Method and device for measuring concentration levels of blood constituents non-invasively

• US 5,361,758 A
• Filed: 10/09/1991
• Issued: 11/08/1994
• Est. Priority Date: 06/09/1988
• Status: Expired due to Term

• Current Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Original Assignee: CME Telemetrix, Inc.
• Inventors: Hall, Jeffrey W., Cadell, T. E.
• Primary Examiner(s): Shay, David M.
• Application Number:
  US07/785,430
• Time in Patent Office: 1,126 Days
• Field of Search: 129/632-634, 129/664, 129/665, 129/395, 129/397, 129/398
• US Class Current: 600/322
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/14546 for measuring analytes not otherwise provided for, e.g. ions, cytochromes
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01J 3/433 Modulation spectrometry; Derivative spectrometry
• CPC Class Codes: G01N 21/359 using near infrared light

Abstract

A non-invasive device and method for monitoring concentration levels of blood and tissue constituents within a living subject such as a human or animal utilizes a polychromatic light source that emits light over a broad spectrum of wavelengths in the near infrared range. The light is passed through, or reflected from, a part of the subject such as a finger, ear lobe or other part of the body. That light is then separated into its various components by means of a grating or prism, and the near infrared band is focussed onto a linear array detector. A microprocessor uses the output of the array detector to measure the light transmitted (T), calculate the absorbance (log 1/T) and calculate the second derivative of the absorbance. A calibration equation is used for each constituent to be monitored to convert the second derivative measurements to a concentration level for that constituent. The device is programmed to take measurements between heart beats and to adjust for the temperature of the sample being taken. The device can be used to determine levels of various blood and tissue constituents, including glucose, cholesterol, alcohol, blood gases and various ions. The device is simple to use, painless and does not cause any physical discomfort, skin irritation or present any risk of infection to the user. The device can be used for clinical use or for home use and the memory of the microprocessor can be used to assist with record keeping and with dosage calculations. Previous non-invasive devices are not sufficiently accurate or convenient to use to replace the invasive testing systems presently used.

Claims

1. A non-invasive device for measuring concentration levels of constituents of blood and tissue in a living subject such as a human or animal, said device comprising a polychromatic light source that emits a broad spectrum of light in the near infrared range, said light source being coupled to and powered by a stabilized power source, said device having a receptor shaped so that part of said subject can be placed in contact with said receptor, said receptor having means for eliminating extraneous light, said receptor being located relative to said light source so that when part of said subject is placed in contact with said receptor, said light source can be activated and light from said light source at a continuum of wavelengths is directed onto said part, means coupled to the device for collecting simultaneously a continuum of wavelengths over said broad spectrum after said light has been directed onto said part, means coupled to the device for dispersing said collected light over said broad spectrum into a dispersed spectrum of component wavelengths of said collected light, means coupled to the device for taking absorbance measurements from at least one of transmitted and reflected light from said collected light at several different wavelengths simultaneously over said dispersed spectrum, means coupled to the device for transforming said measurements over said dispersed spectrum to enhance measurement of concentration of at least one constituent from other constituents by using a calibration equation for said at least one constituent, means coupled to the device for determining the concentration level of said at least one constituent of said blood and then producing a result for each concentration level determined.

2. A device as claimed in claim 1 wherein the calibration equation is derived from a least square'"'"'s best fit of spectral data obtained by said device to actual measured levels obtained coincidentally.

3. A device as claimed in claim 2 wherein the means for transforming said measurements to enhance measurement of concentration of at least one constituent from other constituents comprises mean for taking a log of an inverse of at least one of the transmitted and reflected light from said collected light and further taking a second derivative of said log of the inverse.

4. A device as claimed in any one of claims 1, 2 or 3 wherein the means for measuring at least one of the transmitted and reflected light from said collected light at several different wavelengths simultaneously is a linear array detector and a microprocessor, said linear array detector receiving said collected light after the collected light has been directed onto said part and collected, said microprocessor comprising means for scanning said linear array detector, said detector being connected to said microprocessor for taking said measurements.

