Medical fluid cassette leak detection methods and devices

1. A method of detecting leaks in a disposable medical fluid cassette, the medical fluid cassette comprising a base and a flexible membrane attached to the base in such a way that the base and the flexible membrane cooperate to at least partially form a fluid passageway, the method comprising:

applying a first force to the flexible membrane with a piston configured to be advanced against and withdrawn from the flexible membrane;

measuring a first physical property of a system that includes the medical fluid cassette and a medical fluid pumping machine while the first force is applied to the flexible membrane;

removing the first force from the flexible membrane;

separating the piston from the flexible membrane after removing the first force;

advancing the piston against the flexible membrane after separating the piston from the flexible membrane;

applying a second force to the flexible membrane after advancing the piston against the flexible membrane;

measuring a second physical property of the system that includes the medical fluid cassette and the medical fluid pumping machine while the second force is applied to the flexible membrane; and

determining whether the medical fluid cassette leaks based on a comparison of the first physical property and the second physical property.

2. The method of claim 1 wherein the first force is the same as the second force.

3. The method of claim 1 wherein the medical fluid cassette includes fluid inlet ports and fluid outlet ports that provide communication between the fluid passageway and an exterior of the medical fluid cassette, and applying the first force is performed with the fluid inlet ports and fluid outlet ports closed.

4. The method of claim 1 wherein applying the first force to the flexible membrane comprises applying the first force until at least a portion of the flexible membrane contacts the base.

5. The method of claim 1 , wherein the method includes applying a vacuum to an outer surface of the flexible membrane between removing the first force from the membrane and applying the second force to the membrane.

6. The method of claim 1 wherein

applying the first force to the flexible membrane comprises advancing the piston against the flexible membrane until a given pressure within the medical fluid cassette is achieved,

applying the second force to the flexible membrane comprises advancing the piston against the flexible membrane until the given pressure within the medical fluid cassette is achieved,

the first physical property comprises a first position of the piston corresponding to the position of the piston when the given pressure is achieved while applying the first force, and

the second physical property comprises a second position of the piston corresponding to the position of the piston when the given pressure is achieved while applying the second force.

7. The method of claim 6 wherein the comparison of the first physical property and the second physical property comprises calculating a difference between the first position and the second position.

8. The method of claim 1 wherein the medical fluid cassette includes fluid inlet ports and fluid outlet ports that provide communication between the fluid passageway and an exterior of the medical fluid cassette, and

applying the first force is performed with the fluid inlet ports and fluid outlet ports open.

9. The method of claim 8 wherein before removing the first force from the flexible membrane, the fluid inlet ports and fluid outlet ports are closed.

10. The method of claim 1 further comprising waiting for a given period of time to pass between

separating the piston from the flexible membrane and

advancing the piston against the flexible membrane.

11. The method of claim 10 , wherein the given period of time is in a range of 15 seconds to 60 seconds.

12. The method of claim 1 wherein the medical fluid cassette includes fluid inlet ports and fluid outlet ports that provide communication between the fluid passageway and an exterior of the medical fluid cassette, and

between applying the first force to the flexible membrane and measuring the first physical property of the system, the method comprises closing the fluid inlet ports and fluid outlet ports such that fluid is trapped within the medical fluid cassette.

13. The method of claim 12 , wherein the method includes applying a vacuum to an outer surface of the flexible membrane between removing the first force from the membrane and applying the second force to the membrane.

14. The method of claim 1 wherein the medical fluid cassette includes fluid inlet ports and fluid outlet ports that provide communication between the fluid passageway and an exterior of the medical fluid cassette, and

before applying the first force to the flexible membrane, the method comprises closing the fluid inlet ports and fluid outlet ports such that fluid is trapped within the medical fluid cassette.

15. The method of claim 14 wherein between closing the fluid inlet ports and fluid outlet ports such that fluid is trapped within the medical fluid cassette and applying the first force to the flexible membrane, the fluid within the cassette is redistributed.

16. The method of claim 1 wherein the medical fluid pumping machine comprises a piston, and

applying the first force to the flexible membrane comprises advancing the piston toward the cassette to a predetermined position in a manner such that the space between the flexible membrane and the base has a predetermined volume.

17. The method of claim 16 wherein applying the second force to the flexible membrane comprises advancing the piston to a position corresponding to the first physical property.

18. The method of claim 1 wherein the first physical property comprises a first pressure within the medical fluid cassette and the second physical property comprises a second pressure within the medical fluid cassette.

19. The method of claim 18 wherein the medical fluid cassette is determined to have a leak if

the second pressure is greater than the first pressure, and

a difference between the second pressure and the first pressure is at least a given difference value.

20. The method of claim 18 wherein the medical fluid cassette is determined to have a leak if

the second pressure is less than the first pressure, and

a difference between the first pressure and the second pressure is at least a given difference value.