Assessing Cardiovascular Function Using an Optical Sensor

Abstract

This document describes assessing cardiovascular function using an optical sensor, such as through sensing relevant hemodynamics understood by pulse transit times, blood pressures, pulse-wave velocities, and, in more breadth, ballistocardiograms and pressure-volume loops. The techniques disclosed in this document use various optical sensors to sense hemodynamics, such as skin color and skin and other organ displacement. These optical sensors require little if any risk to the patient and are simple and easy for the patient to use.

What is claimed is: 
     
         1 . A computer-implemented method comprising:
 receiving, from one or more optical sensors, a first skin color or a first skin displacement captured at a first region of a patient and a second skin color or a second skin displacement captured at a second region of the patient;   determining a circulatory distance between the first and second regions of the patient;   determining a time correlation between capture of the first color or the first skin displacement and capture of the second color or the second skin displacement; and   determining, based on the circulatory distance and the time correlation, a pulse-wave velocity for blood circulation through the patient.   
     
     
         2 . The method of  claim 1 , wherein determining the circulatory distance is based on:
 a linear distance between the first and second regions;   an axial distance between the first and second regions, the axial distance oriented relative to an axis of the patient's spine; or   an arterial-path distance, the arterial-path distance based on an arterial structure of the patient between the first and second region.   
     
     
         3 . The method of  claim 2 , wherein determining the circulatory distance based on the linear distance, the axial distance, or the arterial-path distance, comprises determining the linear distance, the axial distance, or the arterial-path distance, respectively, and is further based on surface information captured by the one or more optical sensors. 
     
     
         4 . The method of  claim 1 , wherein determining the time correlation is based on a time at which a maximum or minimum blood volume or rate of change in blood volume is determined for each of the first and second regions. 
     
     
         5 . The method of  claim 1 , wherein determining the pulse-wave velocity divides the circulatory distance by the time correlation for a same heartbeat of the patient. 
     
     
         6 . The method of  claim 1 , further comprising determining, based on the pulse-wave velocity, a blood pressure for the patient or a long-term trend in arterial stiffness. 
     
     
         7 . The method of  claim 1 , further comprising calibrating the one or more optical sensors with one or more external sensors effective to calibrate the skin colors or displacements to a calibration pulse-wave velocity, the calibrating prior to determining the pulse-wave velocity, and wherein determining the pulse-wave velocity is based at least in part on the calibration. 
     
     
         8 . The method of  claim 1 , further comprising:
 receiving, from one or more other optical sensors, a third skin color or a third skin displacement captured at a third region of the patient and a fourth skin color or a fourth skin displacement captured at a fourth region of the patient;   determining a second circulatory distance between the third and fourth regions of the patient;   determining a second time correlation between the detection of the third color or the third skin displacement and the detection of the fourth color or the fourth skin displacement;   determining, based on the second circulatory distance and the second time correlation, a second pulse-wave velocity for blood circulation through the patient; and   altering the first pulse-wave velocity based on the second pulse-wave velocity to improve an accuracy or robustness of the first pulse-wave velocity.   
     
     
         9 . The method of  claim 1 , further comprising:
 performing the operations again at a later time to determine a later-time pulse-wave velocity; and   determining a cardiac trend for the patient based on the later-time pulse-wave velocity and the pulse-wave velocity.   
     
     
         10 . The method of  claim 1 , wherein:
 the first skin color or the first skin displacement is a first skin color, the first skin color usable to determine blood in skin of the first region of the patient;   the second skin color or the second skin displacement is a second skin color, the second skin color usable to determine blood in skin of the second region of the patient; and   the blood determined in the skin of the first and second regions of the patient indicates, for multiple images captured at each of the first and second regions, first and second blood waveforms for the first and second regions, respectively.   
     
     
         11 . The method of  claim 1 , wherein:
 the first skin color or the first skin displacement is a first skin displacement, the first skin displacement usable to determine blood flow of the first region of the patient;   the second skin color or the second skin displacement is a second skin displacement, the second skin displacement usable to determine blood flow of the second region of the patient; and   the blood determined in the skin of the first and second regions of the patient indicates, for multiple images captured at each of the first and second regions, first and second blood waveforms for the first and second regions, respectively.   
     
