Impedance monitor for discerning edema through evaluation of respiratory rate

• US 5,957,861 A
• Filed: 01/31/1997
• Issued: 09/28/1999
• Est. Priority Date: 01/31/1997
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Wahlstrandl, John D., Combs, William J., Warkentin, Dwight H., Martin, Roy, Condie, Catherine R.
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US08/791,206
• Time in Patent Office: 970 Days
• Field of Search: 607/1, 607/2, 607/6, 607/7, 607/9, 607/15, 607/16-18, 607/28-30, 607/32-37, 600/481, 600/483, 600/484, 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 5/0809 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. Implantable apparatus for detection of impedance measurement in a region of a living body'"'"'s tissue, having a plurality of electrodes exposed to said body tissue on an outer surface of a housing or on another support coupled to said body, said housing containing electrical energy pulse delivery means connected to at least one of said plurality of electrodes so as to create an electric field in said body in an area of tissue around and adjacent said one electrode and energy measurement means connected to at least one other of said plurality of said electrodes also located within said electric field, so that impedance measurements in the living body can be made in said field, said implantable device further characterized by having:

timing circuit for timing the measurement of impedance to coincide with delivery of said energy pulse,

memory circuit for storing a value representative of a dc value of said measured impedance at an instant in time,

dc sampling offset circuit for determining a dc offset value of a next measurement of said impedance and connected to provide a dc offset value signal to said memory circuit,

edema valuation and output circuit for generating output signals indicative of a level of edema related to the impedance values from in said memory circuit and said offset circuit, and

wherein said memory circuit stores either said dc offset values or said dc values or both, over a period of days.

2. An implantable apparatus as set forth in claim 1 and having circuit process for discriminating impedance noise signals generatable by said living body'"'"'s heart pumping and breathing cycles so as to remove cyclic noise such body activities would otherwise introduce into said impedance measurement signals.

3. 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 such body activities would otherwise introduce into said impedance measurement signals.

4. An implantable device as set forth in claim 3 wherein said noise discriminating circuit process 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.

5. An implantable apparatus as set forth in claim 1 and further comprising a comparitor and trigger circuit means for determining significant events based on a comparison of relative values of the stored impedance value signals to predetermined trigger values.

6. An implantable apparatus as set forth in claim 1 wherein an additional physiologic indicator value is measured by another sensor circuit and said other physiologic value is employed with said edema value to determine appropriate device behavior from a range of preconditioned device behaviors.

7. An implantable apparatus as set forth in claim 1 wherein said memory means stores data related to significant events and history of impedance measurements.

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

9. An implantable apparatus as set forth in claim 1, where said electric energy pulse delivery means is adjustable to produce programmable output values of impedance pulses.

10. An implantable apparatus 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.

11. An implantable apparatus as set forth in claim 1 and having timing means or timing means and sensing means to provide synchronizing output pulses to physiologically recurring signals indicative of body cycles and conditions including:

diurnal cycle indicators, position indicators, posture indicators, resting indicators, heart beat cycle indicators, breathing indicators, or movement indicators.

12. An implantable apparatus as set forth in claim 1 having additional impedance circuit electrodes, at least one of which is adapted to be located in an appendage or near the heart.

13. An implantable apparatus 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.

23. An implantable apparatus as set forth in claim 1, where said means for generating electrical output pulses is adjustable to produce programmable output values of impedance pulses.

29. Device as set forth in claims 1 or 15 and 28 further comprising:

communications means for transmitting said values to an external device.

30. Device as set forth in claims 1, 15 or 28 and further having an associated base station for periodically monitoring, for storing or retransmitting, output data transmitted by said device.

31. Device as set forth in claims 1, 15 or 28 and further having an associated base station for periodically monitoring, for storing or retransmitting, output data transmitted by said device said base station further comprising a connection circuit to telephonically link and to send said data to a monitor system at a remote location.

32. Device as set forth in claims 1, 15 or 28 and further having an Activation device having patient triggerable means activatable outside a patient'"'"'s body to cause the implanted device to output data so as to enable storing data and wherein said implant device further comprises an update trigger circuit means to start record over when signal indicating data was properly received is given.

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

14. Implantable apparatus for detection of impedance measurement in a region of a living body'"'"'s tissue, having a plurality of electrodes exposed to said body tissue on an outer surface of a housing or on another support coupled to said body, said housing containing electrical energy pulse delivery means connected to at least one of said plurality of electrodes so as to create an electric field in said body in an area of tissue around and adjacent said one electrode and energy measurement means connected to at least one other of said plurality of said electrodes also located within said electric field, so that impedance measurements in the living body can be made in said field, said implantable device further characterized by having:

timing circuit for timing the measurement of impedance to coincide with delivery of said energy pulse,

memory circuit for storing a value representative of a dc value of said measured impedance at an instant in time,

dc sampling offset circuit for determining a dc offset value of a next measurement of said impedance and connected to provide a dc offset value signal to said memory circuit,

edema valuation and output circuit for generating output signals indicative of a level of edema related to the impedance values from in said memory circuit and said offset circuit,

wherein said edema valuation and output circuit for generating comprises LTA/STA determining circuit means wherein a processor circuit derives a LTA signal value and a STA signal value based on the values of impedance stored over a predefined long term and short term, respectively for determining an LTA value and an STA value and memory means for storing said determined LTA and STA values and LTA/STA updating circuit means for updating said STA and LTA values based on new measurements of impedance.

