Patent ID: 7273465

Claim:
A body fluid treatment apparatus comprising: a body fluid pumping chamber containing a flexible membrane that is configured to draw body fluid into the pumping chamber under negative gaseous pressure on a gas side of the membrane and alternately to expel body fluid from the pumping chamber under positive gaseous pressure on the gas side of the membrane; a sensor that is configured to provide a flow rate signal representing a predetermined change in the flow rate of body fluid in flowing into the pumping chamber; and a control apparatus that is configured to pressurize the pumping chamber on the gas side of the membrane alternately with positive and negative gaseous pressure with reference to the flow rate signal by pressurizing the gas side with negative gaseous pressure and, upon receiving the flow rate signal, switching the pressure at the gas side from negative to positive; wherein the pumping chamber is one of two body fluid pumping chambers, each of which contains a flexible membrane that is configured to draw body fluid into the respective pumping chamber under negative gaseous pressure on a gas side of the membrane and alternately to expel body fluid from the respective pumping chamber under positive gaseous pressure on the gas side of the membrane, and the control apparatus is configured to pressurize the two pumping chambers alternately with positive and negative gaseous pressure on the gas sides of the membranes to move body fluid through the two pumping chambers in a coordinated relationship that is in phase.