 |
Claims  |
|
|
We claim:
1. A non-invasive, blood chemistry measurement apparatus for measuring a
concentration of a selected blood component within a sample of blood, said
apparatus comprising:
a source of exposing light having a spectral peak at wavenumber k.sub.1
that will excite said blood component to a state from which it emits
light, by stimulated relaxation emission, having a peak at a second
wavenumber k.sub.2 different from k.sub.1 ;
means for imaging said exposing light through an area of epidermis of an
animal into a portion of that animal's blood adjacent to said area of
epidermis on which this exposing light is incident;
means for detecting light that is emitted at wavenumber k.sub.2 from
molecules of said selected blood component in response to exposing light
from said source of light; and
means, responsive to said means for detecting, for calculating a
concentration of said selected blood component.
2. An apparatus as in claim 1 wherein said means for detecting comprises a
detector that is responsive substantially only to light at a wavenumber
k.sub.2 that is emitted by stimulated relaxation emission substantially
only by molecules of said selected blood component.
3. An apparatus as in claim 1 wherein said means for detecting is
responsive to a set of N different wavenumbers, thereby producing N
signals S.sub.1, . . . , S.sub.N, where N is greater than 1, wherein a
first signal S.sub.1 is produced in response to an associated stimulated
relaxation emission peak from said selected blood component, wherein a
second signal S.sub.2 is produced in response to a different, associated
stimulated emission peak from a second selected blood component and
wherein said means for calculating a concentration is responsive to these
N signals to produce the concentration of said selected blood component.
4. An apparatus as in claim 3 wherein said means for detecting detects only
light in a set of N wavenumber bands and wherein each S.sub.k, for k=1, .
. . , N, is proportional to the intensity of light in the kth of these
wavenumber bands.
5. An apparatus as in claim 4 wherein said means for detecting comprises a
set of N detectors, each of which detects light only in a uniquely
associated one of these N wavenumber bands.
6. An apparatus as in claim 1 wherein said source of light is selected from
the class consisting of a super-radiant photodiode and a flash lamp.
7. An apparatus as in claim 1 wherein the light from said source is imaged
onto a region adjacent to said epidermis area of an animal and said means
for detecting light comprises at least one optical detector positioned
such that each ray of emitted light that is received by such at least one
optical detector travels along a substantially minimum length path from
its point of emission to such at least one detector, whereby absorption of
emitted light by the solution is substantially minimized as a function of
the position of said at least one detector.
8. An apparatus as in claim 7 wherein the light from said source is imaged
onto a region within the animal and the light travels from said source to
this region along a path that is substantially perpendicular to said
epidermis area at a point that this light passes through such epidermis
area, whereby the amount of absorption of this light by components of the
solution other than said selected component is substantially minimized.
9. An apparatus as in claim 7 wherein the light has an intensity of at
least 5 Watts/cm.sup.2 within the region in which the light is imaged.
10. An apparatus as in claim 7 wherein said containment vessel is a finger
of a human and the wall is a portion of the epidermis on a front surface
of a finger of this human.
11. An apparatus as in claim 7 wherein said light from the source is
directed onto a papillary bed in a subject under test.
12. An apparatus as in claim 11 wherein said light from the source is
focussed onto this papillary bed.
13. A non-invasive, blood chemistry measurement apparatus for measuring a
concentration of a selected blood component within a sample of blood, said
apparatus comprising:
a source of exposing light having a spectral peak at wavenumber k.sub.1
that will excite said blood component to a state from which it emits
light, by stimulated relaxation emission, having a peak at a second
wavenumber k.sub.2 different from k.sub.1 ;
means for imaging said exposing light through an area of epidermis of an
animal into a portion of that animal's blood adjacent to said area of
epidermis on which this exposing light is incident;
means for detecting light that is emitted at wavenumber k.sub.2 from
molecules of said selected blood component in response to exposing light
from said source of light; and
means, responsive to said means for detecting, for calculating a
concentration of said selected blood component, wherein N=2, wherein said
selected blood component is blood glucose, wherein S.sub.1 is proportional
to an intensity of light within a band substantially centered on an
emission peak of blood glucose substantially at a wavenumber of 1040
cm.sup.-1, wherein S.sub.2 is proportional to an intensity of light within
a band substantially centered on an emission peak of haemoglobin produced
by incident fight substantially at a wavenumber of 1109 cm.sup.-1 and
wherein said means for calculating a concentration calculates a
concentration of blood glucose that is corrected by use of S.sub.2 to take
into account effects due to changes in blood volume intersected by the
light from said light source.
14. A non-invasive, blood chemistry measurement apparatus for measuring a
concentration of a selected blood component within a sample of blood, said
apparatus comprising:
a source of exposing light having a spectral peak at wavenumber k.sub.1
that will excite said blood component to a state from which it emits
light, by stimulated relaxation emission, having a peak at a second
wavenumber k.sub.2 different from k.sub.1 ;
means for imaging said exposing light through an area of epidermis of an
animal into a portion of that animal's blood adjacent to said area of
epidermis on which this exposing light is incident;
means for detecting light that is emitted at wavenumber k.sub.2 from
molecules of said selected blood component in response to exposing light
from said source of light; and
means, responsive to said means for detecting, for calculating a
concentration of said selected blood component,
wherein S.sub.1 is proportional to an intensity of light within a band
substantially centered on an emission peak of blood glucose substantially
at a wavenumber of 1040 cm.sup.-1, wherein S.sub.2 is proportional to an
intensity of light within a band substantially centered on an emission
peak of haemoglobin produced by incident light substantially at a
wavenumber of 1109 cm.sup.-1, wherein S.sub.3 is proportional to an
intensity of light within a band that contains substantially only
blackbody radiation from surrounding portions of this apparatus, and
wherein said means for calculating a concentration calculates a
concentration of blood glucose that is corrected by use of S.sub.2 and
S.sub.3 to take into account effects due to changes in temperature and
volume of blood intersected by the light from said source.
15. An apparatus as in claim 14 wherein light from the source includes a
peak substantially, at 1109 cm.sup.-1, whereby it is effective in
substantially exciting haemoglobin molecules, whereby a measurement can be
corrected to take into account a change in blood concentration being
measured.
16. A non-invasive, blood chemistry measurement apparatus for measuring a
concentration of a selected blood component within a sample of blood, said
apparatus comprising:
a source of exposing light having a spectral peak at wavenumber k.sub.1
that will excite said blood component to a state from which it emits
light, by stimulated relaxation emission, having a peak at a second
wavenumber k.sub.2 different from k.sub.1 ;
means for imaging said exposing light through an area of epidermis of an
animal into a portion of that animal's blood adjacent to said area of
epidermis on which this exposing light is incident;
means for detecting light that is emitted at wavenumber k.sub.2 from
molecules of said selected blood component in response to exposing light
from said source of light;
means, responsive to said means for detecting, for calculating a
concentration of said selected blood component;
a temperature sensor means for measuring a temperature of a region from
which light is received by said means for detecting; and
means for maintaining a substantially constant, selected temperature T of a
region of said apparatus that emits blackbody radiation to said means for
detecting.
17. A non-invasive, blood chemistry measurement apparatus for measuring a
concentration of a selected blood component within a sample of blood, said
apparatus comprising:
a source of exposing light having a spectral peak at wavenumber k.sub.1
that will excite said blood component to a state from which it emits
light, by stimulated relaxation emission, having a peak at a second
wavenumber k.sub.2 different from k.sub.1 ;
means for imaging said exposing light through an area of epidermis of an
animal into a portion of that animal's blood adjacent to said area of
epidermis on which this exposing light is incident;
means for detecting light that is emitted at wavenumber k.sub.2 from
molecules of said selected blood component in response to exposing light
from said source of light;
means, responsive to said means for detecting, for calculating a
concentration of said selected blood component;
a flat plate that is transparent to the emitted light, positioned such that
light emitted from the sample of blood passes through this plate before
reaching said means for detecting;
this plate providing a top surface against which a patient is to press a
portion of the patient's epidermis during a blood test with this
apparatus.
18. An apparatus as in claim 17 further comprising:
an optical fiber that penetrates through this flat plate and carries light
from said source of light to said sample of blood;
said means for detecting is adjacent to this fiber and this plate.
19. An apparatus as in claim 17 further comprising:
an optical fiber that does not penetrate through said flat plate and which
transports light from said source of light and directs this light through
a portion of said flat plate at a point at which a patient is to press a
portion of this patient's epidermis;
said means for detecting is adjacent to this fiber and this plate.
