Monitor of heart failure using bioimpedance

Abstract

In a method of monitoring pulmonary edema in a human being, an electrical current is injected between a first electrode located in or around a heart and a housing of a medical device implanted in a chest region. A voltage potential is measured between a second electrode in a superior vena cava and a third electrode in the superior vena cava, where the voltage potential is created by the electrical current. Pulmonary edema is assessed based on an impedance value calculated from the electrical current and the voltage potential and a stored edema threshold impedance value.

1 - 18 . (canceled) 
     
     
         19 . A method of monitoring pulmonary edema in a human being, the method comprising:
 injecting an electrical current between a first electrode located in or around a heart and a housing of a medical device implanted in a chest region;   measuring a voltage potential between a second electrode and a third electrode, at least one of the second electrode and the third electrode being located in a superior vena cava, the voltage potential created by the electrical current; and   assessing pulmonary edema based on an impedance value calculated from the electrical current and the voltage potential and a stored edema threshold impedance value.   
     
     
         20 . The method of  claim 19 , wherein the injected electrical current is a cardiac pacing pulse configured to initiate a cardiac cycle. 
     
     
         21 . The method of  claim 19 , wherein the injected electrical current is configured such that a cardiac cycle is not initiated in response to injection of the electrical current. 
     
     
         22 . The method of  claim 19 , wherein the second electrode and the third electrode are positioned on a lead, a distal end of which is located in a right ventricle. 
     
     
         23 . The method of  claim 19 , wherein each of the first, second, and third electrodes is positioned on a single lead. 
     
     
         24 . The method of  claim 19 , wherein the current injection, voltage measurement, and impedance value calculation is repeated on a periodic basis and the assessing pulmonary edema includes assessing a change in edema based on two or more of the calculated impedance values. 
     
     
         25 . The method of  claim 19 , wherein the second electrode is in the superior vena cava and the third electrode is in the superior vena cava. 
     
     
         26 . The method of  claim 19 , wherein the second electrode is in a superior vena cava and the third electrode is not in the superior vena cava, and wherein the third electrode is at the housing of the medical device or at the header of the medical device. 
     
     
         27 . The method of  claim 19 , wherein each of the second electrode and the third electrode is in a superior vena cava and is located on a first lead, and wherein the first electrode is located on a second lead, different from the first lead. 
     
     
         28 . The method of  claim 19 , wherein the first electrode is located in a right ventricle of the heart. 
     
     
         29 . The method of  claim 19 , wherein the first electrode located in a coronary vein of a left ventricle of the heart 
     
     
         30 . An implantable medical device, comprising:
 a housing for the implantable device sized for implantation in a chest region of a patient and comprising a housing electrode;   a lead port into which a proximal end of a lead is connectable, the lead having first, second, and third conductors that are insulated from one another and that extend from the proximal end of the lead to corresponding first, second, and third electrodes, the third electrode positioned near a distal end of the lead for location in or around a heart;   an electrical impedance measurement circuit electrically connected to the lead port and the housing electrode, the circuit comprising a current generator, a voltage amplifier and a control module, the current generator designed to inject an electrical current between the third electrode located in or around the heart and the housing electrode, the voltage amplifier designed to measure a voltage potential between the first and second electrodes, wherein the voltage potential is created by the electrical current, and the control module designed to assess pulmonary edema based on an impedance value calculated from the electrical current and the voltage potential and a stored edema threshold impedance value.   
     
     
         31 . The device of  claim 30 , wherein the injected electrical current is a cardiac pacing pulse configured to initiate a cardiac cycle. 
     
     
         32 . The device of  claim 30 , wherein the injected electrical current is configured such that a cardiac cycle is not initiated in response to injection of the electrical current. 
     
     
         33 . The device of  claim 30 , wherein the current injection, voltage measurement, and impedance value calculation is repeated on a periodic basis and the assessing pulmonary edema includes assessing a change in edema based on two or more of the calculated impedance values. 
     
     
         34 . The device of  claim 30 , wherein the control module is further designed to assess heart enlargement based on the calculated impedance values. 
     
     
         35 . The device of  claim 24 , wherein relative contributions to impedance changes attributable to pulmonary edema and heart enlargement are determined by solving a system equations using the calculated impedance values and predetermined coefficients. 
     
     
         36 . The device of  claim 30 , wherein the first electrode is positioned on the lead for location in a superior vena cava. 
     
     
         37 . The device of  claim 30 , wherein the second electrode is positioned on the lead for location in a superior vena cava.