JP2613832B2 - Dye dilution curve measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dye dilution curve measuring device.

[0002]

2. Description of the Related Art As a conventional apparatus of this kind, there is one based on the principle of a pulse oximeter. The device performs measurement using the pulsation of a living tissue including blood. However, measurement using pulsation is difficult when the pulsation is low, and an accurate result cannot be obtained. Further, since a minute change in the signal is used, the subject is easily affected by body movement of the subject.

[0003] Further, there is an apparatus for measuring an earlobe in an ischemic state based on the transmitted light. But according to this,
The ischemia device of the earlobe is complicated, and the ischemic operation requires skill. In addition, an error occurs due to deformation of the tissue at the time of ischemia.

[0004]

As described above, the conventional apparatus cannot obtain an accurate result when the pulsation is low, is susceptible to body motion, or the operation at the time of measurement is complicated and the error is large. There were drawbacks.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional disadvantage, and an object of the present invention is to enable accurate measurement even when a subject's pulsation is low, and to reduce the influence of body movement. It is an object of the present invention to provide a dye dilution curve measuring apparatus which is hardly affected by the above, is easy to operate and has a small measurement error.

[0006]

According to a first aspect of the present invention, there is provided an irradiation unit for irradiating a tissue containing blood with light of three wavelengths, and a photoelectric conversion unit for receiving light transmitted through the tissue and converting the light into an electric signal. A storage unit for storing the irradiation light intensity of the three wavelengths of light, or a ratio of irradiation light intensity of each other, based on the contents stored by the storage unit and the transmitted light intensity obtained from the photoelectric conversion unit, The difference between the logarithm of the irradiation light intensity ratio and the logarithm of the transmitted light intensity ratio of a certain combination of two wavelengths is obtained, and the logarithm of the irradiation light intensity ratio and the transmission light intensity ratio of the other two wavelength combinations are obtained. Dye concentration calculating means for calculating the difference between the logarithm and the ratio between the two and the degree of extinction due to light absorbed in blood to calculate the concentration of a predetermined dye in blood.

According to a second aspect of the present invention, in the configuration of the first aspect, the irradiation light intensity ratio is obtained by transmitting light generated from the irradiation means through a light attenuation plate having a known light attenuation characteristic. It is characterized in that the calculation of the light intensity ratio takes into account the characteristics of the light attenuating plate.

[0008]

According to the first aspect of the present invention, the dye density calculating means calculates the irradiation light intensity ratio of a combination of certain two wavelengths based on the contents stored in the storage means and the transmitted light intensity obtained from the photoelectric conversion means. The difference between the logarithm and the logarithm of the transmitted light intensity ratio is obtained, and the logarithm of the irradiation light intensity ratio of the other two wavelength combinations,
The difference between the logarithm of the transmitted light intensity ratio and the logarithm of the transmitted light intensity ratio is obtained, and a predetermined dye concentration is calculated from the relational expression between the ratio of the two and the degree of extinction due to blood hemoglobin.

According to the second aspect of the present invention, the irradiation light intensity of the light of three wavelengths is obtained by measuring the light transmitted through a light attenuating plate having a known light attenuation characteristic. For this reason, the intensity of light that is weaker than that measured directly is measured. Therefore, the photoelectric conversion means used for the measurement may be the same as the photoelectric conversion means for converting the light transmitted through the tissue into an electric signal. That is, one photoelectric conversion means can measure both the irradiation light intensity and the transmitted light intensity of the tissue. It can be carried out.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of one embodiment of the present invention will be described.

The three wavelengths of light used in the measurement are λ ₁ = 805 nm λ ₂ = 890 nm λ ₃ = 650 nm, and each has the following characteristics. λ ₁ : No influence of oxygen saturation. Dye absorption maximum. λ ₂ : The effect of oxygen saturation is small. No effect of dye absorption. λ ₃ : affected by oxygen saturation and dye absorption. Suffixes 1, 2, and 3 added to symbols used hereinafter indicate light of these wavelengths.

