacent the opposite face of said piston; a dialysis solution supply conduit, as part of said dialysis solution conduit means, communicating with said first chamber portion; first one-way valve means in said supply conduit for causing dialysis solution to be supplied to said first chamber as said piston causes its volume to expand, and to be expelled into said conduit portion and connected dialyzer as said piston causes said volume to contract, said second chamber portion communicating with a dialysis solution withdrawing conduit as part of said dialysis solution conduit means, and second one-way valve means for permitting dialysis solution to be withdrawn from said conduit portion and connected dialyzer into the second chamber as said piston causes the volume of said second chamber to expand, and for permitting dialysis solution to be expelled from said second chamber and from the dialysis system as the volume of said second chamber contracts, through reciprocating motion of said piston.