Personal glucose monitor

• US 5,009,230 A
• Filed: 02/12/1990
• Issued: 04/23/1991
• Est. Priority Date: 05/31/1988
• Status: Expired due to Fees

• Current Assignee: eol, Inc. (Cisco Systems, Inc.)
• Original Assignee: eol, Inc. (Cisco Systems, Inc.)
• Inventors: Hutchinson, Donald P.
• Primary Examiner(s): Jaworski, Francis
• Assistant Examiner(s): Akers, Scott R.
• Application Number:
  US07/475,844
• Time in Patent Office: 435 Days
• Field of Search: 128/632, 128/633, 128/634, 128/664, 128/665, 356/364, 356/366, 356/368
• US Class Current: 600/316
• CPC Class Codes: A61B 5/14558 by polarisation

Abstract

A device for the non-invasive determination of blood glucose of a patient. This glucose monitor is based upon the effect of glucose in rotating polarized infrared light. More specifically, two orthogonal and equal polorized states of infrared light of minimal absorption are passed through a tissue containing blood, and an accurate determination of change in signal intensity is made due to the angle of rotation of these states. This rotation depends upon the glucose level. In order to compensate for absorption in the tissue, another two orthogonal and equal polarized states of infrared light are used, with the wavelength being selected to maximize absorption. At least two embodiments of forming the polarized states are described: an electro-optic switching unit, such as a lithium tantalate crystal with appropriately applied orthogonal voltages; and an infrared beam splitter using two light sources. The device can be applied to a patient, for example, to monitor glucose levels and provide signals to an insulin pump so as to be an artificial pancreas.

Claims

1. A device for the non-invasive determination of the concentration of blood glucose in a patient which comprises:

a first source of infrared light of a selected wavelength;

means for repetitively producing two alternating linearly-polarized orthogonal states of said infrared light, said two states being equal in amplitude;

means for directing said two states of said infrared light non-invasively through a selected tissue of said patient;

polarizing means for receiving said two states subsequent to passage through said selected tissue of said patient, and for passage of portions of said two states in a direction of transmission of said polarizing means;

detector means for detecting the intensities of said portions of said two states passing through said polarizing means, said intensities being related to glucose concentration and absorption in said selected tissue;

means for producing a sum and a difference of said intensities of said states received by said detector means; and

means for providing a ratio of said sum and said difference of said intensities to provide a signal related only to said glucose concentration.

2. The device of claim 1 wherein said means for producing said sum and difference of said intensities of said states, and said means for providing said ratio of said sum and difference value, is a central processing unit programmed for the solution of equations:

##EQU6## where V_s and V_so are the sum of the respective intensities when using the sample and not using the sample, V_d and V_do are the difference of the respective intensities with and without the sample, α

is the attenuation coefficient of the sample, L is the effective sample length, θ

is the angle of rotation caused by the glucose, and C is a calibration constant.

3. The device of claim 2, further comprising:

a second source of infrared light of a second

selected wavelength, said second selected wavelength different from said wavelength of said first source and being a wavelength substantially absorbed in said selected tissue of said patient;

means for repetitively and alternately producing two linearly-polarized orthogonal states of said second infrared light, said two states being equal in amplitude and substantially equal in amplitude of said two states of said first infrared light;

means for directing said two states of said second infrared light non-invasively through said selected tissue of said patient;

second polarizing means for receiving said two states of said second infrared light subsequent to passage through said selected tissue of said patient, and for passage of portions of said two states of said second infrared light in a direction of transmission of said second polarizing means;

second detector means for detecting intensities of said portions of said two states of said second infrared light passing through said second polarizing means, said intensities of said portions of said two states of said second infrared light being related to said glucose concentration and said absorption in said selected tissue of said patient;

means for producing a sum of said intensities of said states of said second infra-red light received by said second detector means; and

means for providing a ratio of said sum of said intensities of said first infrared light and said sum of said second infrared light to provide a signal related only to said glucose concentration.

4. The device of claim 3 wherein said means for producing said sum of said intensities of said states of said second infrared light, and said means for providing said ratio of said sum of said states of said first infrared light and said sum of said second infrared light is a central processing unit programmed for the simultaneous solution of equations ##EQU7## and the solution of equation

5. The device of claim 3 wherein said means for producing said two linearly polarized orthogonal states of said second infrared light comprises:

a second quarter-wave plate for receiving said polarized light from said second source to produce circularly polarized light; and

a second electro-optical switching crystal, having an alternating transverse voltage applied thereto, for receiving said circularly polarized light to repetitively and alternately form said two linearly polarized orthogonal states of said light from said second source having equal intensities.

6. The device of claim 3 wherein said means for producing said two linearly polarized orthogonal states of light from said second source comprises:

a second cubical beam splitter having an internal diagonal semi-reflective plane oriented whereby said infrared light from said second source impinges upon said plane of said second beam splitter at a 45 degree angle whereby light from said second source transmitted through said plane is linearly polarized in a first direction; and

a fourth source of infrared light of said second selected wavelength directed at said second beam splitter whereby light from said fourth source reflected by said plane in a same direction as said transmitted light from said second source is linearly polarized in a second direction orthogonal to said first direction.

7. The device of claim 6 further comprising:

a first detector to produce an output signal proportional to light of said first infrared light source reflected from said plane of said first beam splitter;

a second detector to produce an output signal proportional to light of said further infrared light source transmitted through said plane of said first beam splitter;

means for receiving said output signals of said first and second detector means and for adjusting current to said first and further infrared light sources to maintain said two states of said light from said first beam splitter equal in amplitude;

a third detector to produce an output signal proportional to light of said second infrared light source reflected from said plane of said second beam splitter;

a fourth detector to produce an output signal proportional to light of said fourth infrared light source transmitted through said plane of said second beam splitter; and

further means for receiving said output signals from said third and fourth detectors and for adjusting current to said second and fourth infrared light sources to maintain said two states from said second beam splitter equal in magnitude and equal in magnitude to said two states from said first beam splitter.

8. The device of claim 1 wherein said infrared light of said first source has a wavelength approximating a wavelength having minimal absorption in said selected tissue of said patient.

9. The device of claim 8 wherein said infrared light has a wavelength of about 940 nanometers.

10. The device of claim 1 wherein said means for producing said two states comprises:

a quarter-wave plate for receiving said polarized light to produce circularly polarized light; and

an electro-optical switching crystal, having an alternating transverse voltage applied thereto, for receiving said circularly polarized light to repetitively and alternately form said two linearly polarized orthogonal states having equal intensities.

11. The device of claim 1 wherein said means for producing said two states comprises:

a cubical beam splitter having an internal diagonal semi-reflective plane oriented whereby said infrared light from said first source impinges upon said plane at a 45 degree angle whereby light from said first source transmitted through said plane is linearly polarized in a first direction; and

a further source of infrared light of said selected wavelength directed at said beam splitter whereby light from said further source reflected by said plane in a same direction as said transmitted light from said first source is linearly polarized in a second direction orthogonal to said first direction.

12. The device of claim 11 further comprising a first detector to produce an output signal proportional to light of said first infrared light source reflected by said plane:

a second detector to produce an output signal proportional to light of said further infrared light source transmitted through said plane; and

means for receiving said output signals of said first and second detectors and for adjusting current to said first and further infrared light sources to maintain said two states equal in amplitude.

13. The device of claim 12 wherein said second infrared light has a wavelength of about 1300 nanometers.

14. A device for the non-invasive determination of the concentration of blood glucose in a patient, which comprises:

a first course of infrared light of a selected wavelength;

means for repetitively producing two alternating linearly-polarized orthogonal states of said first infrared light, said two states being equal in amplitude;

means for directing said two states of said first infrared light non-invasively through a selected tissue of said patient;

polarizing means for receiving said two states of said first infrared light subsequent to passage through said selected tissue of said patient, and for passage of portions of said two states in a direction of transmission of said polarizing means;

first detector means for detecting the intensities of said portions of said two states of said first infrared light passing through said polarizing means, said intensities being related to glucose concentration and absorption in said selected tissue;

means for producing a sum and a difference of said intensities of said states received by said first detector means;

a second source of infrared light of a second selected wavelength, said second selected wavelength different from said wavelength of said first source and being a wavelength substantially absorbed in said selected tissue of said patient;

means for repetitively and alternately producing two linearly-polarized orthogonal states producing two linearly-polarized orthogonal states of said second infrared light, said two states being equal in amplitude and substantially equal in amplitude of said two states of said first infrared light;

means for directing said two states of said second infrared light non-invasively through said selected tissue of said patient;

second polarizing means for receiving said two states of said second infrared light subsequent to passage through said selected tissue of said patient, and for passage of portions of said two states of said second infrared light in a direction of transmission of said second polarizing means;

second detector means for detecting intensities of said portions of said two sates of said second infrared light passing through said second polarizing means, said intensities of said portions of said two states of said second infrared light being related to said glucose concentration and said absorption in said selected tissue of said patient;

means for producing a sum of said intensities of said states of said second infrared light received by said second detector means; and

means for providing a ratio of said sum of said intensities of said first infrared light and said sum of said second infrared light to provide a signal related only to said glucose concentration.