Organ rejection monitoring

• US 20050090758A1
• Filed: 11/20/2002
• Published: 04/28/2005
• Est. Priority Date: 11/20/2002
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Combs, William J., Parsonnet, Victor
• Granted Patent: US 7,130,679 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/413 Monitoring transplanted tissue or organ, e.g. for possible rejection reactions after a transplant

Abstract

The invention is directed to techniques for monitoring organ rejection. An implanted device monitors the impedance of the transplanted organ. When the impedance measurements indicate that the organ is being rejected, the device provides early warning of rejection.

Claims

1. An implantable medical device comprising:

an impedance measuring circuit to make measurements of the impedance across at least a portion of a transplanted organ in a patient; and

a processor to determine whether the patient is experiencing rejection of the transplanted organ as a function of the impedance measurements.

2. The device of claim 1, further comprising a communication module that generates a notification signal when the processor determines that the patient is experiencing rejection of the transplanted organ.

3. The device of claim 2, wherein the communication module comprises a telemetry module for communication with an external communication device.

4. The device of claim 2, wherein the communication module comprises an alert module that generates an audible alert.

5. The device of claim 1, further comprising:

a first electrode for placement in contact with the transplanted organ;

a second electrode for placement in contact with the transplanted organ; and

a current driver that delivers an excitation current to the transplanted organ via the first and second electrodes.

6. The device of claim 5, wherein the impedance measuring circuit measures the impedance by comparing the voltage difference between the first and second electrodes with the excitation current.

7. The device of claim 5, further comprising:

a third electrode for placement in contact with the transplanted organ; and

a fourth electrode for placement in contact with the transplanted organ,

wherein the impedance measuring circuit measures the impedance by comparing the voltage difference between the third and fourth electrodes during delivery of the excitation current.

8. The device of claim 5, further comprising:

a third electrode for placement in contact with a non-transplanted organ; and

a fourth electrode for placement in contact with the non-transplanted organ,

wherein the impedance measuring circuit makes measurements of the impedance of at least a portion of the transplanted organ with the first and second electrodes, and makes reference measurements of the impedance of at least a portion of the non-transplanted organ with the third and fourth electrodes.

9. A method comprising:

sensing an impedance across at least a portion of a transplanted organ in a patient; and

determining whether the patient is experiencing rejection of the transplanted organ as a function of the impedance.

10. The method of claim 9, further comprising generating a notification when the patient is experiencing rejection of the transplanted organ.

11. The method of claim 9, wherein determining whether the patient is experiencing rejection of the transplanted organ comprises:

sensing a baseline impedance in the transplanted organ; and

determining that the patient is experiencing rejection of the transplanted organ when the sensed impedance deviates from the baseline impedance by a predetermined amount.

12. The method of claim 9, wherein determining whether the patient is experiencing rejection of the transplanted organ comprises:

sensing a reference impedance in a non-transplanted organ; and

determining that the patient is experiencing rejection of the transplanted organ when the sensed impedance deviates from the reference impedance by a predetermined amount.

13. The method of claim 9, wherein determining whether the patient is experiencing rejection of the transplanted organ comprises:

monitoring variations in the sensed impedance on a periodic basis; and

determining that the patient is experiencing rejection of the transplanted organ when the variations decrease over time.

14. The method of claim 9, wherein sensing the impedance across at least a portion of a transplanted organ in a patient comprises making a plurality of impedance measurements, the method further comprising identifying an average value of the impedance measurements.

15. The method of claim 14, further comprising:

identifying a baseline average value of impedance in the transplanted organ; and

determining that the patient is experiencing rejection of the transplanted organ when the average value deviates from the baseline average value by a predetermined amount.

16. The method of claim 14, further comprising:

identifying a reference average value of impedance in a non-transplanted organ; and

determining that the patient is experiencing rejection of the transplanted organ when the average value deviates from the reference average value by a predetermined amount.

17. The method of claim 14, wherein identifying the average value of the impedance measurements comprises computing an arithmetic mean of the measurements.

18. A computer-readable medium comprising instructions for causing a programmable processor to:

obtain a sensed impedance across at least a portion of a transplanted organ in a patient; and

determine whether the patient is experiencing rejection of the transplanted organ as a function of the impedance.

19. The medium of claim 18, the instructions further causing the processor to generate a notification when the patient is experiencing rejection of the transplanted organ.

20. The medium of claim 18, wherein the instructions causing the processor to determine whether the patient is experiencing rejection of the transplanted organ cause the processor to:

obtain a baseline impedance in the transplanted organ; and

determine that the patient is experiencing rejection of the transplanted organ when the sensed impedance deviates from the baseline impedance by a predetermined amount.

21. The medium of claim 18, wherein the instructions causing the processor to determine whether the patient is experiencing rejection of the transplanted organ cause the processor to:

obtain a reference impedance in a non-transplanted organ; and

determine that the patient is experiencing rejection of the transplanted organ when the sensed impedance deviates from the reference impedance by a predetermined amount.

22. The medium of claim 18, wherein the instructions causing the processor to determine whether the patient is experiencing rejection of the transplanted organ cause the processor to:

monitor variations in the sensed impedance on a periodic basis; and

determine that the patient is experiencing rejection of the transplanted organ when the variations decrease over time.

23. The medium of claim 18, wherein the instructions causing the processor to obtain a sensed impedance comprise instructions causing the processor to obtain a plurality of impedance measurements, the method further comprising identifying an average value of the impedance measurements.

24. The medium of claim 23, the instructions further causing the processor to:

identify a baseline average value of impedance in the transplanted organ; and

determine that the patient is experiencing rejection of the transplanted organ when the average value deviates from the baseline average value by a predetermined amount.

25. The medium of claim 23, the instructions further causing the processor to:

identify a reference average value of impedance in a non-transplanted organ; and

determine that the patient is experiencing rejection of the transplanted organ when the average value deviates from the reference average value by a predetermined amount.

26. The medium of claim 23, wherein identifying the average value of the impedance measurements comprises computing an arithmetic mean of the measurements.

27. A system comprising:

means for measuring an impedance across at least a portion of a transplanted organ in a patient; and

means for determining whether the patient is experiencing rejection of the transplanted organ as a function of the impedance measurements,

wherein the system is implantable in a human body.

28. The system of claim 27, further comprising means for communicating a notification signal when the means for determining whether the patient is experiencing rejection determines that the patient is experiencing rejection of the transplanted organ.

29. The system of claim 27, further comprising:

means for generating an excitation current; and

means for delivering the excitation current to the transplanted organ.

30. The system of claim 29, wherein the means for measuring the impedance measures an impedance that develops in response to the delivered excitation current.

31. The system of claim 27, further comprising means for measuring an impedance across at least a portion of a reference organ in the patient.