Method and apparatus for impedance signal localizations from implanted devices

• US 7,149,573 B2
• Filed: 04/25/2003
• Issued: 12/12/2006
• Est. Priority Date: 04/25/2003
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Wang, Li
• Primary Examiner(s): Hindenburg, Max
• Assistant Examiner(s): TOWA, RENE T
• Application Number:
  US10/423,118
• Publication Number:
  US 20040215097A1
• Time in Patent Office: 1,327 Days
• Field of Search: 600/300, 600/301, 600/309, 600/547, 600/512
• US Class Current: 600/547
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• CPC Class Codes: A61B 5/7285 for synchronising or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal A61B6/5205, A61B6/541, A61B8/5207, A61B8/543 take precedence
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance

Abstract

A patient monitoring system including an implantable medical device for monitoring a plurality of physiological factors contributing to physiological conditions of a patient'"'"'s heart by measuring a first impedance affected by the plurality of physiological factors, across one of a plurality of vectors, and a second impedance affected by the plurality of physiological factors, across a second one of the plurality of vectors subsequent to determining the first impedance. A change in impedance is determined based upon the first impedance and the second impedance measurements. Using an equation ΔZ_VX=α_AVX*Q_A+α_BVX*Q_B, where Q_A is a fractional resistivity change of a first contributing physiological impedance factor, Q_B is a fractional resistivity change of a second physiological impedance factor, α_AVX is an impedance sensitivity factor for physiological impedance factor Q_A, and α_BVX is an impedance sensitivity factor for physiological impedance factor Q_B, the value of one of the contributing physiological impedance factors is determined. The contributing physiological impedance factors may include lung resistivity, blood resistivity, heart muscle resistivity, skeletal muscle resistivity, heart volume and lung volume.

Claims

1. A patient monitoring system comprising:

an implantable medical device comprising;

a housing and a connector block configured to couple to a cardiac lead system having a plurality of electrodes;

means for selecting electrodes of a cardiac lead system to establish an impedance vector in tissue proximate a patient'"'"'s heart;

means coupled to the electrodes selecting means for measuring impedance of tissue proximate a patient'"'"'s heart based on an impedance vector formed between electrodes of a cardiac lead system; and

means for determining a quantifying value for a contributing physiological impedance factor among a plurality of physiological impedance factors associated with a physiological condition of a patient'"'"'s heart, wherein the means for determining a quantifying value for a contributing physiological impedance factor among a plurality of physiological impedance factors associated with a first physiological condition of a patient'"'"'s heart among a plurality of physiological conditions of a patient'"'"'s heart comprises;

a microprocessor operating to

(1) cause the means for measuring impedance of tissue proximate a patient'"'"'s heart based upon an impedance vector formed between electrodes of a cardiac lead system to make first and second impedance measurements spaced apart in time along a first impedance vector and to make first and second impedance measurements spaced apart in time along a second impedance vector;

(2) calculate a value for a change in measured tissue impedance over time along each of the first and second impedance vectors as Δ

Z_V1 and Δ

Z_V2, respectively;

(3) insert each of the calculated values Δ

Z_V1 and Δ

Z_V2 into an equation

Δ

Z=α

_L*Q_L+α

_B*Q_Bα

_HM*Q_HM+α

_SM*Q_SM+α

_HV*K_HV+α

_LV*K_LV,

where Q_L is lung tissue fractional resistivity change,

Q_B is blood fractional resistivity change,

Q_HM is heart muscle fractional resistivity change,

Q_SM is skeletal muscle fractional resistivity change,

K_HV is heart volume fractional change,

K_LV is lung volume fractional change, and

each of Q_L, Q_B, Q_HM, Q_SM, K_HV, and K_LV is a physiological impedance factor,

α

_L is lung tissue impedance sensitivity factor,

α

_B is blood impedance sensitivity factor,

α

_HM is heart muscle impedance sensitivity factor,

α

_SM is skeletal muscle impedance sensitivity factor,

α

_HV is heart volume impedance sensitivity factor,

α

_LV is lung volume impedance sensitivity factor;

(4) subtract Δ

Z_V2 from Δ

Z_V1 to form the equation

Δ

Z_V1−

Δ

Z_V2=(α

_LV1−

α

_LV2)*Q_L+(α

_BV1−

α

_BV2)*Q_B+(α

_HMV1−

α

_HMV2)*Q_HM+(α

_SMV1−

α

_SMV2)*Q_SM+(α

_HVV1−

α

_HVV2)*K_HV+(α

_LVV1−

α

_LVV2)*K_LV; and

(5) solve for one of the physiological impedance factors Q_L, Q_B, Q_HM, Q_SM, K_HV, and K_LV using the equation.

2. The system of claim 1, wherein the plurality of physiological impedance factors includes lung resistivity, blood resistivity, heart muscle resistivity, skeletal muscle resistivity, heart volume and lung volume, and wherein the contributing physiological impedance factor is blood resistivity.

3. The system of claim 1, wherein the plurality of impedance vectors includes a first vector and a second vector, the first vector including a first stimulation path and a first sense path extending between a first electrode of the plurality of electrodes, positioned within a ventricle of the heart, and an uninsulated portion of the housing, and the second vector including a second stimulation path, extending between a second electrode of the plurality of electrodes, positioned within a ventricle of the heart, and the uninsulated portion of the housing, and a second sense path extending between the first electrode and the uninsulated portion of the housing.