20. A non-invasive, blood chemistry measurement apparatus for measuring a
concentration of a selected blood component within a sample of blood, said
apparatus comprising:
a source of exposing light having a spectral peak at wavenumber k.sub.1
that will excite said blood component to a state from which it emits
light, by stimulated relaxation emission, having a peak at a second
wavenumber k.sub.2 different from k.sub.1 ;
means for imaging said exposing light through an area of epidermis of an
animal into a portion of that animal's blood adjacent to said area of
epidermis on which this exposing light is incident;
means for detecting light that is emitted at wavenumber k.sub.2 from
molecules of said selected blood component in response to exposing light
from said source of light;
means, responsive to said means for detecting, for calculating a
concentration of said selected blood component; and
a flat plate, that is transparent to the emitted light, positioned such
that light emitted from the sample of blood passes through this plate
before reaching said means for detecting;
this plate providing a top surface against which a patient is to press a
portion of the patient's epidermis during a blood test with this
apparatus;
wherein said flat plate is of a material selected from the class consisting
of ZnS and ZnSe.
21. An apparatus as in claim 17 further comprising:
a pressure sensor means, in contact with said flat plate, for measuring a
pressure of said patient's epidermis against this plate;
said means for calculating being responsive to a pressure measured by this
pressure sensor to correct the calculated concentration of said selected
blood component to take into account an effect of this pressure on this
calculated concentration.
22. A method of measuring the concentration of a selected blood component
of an animal, said method comprising the steps of:
(a) directing, through an epidermis of said animal, exposing light having
at least one wavenumber selected to excite said selected blood component
to emit light of wavenumber characteristic of that component;
(b) detecting light that is emitted from said selected blood component in
response to the exposing light which has a peak wavelength that produces
stimulated emission of light from said selected blood component; and
(c) calculating a concentration of said selected blood component.
23. A method as in claim 22 wherein said exposing light is imaged onto a
papillary bed, wherein there is a rich supply of blood glucose.
24. A method as in claim 23 wherein the exposing light is substantially
monochromatic, whereby the exposing light can be strongly concentrated
onto the papillary bed.
25. A method as in claim 22 wherein step (b) comprises the steps of:
(b1) detecting emitted light at a first wavenumber k.sub.1 at which there
is a significant level of emission from said selected blood component and
from a second blood component;
(b2) detecting emitted light at a second wavenumber k.sub.2 at which at
least one of the selected blood component and the second blood component
exhibits an emission peak; and
wherein step (c) calculates a concentration for the selected blood
component, utilizing the detected intensities at wavenumbers k.sub.1 and
k.sub.2.
26. A method as in claim 22, wherein, in step (a), a portion of the
epidermis through which the exposing light is directed is contained on a
front surface of a person's finger.
27. A method of measuring the concentration of a selected blood component
of an animal, said method comprising the steps of:
(a) directing, through an epidermis of said animal, exposing light having
at least one wavenumber selected to excite said selected blood component
to emit light of wavenumber characteristic of that component;
(b) detecting light that is emitted from said selected blood component in
response to the exposing light; and
(c) calculating a concentration of said selected blood component,
wherein the exposing light is in the range from 0.6-1.5 microns, whereby a
ratio of the absorbance by blood glucose to the total absorbance by blood
haemoglobin and the animal's epidermis is increased.
28. A method of measuring the concentration of a selected blood component
of an animal, said method comprising the steps of:
(a) directing, through an epidermis of said animal, exposing light having
at least one wavenumber selected to excite said selected blood component
to emit light of wavenumber characteristic of that component;
(b1) detecting emitted light at a first wavenumber k.sub.1 at which there
is a significant level of emission from said selected blood component and
from a second blood component;
(b2) detecting emitted light at a second wavenumber k.sub.2 at which at
least one of the selected blood component and the second blood component
exhibits an emission peak; and
(b3) detecting light at a wavenumber k.sub.3 at which there is a
significant level of blackbody radiation;
(c) calculating a concentration of said selected blood component utilizing
the detected intensities at wavenumbers k.sub.1, k.sub.2 and k.sub.3.
29. A method of measuring the concentration of a selected blood component
of an animal, said method comprising the steps of:
(a) directing, through an epidermis of said animal, exposing light having
at least one wavenumber selected to excite said selected blood component
to emit light of wavenumber characteristic of that component, wherein a
portion of the epidermis through which the exposing light is directed is
contained on a front surface of a person's finger;
(b) detecting light that is emitted from said selected blood component in
response to the exposing light Which has a peak wavelength that produces
stimulated emission of light from said selected blood component; and
(c) calculating a concentration of said selected blood component, wherein
the portion of epidermis through which the exposing light is directed is
pressed into contact with a window through which said exposing light is
directed, said method further comprising the step of:
(d) sensing a pressure of contact between the window and the portion of the
epidermis through which the exposing light is directed; and, in step (c)
adjusting the calculated concentration of the selected blood component,
taking into account the effect of pressure on the measured intensities. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
FIELD OF THE INVENTION
This invention relates in general to medical instrumentation, and more
particularly to the field of non-invasive blood chemistry measurements,
such as measurements of blood glucose concentration levels.
