(12) United States Patent
`Wuori
`
`I 1111111111111111 11111 111111111111111 1111111111 1111111111111111 IIII IIII IIII
`US006898451B2
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6,898,451 B2
`May 24, 2005
`
`(54) NON-INVASIVE BLOOD ANALYTE
`MEASURING SYSTEM AND METHOD
`UTILIZING OPTICAL ABSORPTION
`
`(75)
`
`Inventor: Edward R. Wuori, Mounds View, MN
`(US)
`
`(73) Assignee: Minformed, L.L.C., Mounds View,
`MN (US)
`
`6,039,697 A * 3/2000 Wilke et al. ................ 600/310
`6,119,031 A * 9/2000 Crowley ..................... 600/310
`6,175,750 Bl * 1/2001 Cook et al. ................. 600/310
`6,198,949 Bl * 3/2001 Braig et al. ................. 600/310
`6,215,403 Bl * 4/2001 Chan et al. ................. 600/323
`6,341,257 Bl * 1/2002 Haaland ...................... 702/27
`6,361,501 Bl * 3/2002 Amano et al. .............. 600/500
`6,452,179 Bl * 9/2002 Coates et al. .......... 250/339.09
`6,542,762 Bl * 4/2003 Alam et al. ................. 600/310
`2001/0034477 Al * 10/2001 Mansfield et al.
`.......... 600/316
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by O days.
`
`JP
`
`FOREIGN PATENT DOCUMENTS
`* 10/1987
`
`62-250320
`
`................. 374/121
`
`(21) Appl. No.: 10/104,782
`
`(22) Filed:
`
`Mar. 21, 2002
`
`(65)
`
`Prior Publication Data
`
`US 2003/0050541 Al Mar. 13, 2003
`
`Related U.S. Application Data
`(60) Provisional application No. 60/277,758, filed on Mar. 21,
`2001.
`
`Int. Cl.7 .................................................. A61B 5/00
`(51)
`(52) U.S. Cl. ........................................ 600/322; 600/310
`(58) Field of Search ................................. 600/309-310,
`600/322-326, 316, 476, 473
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`3,596,057 A * 7/1971 Arntz ......................... 219/354
`3,983,751 A * 10/1976 Cipriano ...................... 73/295
`4,271,358 A * 6/1981 Schwarz .................. 250/338.1
`4,651,001 A
`3/1987 Harada et al.
`5,069,214 A * 12/1991 Samaras et al.
`............ 600/323
`5,197,470 A * 3/1993 Helfer et al.
`............... 600/342
`5,348,003 A * 9/1994 Caro .......................... 600/310
`5,355,880 A * 10/1994 Thomas et al. ............. 600/326
`5,361,758 A
`11/1994 Hall et al.
`5,660,181 A * 8/1997 Ho et al.
`.................... 600/408
`5,755,226 A * 5/1998 Carim et al. ................ 600/323
`5,784,507 A * 7/1998 Holm-Kennedy et al.
`.... 385/31
`5,817,007 A
`10/1998 Fodgaard et al.
`5,900,632 A
`5/1999 Sterling et al.
`
`OTHER PUBLICATIONS
`
`Tatsyi Tigawa, Patient Monitoring, Wiley Encyclopedia of
`Electrical and Electronics Engineering Online, 1999.*
`Webster's II New Riverside University Dictionary, River(cid:173)
`side Publishing Company,, 1994, p. 761.*
`
`* cited by examiner
`
`Primary Examiner-Max F. Hindenburg
`Assistant Examiner-Matthew Kremer
`(74) Attorney, Agent, or Firm-Fredrikson & Byron, P.A.
`
`(57)
`
`ABSTRACT
`
`A device and method for measuring the concentration of
`analytes in the blood of a portion of tissue. The device
`includes a sensor module, a monitor, and a processor
`(separate from or integral with the sensor module). The
`sensor module includes a radiation source for emitting
`radiation to the tissue; a collimator and narrow band filter for
`processing the radiation after it has transmitted through or
`been reflected by the tissue; and one or more sensors for
`sensing the transmitted or reflected radiation. The one or
`more sensors send a signal to the processor which algorith(cid:173)
`mically converts the radiation using linear regression or
`orthogonal functions to determine the concentration of one
`or more blood analytes. The device self-calibrates to elimi(cid:173)
`nate error caused by variables such as skin character. The
`sensor module is integrated to reduce size and weight such
`that it is inobtrusive, and the monitor is compact for trans(cid:173)
`port
`
`31 Claims, 11 Drawing Sheets
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`Petitioner Apple Inc. – Ex. 1051, p. 3
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`Petitioner Apple Inc. – Ex. 1051, p. 4
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`Petitioner Apple Inc. – Ex. 1051, p. 5
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`US 6,898,451 B2
`
`1
`NON-INVASIVE BLOOD ANALYTE
`MEASURING SYSTEM AND METHOD
`UTILIZING OPTICAL ABSORPTION
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is entitled to the benefit of Provisional
`Patent Application Ser. No. 60/277,758 entitled "Noninva(cid:173)
`sive Infrared Blood Analyte Measuring System and Meth(cid:173)
`ods" by Edward Wuori, filed Mar. 21, 2001.
