Method and apparatus for control of skin perfusion for indirect glucose measurement

• US 20040039271A1
• Filed: 03/07/2003
• Published: 02/26/2004
• Est. Priority Date: 09/26/2000
• Status: Active Grant

• Current Assignee: Alexander D. Lorenz, Marcy Makarewicz, Mutua Mattu, Stephen L. Monfre, Thomas B. Blank, Timothy L Ruchti
• Original Assignee: Sensys Medical, Inc. (Sensys Medical Limited)
• Inventors: Ruchti, Timothy L., Monfre, Stephen L., Blank, Thomas B., Lorenz, Alexander D., Mattu, Mutua, Makarewicz, Marcy
• Granted Patent: US 7,509,153 B2
• Time in Patent Office: Days
• US Class Current: 600/322
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• 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
• CPC Class Codes: A61B 5/1491 Heated applicators
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: G01N 2021/3595 using FTIR
• CPC Class Codes: G01N 21/31 Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry G01N21/72 takes precedence
• CPC Class Codes: G01N 21/33 using ultraviolet light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/359 using near infrared light
• CPC Class Codes: G01N 21/65 Raman scattering

Abstract

A method and apparatus for noninvasive glucose measurement measures glucose indirectly from the natural response of tissue to variations in analyte concentration. The indirect measurement method utilizes factors affected by or correlated with the concentration of glucose, such as refractive index, electrolyte distribution or tissue scattering. Measurement reliability is greatly improved by stabilizing optical properties of the tissue at the measurement site, thus blood perfusion rates at the sample site are regulated. Perfusion is monitored and stabilized by spectroscopically measuring a control parameter, such as skin temperature, that directly affects perfusion. The control parameter is maintained in a range about a set point, thus stabilizing perfusion. Skin temperature is controlled using a variety of means, including the use of active heating and cooling elements, passive devices, such as thermal wraps, and through the use of a heated coupling medium having favorable heat transfer properties.

Claims

1. A noninvasive method of measuring a tissue analyte, comprising steps of:

stabilizing optical properties of said tissue at a measurement site;

collecting an analytical signal from the tissue, said collected signal comprising a tissue measurement;

extracting features from the analytical signal indicative of the affect of the target analyte on the probed tissue; and

calculating concentration of said analyte indirectly by application of a calibration model to said features.

2. The method of claim 1, wherein said step of stabilizing optical properties comprises stabilizing perfusion at said measurement site.

3. The method of claim 2, wherein said step of stabilizing perfusion comprises:

controlling skin temperature at said measurement site.

4. The method of claim 3, wherein step of controlling skin temperature at said measurement site comprises any of the steps of:

applying a passive means of temperature control; and

applying an active means of temperature control.

5. The method of claim 4, wherein said passive means of temperature control comprises a thermal wrap applied by an operator.

6. The method of claim 4, wherein said active means of temperature control comprises any of:

at least one radiative heating element;

at least one conductive heating/cooling element.

7. The method of claim 6, wherein said one or both of said at least one radiative element and said at least one conductive heating/cooling element are embodied within a subject interface of a measurement sensor.

8. The method of claim 3, wherein said step of controlling skin temperature at said measurement site comprises steps of:

providing a coupling medium;

heating a portion of said coupling medium; and

disposing said heated portion of said coupling medium between a patient interface of patient interface module and said skin at said measurement site, wherein transfer of thermal energy from said heated portion of said coupling medium to said skin occurs.

9. The method of claim 8, wherein said coupling medium comprises any of:

silicone oil;

mineral oil; and

glycerol.

10. The method of claim 8, wherein said coupling medium comprises a perfluorocarbon liquid.

11. The method of claim 10, wherein said perfluorocarbon liquid comprises FLUORINERT perfluorocarbon liquid.

12. The method of claim 11, wherein said FLUORINERT perfluorocarbon liquid comprises one of FC-40 and FC-70.

13. The method of claim 3, wherein skin temperature is controlled to between approximately 30 and 40 degrees centigrade;

14. The method of claim 13, wherein skin temperature is controlled to between approximately 30 and 35 degrees centigrade.

15. The method of claim 3, wherein skin temperature is maintained to within approximately 1 degree centigrade of a set point.

16. The method of claim 15, wherein outermost 100 μ

m of said skin is controlled to within approximately 1 degree centigrade of a set point.

17. The method of claim 1, wherein said analyte comprises glucose.

18. A noninvasive method of measuring a tissue analyte, comprising steps of:

providing a coupling medium;

heating a portion of said coupling medium;

disposing said heated portion of said coupling medium between a measurement probe and a skin surface at a sampling site;

collecting an analytical signal from the tissue, said collected signal comprising a tissue measurement; and

calculating concentration of said analyte from said tissue measurement.

19. The method of claim 18, wherein said coupling medium comprises a perfluorocarbon liquid.

20. The method of claim 19, wherein said perfluorocarbon liquid comprises FLUORINERT perfluorocarbon liquid.

21. The method of claim 20, wherein said FLUORINERT perfluorocarbon liquid comprises one of FC-40 and FC-70.

22. The method of claim 18, further comprising a step of:

extracting features from the analytical signal indicative of the effect of the target analyte on the probed tissue.

23. The method of claim 19, wherein said step of calculating concentration of said analyte from said tissue measurement comprises calculating concentration of said analyte indirectly by application of a calibration model to said features.

24. The method of claim 18, wherein said analyte comprises glucose.