ADAPTATIONS TO INTRA-THORACIC FLUID MONITORING ALGORITHM

• US 20080027349A1
• Filed: 07/28/2006
• Published: 01/31/2008
• Est. Priority Date: 07/28/2006
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Stylos, Lee
• Granted Patent: US 8,055,335 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 5/0538 invasively, e.g. using a catheter
• CPC Class Codes: A61B 5/076 Permanent implantations telemetry using implanted circuitry A61B5/0031; implanted stimulators for therapy A61N1/3605, A61N1/362, A61N1/372
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61B 5/4878 Evaluating oedema
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/37258 Alerting the patient
• CPC Class Codes: G16H 10/60 for patient-specific data, e.g. for electronic patient records
• CPC Class Codes: G16H 10/65 stored on portable record carriers, e.g. on smartcards, RFID tags or CD
• CPC Class Codes: G16H 50/30 for calculating health indices; for individual health risk assessment

Abstract

Adaptations to an intra-thoracic fluid-status-trend indication and/or alert algorithm are disclosed. Some embodiments monitor fluid levels in heart failure patients and others suffering from pulmonary edema and the like. Some embodiments reset a cumulative fluid index when a short-term intra-thoracic impedance value exceeds a baseline impedance value minus a predetermined positive hysteresis value. Many device, system, and method embodiments hereof serve to reduce the number of false positive alerts while retaining the desired sensitivity.

Claims

1. A computer-readable medium programmed with instructions for performing a method of monitoring fluid levels, the medium comprising instructions for causing a programmable processor to:

take a series of intra-thoracic impedance measurements from a patient;

modify a short-term impedance value based on the series of intra-thoracic impedance measurements;

modify a baseline impedance value based on the series of intra-thoracic impedance measurements;

add a difference of the baseline impedance value minus the short-term impedance value to a cumulative index when the short-term impedance value is less than the baseline impedance value minus a predetermined positive hysteresis value;

reset the cumulative index when the short-term impedance value is greater than the baseline impedance value minus the hysteresis value; and

notify the patient of possible fluid accumulation when the cumulative index exceeds a predetermined threshold value.

2. A medium according to claim 1, further comprising instructions for causing a programmable processor to calculate an average value of the series of intra-thoracic impedance measurements, wherein modifying the short-term impedance value and the baseline impedance value is based on the average value.

3. A medium according to claim 1, wherein the medium is housed in a type of implantable medical device, and the hysteresis value is based on the type of implantable medical device.

4. A medium according to claim 1, wherein the series of intra-thoracic impedance measurements from the patient include a degree of variation from day to day, and wherein the hysteresis value is based on the degree of variation.

5. A medium according to claim 1, further comprising instructions for causing a programmable processor to calculate an initial baseline impedance value.

6. A medium according to claim 5, wherein the predetermined hysteresis value comprises a percentage of the initial baseline impedance value.

7. A medium according to claim 5, wherein the predetermined threshold value is based on the initial baseline impedance value.

8. A medium according to claim 1, further comprising instructions for causing a programmable processor to perform a subsequent cycle of the method and to modify one or more steps in the subsequent cycle when the cumulative index exceeds the predetermined threshold value.

9. A medium according to claim 1, further comprising instructions for causing a programmable processor to initiate therapy to the patient or to modify therapy being provided to the patient when the cumulative index exceeds the predetermined threshold value.

10. A medium according to claim 1, wherein notifying the patient of possible fluid accumulation is selected from the group consisting of (a) sounding an audible alarm, (b) vibrating, (c) causing stimulation, (d) communicating to an external medical device, and (e) combinations of two or more of (a)-(d).

11. An implantable medical device, comprising:

(a) a hermetically-sealed enclosure carrying an enclosure electrode;

(b) a lead functionally coupled to the enclosure at its proximal end, the lead carrying a lead electrode at its distal end; and

(c) circuitry housed within the enclosure, the circuitry being configured to;

(i) take a series of intra-thoracic impedance measurements from a patient via the enclosure electrode and the lead electrode,

(ii) modify a short-term impedance value and a baseline impedance value based on the series of intra-thoracic impedance measurements,

(iii) add a difference of the baseline impedance value minus the short-term impedance value to a cumulative index when the short-term impedance value is less than the baseline impedance value minus a predetermined positive hysteresis value,

(iv) reset the cumulative index when the short-term impedance value is greater than the baseline impedance value minus the hysteresis value, and

(v) trigger a notification relating to possible fluid accumulation when the cumulative index exceeds a predetermined threshold value.

12. An implantable medical device according to claim 11, wherein the enclosure has a characteristic size, and the predetermined positive hysteresis value is based on the characteristic size.

13. An implantable medical device according to claim 11, wherein the series of intra-thoracic impedance measurements from the patient have a degree of variation from day to day, and wherein the hysteresis value is based on the degree of variation.

14. An implantable medical device according to claim 14, wherein the circuitry calculates an initial baseline impedance value.

15. An implantable medical device according to claim 14, wherein the hysteresis value comprises a percentage of the initial baseline impedance value.

16. An implantable medical device according to claim 14, wherein the predetermined threshold value is based on the initial baseline impedance value.

17. A computer-readable medium programmed with instructions for performing a method of monitoring fluid levels, the medium comprising instructions for causing a programmable processor to:

calculate an initial baseline impedance value;

take a series of intra-thoracic impedance measurements from a patient;

calculate an average value of the series of intra-thoracic impedance measurements;

modify a short-term impedance value based on the average value;

modify a baseline impedance value based on the average value;

add a difference of the baseline impedance value minus the short-term impedance value to a cumulative index when the short-term impedance value is less than the baseline impedance value minus a predetermined positive hysteresis value, wherein the hysteresis value is a percentage of the initial baseline impedance value;

reset the cumulative index when the short-term impedance value is greater than the baseline impedance value minus the hysteresis value; and

generate a notification signal in the event that the cumulative index exceeds a predetermined threshold value, wherein the predetermined threshold value is based on the initial baseline impedance value.

18. A medium according to claim 17, wherein the series of intra-thoracic impedance measurements from the patient have a degree of variation from day to day, and wherein the hysteresis value is based on the degree of variation.

19. A medium according to claim 17, further comprising instructions for causing a programmable processor to perform a subsequent cycle of the method and to modify one or more steps in the subsequent cycle when the cumulative index exceeds the predetermined threshold value.

20. A medium according to claim 17, further comprising instructions for causing a programmable processor to initiate therapy to the patient or to modify therapy being provided to the patient when the cumulative index exceeds the predetermined threshold value.