EP1622503A1

EP1622503A1 - Method and device for determining blood components using ratiometric absolute pulse spectroscopy

Info

Publication number: EP1622503A1
Application number: EP04720580A
Authority: EP
Inventors: Klaus Forstner
Original assignee: Mcc Gesellschaft fur Diagnosesysteme In Medizin und Technik Mbh & Co KG
Current assignee: Mcc Gesellschaft fur Diagnosesysteme In Medizin und Technik Mbh & Co KG
Priority date: 2003-05-13
Filing date: 2004-03-15
Publication date: 2006-02-08
Also published as: US20080214911A1; DE10321338A1; WO2004100780A1; JP2007502681A

Abstract

The method and the device according to the invention are used for the non-invasive measurement of concentrations of blood components. At least one light source generates light using spectrophotometry and the light is guided to at least one photodetector through a tissue present at the location of application and supplied with pulsating blood. At least the measuring signal of the photodetector is guided to an evaluation unit. The light signals of a first, second, third to (n+1)<st> wavelength are generated at subsequent pairwise times T1 and T2, T3 and T4 and T5 and T6 to Tn and Tn+1. The evaluation unit takes into consideration the received signals of the photodetector for all wavelengths according to a defined arithmetic pattern and determines a concentration of the blood component. The inventive device comprises at least three light sources that generate light of different wavelength in relation to each other. The evaluation unit is provided with an arithmetic unit for carrying out logarithms, divisions, multiplications, additions and subtractions. The inventive method is especially used for determining the total hemoglobin concentration CHb and for determining physiological substances that are iatrogenically applied to the area that is supplied with pulsating blood.

Description

Method and device for determining blood components using the method of ratiometric absolute pulse spectroscopy

The invention relates to a method for the metrological determination of blood components in which light is generated using at least one light source using spectral photometry and is passed through perfused tissue located at an application site to at least one photo receiver, and in which at least one measurement signal from the photo receiver is sent to an evaluation unit becomes.

The invention further relates to a device for the measurement of blood components by measurement, which has at least one light source, at least one photo receiver and at least one evaluation unit which is connected to the photo receiver. Such methods and devices are used in order to be able to carry out blood tests in the field of medical technology without having to take blood from a patient. Typically, such devices are arranged, for example, on a patient's fingers, toes, ears or on the nose.

In the blood space, a distinction can be made between components that have an association with hemoglobin and those that do not. Those components that are associated with hemoglobin are predominantly in the red blood cells and to a lesser extent dissolved in the blood.

Hemoglobin derivatives can be divided into

^■ functional and non-functional components. Functional components are the 0∑ - hemoglobin and the deoxygenated hemoglobin fraction, while the dysfunctional 11 hemoglobin fractions mainly include carboxymonoxide hemoglobin, methemoglobin and sulfhemoglobin.

In addition to these hemoglobin components, there are a large number of other substances that are independent of hemoglobin within the blood. Some of these are of diagnostic and therapeutic importance. A distinction is made between native and iatrogenically applied substances.

Native components are those that are present within the blood space in a physiologically or pathologically modified manner. Iatrogenic substances are substances applied by the doctor, eg dyes for marking certain clinical parameters. A diagnostic method that uses spectrophotometry to refer to the pulsating blood compartment in biological tissues is called PULSE SPECTROSCOPY.

A distinction must be made here whether relative fractions with respect to a reference substance or an absolute concentration are recorded using the pulse spectroscopy method. As a result, fractional or relative pulse spectroscopy must be distinguished from absolute pulse spectroscopy.

A well-known example of relative pulse spectroscopy is the determination of arterial oxygen saturation by means of the pulse oximetry method. The percentage of hemoglobin that accumulates with oxygen is determined. In this case, hemoglobin is the reference substance, but its absolute concentration cannot be determined in relative pulse spectroscopy.

Using relative pulse spectroscopy, e.g. dysfunctional hemoglobin saturations, such as carbon monoxide saturation, can be determined. This is described in various publications, including by the inventor himself, in the literature.

