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

• US 7,509,153 B2
• Filed: 03/07/2003
• Issued: 03/24/2009
• Est. Priority Date: 09/26/2000
• Status: Expired due to Fees

• Current Assignee: GLT Acquisition Corporation
• Original Assignee: Sensys Medical, Inc. (Sensys Medical Limited)
• Inventors: Lorenz, Alexander D., Mattu, Mutua, Makarewicz, Marcy, Ruchti, Timothy L., Monfre, Stephen L., Blank, Thomas B.
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US10/384,049
• Publication Number:
  US 20040039271A1
• Time in Patent Office: 2,209 Days
• Field of Search: 600/322, 600/316, 600/334
• US Class Current: 600/310
• 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:

controlling skin temperature proximate sampling tissue by applying a coupling medium, said coupling medium comprising a liquid having been pre-heated apart from the tissue;

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

extracting at least one feature from the analytical signal indicative of the effect of the target analyte on the probed tissue;

performing one of;

correcting a direct analyte measurement based on said at least one feature, or calculating concentration of said analyte indirectly by application of a calibration model to said at least one feature.

2. The method of claim 1,

further comprising a step of pre-heating the coupling medium apart from the tissue prior to applying the coupling medium.

3. The method of claim 1, where the step of collecting an analytical signal from the tissue comprises:

directing near-infrared energy upon the tissue via the coupling medium and measuring one or more properties of infrared energy exiting the tissue.

4. The method of claim 1, the coupling medium comprising one of:

a perfluorocarbon, or a fluorocarbon.

5. The method of claim 1, wherein said coupling medium comprises any of:

silicone oil;

mineral oil;

or

glycerol.

6. The method of claim 1, wherein said coupling medium comprises a perfluorocarbon liquid.

7. The method of claim 6, wherein said perfluorocarbon liquid has a fluorocarbon chain length of at least twelve carbons.

8. The method of claim 7, wherein said perfluorocarbon liquid has a fluorocarbon chain length of at least fifteen carbons.

9. The method of claim 1, wherein skin temperature is controlled to between approximately 30 and 40 degrees centigrade.

10. The method of claim 9, wherein skin temperature is controlled to between approximately 30 and 35 degrees centigrade.

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

12. The method of claim 11, wherein outermost 100 μ

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

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

14. The method of claim 1, wherein said feature represents redistribution of fluids between at least two of:

an extra-cellular compartment;

an intra-cellular compartment;

an extra-vascular compartment; and

an intra-vascular compartment.

15. The method of claim 1, wherein said analytical signal comprises an indirect representation of said concentration of said analyte.

16. The method of claim 15, wherein said indirect representation comprises a scattering signal.

17. A noninvasive method of measuring a tissue analyte, comprising acts 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 at least one feature from the analytical signal indicative of the effect of the target analyte on the probed tissue; and

calculating concentration of said analyte indirectly by application of a calibration model to said feature;

where the act of stabilizing optical properties comprises controlling skin temperature at the measurement site by performing acts comprising;

an operator applying a thermal wrap.