Abstract:
Method and apparatus for non-invasive measurement of the blood glucose concentration (or other selected physiological content) of a body tissue specimen by irradiating the specimen with modulated laser light, and receiving light re-emitted from the specimen to produce an electrical signal which controls the duration of laser energization and is decoded before operating a counter from a variable frequency pulse generator.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to non-invasive measurement of the physiological glucose concentration in a human or animal tissue specimen, such as a person&#39;s finger.  
         [0003]     2. Prior Art  
         [0004]     To determine the glucose content, particularly the blood glucose level, of human and animal tissues various methods invasive methods have been used which involve spectrophotometric or other analysis of the tissue. The invasive nature of such methods has been a principal drawback to their use.  
         [0005]     Various non-invasive methods of determining the blood glucose level in humans have been proposed heretofore which are cumbersome, difficult to use, and require frequent re-calibration of instruments involved in the method.  
         [0006]     Also, it has been proposed heretofore to direct high frequency radio waves onto the specimen and analyze the resulting energy emitted from the specimen to determine its glucose level. This radio frequency technique is complicated and requires complex circuitry.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention relates to a simple and reliable method and apparatus for non-invasive testing which is applicable to various types of human or animal tissue specimens, requires no calibration, and can be readily operated by a lay person who does not have special expertise.  
         [0008]     One aspect of the present invention is a non-invasive method of measuring the glucose concentration in the body of a human being or an animal. In accordance with this aspect, a principal object of this invention is to provide a novel and advantageous method of measuring the physiological glucose concentration of a body tissue specimen, particularly an in vivo specimen, such as a person&#39;s finger.  
         [0009]     Another aspect of this invention is an apparatus for conducting non-invasive testing of a body tissue specimen, particularly an in vivo specimen, for its glucose content. In accordance with this aspect, another principal object of this invention is to provide a novel and advantageous apparatus for measuring the glucose concentration of a body tissue specimen.  
         [0010]     Further objects and advantages of this invention will be apparent from the following detailed description of a presently preferred embodiment thereof, with reference to the single Figure of the accompanying drawing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0011]      FIG. 1  is a schematic circuit diagram of apparatus in accordance with the present invention for performing the method of this invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]     Before explaining the present invention in detail it is to be understood that the invention is not limited in its application to the particular arrangement shown and described since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation.  
         [0013]     The illustrated apparatus of this invention comprises a laser diode  10  of known design which transmits red light to irradiate a body tissue specimen  11 , such as a human person&#39;s finger in vivo. The position of the laser beam&#39;s impingement on the specimen is under the control of a signal applied to a coil of fine wire  12  wound around the laser. The laser does not focus the laser light on a very specific point on the surface of the specimen, and the time period of the laser&#39;s energization is very short so that there is no danger of damaging the specimen tissue. The laser is energized by a driver  13 , which preferably includes a unijunction transistor. The driver modulates the laser  10  at a suitable high frequency in the audio range, such as 10 MHz.  
         [0014]     Laser light incident on the specimen  11  is selectively absorbed by the material of the specimen, depending upon the type and concentration of chemicals in the specimen. In the present invention glucose is the chemical of particular interest in the in vivo specimen. In response to its irradiation with laser light, the specimen emits red light which has an intensity that depends on the concentration of glucose in the specimen&#39;s blood. The light coming from the specimen impinges on a photocell  14  positioned close to the laser. This photocell converts the incident light coming from the specimen  11  into an electrical output signal which is amplified by an amplifier  15  and filtered by a filter  16 . Preferably, amplifier  15  and filter  16  are embodied in an integrated circuit amplifier of known design. The amplified and filtered signal is applied via line  17  to the laser driver  13  to control the duration of the energization of the laser  10 , thereby determining the length of time for the test of a particular specimen.  
         [0015]     The amplified and filtered output signal of the photocell also is applied through line  18  to the input of a decoder  19 , which operates to effectively extract from this signal the pertinent information about the body tissue specimen, in this case, its glucose content. The decoder, which preferably is an integrated circuit, is programmed to receive needed information from the light with specific density and frequency which is received by photocell  14  from the specimen and amplified and filtered as described, and converts this information into an output signal which is applied to a variable frequency pulse generator  20  to produce a string of pulses which are counted in a counter circuit  21  of known design. The pulse input to counter  21  ends when the laser driver  13  turns off the laser  10 , in accordance with the amplified and filtered signal from photocell  14 , as described. The time interval during which the laser is energized by driver  13  is proportional to the amplitude of the signal applied to driver  13  via line from amplifier and filter  15 ,  16 . Decoder  19  scales the electrical signal it receives in such a way that the final count in counter  21  at the end of the test interval represents the glucose (or other selected chemical) concentration in standard units. The pulse count accumulated in counter  21  gives an accurate measure of the glucose level of the body specimen under test.  
         [0016]     As explained, the present apparatus turns off automatically at the completion of the test interval for a particular body specimen, thus requiring no expert judgment on the part off the person operating the apparatus to conduct the test method of the present invention. The test apparatus is easily handled by a person of no specialized skill, and it does not require frequent re-calibration to yield an accurate measurement of the physiological component that is being tested for.