5. A device as claimed in any one of claims 1, 2 or 3 wherein the means for dispersing said collected light into component wavelengths of said collected light is a grating.

6. A device as claimed in any one of claims 1, 2 or 3 wherein there are means for detecting a pulse within that part of the subject placed in contact with said receptor, there being means to control said device to use measurements taken immediately subsequent to the detection of a pulse and prior to a next pulse so that all measurements upon which a result is based are taken between pulses.

7. A device as claimed in claim 2 wherein the device has a temperature sensor for measuring the temperature at that part of the subject located in contest with the receptor with means for adjusting the measurements taken based on variations in said temperature.

8. A device as claimed in claim 7 wherein the temperature sensor is a thermo-couple designed with a fast response time, of less than 200 milliseconds, and there is a microprocessor to compensate for spectrum deviations due to temperature.

9. A device as claimed in any one of claims 1, 2 or 3 wherein said receptor is shaped to receive said part of the subject within said receptor and the means for collecting is a means for collecting transmitted light.

10. A device as claimed in any one of claims 1, 2 or 3 wherein the means for eliminating extraneous light from the receptor is a flexible seal surrounding an entrance to said receptor, said seal being small enough to form a light barrier around that part of the subject onto which light is directed.

11. A device as claimed in any one of claims 1, 2 or 3 wherein the means for collecting said light at several different wavelengths simultaneously after said light has been directed onto said part are lenses.

12. A device as claimed in any one of claims 1, 2 or 3 wherein the means for detecting a pulse is a means for monitoring plethysmographic blood pressure.

13. A device as claimed in any one of claims 1, 2 or 3 wherein the means for detecting a pulse is a means for detecting the pulse from a sonogram.

14. A device as claimed in any one of claims 1, 2 or 3 wherein the means for detecting a pulse is a means for detecting the pulse from a an electrocardiogram.

15. A device as claimed in any one of claims 1, 2 or 3 wherein there is a collimator located between the polychromatic light source and said receptor so that light from the polychromatic light source passes through said collimator before passing into said receptor.

16. A device as claimed in any one of claims 1, 2 or 3 wherein the means for collecting said light after said light is directed onto said receptor is a lens, said lens being oriented and shaped to focus said light on a slit, said light passing through said slit to a second lens to collimate the light onto a diffraction grating, the means for taking absorbance measurements from at least one of the transmitted and reflected light from said light being a linear array detector, said detector having an output coupled to a microprocessor which is the means for taking the absorbance the measurements and is controlled by computer software to transform said measurements and determine the concentration level of at least one component of said mixture and produce a result.

17. A device as claimed in any one of claims 1, 2 or 3 wherein the near infrared region in which measurements are taken extends from 650 nm to 2800 nm.

18. A device as claimed in any one of claims 1, 2 or 3 wherein the near infrared region in which measurements are taken extends from 700 nm to 1100 nm.

19. A device as claimed in any one of claims 1, 2 or 3 wherein the means for taking absorbance measurements from at least one transmitted and reflected light from said collected light at several different wavelengths simultaneously is a linear array detector and a microprocessor, and there are means for reducing noise levels within said device by a scanning technique whereby the linear array detector scans the entire spectrum of interest many times per second for several repetitions ranging from approximately 8 to approximately 64 repetitions and the microprocessor then averages the results.

20. A device as claimed in any one of claims 1, 2 or 3 wherein the means for collecting said light after said light is directed onto said receptor are fibre optics that transmit said light to means for dispersing.

21. A device as claimed in any one of claims 1, 2 or 3 wherein the means for collecting said light after said light is directed onto said receptor is a hologram comprising means for focussing said light onto a diffraction grating.

22. A device as claimed in any one of claims 1, 2 or 3 wherein the means for dispersing said collected light into component wavelengths of said collected light is a holographic diffraction grating.

