Patent ID: 7149573

Claim:
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 ΔZ V1 and ΔZ V2 , respectively; (3) insert each of the calculated values ΔZ V1 and ΔZ V2 into an equation Δ Z=α L *Q L +α B *Q B α 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 ΔZ V2 from ΔZ V1 to form the equation Δ Z V1 −ΔZ 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.