     
         12 . A system comprising:
 one or more optical sensors capable of detecting skin color or skin displacement at two or more regions of a patient;   a computer processor; and   one or more computer-readable storage media having instructions stored thereon that, responsive to execution by the computer processor, performs operations comprising:
 receiving, from the one or more optical sensors, a first skin color or a first skin displacement captured at a first region of a patient and a second skin color or a second skin displacement captured at a second region of the patient; 
 determining a circulatory distance between the first and second regions of the patient; 
 determining a time correlation between capture of the first color or the first skin displacement and capture of the second color or the second skin displacement; and 
 determining, based on the circulatory distance and the time correlation, a pulse-wave velocity for blood circulation through the patient. 
   
     
     
         13 . The system of  claim 12 , wherein determining the circulatory distance is based on:
 a linear distance between the first and second regions;   an axial distance between the first and second regions, the axial distance oriented relative to an axis of the patient's spine; or   an arterial-path distance, the arterial-path distance based on an arterial structure of the patient between the first and second region.   
     
     
         14 . The system of  claim 13 , wherein determining the circulatory distance based on the linear distance, the axial distance, or the arterial-path distance, comprises determining the linear distance, the axial distance, or the arterial-path distance, respectively, and is further based on surface information captured by the one or more optical sensors. 
     
     
         15 . The system of  claim 12 , the operations further comprising:
 receiving, from one or more other optical sensors, a third skin color or a third skin displacement captured at a third region of the patient and a fourth skin color or a fourth skin displacement captured at a fourth region of the patient;   determining a second circulatory distance between the third and fourth regions of the patient;   determining a second time correlation between the detection of the third color or the third skin displacement and the detection of the fourth color or the fourth skin displacement;   determining, based on the second circulatory distance and the second time correlation, a second pulse-wave velocity for blood circulation through the patient; and   altering the first pulse-wave velocity based on the second pulse-wave velocity to improve an accuracy or robustness of the first pulse-wave velocity.   
     
     
         16 . The system of  claim 12 , the operations further comprising:
 performing the operations again at a later time to determine a later-time pulse-wave velocity; and   determining a cardiac trend for the patient based on the later-time pulse-wave velocity and the pulse-wave velocity.   
     
     
         17 . The system of  claim 12 , wherein:
 the first skin color or the first skin displacement is a first skin color, the first skin color usable to determine blood in skin of the first region of the patient;   the second skin color or the second skin displacement is a second skin color, the second skin color usable to determine blood in skin of the second region of the patient; and   the blood determined in the skin of the first and second regions of the patient indicates, for multiple images captured at each of the first and second regions, first and second blood waveforms for the first and second regions, respectively.   
     
     
         18 . The system of  claim 12 , wherein:
 the first skin color or the first skin displacement is a first skin displacement, the first skin displacement usable to determine blood flow of the first region of the patient;   the second skin color or the second skin displacement is a second skin displacement, the second skin displacement usable to determine blood flow of the second region of the patient; and   the blood determined in the skin of the first and second regions of the patient indicates, for multiple images captured at each of the first and second regions, first and second blood waveforms for the first and second regions, respectively.   
     
     
         19 . One or more computer-readable storage media having instructions stored thereon that, responsive to execution by a computer processor, performs operations comprising:
 receiving, from one or more optical sensors, a first skin color or a first skin displacement captured at a first region of a patient and a second skin color or a second skin displacement captured at a second region of the patient;   determining a circulatory distance between the first and second regions of the patient;   determining a time correlation between capture of the first color or the first skin displacement and capture of the second color or the second skin displacement; and   determining, based on the circulatory distance and the time correlation, a pulse-wave velocity for blood circulation through the patient.   
     
     
         20 . The computer-readable media of  claim 19 , wherein the instructions further perform operations comprising:
 performing the operations again at a later time to determine a later-time pulse-wave velocity; and   determining a cardiac trend for the patient based on the later-time pulse-wave velocity and the pulse-wave velocity.