Convention Regarding Reference Numerals
In the figures, the first digit of a reference numeral indicates the first
figure in which is presented the element indicated by that reference
numeral.
BACKGROUND OF THE INVENTION
An estimated 14 million Americans have diabetes, a disease in which the
body does not produce or respond properly to insulin. The resulting high
blood glucose concentration levels (also referred to as blood glucose
level or blood-sugar levels) can cause severe damage to the heart, blood
vessels, kidneys, eyes and nerves. If untreated, diabetes can lead to
death in an unexpectedly short period of time. People with diabetes must
balance diet, exercise and medication (e.g., insulin, which can be taken
orally or by injections) in order to maintain their blood glucose levels
as close as possible to normal levels. Insulin pumps have been developed
to enable continuous administration of insulin to a diabetic.
Regardless how insulin is administered to a diabetic, it is very important
to continually monitor the blood glucose level to avoid the problems that
arise from low glucose levels as well as those that arise from excessive
glucose levels. Therefore, diabetics have to test their blood glucose
levels frequently (as often as six times a day) in order to maintain a
proper level of insulin in their blood.
Several different techniques have been developed for measuring blood
glucose concentration levels. A change in blood glucose level affects the
index of refraction and the absorbance spectrum of the blood. For example,
in U.S. Pat. No. 4,704,029, discussed in more detail below, this change in
the index of refraction of blood alters the fraction of light reflected at
an interface in contact with the blood being tested. This technique is not
amenable to a non-invasive method of detecting a person's blood glucose
level. Several references, discussed below, utilize absorbance
spectroscopy to measure the glucose concentration in a patient's blood.
Unfortunately, because of the strong level of absorption of water at the
wavelength of infrared absorption peaks for blood glucose, these
techniques result in small output signals so that there is a smaller than
desired signal-to-noise ratio for such tests.
Infrared absorption spectroscopy has long been used for the identification
of unknown organic and biological substances in aqueous solutions. This
technique is based upon the fact that all molecules exhibit, to some
extent, their own unique oscillatory motions characterized by specific
resonance absorption peaks in the infrared portion of the electromagnetic
spectrum. These characteristic absorption peaks are caused by the resonant
vibrational and rotational oscillations of the molecules themselves. In
several references discussed in more detail below, absorption spectra are
used to monitor changes in blood glucose levels. These resonant
vibrational modes can also be utilized to implement fluorescence
techniques for measuring blood glucose levels.
In U.S. Pat. No. 4,055,768 entitled Light Measuring Apparatus issued to
Nathan S. Bromberg on Oct. 25, 1977, the level of zinc protoporphyrin in
blood is detected by smearing a blood sample on a slide and illuminating
this sample with pulsed light that induces fluorescent emission from the
zinc protoporphyrin. Synchronous detection is used to measure the
intensity of the pulsing fluorescent light emitted from these zinc
protoporphyrin molecules.
In U.S. Pat. No. 4,704,029 entitled Blood Glucose Monitor, issued to Alan
Van Heuvelen, a blood glucose monitor is presented that is particularly
applicable for use as an implant for controlling an insulin pump. This
glucose monitor measures the glucose level of blood by utilizing a
refractometer which measures the index of refraction of blood adjacent to
an interface with a transparent surface of the refractometer. Within this
implanted monitor, light is directed at a transparent interface that is in
contact with the diabetic's blood. The angle of incidence is near the
critical angle of total internal reflection, so that the small changes in
the index of refraction of blood caused by changes in the blood glucose
level will significantly alter the fraction of light reflected from this
surface. In order to eliminate a similar change in the amount of reflected
light due to changes in the concentration of albumin in the diabetic's
blood, two light beams of unequal wavelengths are each directed at the
interface at an angle near it's associated critical angle.
The problem with this proposed technique is that it is not specific. The
index of refraction of blood is affected by numerous chemical substances
in blood, only one of which is the blood glucose level. Therefore, a
change in this index of refraction may not indicate a change in the blood
glucose level.
The usual procedure for testing blood glucose levels involves pricking a
finger to obtain a small sample of blood for analysis. In addition to the
unwelcome pain, frequent finger-pricks of a person with diabetes can
produce inflammation and/or callousing of that person's fingers.