15. An implantable device for chronic implant into a living body having at least one lead adapted for location in the heart of said body and means for generating electrical output pulses between said at least one lead and another electrode so as to enable the measurement of impedance between said at least one lead and said other electrode, the improvement comprising a

impedance determination means to determine the impedance of the thoracic cavity of the body based on the dc value of impedance measured between said lead and said electrode,

edema evaluation means to determine values representing a level of edema based on said measurement at times over a course of days, and

means for storing said value representing a level of impedance in said device for said times over said course of days.

16. An implantable device as set forth in claim 15 and having circuit process for discriminating impedance noise signals generatable by said living body'"'"'s heart pumping and breathing cycles so as to remove cyclic noise such body activities would otherwise introduce into said impedance measurement signals.

17. An implantable device as set forth in claim 15 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 such body activities would otherwise introduce into said impedance measurement signals.

18. An implantable device as set forth in claim 17 wherein said noise discriminating circuit process 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.

19. An implantable device as set forth in claim 15 and further comprising a comparitor and trigger circuit means for determining significant events based on a comparison of relative values of the stored impedance value signals to predetermined trigger values.

20. An implantable device as set forth in claim 15 wherein an additional physiologic indicator value is measured by another sensor circuit and said other physiologic value is employed with said edema value to determine appropriate device behavior from a range of preconditioned device behaviors.

21. An implantable device as set forth in claims 15 wherein said memory means stores data related to significant events and history of impedance measurements.

22. An implantable device as set forth in claim 15 and having power generator means for continuous long term operation of said device.

24. An implantable device as set forth in claim 15 and wherein the impedance measurement is switchable between more than two electrodes to obtain best position for signal to noise.

25. An implantable device as set forth in claim 15 having additional impedance circuit electrodes, at least one of which is adapted to be located in an appendage or near the heart.

26. An implantable device as set forth in claim 15 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.

27. Apparatus for implant into a living body having at least one lead adapted for location in the heart of said body and means for generating electrical output between said at least one lead and another electrode so as to enable the measurement of impedance between said at least one lead and said other electrode, the improvement comprising

means to determine the impedance of the thoracic cavity of the body based on the value of impedance measured between said lead and said electrode, and means to determine a value representing a level of edema based on said measurement

wherein said means for interpreting comprises LTA/STA determining circuit means wherein a processor circuit derives a LTA signal value and a STA signal value based on the values of impedance stored over a predefined long term and short term, respectively for determining an LTA value and an STA value and memory means for storing said determined LTA and STA values and LTA/STA updating circuit means for updating said STA and LTA values based on new measurements of impedance.

28. Implantable apparatus and system having monitor means for determining edema values and to record such values and having at least one additional value monitor means for monitoring physiologic values from a list of physiologic parameters comprising:

activity, activity per unit of time, activity variability, heart rate, heart rate variability, respiration, minute ventilation, pulmonary edema, transthoracic edema, local edema, variability in edema, arrhythmia senses, frequency of arrhythmia senses, duration of arrhythmia episodes, long term values of preceding sense values, pressure values, blood oxygen, or patient activation temporal markers.

34. A method of determining patient pulmonary edema comprising:

measuring impedance between two electrodes implanted within a patient'"'"'s body a multiplicity of times throughout a chronic period greater than a day,

filtering cyclic body effects on the impedance signal value from the signal to generate a DC signal value for each said measurement step,

storing a history of filtered impedance changes representative of changes in said DC impedance signal value within said patient in an implanted device, and

determining a level of edema based on said changes in said DC impedance signal values that have occurred during said monitored history.

35. An implantable medical device for chronic implant into a living body having at least two electrodes exposed to tissue within said body and pulse generator means for generating electrical output so as to provide for measurement of impedance between said at least two electrodes, the improvement comprising

impedance determination means to determine the impedance of the thoracic cavity of the body based on the dc value of impedance measured between said two electrodes,

means to determine values representing a level of edema based on said measurement at times over a course of days, and

means for storing said value representing a level of impedance in said device for said times over said course of days.

36. An implantable device as set forth in claim 35 having additional impedance circuit electrodes, at least one of which is adapted to be located in an appendage or near the heart.