Impedance monitor for discerning edema through evaluation of respiratory rate

• US 5,876,353 A
• Filed: 01/31/1997
• Issued: 03/02/1999
• Est. Priority Date: 01/31/1997
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Riff, Kenneth M.
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US08/792,204
• Time in Patent Office: 760 Days
• Field of Search: 607/1, 607/2, 607/6, 607/7, 607/9, 607/15, 607/16, 607/17, 607/18, 607/28, 607/29, 607/30, 607/32-37, 600/481, 600/484, 600/483, 600/508, 600/509, 600/513, 600/529, 600/536, 600/547, 600/573, 600/579
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• CPC Class Codes: A61B 5/4878 Evaluating oedema
• 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 1/3702 Physiological parameters A61N1/365 takes precedence; evoked response A61N1/371

Abstract

An impedance monitor for discerning edema through evaluation of respiratory rate. Preferred embodiment includes edema monitor and trigger to initiate diagnostic reporting or corrective action when activated. Recording of Long Term Average and Short Term Average values for secondary edema measure based on DC signal level are described as are methods and apparatus for removing unwanted recurring noise.

Claims

1. An implantable edema monitoring device having:

an impedance sensor for making impedance measurements in a living body into which said device is implanted, and

memory and evaluation circuitry means for monitoring said impedance measurements, and for generating a value representative of respiratory rate based on evaluation of said impedance measurements over time,

edema value generator circuitry means for monitoring changes in said respiratory rate value, so as to generates an edema level value indicative of a measured value of edema in said living body based solely on said changes in said respiratory rate value.

2. An implantable device as set forth in claim 1 further comprising edema evaluation circuitry for storing at least two edema values taken over time and comparing these at least two edema values to so as to determine whether and in what direction a change in edema may be occurring.

3. An implantable device as set forth in claim 1 further comprising edema memory circuitry means for recording changes in said edema value for later transmission to a second device adapted to receive such information outside the body from said implanted monitoring device.

4. An implantable device as set forth in claim 1 further comprising an alarm means for generating an alarm based on predetermined changes in said edema level value.

5. An implantable device as set forth in claim 1 wherein said memory and evaluation circuitry means for monitoring said impedance measurements senses DC changes in impedance indicative of interstitial fluid build-up and generates a second edema level value signal indicative of the presence of edema, based solely on this DC change, with said respiratory rate filtered out.

6. An implantable device as set forth in claim 5 wherein said device further comprises an alarm generator means for generating an alarm based on predetermined changes in both said edema level value and said second edema level value.

7. An implantable device as set forth in claim 5 further comprising:

sensor and evaluation means for evaluating a level of patient activity independent from impedance based measurement of respiratory rate and generating a value for said independent activity level evaluation, and

memory storage circuitry means for storing respiratory activity and said activity level value or a ratio thereof over time.

8. A device as set forth in claim 7 wherein said activity sensor is used to remove from consideration those respiratory rate signals not taken at rest.

9. An implantable device as set forth in claim 1 and further comprising determination circuitry means to determine if said respiration rate value exceeds a Cheyne-Stokes(CS) minimum value and if so, then determines if after a predetermined period of exceeding said minimum and if said respiration rate then falls substantially, to generate a CS episode indicator signal to indicate that an episode of Chyene-Stokes syndrome has occurred.

10. An implantable device as set forth in claim 1 further:

sensor and evaluation means for evaluating a level of patient activity independent from impedance based measurement of respiratory rate and generating a value for said other activity level evaluation, and

memory storage circuitry means for storing respiratory activity and said activity level value or a ratio thereof over time.

11. An implantable device as set forth in claim 7 wherein said device further comprises a storage circuit for storing a respiratory rate to activity level parameter.

12. A device as set forth in claim 11 wherein said parameter is a ratio and a timing circuit causes said paremeter to be stored on a daily basis.

13. A device as set forth in claim 11 wherein said parameter is a ratio and having a second physiologic indicator sensor circuit for generating a second physiologic sensor level signal for communication to a storage trigger circuit for generating a trigger signal to cause said respiratory rate to activity level parameter to be stored in said storage circuit when said second physiologic indicator sensor circuit determines a second physiologic indicator signal matches a predetermined trigger condition.

14. An implantable device as set forth in claim 11 wherein said device further comprises a storage circuit means for storing said respiratory rate to activity level parameter historically, longitudinally over time and having an edema level indicator circuit for monitoring said parameter level longitudinal history to generate a signal value representative of an amount of worsening or improving edema based on evaluation of said parameter history.

15. An implantable device as set forth in claim 1 and having a circuit process for discriminating impedance noise signals generatable by said living body'"'"'s electromyographic and motion signals so as to remove the noise signals such body activities would otherwise introduce into said impedance measurement signals.

16. An implantable device as set forth in claim 15 wherein said noise circuit process for discriminating said impedance noise signals comprises a rest cycle determining timing circuit means for generating a timing signal to limit impedance measurements to times that the body is determined by said rest cycle timing and determining circuit means to be at rest.

17. An implantable device as set forth in claims 1 wherein said memory means stores data related to significant events and history of impedance measurements.

18. An implantable device as set forth in claim 1 and having power generator means for continuous long term operation of said device.

19. An implantable device as set forth in claim 1 and having programmable output values of impedance pulses.

20. An implantable device as set forth in claim 1 and wherein the impedance measurement is switchable between more than two electrodes to obtain best position for signal to noise.

21. An implantable device as set forth in claim 1 wherein said device housing additionally houses or communicates with an implanted device of the kind listed:

Pacemaker, Implantable Defibrillator, Drug pump, Loop ECG recorder, hemodynamic paramater recorder/monitor.

22. A device as set forth in claim 1 further comprising an activation circuit for activating drug therapy responsive to impedance value changes.

23. A method of determining patient pulmonary edema comprising:

storing a history of respiratory rate in an implanted device, thereby creating a monitored history in storage,

monitoring changes in the respiratory rate of the patient,

determining a level of edema based on said changes in said respiratory rate that have occurred during said monitored history.

24. A method of determining patient pulmonary edema comprising:

storing a history of respiratory rate in an implanted device,

monitoring changes in the respiratory rate of the patient,

determining a level of patient health based on said changes in said respiratory rate that have occurred during said monitored history.

25. An implantable edema monitoring device having:

an impedance sensor for making impedance measurements in a living body into which said device is implanted, and

memory and evaluation circuitry means for monitoring said impedance measurements, and for generating a value representative of respiratory rate based on evaluation of said impedance measurements over time,

patient health value generator circuitry means for monitoring changes in said respiratory rate value, so as to generates a patient health level value indicative of general physical health in said living body based solely on said changes in said respiratory rate value.