23. A device as claimed in claim 1 wherein the means for simultaneously taking measurement from at least one of transmitted and reflected light from said collected light over said continuum of wavelengths is a linear array detector coupled to microprocessor, said microprocessor having a memory constituting a means for comprising concentration level changes over a period of time.

24. A device as claimed in claim 22 wherein the linear array detector is a photo diode array and the means for dispersing said collected light into component wavelengths of said collected light is a grating, the light being collected from the grating by the photo diode array that is positioned to intercept the dispersed spectrum of light across its length.

25. A device as claimed in any one of claims 1, 2 or 3 wherein the concentration level of constituents that are measured are selected from, but not limited to, the group of:

amino acid, nitrogen, blood oxygenation, carbon dioxide, cortisol, creatine, creatinine, glucose, ketones, lipids, fat, urea, amino acids, fatty acids, glycosolated hemoglobin, cholesterol, alcohol, lactate, Ca++, K+, Cl-, HCO_3-, and HPO_4-.

26. A device as claimed in any one of claims 1, 2 or 3 wherein the means for measuring concentration include one calibration equation for each constituent to be measured, each calibration equation including measurements taken at all of the wavelengths measured.

27. A device as claimed in any one of claims 1, 2 or 3 wherein there are means for transforming said measurements to enhance measurement of concentration of at least two constituents by using a calibration equation for each of said at least two constituents.

31. A method as claimed in any one of claims 27, 28 or 29 including the step of deriving the calibration equation from a least square'"'"'s best fit of spectral data obtained using the device to actual measured levels obtained coincidentally.

28. A non-invasive method for measuring concentration levels of blood and tissue constituents within a living subject such as a human or animal, using a polychromatic light source that emits a broad spectrum of light in the near infrared range from 650 nm to 2700 nm, said method comprising directing said light at a continuum wavelengths simultaneously onto a part of said subject, collecting the continuum of light after said light has been directed onto said part, focusing the collected light onto a grating, dispersing continuum of light into a dispersed spectrum of component wavelengths of said collected light onto a linear array detector, said linear array detector taking absorbance measurements of at least one of transmitted and reflected light from said collected light in said near infrared range simultaneously our said continuum of wavelengths said dispersed spectrum, scanning said linear array detector and passing said measurements to a microprocessor, taking a reference set of measurements, transforming said measurements over said broad range to enhance the measurement of concentration of at least one constituent from other constituents by using a calibration equation for said at least one constituent, determining the concentration level of at least one constituent of said blood and tissue and producing a result for each concentration level determined.

29. A method as claimed in claim 28 wherein the measurements are transformed to enhance the detection of at least one constituent from other constituents by taking a log of an inverse of at least one of the transmitted and reflected light from and further by calculating a second derivative of said log of said inverse.

30. A method as claimed in claim 29 including the step of producing the result on a display.

32. A method as claimed in claim 28 wherein there are at least two constituents to be measured and the method includes the step of transforming said measurements to enhance the measurement of concentration of at least two constituents from other constituents by using a calibration equation for each of said at least two constituents.

33. A non-invasive method for measuring concentration levels of blood and tissue constituents within a living subject such as a human or animal, using a polychromatic light source that emits a broad spectrum of light in the near infrared range from 650 nm to 1100 nm, said method comprising simultaneously directing said continuum of light onto a part of said subject, collecting the continuum of light after said light has been directed onto said part, focusing the collected light onto a grating to disperse said collected continuum of light into a dispersed spectrum of component wavelengths of said collected light, dispersing said light onto a linear array detector, said linear array detector simultaneously taking absorbance measurements transmitted light from said collected light in said near infrared range over said continuum of, scanning said linear array detector and passing said measurements to a microprocessor, taking a reference set of measurements, transforming said measurements over said continuum of wavelengths to enhance the measurement of concentration of at least one constituent from other constituents by using a calibration equation for said at least one constituent and by taking a log of an inverse of said measurements and calculating a second derivative of said log, determining the concentration level of at least one constituent of said blood and tissue and producing a result for each concentration level determined.