`
`FIELD OF THE INVENTION
`
`The present invention relates to a method and apparatus
`for non-invasive monitoring of various blood analytes in
`humans and other animals in the fields of medicine, sports
`medicine, military hardware, anemia treatment, diabetes
`treatment, and traumatic injury treatment.
`
`BACKGROUND OF THE INVENTION
`
`This invention relates to a non-invasive apparatus and
`methods for in vivo monitoring of the concentration levels
`of various blood analytes within a living subject, using
`optical absorption spectrophotometry. The device and meth(cid:173)
`ods may be used to simultaneously monitor several analytes
`found in the blood outside of a laboratory setting. The device
`and methods are able to resolve analytes down to approxi(cid:173)
`mately one mg/dL. Further, the device and methods are able
`to measure all blood analytes present at approximately one
`mg/dL, including glucose and lactate, for example.
`Information concerning the concentrations of blood ana(cid:173)
`lytes is widely used to assess the health characteristics of
`people. For example, lactate is becoming the measurement
`of choice in sports and coaching to assess levels of condi(cid:173)
`tioning for athletes and to prevent over-training. Lactate
`threshold and other related parameters are used to assess the
`aerobic and anaerobic status of athletes, are correlated to
`athletic performance, and may be used to "rank" athletes
`according to actual performance history. Lactate monitoring, 40
`as used in athletics, may also be useful for Military
`Academies, Army boot camps, and other physical training
`operations to assess the physical condition of trainees, to
`improve training programs, and to evaluate the effectiveness
`of training regimens on specific individuals. Lactate is also 45
`widely used to assess the medical condition of injured
`people. When serum lactate elevates after an injury, whether
`or not the lactate clears is correlated strongly with mortality,
`thus, measurement of serum lactate levels is a key tool in
`assessing treatment.
`Likewise, the monitoring of blood glucose has long been
`an important tool in controlling diabetes in diabetic patients.
`Diabetes is a high maintenance disease, generally requiring
`several measurements of blood glucose daily. At present,
`this is typically accomplished using a glucometer, in which 55
`a fresh blood sample must be obtained for each measure(cid:173)
`ment. Each measurement typically requires a new "test
`strip" for receiving the blood sample, the test strips charac(cid:173)
`teristically being relatively expensive. Such measurements
`are often painful, cumbersome, and moderately time- 60
`consuming. The method of testing blood glucose using a test
`strip is generally referred to as the "finger stick" method. It
`specifically involves applying a drop of blood to the test
`strip, the test strip using molecular sieves to block molecules
`larger than molecular weight of about 200. The sieves 65
`consequently block, for example, large glycosylated pro(cid:173)
`teins from being included in the blood glucose measure-
`
`5
`
`2
`ment. Due to the inconvenience and expense, many diabetic
`patients do not monitor their blood glucose levels as often as
`recommended. About 16 million diabetic patients in the
`United States need to regularly monitor their blood glucose
`levels.
`A non-invasive device enabling painless and convenient
`monitoring of blood glucose would be of great benefit to
`diabetic patients. The relative ease of measurement may
`contribute to a more regular blood glucose monitoring
`10 regime by diabetic patients. Various attempts have been
`made at a blood glucose measurement device using spec(cid:173)
`troscopy. However, those attempts have generally had prob(cid:173)
`lems with "baseline drift" of unknown origin. It is hypoth(cid:173)
`esized that the absorption method used in most spectroscopy
`15 devices for measuring glucose in the blood measures all
`glucose in the blood, both the bound glucose and the free
`glucose. For the purpose of diabetes management, measure(cid:173)
`ment of the concentration of free glucose is desired. That is,
`the concentration of free glucose in the blood is generally
`20 recommended to be in the range of 80 mg/dL and 120
`mg/dL. A diabetic patient will measure their blood glucose
`level to determine whether the level is within the recom(cid:173)
`mended range. If the blood glucose level is outside of the
`recommended range, the diabetic patient will typically inject
`25 insulin to reduce the blood glucose level. Again, it is the free
`glucose concentration level that is relevant to determining
`whether the patient's blood glucose concentration is within
`the recommended range. Because absorption techniques
`may measure both free and bound glucose levels as one
`30 measurement, there may be an overstatement of the blood
`glucose level that results in faulty treatment by the patient.
`The molecular sieves of the test strip glucometers described
`above correct for the possibility of measuring bound and
`free glucose by preventing the bound glucose, with a rela-
`35 tively high molecular weight, from passing through the
`sieve.
`It is notable, however, that the finger stick methods take
`only one measurement of the glucose concentration level in
`the blood and, for a series of measurements, require a series
`of blood samples, generally obtained by a series of finger
`pricks. Consequently, the finger stick methods do not offer
`an appealing method of continuous measurement of blood
`glucose concentration in the blood. Continuous measure(cid:173)
`ment of blood glucose levels enable near instant recognition
`of abnormal blood glucose levels whereas a series of indi(cid:173)
`vidual measurements inevitably includes periods of time
`where the precise blood glucose level is unknown. Thus, a
`diabetic patient may be better able to control blood glucose
`levels. It may also assist the person in adjusting their
`50 lifestyle, diet, and medication for optimum benefits. Provid(cid:173)
`ing the easy, non-invasive, and optionally continuous moni(cid:173)
`toring provides a great improvement in the treatment of the
`diabetes and allows the treatment to be tailored to the
`individual.
`Many other blood analytes with concentrations similar to
`or greater than lactate and glucose are of fundamental
`importance; for example, hemoglobin and its sub-types,
`albumin, globulins, electrolytes, and others. Hemoglobin is
`important especially in the monitoring of anemia caused by
`various various factors such as HIV infection and chemo(cid:173)
`therapy. Anemia treatments need frequent monitoring of
`hemoglobin to assess effectiveness of various treatments
`such as Epoetin-Alpha therapy.
`Spectrophotometry provides a useful method for deter(cid:173)
`mining the presence of analytes in a system. A typical
`spectrometer exposes a dissolved compound to a continuous
`wavelength range of electromagnetic radiation. The radia-
`
`Petitioner Apple Inc. – Ex. 1051, p. 13
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`

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`US 6,898,451 B2
`
`3
`tion is selectively absorbed by the compound, and a spec(cid:173)
`trograph is formed of radiation transmitted ( or absorbed) as
`a function of wavelength or wave number. Absorption peaks
`are usually plotted as minima in optical spectrographs
`because transmittance or reflectance is plotted with the
`absorbance scale superimpose, creating IR absorption
`bands.
`At a given wavelength the absorption of radiation follows
`Beers' Law, an exponential law of the form:
`
`A-ECb Where: A-absorbance--log 10(t; ).
`
`t=fraction of radiation transmitted ( or reflected).
`E=molar extinction coefficient, cm2/mol.
`C=concentration, mol/cc.
`b=thickness presented to radiation, cm.
`The wavelengths of maximum absorption, "-max, and the
`corresponding maximum molar extinction coefficient, Emax,
`are identifying properties of a compound. Radiation causes
`excitation of the quantized molecular vibration states. Sev(cid:173)
`eral kinds of bond stretching and bond bending modes may
`be excited, each causing absorption at unique wavelengths.
`Only vibrations that cause a change in dipole moment give
`rise to an absorption band. Absorption is only slightly
`affected by molecular environment of the bond or group. 25
`Nevertheless, these small chemical shifts may aid in
`uniquely identifying a compound. A "fingerprint region"
`exists between 42 and 24 THz (1400 and 800 cm- 1
`) because
`of the many absorption peaks that occur in this region. It is
`virtually impossible for two different organic compounds to 30
`have the same infrared (IR) spectrum, because of the large
`number of peaks in the spectrum. While the peaks and
`valleys are the traditional features used in this type of
`spectrophotometry, the overall shape of the spectra may also
`provide useful information, especially in mathematically 35
`separating mixed spectra where more than one analyte is
`present.
