Measurement of cardiac output and blood volume by non-invasive detection of indicator dilution

Abstract

A system for evaluating the cardiovascular system parameters using indicator dilution and non-invasive or minimally invasive detection methods is disclosed. Intravascular indicators are stimulated, and emissions patterns detected for computation of cardiac output, cardiac index, blood volume and other indicators of cardiovascular health.

1 . A method of measuring a parameter of a cardiovascular system in a subject in absolute physical units comprising:
 a. determining the volume of blood in the cardiovascular system;   b. administering to the cardiovascular system a detectable amount of an indicator that fluoresces when illuminated;   c. illuminating the indicator;   d. measuring the intensity of the fluorescence of the indicator while it is illuminated; and   e. determining the magnitude of the parameter in absolute physical units based on the measured intensity of the fluorescence, the administered amount of the indicator and the determined blood volume.   
   
   
       2 . The method of  claim 1 , further including:
 determining a conversion factor that converts the measured intensity of the fluorescence to the concentration of indicator in the cardiovascular system; and wherein determining the magnitude of the parameter is also based on the conversion factor.   
   
   
       3 . The method of  claim 1 , further including determining the concentration of the indicator in the cardiovascular system based on the amount of the indicator that was administered and the determined volume of blood. 
   
   
       4 . The method of  claim 3 , wherein:
 measuring the intensity of the fluorescence includes measuring the intensity as a function of time;   measuring the intensity of the fluorescence as a function of time results in an initial fast rising portion and a subsequent slow decay portion; and   determining the conversion factor, wherein the determining the conversion factor includes determining the point on the fast rising portion that is intercepted by an extrapolation of a portion of the slow decay portion.   
   
   
       5 . The method of  claim 4 , wherein the determining the conversion factor is based on the ratio of the determined concentration to the measured intensity of the fluorescence at the intercepted point. 
   
   
       6 . A system of measuring a parameter of a cardiovascular system in a subject in absolute physical units comprising:
 a. an illumination source configured to illuminate an administered indicator in the cardiovascular system of the subject to emit fluorescence;   b. a photodetector configured to measure the intensity of the fluorescence from the indicator while it is illuminated;   c. a computing system configured to determine the magnitude of the parameter in absolute physical units based on the measured intensity of the fluorescence, the amount of the administered indicator and a determined blood volume of the subject.   
   
   
       7 . The system of  claim 6 , wherein the computing system is configured to determine a conversion factor that converts the measured intensity of the fluorescence to the concentration of the indicator in the cardiovascular system. 
   
   
       8 . The system of  claim 6 , wherein the computing system is further configured to measure the intensity as a function of time so as to create an intensity curve having an initial fast rising portion and a subsequent slow decay portion; and to determine the point on a fast rising portion of the intensity curve that is intercepted by the extrapolation of a portion of the slow decay portion of the curve. 
   
   
       9 . The system of  claim 8 , wherein the computing system is further configured to determine the conversion factor based on a ratio of the determined concentration to the measured intensity of the fluorescence at the intercepted point. 
   
   
       10 . The system of  claim 6 , wherein the photodetector is positioned transcutaneously, perivascularly or intravascularly. 
   
   
       11 . The system of  10 , wherein the computing system is further configured to determine the indicator dilution curve, wherein the indicator dilution curve having a sharply rising initial portion and a slowly decaying subsequent portion. 
   
   
       12 . The system of  claim 11 , wherein the computing system is further configured:
 to back extrapolate the indicator dilution curve from the subsequent portion to a point on the initial portion;   to calculate the concentration of the indicator in the blood by dividing the amount of the administered indicator by the blood volume; and   to relate the extrapolated point to the calculated concentration.   
   
   
       13 . The system of  claim 10 , wherein the photodetector is positioned in proximity to an arterialized detection area.