초록 ▼

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 vector

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 ΔZVX =αAVX*QA+αBVX*QB, where QA is a fractional resistivity change of a first contributing physiological impedance factor, QB is a fractional resistivity change of a second physiological impedance factor, αAVX is an impedance sensitivity factor for physiological impedance factor Q A, and αBVX is an impedance sensitivity factor for physiological impedance factor QB, 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.

대표청구항 ▼

The invention claimed is: 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 impe

The invention claimed is: 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 ΔZV1 and ΔZV2, respectively; (3) insert each of the calculated values ΔZV1 and ΔZV2 into an equation description="In-line Formulae" end="lead"Δ Z=αL*QL+αB*Q BαHM*QHM+αSM*Q SM+αHV*KHV+αLV *KLV,description="In-line Formulae" end="tail" where QL is lung tissue fractional resistivity change, QB is blood fractional resistivity change, QHM is heart muscle fractional resistivity change, QSM is skeletal muscle fractional resistivity change, KHV is heart volume fractional change, KLV is lung volume fractional change, and each of QL, QB, QHM, QSM, KHV, and KLV is a physiological impedance factor, αL is lung tissue impedance sensitivity factor, αB is blood impedance sensitivity factor, αHM is heart muscle impedance sensitivity factor, αSM is skeletal muscle impedance sensitivity factor, αHV is heart volume impedance sensitivity factor, αLV is lung volume impedance sensitivity factor; (4) subtract ΔZV2 from ΔZV1 to form the equation description="In-line Formulae" end="lead"Δ ZV1-ΔZV2=(αLV1-α LV2)*QL+(αBV1-αBV2) *QB+(αHMV1-αHMV2)*Q HM+(αSMV1-αSMV2)*Q SM+(αHVV1-αHVV2)*KHV+ (αLVV1-αLVV2)*KLV; anddescription="In-line Formulae" end="tail" (5) solve for one of the physiological impedance factors Q L, QB, QHM, QSM, KHV, 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 ΔZV1 and ΔZV2, respectively; (3) insert each of the calculated values ΔZV1 and ΔZV2 into an equation description="In-line Formulae" end="lead"Δ ZVX=αAVX*QA+α BVX*QBdescription="In-line Formulae" end="tail" where QA is a first fractional resistivity change of a physiological impedance factor, QB is a second fractional resistivity change of a physiological impedance factor, αAVX is an impedance sensitivity factor for physiological impedance factor QA, and αBVX is an impedance sensitivity factor for physiological impedance factor QB; (4) subtract ΔZV2 from ΔZV1 to form the equation description="In-line Formulae" end="lead"Δ ZV1-ΔZV2=(αAV1-α AV2)*QA+(αBV1-αBV2)* QB; anddescription="In-line Formulae" end="tail" (5) solve for a quantifying value for one of the physiological impedance factors QA and QB using the equation. 14. The system of claim 13 wherein QA and QB 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 QA and QB are fractional changes in resistivity and given by the equations QA=ΔρA/ρA=(ρAT2-ρAT1)/ρAT1 and QB=Δρ B/ρB=(ρBT2-ρBT1)/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.