`In addition to the IR absorption bands, absorption peaks
`also occur in the near-IR region (700---2500 nm). Absorp(cid:173)
`tions in this region are most often associated with the 40
`overtone and combination bands of the fundamental molecu-
`lar vibrations of -OH, -NH, and -CH functional groups
`that are also seen in the mid IR region. As a result, most
`biochemical species will exhibit unique absorptions in the
`near-IR. In addition, a few weak electronic transitions of
`organometallic molecules, such as hemoglobin, myoglobin,
`and cytochrome, also appear in the near-IR. These highly
`overlapping, weakly absorbing bands were initially per(cid:173)
`ceived to be too complex for interpretation and too weak for
`practical application. However, recent improvements in
`instrumentation and advances in multivariate chemometric
`data analysis techniques, which may extract vast amounts of
`chemical information from near-IR spectra, allow meaning-
`ful results to be obtained from a complex spectrum. Absorp(cid:173)
`tion bands also occur in the visible range (400---700 nm). For
`example, hemoglobin and bilirubin absorb strongly in this
`region.
`Traditionally, Near Infrared Spectroscopy (NIRS) has
`been used to estimate the nutrient content of agricultural
`commodities. More recently NIRS has become widely 60
`applied in the food processing, chemical, pulp and paper,
`pharmaceutical, polymer, and petrochemical industries.
`Invasive devices and methods of quantifying and classi(cid:173)
`fying blood analytes using IR and other optical spectropho(cid:173)
`tometry methods are very commonly known. Invasive pro- 65
`cedures are those where a sample such as blood is taken
`from the body by puncture or other entry into the body
`
`4
`before analysis. Invasive procedures are undesirable because
`they cause pain and increase the risk of spread of
`communicable, blood-borne diseases. Further, after the
`invasive collection of body samples, these samples may
`s need to be further prepared in the laboratory by adding water
`or ions to the samples to increase the accuracy of the
`spectrophotometry readings. Thus, these commonly known
`devices and methods are often only suitable for use under
`laboratory in vitro conditions and are too difficult to be
`10 practically applied in athletic training and military situa(cid:173)
`tions. It is noted, of course, that the finger stick method of
`measuring blood glucose concentration levels using a glu(cid:173)
`cometer has been adapted for home use.
`Recently, non-invasive devices for monitoring levels of
`15 blood analytes using infrared spectroscopy have been devel(cid:173)
`oped. For example, U.S. Pat. No. 5,757,002 by Yamasaki
`relates to a method of and an apparatus for measuring lactic
`acid in an organism in the field of sports medicine or
`exercise physiology. Also, U.S. Pat. No. 5,361,758 by Hall
`20 relates to a non-invasive device and method for monitoring
`concentration levels of blood and tissue constituents within
`a living subject.
`Previous non-invasive devices and methods typically
`require time-consuming custom calibrations to account for
`the differences between individuals and environmental fac(cid:173)
`tors which cause variation in energy absorption. There are
`several factors that may result in variation in energy absorp(cid:173)
`tion; for example, environmental factors such as tempera(cid:173)
`tures and humidity that may affect the equipment, and
`individual factors such as skin coloration, skin weathering,
`skin blemishes or other physical or medical conditions. This
`need for custom calibration to each individual makes it
`impractical to use previous devices on demand in training
`situations or at the scene of accidents. A universal or
`self-calibrating device that is capable of taking into account
`these variations would be useful.
`Further, many previous non-invasive devices and meth-
`ods accurately measure only a single blood analyte at a time.
`Most typically, the devices are designed to measure blood
`glucose. To measure a different analyte, the device must be
`reprogrammed or otherwise altered. Even with such repro-
`gramming or alteration, the devices may not typically mea(cid:173)
`sure the results of two or more analytes at the same time
`without significant inaccuracies. Each analyte in the blood
`45 sample contributes a unique absorption pattern to the overall
`infrared spectrum, governed by the unique set of molecular
`vibrations characteristic of each distinct molecular species.
`The infrared spectral range extends from 780 nm to 25,000
`nm and is commonly subdivided further into the near-
`so infrared and mid-infrared regions. Most devices obtain an
`measurement of an analyte by using only a small portion of
`the IR spectrum reflecting the particular analyte of interest.
`In those devices that do attempt to use a wider spectrum to
`obtain multiple analyte readings, relatively ineffective meth-
`ss ods are used to separate and account for multiple analyte
`spectral interferences, leading to decreased accuracy. Thus,
`there exists a need for a device that may successfully use a
`wider spectrum to accurately and simultaneously isolate and
`determine the concentrations of multiple analytes.
