Single needle dialysis systems are known in the art and basically operate by cyclically withdrawing a volume of blood from a patient, passing it through a hemodialyzer, and returning it to the patient. The process then repeats, intermittently processing volumes of blood through the hemodialyzer. A single needle is used for both withdrawing and returning the blood--hence the name. (In two-needle systems, in contrast, one needle withdraws the blood and the second returns it, permitting continuous operation instead of cyclical.)
A principal problem with prior art single needle apparatuses has been the wide swings in the hemodialyzer blood pressure that are inherent in their designs. These pressure swings can cause intermittent massive ultrafiltration of the patient's blood. There is a need for a single needle dialysis device that overcomes this and other drawbacks of the prior art.
The present invention overcomes these pressure swings and the attendant ultrafiltration by use of an expansion chamber that extends from the blood circuit and is hydraulically isolated from the dialyzer by a blood pump. The invention also uses one pump (a reversible type) instead of the two conventionally used.
The foregoing and additional features and advantages of the present invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawing.