Method and apparatus for detecting change in intrathoracic electrical impedance

• US 9,895,080 B2
• Filed: 08/08/2016
• Issued: 02/20/2018
• Est. Priority Date: 12/04/2002
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Stadler, Robert W., Wang, Li
• Primary Examiner(s): Alter, Alyssa M
• Application Number:
  US15/231,523
• Publication Number:
  US 20170035322A1
• Time in Patent Office: 561 Days
• Field of Search: 607 17, 600547
• 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 5/4836 Diagnosis combined with treatment in closed-loop systems or methods A61B5/0036 takes precedence
• CPC Class Codes: A61B 5/4875 Hydration status, fluid retention of the body
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61B 5/7275 Determining trends in physiological measurement data; Predicting development of a medical condition based on physiological measurements, e.g. determining a risk factor
• CPC Class Codes: A61N 1/05 for implantation or insertion into the body, e.g. heart electrode A61N1/06 takes precedence
• CPC Class Codes: A61N 1/3627 for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy
• CPC Class Codes: A61N 1/3629 in combination with non-electric therapy
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: G06F 12/0802 Addressing of a memory level in which the access to the desired data or data block requires associative addressing means, e.g. caches
• CPC Class Codes: G06F 12/0862 with prefetch
• CPC Class Codes: G06F 12/0877 Cache access modes

Abstract

A method and apparatus for detection of changes in impedance a patient that includes generating measured impedances, generating an adaptive baseline trend of the measured impedances corresponding to a first time period, generating a short term trend of the measured impedances corresponding to a second time period less than the first time period, determining changes in relative position of the short term trend and the baseline trend, the determined changes in relative position corresponding to determining intersecting of the baseline trend by the short term trend, determining differences between the baseline trend and calculated period average impedances, and accumulating, in response to determining no intersecting of the baseline trend by the short term trend, the determined differences between the baseline trend and the calculated period average impedances.

Claims

1. An implantable medical device, comprising:

a plurality of electrodes;

an output circuit outputting a plurality of output pulse signals along a vector formed by electrodes of the plurality of electrodes;

a measurement circuit generating a corresponding plurality of measurement signals in response to the plurality of output pulse signals; and

a microprocessor configured to;

determine a plurality of period average impedances in response to the plurality of output pulse signals and the plurality of measurement signals corresponding to a predetermined time period,

determine an adaptive baseline trend of period average impedances of the plurality of period average impedances corresponding to a first time period,

determine a short term trend of period average impedances of the plurality of period average impedances corresponding to a second time period different from the first time period,

determine changes in relative position of the short term trend and the baseline trend,

determine differences between the baseline trend and the calculated period average impedances,

determine no intersecting of the baseline trend by the short term trend, and

accumulate, in response to determining no intersecting of the baseline trend by the short term trend, the determined differences between the baseline trend and the calculated period average impedances.

2. The implantable medical device of claim 1, wherein the accumulated determined differences is set to zero when the short term trend intersects the adaptive baseline trend.

3. The implantable medical device of claim 1, wherein the microprocessor initially generates the adaptive baseline trend and the short term trend using a first computation scheme and the microprocessor subsequently generates the adaptive baseline trend and the short term trend using a second computation scheme different from the first computation scheme.

4. The implantable medical device of claim 3, wherein the microprocessor performs the first computation scheme at a first rate and the microprocessor performs the second computation scheme at a second rate less that the first rate.

5. The implantable medical device of claim 4, wherein the microprocessor computes the first rate in response to a predetermined number of the generated measured impedances.

6. The implantable medical device of claim 1, wherein the microprocessor is further configured to determine the changes in relative position of the short term trend and the baseline trend by at least determining intersecting of the baseline trend by the short term trend.

7. The implantable medical device of claim 1, wherein the microprocessor compares the accumulated determined differences to a predetermined threshold and determines corresponding significant events in response to the comparing.

8. The implantable medical device of claim 7, wherein the significant events determined by the microprocessor include one of storing data within the implantable medical device, apply or modifying a delivered therapy, notifying the patient, notifying medical personnel, and modifying frequency of impedance measurement.

9. The implantable medical device of claim 1, wherein the microprocessor determines each period average impedance of the plurality of period average impedances between 12 pm and 5 pm.

10. The implantable medical device of claim 1, wherein the microprocessor updates the short term trend by generating a weighted sum of the short term trend for two previous days and the period average impedance determined for the current day and the two previous days.

11. The implantable medical device of claim 1, wherein the microprocessor sets the accumulated determined differences to zero in response to the short term trend being equal to the adaptive baseline trend.

12. The implantable medical device of claim 1, wherein the microprocessor determines period average impedances of the plurality of period average impedances a predetermined number of days prior to generation of the adaptive baseline trend and the short term trend.

13. A method for detecting changes in impedance in a medical device, comprising:

generating measured impedances;

calculating period average impedances corresponding to a plurality of the measured impedances generated during a first time period;

generating an adaptive baseline trend of the calculated period average impedances;

generating a short term trend of the measured impedances corresponding to a second time period different from the first time period;

determining changes in relative position of the short term trend and the baseline trend, the determined changes in relative position corresponding to determining intersecting of the baseline trend by the short term trend;

determining differences between the baseline trend and calculated period average impedances;

determining no intersecting of the baseline trend by the short term trend; and

accumulating, in response to determining no intersecting of the baseline trend by the short term trend, the determined differences between the baseline trend and the calculated period average impedances.

14. The method of claim 13, further comprising setting the accumulated determined differences to zero when the short term trend intersects the adaptive baseline trend.

15. The method of claim 13, wherein the adaptive baseline trend is initially generated using a first computation scheme and is subsequently generated using a second computation scheme different from the first computation scheme.

16. The method of claim 15, wherein the first computation scheme is performed at a first rate and the second computation scheme is performed at a second rate less that the first rate.

17. The method of claim 16, wherein the first rate is computed in response to a predetermined number of the generated measured impedances.

18. The method of claim 17, wherein the predetermined number is equal to four.

19. The method of claim 13, wherein the short term trend is initially generated using a first computation scheme and is subsequently generated using a second computation scheme different from the first computation scheme.

20. The method of claim 19, wherein the first computation scheme is performed at a first rate and the second computation scheme is performed at a second rate less that the first rate.

21. The method of claim 20, wherein the first rate is computed in response to a predetermined number of the generated measured impedances.

22. The method of claim 21, wherein the predetermined number is equal to four.

23. The method of claim 13, further comprising comparing the accumulated determined differences to a predetermined threshold and determining corresponding significant events in response to the comparing.

24. The method of claim 23, wherein the significant events include one of storing data within the implantable medical device, apply or modifying a delivered therapy, notifying the patient, notifying medical personnel, and modifying frequency of impedance measurement.

25. The method of claim 13, wherein the measured impedance is generated between 12 pm and 5 pm.

26. A computer readable medium having computer executable instructions for performing a method, the method comprising:

generating measured impedances;

calculating period average impedances corresponding to a plurality of the measured impedances generated during a first time period;

generating an adaptive baseline trend of the calculated period average impedances;

generating a short term trend of the measured impedances corresponding to a second time period different from the first time period;

determining changes in relative position of the short term trend and the baseline trend, the determined changes in relative position corresponding to determining intersecting of the baseline trend by the short term trend;

determining differences between the baseline trend and calculated period average impedances;

determining no intersecting of the baseline trend by the short term trend; and

accumulating, in response to determining no intersecting of the baseline trend by the short term trend, the determined differences between the baseline trend and the calculated period average impedances.