Unfortunately, although the frequent finger pricks are avoided by use of
an implanted monitor, not only must the diabetic be subjected to the
discomfort of implanting such a monitor, these monitors are often attacked
by the body in a manner that degrades device operation. Because of this,
the diabetic might require a succession of such implants. Thus, a
portable, non-invasive, inexpensive, reliable blood glucose sensor is
badly needed to enable diabetics to take better care of themselves without
having to draw blood each time they need to check their blood glucose
levels.
Over the years, many purportedly non-invasive methods of monitoring blood
glucose have been proposed. For example, in the following three U.S.
patents, a light beam is directed through a person's eye to monitor that
person's blood glucose level. In U.S. Pat. No. 3,963,019 entitled Ocular
Testing Method and Apparatus issued to Quandt on Jun. 15, 1976, a beam of
polarized light is directed through the aqueous humor of the person's eye
to measure that person's blood glucose level. The fraction of this light
that is absorbed during transit through that person's eye indicates the
glucose level in the blood.
In U.S. Pat. No. 3,958,560 entitled Non-Invasive Automatic Glucose Sensor
System, issued on May 25, 1976 to Wayne Front March, an infrared light
source, mounted on a scleral contact lens, transmits 0.975 micron,
infrared light through this contact wearer's cornea and aqueous humor to
an infrared detector, also mounted on this lens. This wavelength is used
because it is absorbed strongly by the hydroxyl in glucose. Test results
are transmitted to a receiver mounted on or near this person, thereby
providing nearly continuous monitoring of that person's blood glucose
level. For example, a test can be initiated each time a person blinks.
In U.S. Pat. No. 4,014,321 entitled Non-invasive Glucose Sensor System
issued to Wayne Front March on Mar. 29, 1977, a polarized beam of light is
directed through a person's eye and the blood glucose level is determined
from the amount that this polarized light is rotated by passage through
this person's eye.
There are several disadvantages of using a person's eye as the target for
blood glucose measurements. Considerable care must be exercised to prevent
physical damage to the eye. The scleral contacts, containing blood
chemistry test equipment, can be uncomfortable to the wearer. Professional
care is required if insertion of an object into the eye is part of the
measurement routine, such as is the case in U.S. Pat. No. 3,963,019 cited
above. Such a blood glucose monitor would not be desirable for diabetic
patients who have to measure their own blood glucose levels daily.
The following references describe blood glucose monitors that inject a beam
of light through a person's skin to interact with the blood adjacent to
the skin.
German Offenlegungsschrift DE 38 01 158 A1 entitled Blood Sugar Measuring
Apparatus filed by Marina Struck on Jan. 16, 1988, is a rather confusing
application, in which a monochromatic laser transmits a polarized,
monochromatic, laser beam, through the skin of a person's finger,
apparently for the purpose of rotating glucose molecules in the blood.
There is some discussion of this light causing rotation of sugar
molecules, some discussion of the polarization being caused by a
reflection from the sugar molecules of a proper orientation, some
discussion that photons are emitted from excited glucose molecules in the
blood and some discussion that this light is tuned to a characteristic
wavelength of glucose. This teaching appears to be inconsistent and is so
confusing that it does not really teach the true nature of that invention.
In U.S. Pat. No. 4,901,728 entitled Personal Glucose Monitor issued to
Donald P. Hutchinson on Feb. 20, 1990, two infrared beams are formed which
are polarized, respectively, at +45.degree. and -45.degree. relative to a
polarizer and, therefore, these two beams normally produce equal intensity
output signals. However, when these beams are passed through a person's
tissue, such as that person's ear lobe, these polarized beams are rotated
by glucose by equal angles, thereby reducing the intensity of one of the
output signals and increasing the other. These pulses are chopped so that
the detector receives, at any given time, only light from one of these
beams.
In recognition of the strong absorption of (long wavelength) infrared
radiation by tissue and the effects of other variable parameters
associated with tissue such as its thickness, pigmentation, temperature
and blood volume etc., this reference recommends the use of two radiation
sources which emit infrared light at two different wavelengths.
Specifically, this reference uses light beams of wavelength 0.94 microns
and 1.3 microns, in what is commonly referred to as the "near-infrared"
region (i.e., wavenumber in the range 10,638-7,692 cm.sup.-1).