It is theorized that the dimming degrees A ₁ , A ₂ , and A ₃ of the three wavelengths of light transmitted through the living tissue including blood are as follows if the incident light is appropriate scattered light (Shaster's report). Theory) and experiments. Before dye injection A ₁ = log (Ie ₁ / It ₁ ) = {Eh ₁ Hb (Eh ₁ Hb + G)} ^1/2 Db + Zt Dt (1) A ₂ = log (Ie ₂ / It ₂ ) = ｛Eh _{2 Hb (Eh 2 Hb + G)} } 1/2 Db + Zt Dt (2) A 3 = log (Ie 3 / It 3) = {Eh 3 Hb (Eh 3 Hb + G)} 1/2 Db + Zt Dt (3) dye After injection A ₁ = log (Ie ₁ / It ₁ ) = {(Eh ₁ Hb + Ed ₁ Cd) (Eh ₁ Hb + Ed ₁ Cd + G)} Db + Zt Dt (4) A ₂ = log (Ie ₂ / It ₂ ) = ｛(Eh ₂ Hb) (Eh ₂ Hb + G)｝ Db + Zt Dt (5) A ₃ = log (Ie ₃ / It ₃ ) = ｛(Eh ₃ Hb + Ed ₃ Cd) (Eh ₃ Hb + Ed ₃ Cd + G) ｝ Db + Zt Dt (6) where, Ie: irradiation light intensity (energy per unit area) It: transmitted light intensity (energy per unit area) Eh: absorption coefficient of hemoglobin Hb: concentration of hemoglobin in blood G: blood Scattering Constant Ed: extinction coefficient of dye Cd: blood dye concentration Db: effective thickness of blood layer Zt: extinction ratio of tissue excluding blood (referred to as pure tissue) = extinction ratio / thickness at any of the above wavelengths Is also constant. Dt: Thickness of pure tissue The "scattered light suitable as irradiation light" is as follows.

When the parallel incident light enters the scatterer, it is scattered as it enters the scatterer, and reaches a scatterer unique to the scatterer at a certain depth or more. Therefore, in the straight light irradiation, the light attenuation rate differs between a shallow part and a deep part of the scatterer.

For example, if the irradiation light is scattered by a scattering plate having the same scattering property as that of the living tissue, the extinction ratio becomes the same over the whole living tissue.

Therefore, if such a scattering plate is arranged on the back surface of the light emitting diode, the above-mentioned "scattering light suitable as irradiation light"
Is obtained.

Here, the ratio 減 of the dimming degree between the respective wavelengths is defined as follows. Ψ = (A ₁ −A ₂ ) / (A ₃ −A ₂ ) (4) Expanding equation (4) from equations (1), (2) and (3) gives the following. Ψ = (A ₁ −A ₂ ) / (A ₃ −A ₂ ) = log [(I e ₁ / It ₁ ) / (Ie ₂ / It ₂ )] / log (Ie ₃ / It ₃ ) / (Ie ₂ / It ₂ )] = {log (Ie ₁ / Ie ₂ ) −log (It ₁ / It ₂ )} / {log (Ie ₃ / Ie ₂ ) −log (It ₃ / It ₂ )} (4a) In 4a), Ie ₃ / Ie ₂ and Ie ₁ / Ie ₂ are irradiation light intensity ratios.

The irradiation light intensity itself is greatly affected by measurement conditions such as the distance between the light source and the light receiving unit, but the irradiation light intensity ratio, which is the light intensity ratio between the three wavelengths, is not affected by the above measurement conditions. . There are the following methods for obtaining the irradiation light intensity ratio.

In order to directly measure the irradiation light, the illuminance is so strong that it may not be possible to measure the transmitted light with a light receiving section that receives the transmitted light. Therefore, for example, the irradiation light is transmitted through a light attenuating plate having a uniform dimming degree with respect to the light in the wavelength range to be used, and the irradiation light intensity ratio among the three wavelengths of the transmitted light is calculated.