4. The system of claim 1, wherein the plurality of impedance vectors include a first vector and a second vector, the first vector including a first stimulation path and a first sense path extending between a first electrode of the plurality of electrodes, positioned within a ventricle of the heart, and an uninsulated portion of a housing of the device, and the second vector including a second stimulation path extending between the first electrode and the uninsulated portion of the housing and a second sense path extending between the first electrode and a second electrode of the plurality of electrodes, positioned along the housing.

5. The system of claim 4, wherein the plurality of physiological impedance factors include lung resistivity, blood resistivity, heart muscle resistivity, skeletal muscle resistivity, heart volume and lung volume, and wherein the contributing physiological impedance factor is skeletal muscle resistivity.

6. The system of claim 1, wherein the contributing physiological impedance factor is one of a group consisting of lung resistivity, blood resistivity, heart muscle resistivity, skeletal muscle resistivity, heart volume, and lung volume.

7. The system of claim 1 wherein the means for selecting electrodes of a cardiac lead system to establish an impedance vector in tissue proximate a patient'"'"'s heart comprises an electrode switch matrix and a controller.

8. The system of claim 1 further comprising means for establishing a pattern of sensitivities of physiological impedance factors that contribute to tissue impedance, the pattern being established according to each of the plurality of impedance vectors formed between a plurality of electrodes of a cardiac lead system.

9. The system of claim 1 wherein the means for establishing a pattern of sensitivities of physiological impedance factors that contribute to tissue impedance comprises a look-up table of coefficient values.

10. The system of claim 7 wherein the means for measuring impedance in tissue proximate a patient'"'"'s heart comprises an impedance measurement interface coupled to the electrode switch matrix.

11. The system of claim 1 wherein the plurality of electrodes of the cardiac lead system comprises a right ventricular (RV) coil, a right ventricular (RV) ring, right ventricular (RV) tip, an uninsulated portion of the housing, and a button electrode positioned along the housing;

and wherein the means for selecting electrodes of a cardiac lead system to establish an impedance vector in tissue proximate a patient'"'"'s heart forms an impedance vector from a group of impedance vectors consisting of (1) a stimulation path and a sense path between the RV coil and the housing, (2) a stimulation path from the RV ring to the housing and a sense path from the RV coil to the housing, (3) a stimulation path and a sense path from the RV ring to the housing, (4) a stimulation path from the RV ring to the housing and a sense path from the RV tip to the housing, (5) a stimulation path from the RV coil to the housing and a sense path from the RV coil to the button electrode.

12. The system of claim 1 further comprising:

a memory coupled to the means for determining a quantifying value for a contributing physiological impedance factor, the memory accepting quantifying values for storage and subsequent retrieval.

13. A patient monitoring system comprising:

an implantable medical device comprising;

a housing and a connector block configured to couple to a cardiac lead system having a plurality of electrodes;

means for selecting electrodes of a cardiac lead system to establish an impedance vector in tissue proximate a patient'"'"'s heart;

means coupled to the electrodes selecting means for measuring impedance of tissue proximate a patient'"'"'s heart based on an impedance vector formed between electrodes of a cardiac lead system; and

means for determining a quantifying value for a contributing physiological impedance factor among a plurality of physiological impedance factors associated with a physiological condition of a patient'"'"'s heart, wherein the means for determining a quantifying value for a contributing physiological impedance factor among a plurality of physiological impedance factors associated with a first physiological condition of a patient'"'"'s heart among a plurality of physiological conditions of a patient'"'"'s heart comprises;

a processor operating to

(1) cause the means for measuring impedance of tissue proximate a patient'"'"'s heart based upon an impedance vector formed between electrodes of a cardiac lead system to make first and second impedance measurements spaced apart in time along a first impedance vector and to make first and second impedance measurements spaced apart in time along a second impedance vector;

(2) calculate a value for a change in measured tissue impedance over time along each of the first and second impedance vectors as Δ

Z_V1 and Δ

Z_V2, respectively;

(3) insert each of the calculated values Δ

Z_V1 and Δ

Z_V2 into an equation

Δ

Z_VX=α

_AVX*Q_A+α

_BVX*Q_B

where Q_A is a first fractional resistivity change of a physiological impedance factor,

Q_B is a second fractional resistivity change of a physiological impedance factor,

α

_AVX is an impedance sensitivity factor for physiological impedance factor Q_A, and

α

_BVX is an impedance sensitivity factor for physiological impedance factor Q_B;

(4) subtract Δ

Z_V2 from Δ

Z_V1 to form the equation

Δ

Z_V1−

Δ

Z_V2=(α

_AV1−

α

_AV2)*Q_A+(α

_BV1−

α

_BV2)*Q_B; and

(5) solve for a quantifying value for one of the physiological impedance factors Q_A and Q_B using the equation.

14. The system of claim 13 wherein Q_A and Q_B are selected from a group of physiological impedance factors consisting of lung resistivity, blood resistivity, heart muscle resistivity, skeletal muscle resistivity, heart volume and lung volume.

15. The system of claim 13 wherein Q_A and Q_B are fractional changes in resistivity and given by the equations Q_A=Δ

ρ

_A/ρ

_A=(ρ

_AT2−

ρ

_AT1)/ρ

_AT1 and Q_B=Δ

ρ

_B/ρ

_B=(ρ

_BT2−

ρ

_BT1)/ρ

_BT1.

16. The system of claim 13 wherein the processor is a microprocessor executing a set of instructions stored in a memory.

17. The system of claim 16 further comprising a computer-readable medium having the set of executable instructions for downloading into the memory.

18. The system of claim 13 further comprising a memory coupled to the processor to accept a physiological impedance factor quantifying value for storage and subsequent retrieval.