Blood Flow Monitoring

Abstract

The present invention relates to a method of utilizing photoplethysmography obtained from a central site and a non-central site to detect a low blood flow or low blood volume condition. Also disclosed are apparatuses and systems designed to acquire and process physiological information based on photoplethysmograpy signal information from dual sites.

1 . A method of determining hypovolemia in a subject, said method comprising obtaining a first photoplethysmographic (PPG) signal from a central source site of said subject;
 obtaining a second PPG signal from a non-central site of said subject; and   monitoring for a difference between said first PPG signal relative to said second PPG signal;   
       wherein a change between said second PPG signal relative to said first PPG signal indicates a low blood volume condition in the subject. 
     
     
         2 . The method of  claim 1 , wherein said central source site is a nasal alar, nasal septum, cheek or lip of said subject. 
     
     
         3 . The method of  claim 1 , wherein said central source site is a nasal alar of said subject. 
     
     
         4 . The method of  claim 1 , wherein said central source site is a nasal septum of said subject. 
     
     
         5 . The method of  claim 1 , wherein said non-central site is an extremity of said subject. 
     
     
         6 . The method of  claim 1 , wherein said non-central site is a finger or toe of said subject. 
     
     
         7 . The method of  claim 1 , wherein a decrease of said second PPG signal relative to said first PPG signal indicates a low blood flow/low blood volume condition in the subject. 
     
     
         8 . A method of determining hypovolemia in a subject, said method comprising
 monitoring for a difference between a first PPG signal obtained from a central source site of said subject and a second PPG signal obtained from a non-central site of said subject;   
       wherein a decrease of said second PPG signal relative to said first PPG signal indicates a low blood flow/low blood volume condition in the subject. 
     
     
         9 . The method of  claim 8 , wherein said central source site is a nasal alar, nasal septum, cheek or lip of said subject. 
     
     
         10 . The method of  claim 8 , wherein said central source site is a nasal alar of said subject. 
     
     
         12 . The method of  claim 8 , wherein said central source site is a nasal septum of said subject. 
     
     
         13 . The method of  claim 8 , wherein said non-central source site is an extremity of said subject. 
     
     
         14 . The method of  claim 8 , wherein said non-central source site is a finger or toe of said subject. 
     
     
         15 . An apparatus for analyzing photoplethysmography signals from at least two sites on a living vertebrate, to determine the presence or absence of, or to monitor changes in, impaired peripheral perfusion or volume status comprising:
 a. means for receiving pulse oximeter probe signals from at least two sites on a living vertebrate, wherein at least one said site is a central source site and at least one said site is a non-central site; and   
       means for determining a change in blood volume at at least one non-central site based on the extent to which said at least one non-central site has a lower photoplethysmography signal than said central source site or the photoplethysmograpy signal from one non-central site decreases relative to the signal at the central site over time. 
     
     
         16 . The apparatus of  claim 15 , further comprising a means for presenting results to a user of said apparatus. 
     
     
         17 . A monitor system for analyzing photoplethysmography signals from at least two sites on a living vertebrate, to monitor changes in blood flow, comprising:
 a. output circuitry to deliver timed signals to energize light generating components of at least two pulse oximeter probes;   b. input circuitry to receive signals from said at least two pulse oximeter probes positioned said at least two sites on a living vertebrate, wherein at least one said site is a central source site and at least one said site is a non-central site;   c. a computer loaded with software to
 1. provide timed signals to energize said light generating components; 
 2. average sufficient signals from each pulse oximeter probe site to obtain a statistically reliable average; 
 3. calculate a time-set estimate of a photoplethysmography signal based on said statistically reliable average; 
 4. repeat steps 2 and 3 to obtain sequential time-set estimates of a photoplethysmography signal from each site; 
 5. compare a sequential time-set estimate of the photoplethysmography signal from the central source site with a sequential time-set estimate, taken at a similar time, of the photoplethysmography signal from the at least one non-central site; and 
 6. determine a change in blood volume to said at least one non-central site based on the extent to which said non-central site has a lower photoplethsymography signal than said central source site. 
   
     
     
         18 . A monitor system of  claim 17 , further comprising a read-out device to provide results to a user of said system. 
     
     
         19 . The monitor system of  claim 17 , further comprising software in said computer for estimating blood pressure through analysis of pulse time delay between said at least two sites. 
     
     
         20 . A method of observing respiration in a patient, said method comprising monitoring changes in the envelope of a PPG signal from a central source site of said patient.