Absolute pulse spectroscopy determines substance concentrations that are present within the pulsating arterial or venous blood space. These can be both corpuscularly bound (i.e. Be part of blood cells or be dissolved within the blood plasma.

In principle, the determinable substances are not necessarily substances associated with hemoglobin. They can exist independently of this molecule.

Various methods of absolute pulse spectroscopy are described in the literature. The invention relates to the novel method of ratiometric absolute pulse spectroscopy.

The previously known methods and devices of absolute pulse spectroscopy are currently not sufficiently suitable to enable the determination of blood substance concentrations with an acceptable clinical measurement accuracy.

It is therefore an object of the present invention to use the method of ratiometric absolute pulse spectroscopy to achieve a measurement accuracy that can be described as clinically sufficient for the determination of substance concentrations.

This object is achieved in that light signals of a first wavelength are generated at two successive times T-_ and T ₂ , that light signals of a second wavelength are generated at two successive times T ₃ and T ₄ , that at two successive times T _s and T ₆ light signals of a third wavelength are generated and this for n pairs of times at n wavelengths applies. The times T _x ... T _{n + 1} are in a well-defined temporal relationship to each other. Time differences between the times can be small and can be neglected in the evaluation in individual cases. The evaluation unit takes into account the received signals of the photoreceiver for all n wavelengths according to a predetermined calculation scheme to determine a concentration of the blood component.

Another object of the present invention is to provide a device of the type mentioned in the introduction in such a way that improved measurement accuracy is achieved.

This object is achieved according to the invention in that at least three light sources are used which generate light of different wavelengths relative to one another and in that the evaluation unit has a computing module for performing logarithmizations as well as for divisions, multiplications, additions and subtractions.

By measuring the light absorption at different wavelengths and at different times, it is possible to eliminate unknown parameters by means of a suitable linking of the measured values. As a result, it is neither necessary to determine these parameters yourself in a time-consuming process, nor is it necessary to accept the measurement inaccuracies which result from the elimination of these parameters. Rather, the elimination can provide a simple and extremely precise method and an apparatus for carrying out this method can be produced with relatively little effort and therefore inexpensively.

A signal processing step for eliminating unknown parameters consists in that the evaluation unit takes into account a quotient of parameters resulting from measurement signals ("ratiometric method")

A transformation of a division into a subtraction that occurs during logarithization is exploited by taking into account a quotient from the logarithmized measured values.

A simple device structure is supported in that the light is generated by light-emitting semiconductor diodes. These classic emission diodes (or laser diodes) can be used as photometric emission elements without further spectral filtering.

A small size of the measuring device is supported in that the received signal is received by semiconductor photodiodes. These semiconductor photodiodes have different spectral sensitivities.

A simple generation of light of different emission frequencies can be achieved by using at least three different light sources.

A typical application example is that the concentration of total hemoglobin is determined. In particular, it is also contemplated that concentrations of non-hemoglobin associated components are determined. This applies to both native and iatrogenic blood substances.

One application example is that both bilirubin derivatives and the total bilirubin concentration are determined.

It is also possible that a concentration of myoglobin is determined.

In addition, it is thought that concentrations and their kinetics of iatrogenically applied dyes are determined.

Exemplary embodiments of the invention are shown schematically in the drawings. Show it:

1 Principle of multi-wavelengths - measurement technology on biological tissue,

2 two-layer model of pulse spectroscopy including a pulsating non-Hb associated absorber of the concentration c _x and the spectral absorption e _x (?),

3 shows a schematic representation of the formation of the measured value variables Omega 1,2 and Omega 1,3 from two sampling times t _x and t ₂ three plethysmograms of different wavelengths,

4 signal flow diagram of the method RAPS cHb with regard to the determination of the total hemoglobin concentration c _Hb with known pulsatile absorption of a substance X,

5 signal flow diagram of the RAPS cHb method with regard to the determination of the concentration c _{x of} a pulsatile absorber with the spectral absorptions e _x (? _! ) And e _x (? ₂ ), (eg bilirubin; Evans - Blue) with known hemoglobin concentration cHb,

Fig. 6 absorption spectrum whole blood at sa02 approx. 98% and absorption spectrum water. Please note the spectral absorption curve H20 between 1000 [nm] and 1600 [nm],

7 VIS and NIR absorption spectra of functional and dysfunctional Hb derivatives,

Fig. 8 absorption spectrum of the clinical marker substance Evans-Blue (aqueous solution 70 [μmol / 1]) and

Fig. 9 Influence of a pulsatile, non-Hb-associated absorber of the concentration c _x on the pulse oximetric calibration. Basis of substance determination c _x .

The device for determining a concentration of blood components by measurement consists, for example, of consists of three light sources (1, 2, 3) and a number of photo receivers (4). The light sources (1, 2, 3) are designed as light-emitting diodes, selected by a multiplexer and connected to a control unit (5). The photo receivers

(4) are connected to an evaluation unit (6) via a light phase synchronous demultiplexer. The evaluation unit (6) has a computing module (7) which contains the measurement signals of the photo receiver

(4) processed according to specified calculation rules. The determined concentrations of the blood components can be shown on a display (8) and / or passed on or saved via an output device (9). The control unit (5) is connected to the evaluation unit (6) for function coordination.

Figure 2 shows a typical layer model to illustrate the basics of pulse spectroscopy. Shown is the weakening of the light intensity due to the absorption on the one hand in the non-pulsating tissue part (layer 1) and the weakening within the pulsating tissue part (layer 2), which causes the pulsating fluctuation in the emerging light intensity.

In the area of the computing module (7), the measured light intensities are arithmetically linked at different times and with respect to different light wavelengths in such a way that certain unknown measurement parameters drop out. The arithmetic logic of the measured values takes advantage of the fact that a division is transformed into a subtraction during logarithmization. If the quotient of two measured variables is thus formed at different points in time, the respective measured variable influencing but constant in time and unnecessary parameters drop out.

The calculation steps explained below are carried out in detail during the processing of measured values. It is assumed that in a first approximation the passage of light can be described by the Lambert-Bers law and that the weakening of the light occurs primarily at the following biological substances at the measuring location:

1. on Hb derivatives

2. substances that are also present in the pulsating blood space but do not have to be Hb-associated,

3. on non-pulsating constant tissue.

The relationships are illustrated in FIG. 2.

The passage of light is given as follows for the signals I (FIG. 2):

' ^C HbV d _A (ή ^{~ ε} x' xd _A {t) (1)

e are the molar extinctions on which the respective substances are based, c the respective concentrations. D _κ is the total thickness of the constant tissue. d _A (t) is the pulse-cyclic, time-dependent thickness of the pulsating blood vessels.

If two points in time t1 and t2 are considered, the weakening part of the constant tissue falls out:

^'C Hbv ~ ^{r S} x ^{' C} X + [d _A (t ₂ ) -d _Ä (t _l )] (2)

4 (0

With

After logarithming on both sides:

The hemoglobin derivatives are given, for example, with O ₂ Hb and HbR. Then we get:

^S X ^'C X

'HbO,' HbR saO. 2 + ^S bR ^{Jr S} X 'Hb (4)

'Hb

With

-ΗbO, saO (4a)

'Hb saR = XflbR (4b)

^C Hb

sa0 ₂ + aR- = 1 (4C)

This now results in two distinct clinical applications of absolute ratiometric pulse spectroscopy. On the one hand, a blood component X can be determined non-invasively and continuously if the hemoglobin concentration c _{Hb is} known (measured, for example, by reference method) (I). Secondly, the hemoglobin concentration c ^ itself can be determined if another pulsating absorber is known regarding its concentration (II). In principle, both determination methods can be implemented independently of one another.

I. Determination of the concentration of the concentration of a substance X in the pulsating blood space.

As is known, Epsilon X and c _{x are} the molar extinction and the concentration of a blood component that must not be hemoglobin-associated.

If two wavelengths are now § ₃ . and §2 ^ ⁿ (^ introduced, then after division from (4):

Is § _1/2 the measured variable of the two wavelengths? _! and ? _2nd The formation of the measured value Blen in the case of 3-wavelength pulse spectroscopy is shown in Figure 3. Dissolved after saθ ₂ :

It is important to note that the relationship modifies the determination of arterial oxygen saturation when an absorbing substance X with the concentration Cx and the extinctions §χ (§ ₂ ) and § (§ι) is within the pulsating blood compartment. This can also be formulated explicitly:

Relationships (6) and (6a) can be used to determine the substance concentration X, which may not be associated with hemoglobin. This can be, for example, bilirubin or other native blood substances, and furthermore this substance X can be an iatrogenically applied substance, such as e.g. represent a dye marker substance. These iatrogenically administered substances can also be applied in order to dope native or pharmacologically active substances.

With known arterial oxygen saturation sa0 ₂ (e.g. by pulse oximetry), known concentration tration of the hemoglobin c _Hb (eg using a reference method), c _x can finally be determined, since all relevant molar extinctions as well as the measured value variables § _{12 are known} from pulse spectroscopy.

FIG. 9 shows an example of the influence of a concentration c _x on the ideal pulse oximetric calibration (? _X = 660 [nm],? ₂ = 905 [nm]; c _x / c _Hb = 0.25, ß _x (660, 905 ) = 3). It should be noted that depending on c _x _, the assignment to oxygen saturation changes characteristically for each value of the measured value variable § _{1; 2} .

It should be pointed out that the measurement variable mentioned § ₁₂ does not necessarily have to be the measurement variable on which the pulse oximetric determination of arterial oxygen saturation is based.

II. Determination of the total hemoglobin concentration C _m , with previously known substance concentration c _x

With the definitions of the spectral extinction ratio i§χ (§ ₂ / - $ _l ) and the absorption A _x (§) =

«X ⁽ « ^{) c} x results in:

This determination equation of saθ ₂ depends on the as yet unknown substance concentration CJJJ-, if A _x (§) and S (§2 / Sl) are known. This concentration tion can now be determined that a further wavelength § _{3 is} introduced, and this is also used according to the given arrangement for determining saθ ₂ .

This then results analogously to equation (7) with the additional measurement variable ^

1.3 *

The designations (7) and (8) now represent two independent calculation relationships for the saturation saθ _2. This can only be eliminated and the unknown Cjjk determined. The result is:

_ A _x (A ₁ ) - [AE-ι + ß _x (A ₂ , λ _i ) -n _U2 -AE -ß _x (A ₃ , λ _i ) -n ₌ z (ΛΛ)

'Hb (9) ^ε _R (4) ^• 6 ^~ Δ ^] + ^ε _R (4) ^• ΔE ^• Ω _Iι3 - ε _HbR (Ä ₂ ) ^• Ω _{I> 2} N (4, λ ₂ , λ,)

A _x (§ ₃ ) = c _x § _x (§] _) is the known absorption of a substance X.

With the counted Z: Z {λ, λ ₂ ,) / _

/ (4) ^~

+ ϊ ^S Hb0 ₂ (4) - ^S HbR

+ (4) - «ÄSÄ (4) J ^{■ Ω}

As well as the denominator term N:

N (4 »4'4) ⁼

IψHbO, (4) - ^S HbR (4) ^{• ε} HbR (Λ) - ψHb0 ₂ (4) ^~ * ff _M (4) "^ WJ (4)] ^{• Ω} I, 2 ^{• Ω} ., 3

+

+ Ll ^≤: / ϊÄo ₂ () ^"6r ^ Λ (4j ^{-5 '} mΛ (4) ^_ l ^{£ r} rao ₂ (4) ^{_ £:} 4Ä (4j' ^£: ffiÄ () J ^-Ω " ι1.3

The provisions of the desired concentration c ^ bi ^st so clearly because it is determined from the measured Meßwertvariablen and the known extinctions. The entire procedure shown applies to the assumption of an idealized Lambert - Beer's weakening. This simplifying physical modeling can be adapted to the real conditions or the optical properties of the biological application sites by empirically modified modeling.

If several dysfunctional 11 Hb fractions are present, the total hemoglobin concentration must be determined by introducing additional light wavelengths. As a result, absolute ratiometric pulse spectroscopy allows

(1) the determination of the hemoglobin concentration c _Hb and its derivatives in the presence of the concentration c _{s of} an iatrogenically applied or native absorber X which must not be Hb - associated.

(2) the determination of the concentration c _{x of} a natively present or iatrogenically administered substance X of the pulsating blood space if the concentration C _{Hb of} the hemoglobin is present.

Claims

Patent claims

1. Non-invasive method for the metrological determination of blood components, in which, using spectrophotometry, the light generated by at least one light source and passed through tissue located at an application site to at least one photo receiver, and in which at least one measurement signal from the photo receiver is sent to an evaluation unit is characterized in that at two successive times T _x and T ₂ light signals of a first wavelength are generated, that at two successive times T ₃ and T ₄ light signals of a second wavelength are generated that at two successive times T _s and T _s light signals of a third wavelength are generated, and this applies to n wavelengths with respect to the times T _n and T _{n + 1} . The times T _x ... T _{n + 1} have a well-defined temporal relationship to each other. Time differences between individual times can be small. The evaluation unit takes into account the reception signals of the photo receiver for all n wavelengths according to a predetermined calculation scheme to determine a concentration of the blood component.

2. The method according to claim 1, characterized in that a quotient of the measurement signals is taken into account by the evaluation unit.

3. The method according to claim 1 or 2, characterized in that the measured values are logarithmic.

4. The method according to any one of claims 1 to 3, characterized in that a quotient of the logarithmic measured values is taken into account.

5. The method according to any one of claims 1 to 4, characterized in that the light is generated by light-emitting diodes.

6. The method according to any one of claims 1 to 5, characterized in that the received signal is received by a photodiode.

7. The method according to any one of claims 1 to 6, characterized in that at least three different light sources can be used.

8. The method according to any one of claims 1 to 7, characterized in that a concentration of total hemoglobin is determined.

9. The method according to any one of claims l to 7, characterized in that a concentration of non-hemoglobin-associated components is determined.

10. The method according to any one of claims 1 to 7, characterized in that a concentration of bilirubin is determined.

11. The method according to any one of claims 1 to 7, characterized in that a concentration of myoglobin is determined.

12. The method according to any one of claims 1 to 7, characterized in that a concentration of iatrogenically applied dyes is determined.

13. Device for measuring blood components, which has at least one light source, at least one photo receiver and at least one evaluation unit which is connected to the photo receiver, characterized in that at least three light sources (1, 2, 3) are used, which generate light of different wavelengths relative to one another and that the evaluation unit (6) has a computing module (7) both for carrying out logarithms and for divisions, multiplications, additions and subtractions.

14. The apparatus according to claim 13, characterized in that at least one of the light sources (1, 2, 3) is designed as a light-emitting diode.

15. The apparatus according to claim 13 or 14, characterized in that the photo receiver (3) is designed as a photodiode.

16. The device according to one of claims 13 to

15, characterized in that the light sources (1, 2, 3) each generate light in a narrowly limited frequency band.

17. The device according to one of claims 13 to

16, characterized in that one of the light sources (1, 2, 3) generates light with a wavelength of about 660 microns.

18. Device according to one of claims 13 to 16, characterized in that one of the light sources (1, 2, 3) generates light with a wavelength of about 805 μ.

9. Device according to one of claims 13 to 16, characterized in that one of the light sources (1, 2, 3) generates light with a wavelength of about 950 microns.