Optics: measuring and testing – Blood analysis
Reexamination Certificate
1997-05-06
2001-01-09
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Blood analysis
C128S126100
Reexamination Certificate
active
06172743
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to measuring the concentration of blood analytes such as glucose, cholesterol, potassium, bilirubin and other substances of interest present in the blood and tissue. Particularly, the invention relates to measurements made with an electromagnetic source of radiation in the wavelength range of 0.4 to 150 microns interacting with blood containing tissue so as to differentiate specific blood analytes from any contained or trapped in the tissue which is not freely transported through the blood.
BACKGROUND
It is frequently necessary to determine the concentration of various blood analytes when maintaining or treating mammals, including humans. An important example is the diabetic, whose glucose must constantly be monitored. Presently, diabetic blood is sampled invasively, typically through a finger prick or by drawing a blood sample. Other analytes of potential interest include lipids, cholesterol, serum proteins and electrolytes.
Much work has been done to monitor glucose by various non-invasive methods. These methods include infrared spectrophotometry. See Barnes et al., U.S. Pat. No. 5,070,874 (assigned to Biocontrol Technology, Inc.), Rosenthal et al., U.S. Pat. No. 5,028,787 (assigned to Futrex, Inc.), D{overscore (a)}hne et al., European Patent Publication No. 0,160,768 (Batelle Memorial Institute), and Robinson et al., U.S. Pat. No. 4,975,581 (assigned to the University of New Mexico). Other methods include alternative optical means such as that proposed in the article “Noninvasive Glucose Monitoring of the Aqueous Humor of the Eye” by Rabinovitch et al., Diabetes Care, Vol. 5 (No. 3): pp. 254-258 (May-June 1982). Other methods have been devised, including sampling of interstitial fluid in the mouth (unpublished communication from Mary Anne MacGillivray and Richard Battelle of Healthcraft International, Pasadena, Calif., 1988). Although non-invasive measurements can be made, all known prior art methods fail to distinguish whether an analyte, e.g. glucose, is in the subject's bloodstream or in surrounding tissue. This can result in incorrect and inappropriate determinations because of chemical interactions of the same or a spectrophometrically similar analyte located in the tissue where transport and utilization is distinctly different from the analyte moving through veins and arteries.
In addition, all prior methods suffer from low signal to noise of the spectrophotometric signals due to limitations of the light source and the limited resolution of spectral means such as gratings, prisms, filters, Hadamard or Fourier Transform (interferometric) spectrometers. These limitations result in poor analyte resolution or lengthy sample times, unnecessarily confining or restricting the movements of the subject or patient being tested.
In the known, non-invasive measurement prior art, no effort is made to distinguish analyte in the blood from that in tissue or interstitial fluids. Additionally, previous workers such as Robinson, Rosenthal and others limit spectroscopic non-invasive measurements to the near infrared region of the electromagnetic spectrum ignoring the visible and the medium and long infrared regions, limiting performance, accuracy, and range of blood analytes which can be detected and resolved.
Additionally, many medical conditions cause a physiological change in certain tissues which are otherwise suitable for non-invasive monitoring. For example, diabetics frequently suffer substantial reductions in peripheral blood flow to peripheral tissue such as the ear or finger.
Current methods and devices fail to provide adequate information about blood flows, blood volumes, and tissue temperatures at and across the tissue field. This information may be important to the determination of blood analytes and/or the proper medical evaluation of the blood analyte level and/or the medical condition, and temperature dependant behavior of the analyte and tissue. Current methods and devices also fail to provide information about the blood analytes located specifically in the tissue and interstitial fluid.
SUMMARY OF THE INVENTION
The present invention includes a device for non-invasively measuring an analyte within the body of a mammal. The device uses a source of light at one or more selected wavelengths for illuminating a tissue component of a mammal, then detects the light and measures the light during more than one selected time period. The light source may be a flash tube and a halogen lamp, which may have an envelope of quartz, sapphire, silicon, germanium, or other material which can pass selected light wavelengths. The light source may also be a laser, a laser diode, an LED, an array of lasers, laser diodes, or LEDs, any of which may be tuned to emit a selected range of wavelengths. Any of these light sources may be coupled with one or more filters, each of which passes one selected wavelength or selected wavelengths, which may be continuous or discontinuous. The filters may be switched as well, passing light or not light depending on the state of the filter.
The tissue component may be any extremity which contains blood and can conduct light. Preferred extremities are the finger and the ear lobe, but most any extremity will do if it will conduct any light. In one embodiment, light can be reflected from most any tissue, including deep tissue, an arm, a leg, the torso, scalp or the head.
The detector may be a charge coupled device, a photomultiplier, or other device capable of converting incident light into an electrical signal. The detector may be tuned to be sensitive to a selected wavelength or group of wavelengths, or may be coupled with one or more filters sensitive to a selected wavelength or group of wavelengths.
To provide signals at selected times, the light source may be varied, the source filters may be modulated, or the detector may be sampled at selected times, or a combination of the above. In general, it is desirable to take one measurement during maximum blood flow in the tissue component and a second measurement during minimum blood flow. The minimum blood flow measurement provides a reference for the other reading, allowing all background signals from tissue, bone, etc. and any analyte bound in tissue to be subtracted from the signal for the analyte of interest in blood. It may be helpful to take measurements at repeated blood flow cycles in order to improve signal to noise in a signal.
The difference in maximal and minimal blood flow can be accentuated by reducing the blood flow in the tissue region, for example by compression of the tissue. An inflatable cuff around a finger or a clamp on an ear lobe are useful examples. In addition, the temperature of the tissue can be modified through heating or cooling elements. A restrictive cuff around the base of a finger can exclude blood or can entrap blood for additional measurements.
The method of analysis includes measuring the analyte during both high and low blood flow. By selecting a variety of wavelengths and using multivariate analysis, one or more analytes can be distinguished from other blood and tissue components.
It is therefore an object of this invention to provide a new and improved apparatus for the non-invasive measurement of blood analytes using a broad range of electromagnetic wavelengths.
Another object of this invention is to provide a means to distinguish a blood analyte from the same or a similar analyte in the tissue or interstitial fluids.
Yet another object of this invention is to provide an apparatus which measures both blood analytes and tissue/interstitial analytes.
Another object of this invention is to provide an apparatus which measures blood flow and blood volume in vasculature and also to provide an apparatus which measures blood flows and blood volumes across a tissue field.
Another object of this invention is to measure temperature within a tissue field and also to provide an apparatus which measures temperature across the tissue field.
Another object is to provide a new apparatus for non-invasive measure of blood analytes an
Kley Vic
Schwartz Melvin
Chemtrix, Inc.
Font Frank G.
Punnoose Roy M.
Townsend and Townsend / and Crew LLP
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