Method and apparatus for monitoring blood analytes noninvasively by pulsatile photoplethysmography

• US 5,137,023 A
• Filed: 04/19/1990
• Issued: 08/11/1992
• Est. Priority Date: 04/19/1990
• Status: Expired due to Term

• Current Assignee: Worcester Polytechnic Institute
• Original Assignee: Worcester Polytechnic Institute
• Inventors: Harjunmaa, Hannu, Peura, Robert A., Mendelson, Yitzhak
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): Pontius, Kevin
• Application Number:
  US07/511,229
• Time in Patent Office: 845 Days
• Field of Search: 128/632-634, 128/664, 128/666, 356/39-41, 250/215
• US Class Current: 600/316
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters

Abstract

A non-invasive system for measuring the concentration of an analyte, such as glucose, in an absorbing matrix is described. The system directs beams of light at the matrix using an analyte sensitive wavelength and an analyte insensitive wavelength. The principles of photoplethysmography are applied to measure the change in light intensity caused by matrix absorption before and after the blood volume change caused by the systolic phase of the cardiac cycle. The change in light intensity is converted to an electrical signal which is used to adjust the light intensity and as a measure of analyte concentration.

Claims

1. A method for determining the concentration of glucose in the blood of a body matrix which is subject to the systolic and diastolic phases of blood flowing through the matrix during the cardiac cycle, comprising the steps of:

a) generating a composite beam of electromagnetic radiation at each of two distinct wavelengths, a first such wavelength being glucose sensitive and a second such wavelength being glucose insensitive and wherein the two distinct wavelengths have the same matrix extinction in the body matrix and are in the infrared band of light;

b) directing said composite radiation at said matrix;

c) detecting said composite radiation after it has traversed a portion of said matrix; and

d) generating a composite electrical intensity signal proportional to the intensity of the detected composite radiation, which intensity signal is comprised of an alternating component produced by the variation in volume of blood flowing through the matrix and a non-alternating component produced by the non-varying portions of the matrix;

e) separating the composite electrical signal into a first channel signal consisting of that portion of the electrical signal produced by detecting radiation at said first wavelength and a second channel signal consisting of that portion of the electrical signal produced by detecting radiation at said second wavelength;

f) decomposing the first channel signal into a first alternating signal and a first non-alternating signal;

g) decomposing the second channel signal into a second alternating signal and a second non-alternating signal;

h) determining the amplitude ratio of the alternating to the non-alternating signal of each of the first and second channel signals;

i) generating an error signal from said ratio;

j) integrating the error signal to produce a control signal;

k) generating a difference signal proportional to the difference between said control signal and a reference signal;

said difference signal representing the instantaneous glucose concentration in the matrix.

2. A method for determining the concentration of an analyte in the blood of a body matrix which is subject to the systolic and diastolic phases of blood flowing through the matrix during the cardiac cycle, comprising the steps of:

a) generating a composite beam of electromagnetic radiation at each of two distinct wavelengths, a first such wavelength being analyte sensitive and a second such wavelength being analyte insensitive;

b) directing said composite radiation at said matrix;

c) detecting said composite radiation after it has traversed a portion of said matrix; and

d) generating a composite electrical intensity signal proportional to the intensity of the detected composite radiation, which intensity signal is comprised of an alternating component produced by the variation in volume of blood flowing through the matrix and a non-alternating component produced by the non-varying portions of the matrix;

e) separating the composite electrical signal into a first channel signal consisting of that portion of the electrical signal produced by detecting radiation at said first wavelength and a second channel signal consisting of that portion of the electrical signal produced by detecting radiation at said second wavelength;

f) decomposing the first channel signal into a first alternating signal and a first non-alternating signal;

g) decomposing the second channel signal into a second alternating signal and a second non-alternating signal;

h) determining the difference between the value of the alternating and the non-alternating signal of each of the first and second channel signals;

i) from said difference, determining the concentration of analyte in the matrix.