Hutchinson's proposed intricate optical technique in the monitoring of
blood glucose in tissue is rather complicated and requires a number of
very delicate and difficult adjustments in its operation. It is therefore
not readily amenable to the realization of a reliable, low-cost and rugged
blood glucose sensor, such as is badly needed today. It is asserted,
without discussion, that the use of an additional pair of analogous beams
at different wavelengths enables correction for tissue absorption. U.S.
Pat. No. 5,009,230 entitled Personal Glucose Monitor issued to Donald P.
Hutchinson on Apr. 23, 1991, provides the missing details regarding this
correction for tissue absorption.
The following references utilize absorption spectroscopy to detect various
blood chemicals:
In the article by H. Zeller, et al entitled Blood Glucose Measurement by
Infrared Spectroscopy, p. 129-134, (1989), the absorption spectra of blood
glucose and some other blood components, are analyzed for the purpose of
identifying those wavelength ranges in which accurate measurements of
blood glucose can be detected. Differences between absorption spectra for
a water-only solution and for a water-plus-glucose solution is observed
only in an wavenumber range, referred to therein as the "finger-print
region", which extends from 1650 to 800 cm.sup.-1.
A strong absorption peak, which occurs at a wavelength of 9.02 micron
(i.e., wavenumber 1109 cm.sup.-1), is caused by the stretching vibrations
of the endocyclic C--O--C group. Water absorption washes out all glucose
spectra in the near infrared (NIR) (i.e., wavenumber in the range
12,500-4,000 cm.sup.-1) and the mid infrared (MIR) wavelength regions
(i.e., wavenumber in the range 4,000-500 cm.sup.-1), so that, except for
the finger-print region, these regions are not suitable for monitoring
blood glucose levels. In the fingerprint region, only glucose and
haemoglobin exhibit intense absorption at this wavelength. Only the
following five wavenumbers give enough sensitivity for measurement of
blood glucose: 1040, 1085, 1109, 1160 and 1365 cm.sup.-1. Only the 1040
cm.sup.-1 band is free of superimposed absorption of other blood
constituents, and only glucose and haemoglobin exhibit intense absorption
at 1109 cm.sup.-1. Therefore, the most attractive choices for monitoring
blood glucose levels are the 1040 and 1109 cm.sup.-1 absorption bands.
In the article by Yitzhak Mendelson, et al entitled Blood Glucose
Measurement by Multiple Attenuated Total Reflection and Infrared
Absorption Spectroscopy, IEEE Transactions On Biomedical Engineering, Vol.
17, No. 5, May 1990, it is recognized that, of the more than 20 absorption
peaks of D-glucose in the 2.5-10 micron range, not all of those peaks are
specific to D-glucose. However, the peak at an wavenumber of 640 cm.sup.-1
is prominent and is due to the carbon-oxygen-carbon bond in the pyrane
ring of D-glucose. It is also recognized that, because of the intrinsic
high background absorption of water in the infrared wavelength range and
the relatively low glucose concentrations in blood, it is important to use
a CO.sub.2 laser, because it produces a powerful beam having a narrow peak
that is effective in detecting such low concentrations. Sensitivity is
further increased by using a multiple attenuated total reflection (ATR) to
pass the laser beam through the sample several times. Unfortunately,
equipment implementing such a laser/ATR technique is very expensive.
Biological molecules, due to their very complicated structures, possess a
large number of similar infrared absorption peaks that are often
overlapping. For example, the characteristic infrared spectrum of
anhydrous D-glucose (ADG) has more than 20 absorption peaks in the
wavelength region of 2.5-10 microns as shown in FIG. 1. It is important to
note that not all the absorption peaks shown in FIG. 1 are specific to
this molecule. The prominent absorption peak around 9.61 microns (1,040
cm.sup.-1), however, is somewhat specific to the carbon-oxygen--carbon
bond of glucose, because of its pyrane ring.
In U.S. Pat. No. 5,028,787 entitled Non-invasive Measurement of Blood
Glucose, issued to Robert D. Rosenthal on Jul. 2, 1991, a near-infrared
quantitative analysis instrument and method are presented that
non-invasively measures blood glucose by analyzing near-infrared energy
following "interactance" with venous or arterial blood, or transmission
through a blood containing body part, such as a finger tip. Because of the
strong absorption of long wavelength, infrared radiation by body tissues,
only near-infrared radiation of wavelength less than approximately one
micron is used. A set of filters are utilized to pass through a sample
only wavelengths that are much more strongly absorbed by glucose than by
other interfering substances in the blood. The effect is that the
interference from these other substances is substantially removed. Because
Rosenthal has worked in this field since 1978 without yet producing a
commercial non- | | |