`IR spectroscopy typically involves radiating light onto a
`portion of tissue for either transmission through the tissue or
`reflection from the tissue. The transmitted or reflected radia(cid:173)
`tion is then analyzed to determine concentrations of ana(cid:173)
`lytes. However, the radiation that is transmitted or reflected
`is not just transmitted through or reflected from the blood,
`but instead includes transmissions or reflection from the
`skin, subdermal tissue, and blood. Thus, the received radia-
`
`Petitioner Apple Inc. – Ex. 1051, p. 14
`
`

`

`US 6,898,451 B2
`
`5
`tion is a mixture of absorption signals from skin and tissues
`and blood. The signals contributed by the skin and tissues
`make it difficult to accurately measure the presence of blood
`analytes. These signals need to be separated to eliminate the
`effects of skin and tissue in order to measure the analytes in 5
`the blood. Previous non-invasive devices and methods were
`unable to separate blood-related readings from body tissue
`readings. Therefore, there is a need for a device capable of
`separating the blood-related component of the signal from
`the tissue component.
`One method of achieving the separation of a blood-related
`component of the signal is to accept only the portion of the
`mixed signal which has a pulse synchronized with the heart
`pulse, known as a pulsatile technique or synchronous detec(cid:173)
`tion. The pulsatile signal is the time varying portion of the 15
`whole signal that is synchronized with the heart beat. This
`method presumes that the pulsations come from the move(cid:173)
`ment of arterial blood or closely related volume and allows
`a signal associated with the blood to be separated from that
`of tissue. The synchronous method is widely used for 20
`separating blood-related components in pulse oximeters.
`Another possible method for achieving separation of the
`blood related components of the signal from tissue and skin
`related components uses a hematocrit-type method to deter(cid:173)
`mine the portion of the signal associated with the blood. The 25
`hematocrit is the proportion, by volume, of the blood that
`consists of red blood cells. The hematocrit is typically
`measured from a blood sample by an automated machine
`that makes several other measurements at the same time.
`Most of these machines do not directly measure the 30
`hematocrit, but instead calculate it based on the determina(cid:173)
`tion of the amount of hemoglobin and the average volume of
`the red blood cells. Using a hematocrit method generally is
`faster than using a synchronous method because there is no
`need to wait for heart beats. Further, there is less signal loss 35
`associated with hematocrit methods than with the synchro(cid:173)
`nous method, the synchronous method removing some
`blood associated signal unnecessarily.
`Finally, many non-invasive devices for in vivo monitoring
`of blood analyte concentrations do not allow for an ambu- 40
`latory application. They typically utilize permanent equip(cid:173)
`ment set up in a laboratory or other test site, which makes
`it impossible to use while away from the laboratory or other
`test site. Thus, there is a need for a device that may be easily
`transported and used away from the laboratory. The device 45
`would preferably not interfere with the user's normal func(cid:173)
`tioning and would greatly increase the utility and range of
`analyte concentration monitoring beyond the laboratory
`setting.
`
`SUMMARY OF THE INVENTION
`The present invention provides an improved apparatus
`and method for the rapid, non-intrusive determination of the
`concentration of blood analytes. In one embodiment, it
`provides a portable tabletop unit for measurement of blood 55
`analyte concentrations where the subject may walk up to the
`device for measurement from a body part, such as a finger.
`However, there are many situations where blood analyte
`measurement must be done outside of a domestic or labo(cid:173)
`ratory environment. Thus, another embodiment of the
`present invention provides a portable system which may be
`positioned on body tissue and transported on the user's
`person. Features such as small size, a wireless sensor, battery
`operation, portability, and downloadability demonstrably
`increase the utility and range of the analyte measurement
`apparatus of the present invention beyond the hospital or
`laboratory setting.
`
`6
`The present invention also provides a method and appa(cid:173)
`ratus with increased sensitivity and accuracy. A problem
`encountered in the area of blood analyte measurement via IR
`spectroscopy is accuracy and drift. In general, other analytes
`and various other substances present interfere with the IR
`measurement of the desired analyte. These analytes vary in
`concentration and thus vary the IR spectrum in the regions
`being used to determine specific analyte concentration. The
`present invention corrects for all other analytes with con-
`10 centrations sufficient to interfere in the determination of the
`concentration of the analyte or analytes of interest. Measur(cid:173)
`ing the entire visible and IR spectrum provides enough data
`to simultaneously determine all of the analytes and thereby
`compensate for any accuracy or drift problems their con(cid:173)
`centration may cause in measuring the concentration of the
`analyte(s) of interest. Data processing using orthogonal
`functions is used to accomplishing this task. Other proper(cid:173)
`ties of blood may also effect the IR measurement of the
`desired analyte. For example, turbidity of the blood, as may
`be caused by elevated white cell count or high blood lipids,
`may affect the measurement. These factors appear in the
`spectra and are compensated for by the present invention.