3. The method of claim 2 wherein the analyte is glucose.

4. The method of claim 3 wherein the two distinct wavelengths have the same matrix extinction in the body matrix and are in the infrared band of light.

5. A method for determining the concentration of an analyte in the blood of a body matrix which is subject to the systolic and diastolic phases of blood flowing through the matrix during the cardiac cycle, comprising the steps of:

a) generating a composite beam of electromagnetic radiation at each of two distinct wavelengths, a first such wavelength being analyte sensitive and a second such wavelength being analyte insensitive and wherein the matrix extinction of the two wavelengths is the same in the body matrix;

b) directing said composite radiation at said matrix;

c) detecting said composite radiation after it has traversed a portion of said matrix; and

d) generating a composite electrical intensity signal proportional to the intensity of the detected composite radiation, which intensity signal is comprised of an alternating component produced by the variation in volume of blood flowing through the matrix and a non-alternating component produced by the non-varying portions of the matrix;

e) separating the composite electrical signal into a first channel signal consisting of that portion of the electrical signal produced by detecting radiation at said first wavelength and a second channel signal consisting of that portion of the electrical signal produced by detecting radiation at said second wavelength;

f) decomposing the first channel signal into a first alternating signal and a first non-alternating signal;

g) decomposing the second channel signal into a second alternating signal and a second non-alternating signal;

h) determining the amplitude ratio of the alternating to the non-alternating signal of each of the first and second channel signals;

i) from said ratio, determining the concentration of analyte in the matrix.

6. A method for determining the concentration of an analyte in the blood of a body matrix which is subject to the systolic and diastolic phases of blood flowing through the matrix during the cardiac cycle, comprising the steps of:

a) generating a composite beam of electromagnetic radiation at each of two distinct wavelengths, a first such wavelength being analyte sensitive and a second such wavelength being analyte insensitive and wherein the matrix extinction of the two wavelengths is the same in the body matrix;

b) directing said composite radiation at said matrix;

c) detecting said composite radiation after it has traversed a portion of said matrix; and

d) generating a composite electrical intensity signal proportional to the intensity of the detected composite radiation, which intensity signal is comprised of an alternating component produced by the variation in volume of blood flowing through the matrix and a non-alternating component produced by the non-varying portions of the matrix;

e) separating the composite electrical signal into a first channel signal consisting of that portion of the electrical signal produced by detecting radiation at said first wavelength and a second channel signal consisting of that portion of the electrical signal produced by detecting radiation at said second wavelength;

f) decomposing the first channel signal into a first alternating signal and a first non-alternating signal;

g) decomposing the second channel signal into a second alternating signal and a second non-alternating signal;

h) determining the difference between the value of the alternating and the non-alternating signal of each of the first and second channel signals;

i) from said difference, determining the concentration of analyte in the matrix.

7. A method for determining the concentration of glucose in the blood of a body matrix which is subject to the systolic and diastolic phases of blood flowing through the matrix during the cardiac cycle, comprising the steps of:

a) generating a composite beam of electromagnetic radiation at each of two distinct wavelengths, a first such wavelength being glucose sensitive and a second such wavelength being glucose insensitive and wherein the matrix extinction of the two wavelengths is the same in the body matrix;

b) directing said composite radiation at said matrix;

c) detecting said composite radiation after it has traversed a portion of said matrix; and

d) generating a composite electrical intensity signal proportional to the intensity of the detected composite radiation, which intensity signal is comprised of an alternating component produced by the variation in volume of blood flowing through the matrix and a non-alternating component produced by the non-varying portions of the matrix;

e) separating the composite electrical signal into a first channel signal consisting of that portion of the electrical signal produced by detecting radiation at said first wavelength and a second channel signal consisting of that portion of the electrical signal produced by detecting radiation at said second wavelength;

f) decomposing the first channel signal into a first alternating signal and a first non-alternating signal;

g) decomposing the second channel signal into a second alternating signal and a second non-alternating signal;

h) comparing the alternating to the non-alternating signal of each of the first and second channel signals;

i) from said comparison, determining the concentration of glucose in the matrix.