Implantable medical device for measuring time varying physiologic conditions especially edema and for responding thereto

• US 6,512,949 B1
• Filed: 07/12/1999
• Issued: 01/28/2003
• Est. Priority Date: 07/12/1999
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Combs, William J., Wang, Li, Warkentin, Dwight H., Martin, Roy, Condie, Catherine R., Thompson, David L., Wahlstrand, John D.
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US09/352,179
• Time in Patent Office: 1,296 Days
• Field of Search: 600/547, 600/300, 600/481, 607/508, 607/9
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• 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 1/36521 the parameter being derived from measurement of an electrical impedance

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 medical device for detection of impedance measurement in a region of a living body'"'"'s tissue and for reacting to a predetermined level of edema in said region, comprisinf:

a plurality of electrodes, each adapted to be exposed to the body;

electrical energy pulse delivery means coupled to at least one of said plurality of electrodes for creating an electric field in the body;

energy measurement means for obtaining impedance measurements in the electrical field in the body;

a timing circuit coupled to the energy measurement means to time the measurement of impedance to coincide with delivery of said energy pulse;

a memory circuit to store a value representative of a dc value of said measured impedance at an instant in time;

a dc sampling offset circuit to determine a dc offset value of a next measurement of said impedance and connected to provide a dc offset value signal to said memory circuit;

an edema valuation and output circuit coupled to said memory circuit to generate output signals indicative of a level of edema related to the the value stored in the memory circuit and to the dc offset value;

wherein said memory circuit stores either said dc offset values of said dc values or both, over a period of more than a day, and

therapy delivery apparatus responsive to predetermined levels of said output signals when said output signals indicative of a level of edema match a predetermined level of edema value stored by said therapy delivery apparatus.

2. The implantable device of claim 1 wherein said therapy delivery apparatus is a therapy delivery apparatus of the set comprising:

implantable drug pump, implantable cardiodefibrillator, pacemaker, implantable nerve stimulator.

3. The implantable device of claim 1 wherein said therapy delivery apparatus is a pacemaker responsive to produce pacing pulses in a temporal pattern that increases cardiac output contemporaneously with said output signals indicative of a level of edema matching said predetermined level of edema value.

4. The implantable device of claim 1 wherein said therapy delivery apparatus is a pacemaker responsive to produce pacing pulses with a higher energy level to increase cardiac output contemporaneously with said output signals indicative of a level of edema matching said predetermined level of edema value.

5. The implantable device of claim 1 wherein said therapy delivery apparatus is a drug pump responsive to release drugs which increase cardiac output contemporaneously with said output signals indicative of a level of edema matching said predetermined level of edema value.

6. The implantable device of claim 1 wherein said therapy delivery apparatus is a drug pump responsive to release drugs which reduce edema contemporaneously with said output signals indicative of a level of edema matching said predetermined level of edema value.

7. The implantable device of claim 6, wherein said drug is chosen from the set of drugs comprising:

Berberine;

Digitalis;

ACE inhibitors; and

diuretics, comprising the set of loop-type, thiazide type and potassium sparing types comprising torsemide, furosemide, bumetanide, indomethacin, metolazone, hydrochlorothiazide, spirnolatactone.

8. The implantable medical device of claim 7 wherein a combination of said drugs is administered.

9. 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.

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

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.

11. Implantable Medical Device (IMD) for detection of impedance measurement in a region of a living body'"'"'s tissue and for reacting to a predetermined level of edema in said region, the IMD having electrical energy pulse delivery means for creating an electric field in the living body, said IMD further comprising:

energy measurement means for obtaining a plurality of impedance measurements in the living body as a plurality of vectors in the electrical field;

a timing circuit coupled to the energy measurement means to time impedance measurements for each vector to coincide with delivery of said energy pulse;

a memory circuit to store a value representative of a dc value of said measured impedance at an instant in time for each vector;

a dc sampling offset circuit connected to provide a dc offset value signal to said memory circuit for each of the plurality of vectors;

an edema valuation and output circuit comprising a processing circuit to combine each dc offset value signal for each of the plurality of vectors and to generate output signals indicative of a level of edema related to the value stored by the memory circuit and to the dc offset value.

12. An implantable apparatus as set forth in claim 11 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.

13. An implantable device as set forth in claim 11 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.

14. An implantable device as set forth in claim 11 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.

15. An implantable device as set forth in claim 11 said means for interpreting comprising LTA/STA determining circuit means 1 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.

16. An implantable device as set forth in claim 11 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.

17. An implantable device as set forth in claim 11 wherein said memory means stores data related to significant events and history of impedance measurements.

18. A method for altering therapy parameters responsive to measured edema comprising:

implanting into a living body, a medical device to measure edema changes by generating impedance pulses through a plurality of vectors through tissue in said living body,

combining the measured edema from said plurality of vectors to produce a single edema value of interest,

evaluating said single edema value of interest,

altering therapy parameters based on said evaluation.