`The analyte measurement apparatus of the present invention
`is sufficiently sensitive to detect blood glucose or lactate
`with accuracy within, approximately, 10% of the level
`actually present, and may do so in a short period of time ( e.g.
`5 seconds or less). Due to the non-intrusive nature of the
`measurement and its relative rapidity, it is also possible to
`monitor blood analyte levels essentially continuously.
`The blood analyte measurement apparatus of the present
`invention includes a radiation source for generating and
`transmitting a spectrum of radiation onto a portion of tissue
`(for transmission therethrough or reflection therefrom), one
`or more sensors for detecting the radiation either transmitted
`through or reflected from the tissue over a broad spectrum
`and generating an output in response to the detected
`radiation, and a processor for receiving output from the
`sensors to determine the concentration of blood analytes in
`the portion of tissue. In a preferred embodiment, the appa(cid:173)
`ratus also makes use of a mounting device to position the
`radiation source and the sensors relative to a portion of tissue
`so the one or more sensors may receive a substantial portion
`of the radiation produced by the radiation source and trans(cid:173)
`mitted through or reflected by the portion of tissue. In a
`further preferred embodiment, the information regarding
`absorption of the radiation is then algorithmically processed
`to clarify the signal(s) of the desired blood analytes. Thus,
`the invention, in a typical configuration, includes a sensor
`module which is preferably attached to an earlobe, a pocket
`50 monitor for immediate readout and data logging, and a data
`link to a PC for long term storage and compilation of data.
`Thus, blood analyte levels may be continuously monitored
`without the constraints of attachment wires or bulky appa(cid:173)
`ratus.
`The blood analyte sensor module is integrated as much as
`possible to reduce the size and weight. In one embodiment,
`the sensor module is completely self-contained. The sensor
`module illuminates the measurement site with a built-in
`radiation source tailored to the spectral region of interest.
`60 The radiation source and the sensors are each positioned on
`a chip. The radiation source may be integrated onto a custom
`chip in transmission mode, or onto the same chip as the
`sensors in reflection mode. That is, when it is desired to
`receive and interpret radiation transmitted through the
`65 tissue, the apparatus is working in transmission mode and
`the radiation source is positioned on a chip separate from the
`chip on which the sensors are positioned. In contrast, when
`
`Petitioner Apple Inc. – Ex. 1051, p. 15
`
`

`

`US 6,898,451 B2
`
`8
`the one or more sensors in response to the detected radiation,
`communicating the signal to the processor, and finally
`interpreting the signal communicated to the processor to
`determine the concentration of one or more blood analytes.
`5 Preferably, the method of the present invention also includes
`the step of displaying the results so they may be perceived
`by the user.
`The preferred tissue exposed to the radiation in the
`method is either an earlobe or a finger. Preferably, the
`positioning of the tissue is carried out so that the sensors and
`the radiation source have minimal or no contact with the
`tissue itself. While any analyte which has infrared absorp(cid:173)
`tion may be measured by this method, specific examples are
`lactate/lactic acid, glucose, insulin, ethanol, triglycerides,
`15 albumin, proteins, hemoglobin, immunoglobulins,
`cholesterol, and urea.
`An important aspect of the present invention is the
`interpreting of the signals communicated to the processor by
`an algorithm. One type of algorithm used to interpret this
`20 data is linear regression. A more preferred algorithm makes
`use of orthogonal functions. The concept is to use the
`reference spectrum for each blood analyte as basis functions
`and determine a weighting function or functions that create
`an orthogonal set. This permits easy separation algorithms
`25 for mixed spectra. The use of algorithms is very helpful for
`self-calibrating to eliminate data artifacts caused by indi(cid:173)
`vidual variation in tissue character.
`The least squares method of orthogonal functions is
`30 preferably used to separate the concentrations of the indi(cid:173)
`vidual analytes from the total spectrum measured. This is
`also referred to as "principle component analysis" and is
`similar to "Fourier series decomposition." Separating the
`various analyte concentrations is statistically challenging
`35 because of an overlap of the spectra which causes interac(cid:173)
`tions and cross-coupling. Trying to evaluate one analyte
`concentration is affected by the other overlapping concen(cid:173)
`trations. The orthogonal decomposition is a mathematical
`way of processing the overlapping concentratio