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 enabling detection of physiological changes in a subject, the method comprising:
 generating a cardiovascular waveform representing physiological characteristics of a subject; and   analyzing the cardiovascular waveform, wherein the analyzing the cardiovascular waveform includes:
 identifying a first component of the cardiovascular waveform related to the amplitude of the cardiovascular waveform; and 
 calculating an index responsive to changes in the first component of the cardiovascular waveform; wherein index variations are reflective of physiological changes in the subject. 
   
   
   
       67 . The method of  claim 66 , further comprising means for displaying the index. 
   
   
       68 . The method of  claim 66 , wherein a processor is used for the step of analyzing the cardiovascular waveform. 
   
   
       69 . The method of  claim 66 , wherein the first component is based on differences between corresponding per heart-beat maximums and per heart-beat minimums of the cardiovascular waveform. 
   
   
       70 . The method of  claim 66 , wherein the index is responsive to changes in differences between corresponding per respiratory-cycle maximums and per respiratory-cycle minimums of the first component. 
   
   
       71 . The method of  claim 66 , wherein the analyzing the cardiovascular waveform further includes normalizing the first component of the cardiovascular waveform, wherein the index is responsive to changes in the normalized component of the cardiovascular waveform. 
   
   
       72 . The method of  claim 66 , wherein the index is responsive to changes in a plurality of components of the cardiovascular waveform. 
   
   
       73 . The method of  claim 66 , further comprising monitoring the physiological changes in the subject based on the index. 
   
   
       74 . The method of  claim 66 , wherein the physiological changes in the subject are changes in blood volume of the subject. 
   
   
       75 . The method of  claim 66 , further comprising monitoring fluid responsiveness based on the index variations. 
   
   
       76 . The method of  claim 66 , further comprising detecting at least one of (i) hypovolemia and (ii) dehydration, based on the index variations. 
   
   
       77 . The method of  claim 66 , wherein the cardiovascular waveform is a photoelectric plethysmographic signal. 
   
   
       78 . The method of  claim 66 , wherein the cardiovascular waveform is analyzed in one of:
 (i) the time domain, (ii) the frequency domain and (iii) the joint time-frequency domain.   
   
   
       79 . A method for detecting physiological changes in a subject, the method comprising:
 generating a cardiovascular waveform representing physiological characteristics of a subject; and   analyzing the cardiovascular waveform, wherein the analyzing the cardiovascular waveform includes:
 identifying a first component of the cardiovascular waveform; 
 identifying a second component of the cardiovascular waveform; 
 wherein one of the first and second components of the cardiovascular waveform is related to the amplitude of the cardiovascular waveform; 
 comparing the first and second components of the cardiovascular waveform relative to one another; and 
 calculating an index responsive to the changes in the comparison of the first and the second components of the cardiovascular waveform relative to one another; whereby the index is also responsive to changes in the one of the first and second components related to the amplitude of the cardiovascular waveform, wherein index variations are reflective of physiological changes in the subject. 
   
   
   
       80 . The method of  claim 79 , further comprising means for displaying the index. 
   
   
       81 . The method of  claim 79 , wherein a processor is used for the analyzing the cardiovascular waveform. 
   
   
       82 . The method of  claim 79 , wherein the one of the first and second components related to the amplitude of the cardiovascular waveform is based on differences between corresponding per heart-beat maximums and per heart-beat minimums of the cardiovascular waveform. 
   
   
       83 . The method of  claim 79 , wherein the first component is a pulsatile component and the second component is a non-pulsatile component. 
   
   
       84 . The method of  claim 79 , wherein the first component is an arterial component. 
   
   
       85 . The method of  claim 84 , wherein the second component is a venous component. 
   
   
       86 . The method of  claim 79 , wherein the first component is identified based on at least one of: (i) per heart-beat maximums of the cardiovascular waveform, (ii) per heart-beat minimums of the cardiovascular waveform and (iii) averages of corresponding per heart-beat maximums and per heart-beat minimums of the cardiovascular waveform; and wherein the second component is identified based on differences of corresponding per heart-beat maximums and per heart-beat minimums of the cardiovascular waveform. 
   
   
       87 . The method of  claim 79 , wherein the index is responsive to a normalization of the first component relative to the second component. 
   
   
       88 . The method of  claim 79 , further comprising monitoring the physiological changes in the subject based on the index. 
   
   
       89 . The method of  claim 79 , wherein the physiological changes in the subject are changes in blood volume of the subject. 
   
   
       90 . The method of  claim 79 , further comprising monitoring fluid responsiveness based on the index variations. 
   
   
       91 . The method of  claim 79 , further comprising detecting at least one of (i) hypovolemia and (ii) dehydration, based on the index variations. 
   
   
       92 . The method of  claim 79  wherein the cardiovascular waveform is a photoelectric plethysmographic signal. 
   
   
       93 . The method of  claim 79 , wherein the cardiovascular waveform is analyzed in one of: (i) the time domain, (ii) the frequency domain and (iii) the joint time-frequency domain.