Method of Assessing Blood Volume Using Photoelectric Plethysmography

Abstract

A method and system for assessing blood volume within a subject includes generating a cardiovascular waveform representing physiological characteristics of a subject and determining blood volume of the subject by analyzing the cardiovascular waveform. The step of analyzing includes generating a first trace of the per heart-beat maximums of the cardiovascular waveform, which is representative of the systolic pressure upon the cardiovascular signal, generating a second trace of the per heart-beat minimums of the cardiovascular waveform, which is representative of the diastolic pressure upon the cardiovascular signal, and comparing the respective first trace and the second trace to generate an estimate of relative blood volume within the subject. In accordance with an alternate method of analyzing harmonic analysis is applied to the cardiovascular waveform, extracting a frequency signal created by ventilation and applying the extracted frequency signal in determining blood volume of the subject.

1 - 65 . (canceled) 
     
     
         66 . A method of monitoring a hypovolemia parameter of a patient with electronic oximetry monitoring circuitry configured to noninvasively and electronically monitor the patient, the method comprising the steps of:
 inputting a plethysmograph responsive to an output from a noninvasive oximetry sensor applied to said patient, said output responsive to light intensity after absorption by fleshy tissue;   electronically measuring a respiration-induced variation in said input;   electronically normalizing said measurement;   electronically converting said normalized measurement into a numeric value indicating a blood volume level wherein said value indicates hypovolemia; and   providing at least one of an audible indication and a visual indication of said value to a caregiver of said patient.   
     
     
         67 . The hypovolemia monitoring method according to  claim 66 , wherein said inputting step comprises the substep of generating a pulse oximeter plethysmograph. 
     
     
         68 . The hypovolemia monitoring method according to  claim 67 , wherein said measuring step comprises the substeps of:
 detecting an envelope of said plethysmograph; and   determining a magnitude of said envelope.   
     
     
         69 . The hypovolemia monitoring method according to  claim 67 , wherein said measuring step comprises the substeps of:
 fitting a curve to a locus of points on said plethysmograph;   determining a magnitude of said variation from a characteristic of said curve.   
     
     
         70 . The hypovolemia monitoring method according to  claim 67 , wherein said measuring step comprises the substeps of:
 determining a frequency spectrum of said plethysmograph;   identifying a frequency component of said frequency spectrum proximate a respiration rate; and   calculating a magnitude of said frequency component.   
     
     
         71 . A hypovolemia monitor comprising
 one or more processors programmed to include a variation function having a sensor input and generating a variation parameter, said sensor input responsive to light intensity after absorption by fleshy tissue, said variation parameter providing a measure of respiration-induced cyclical variation in said sensor input; the one or more processor also programmed to include a normalization function applied to said variation parameter so as to generate a normalized variation parameter responsive to an average value of said sensor input; and the one or more processor programmed to include a conversion function applied to said normalized variation parameter so as to generate a numeric value indicating a blood volume level wherein said value indicates hypovolemia; and   an output providing at least one of an audible indication and a visual indication to one of a display and additional instrumentation.   
     
     
         72 . The hypovolemia monitor according to  claim 71 , wherein said variation function comprises:
 an envelope detector adapted to determine an envelope of said sensor input; and   a magnitude function configured to calculate a magnitude of said envelope.   
     
     
         73 . The hypovolemia monitor according to  claim 71 , wherein said variation function comprises:
 a curve-fit function adapted to determine a locus of said sensor input representative of said cyclical variation; and   a magnitude function configured to calculate a magnitude of said cyclical variation from said locus.   
     
     
         74 . The hypovolemia monitor according to  claim 71 , wherein said variation function comprises:
 a frequency transform function configured to generate a frequency spectrum of said sensor input; and   a frequency component function configured to determine the magnitude of a frequency component of said spectrum corresponding to a respiration rate of said living subject.   
     
     
         75 . A method for facilitating detection of physiological changes of a subject, the method comprising:
 analyzing a cardiovascular waveform representing physiological characteristics of a subject using a processor, wherein the analyzing of the cardiovascular waveform includes:
 identifying a first component of the cardiovascular waveform reflective of a cardiovascular impact of respiration; 
 analyzing a characteristic of the first component reflective of amplitude variations of the first component, wherein the amplitude variations are indicative of changes in blood volume of the subject, wherein the analyzing the characteristic of the first component of the cardiovascular waveform includes calculating an index responsive to the amplitude variations of the first component, wherein the first component is normalized and wherein index variations are indicative of changes in blood volume of the subject; 
   wherein the cardiovascular waveform is a photoplethysmograph waveform generated using a photoplethysmographic device.   
     
     
         76 . The method according to  claim 75 , further comprising generating the photoplethysmograph waveform. 
     
     
         77 . The method according to  claim 75 , wherein the first component is one of (i) a first trace of the per heart-beat maximums of the cardiovascular waveform, and (ii) a second trace of the per heart-beat minimums of the cardiovascular waveform. 
     
     
         78 . The method according to  claim 75 , wherein the cardiovascular waveform is analyzed using harmonic analysis to identify the first component of the cardiovascular waveform, wherein the first component is identified in the respiratory frequency range, and wherein the amplitude variations of the first component are indicative of changes in venous blood volume of the subject. 
     
     
         79 . The method according to  claim 75 , further comprising detecting hypovolemia based on the index. 
     
     
         80 . The method according to  claim 75 , further comprising providing at least one of (i) a visual indication of the index and (ii) an alarm indication of the index. 
     
     
         81 . The method according to  claim 75 , wherein the analyzing the cardiovascular waveform further includes identifying a second component of the cardiovascular waveform, wherein the index is responsive to changes in a comparison of the first and the second components relative to one another, whereby the first component is normalized. 
     
     
         82 . A system for facilitating detection of physiological changes of a subject, the system comprising a processor configured for analyzing a cardiovascular waveform representing physiological characteristics of a subject, wherein the cardiovascular waveform is a photoplethysmograph waveform generated using a photoplethysmographic device, wherein the analyzing the cardiovascular waveform includes identifying a first component of the cardiovascular waveform reflective of a cardiovascular impact of respiration, and analyzing a characteristic of the first component reflective of amplitude variations of the first component, wherein the analyzing the characteristic of the first component of the cardiovascular waveform includes calculating an index responsive to the amplitude variations of the first component, wherein the first component is normalized and wherein index variations are indicative of changes in blood volume of the subject. 
     
     
         83 . The system according to  claim 82 , wherein the first component is one of (i) a first trace of the per heart-beat maximums of the cardiovascular waveform, and (ii) a second trace of the per heart-beat minimums of the cardiovascular waveform. 
     
     
         84 . The system according to  claim 82 , wherein the cardiovascular waveform is analyzed using harmonic analysis to identify the first component of the cardiovascular waveform, wherein the first component is identified in the respiratory frequency range, and wherein the amplitude variations of the first component are indicative of changes in venous blood volume of the subject. 
     
     
         85 . The system according to  claim 82 , further comprising an output providing at least one of (i) a visual indication of the index and (ii) an alarm indication of the index. 
     
     
         86 . The system according to  claim 82 , wherein the analyzing the cardiovascular waveform further includes identifying a second component of the cardiovascular waveform, wherein the index is responsive to changes in a comparison of the first and the second components relative to one another, whereby the first component is normalized.