Analysis of metabolic gases by an implantable cardiac device for the assessment of cardiac output

Abstract

Analysis of metabolic gases by an implantable medical device allows the assessment of the status of a congestive heart failure patient by providing for the assessment of cardiac output. The present invention is directed to an implanted medical device configured to measure concentrations of metabolic gases in the blood to determine cardiac output of a patient. The device is also configured to measure changes in the cardiac output of a patient. The present invention is also directed to a method of measuring cardiac output by an implanted medical device. Further, the detection of changes in cardiac output utilizing an implanted medical device as disclosed herein is useful in a method of detecting exacerbation of congestive heart failure. The implanted medical device can also be used to pace a heart to modify cardiac output in a patient.

1 . An implantable cardiac device comprising:
 an extravascular, extracardiac sensor for measuring arterial blood gas content;   an intravascular sensor for measuring venous blood gas content; and   an electronic circuit for providing an indication of cardiac output based on the difference between said arterial and venous blood gas contents.   
     
     
         2 . The device of  claim 1 , wherein said extravascular sensor is mounted on or incorporated on a surface of an exterior housing of the electronic circuit. 
     
     
         3 . The device of  claim 1 , wherein said extravascular sensor comprises an O 2  sensor. 
     
     
         4 . The device of  claim 3 , wherein said extravascular sensor is a pulse oximetry sensor. 
     
     
         5 . The device of  claim 1 , wherein said extravascular sensor comprises an electrochemical sensor. 
     
     
         6 . (canceled) 
     
     
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         10 . The device of  claim 1 , wherein said intravascular sensor is an optical sensor. 
     
     
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         17 . A method for deriving an indication of cardiac output by an implantable cardiac device comprising:
 (a) measuring an arterial blood gas content extravascularly with an implanted sensor that is positioned outside a patient's heart;   (b) measuring a venous blood gas content intravascularly; and   (c) deriving a measure of cardiac output from said measured arterial and venous blood gas content measurements.   
     
     
         18 . The method of  claim 17 , further comprising:
 receiving said arterial blood gas content measurement from a sensor mounted on or incorporated within a wall of an exterior housing of an electronic circuit of the implantable cardiac device.   
     
     
         19 . The method of  claim 17 , wherein step (a) further comprises measuring said arterial blood gas content with an O 2  sensor. 
     
     
         20 . The method of  claim 19 , wherein step (a) further comprises measuring said arterial blood gas content with a pulse oximetry sensor. 
     
     
         21 . The method of  claim 19 , wherein step (a) further comprises measuring said arterial blood gas content with an electrochemical sensor. 
     
     
         22 . The method of  claim 21 , wherein step (a) further comprises measuring said arterial blood gas content with an electrochemical sensor capable of measuring blood gases selected from the group consisting of O 2  and CO 2 . 
     
     
         23 . The method of  claim 17 , wherein step (b) comprises:
 performing said measuring step in mixed venous blood.   
     
     
         24 . The method of  claim 23 , wherein step (b) further comprises:
 performing said measuring step with a sensor placed in the right ventricle of a patient's heart.   
     
     
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         29 . The method of  claim 17 , wherein said blood gas content measures comprise measures of oxygen saturation and wherein step (c) comprises:
 calculating a measure of cardiac output based on the difference in oxygen saturation between said arterial and venous blood gas contents as a function of the data from said blood gas content measurements of steps (a) and (b).   
     
     
         30 . The method of  claim 17 , further comprising measuring at least one of O 2  and CO 2  as said blood gas. 
     
     
         31 . A method of monitoring relative changes in cardiac output by an implantable cardiac device comprising:
 (a) measuring an arterial blood gas content extravascularly with an implanted sensor that is positioned outside a patient's heart;   (b) measuring a venous blood gas content intravascularly;   (c) deriving a measure of cardiac output from said arterial and venous blood gas content measurements to detect relative changes in cardiac output.   
     
     
         32 . The device of  claim 31  wherein the content is one of oxygen content and CO 2  content. 
     
     
         33 . The method of  claim 31 , wherein step (a) comprises measuring arterial blood gas content with a pulse oximetry sensor mounted on or incorporated within an exterior housing of an electronic circuit of the implantable cardiac device. 
     
     
         34 . The method of  claim 33 , further comprising transforming data measured by said extravascular pulse oximeter into a measure of cardiac output based on the difference in oxygen content between said arterial and venous blood gas content measurements. 
     
     
         35 - 49 . (canceled)