Thus, the irradiation light intensity ratio Ie ₃ / Ie
₂ and Ie ₁ / Ie ₂ are obtained, the transmitted light intensities It ₁ and It _1
2 and It ₃ can be measured, and Ψ can be easily calculated by equation (4a).

Prior to dye injection, Ψ can also be written as follows based on equations (1), (2) and (3). Ψ = [｛Eh ₁ Hb (Eh ₁ Hb + G)｝ ^1/2 − ｛Eh ₂ Hb (Eh ₂ Hb + G)｝ ^1/2 ] / [｛Eh ₃ Hb (Eh ₃ Hb + G)} ^1/2 − (Eh ₂ Hb (Eh ₂ Hb + G)｝ ^1/2 ] (7) After dye injection, Ψ can also be written as follows based on equations (4), (5) and (6): Ψ = _{[{(Eh 1 Hb + Ed} 1 Cd) (Eh 1 Hb + Ed 1 Cd + G)} 1/2 · Db - {Eh 2 Hb (Eh 2 Hb + G)} 1/2 Db] / [{(Eh 3 Hb + Ed ₃ Cd) (Eh ₃ Hb + Ed ₃ Cd + G)｝ ^1/2 · Db − {Eh ₂ Hb (Eh ₂ Hb + G)} ^1/2 Db] (8)

When the hemoglobin concentration is not abnormally high,
That is, when Hb <20 [g / dL], G = FHb
(F: constant; referred to as a scattering rate). Before dye injection Ψ = [｛Eh ₁ (Eh ₁ + F)｝ ^1/ _2- ｛Eh ₂ (Eh ₂ + F)｝ ^1/2 ] / [｛Eh ₃ (Eh ₃ + F)｝ ^1/ _2- ｛Eh ₂ (Eh ₂ + F)｝ ^1/2 ] (9) After dye injection Ψ = [{(Eh ₁ + Ed ₁ Cd ′) (Eh ₁ + Ed ₁ Cd ′ + F)} ^1/2 − ｛Eh ₂ (Eh ₂ + F) ^{} 1/2] / [{(Eh} 3 + Ed 3 Cd ') (Eh 3 + Ed 3 Cd' + F)} 1/2 - {Eh 2 (Eh 2 + F)} 1/2] (10) where Cd ' = Cd / Hb (11). When the oxygen saturation S is approximated to 1, Eh = EoS + Er (1-S) (12) Eo: extinction coefficient of oxyhemoglobin Er: extinction coefficient of reduced hemoglobin, the following equation is established. Eh ₁ = Eo ₁ (13) Eh ₂ = Eo ₂ (14) Eh ₃ = Eo ₃ (15) According to this approximation, equation (10) gives: Ψ = [｛(Eo ₁ + Ed ₁ Cd ′) (Eo _{1 + Ed 1 Cd '+ F} )} 1/2 - {Eo 2 (Eo 2 + F)} 1/2] / [{(Eo 3 + Ed 3 Cd') (Eo 3 + Ed 3 Cd '+ F)} 1/2 - {Eo ₂ (Eo ₂ + F)} ^1/2 ] (16) By further approximating Ed ₃ = 0, equation (16) can be expressed as follows: Ψ = [｛(Eo ₁ + Ed ₁ Cd ′) (Eo ₁ + Ed ₁ Cd ′) '+ F)｝ ^1/ _2- ｛Eo ₂ (Eo ₂ + F)｝] / [｛Eo ₃ (Eo ₃ + F)｝ ^1/ _2- ｛Eo ₂ (Eo ₂ + F)｝ ^1/2 ] (17) Z ₂ = Eo ₂ (Eo ₂ + F) (18) Assuming that Z ₃ = Eo ₃ (Eo ₃ + F) (19), the equation (17) can be expressed as follows: ｛(Eo ₁ + Ed ₁ Cd ′) (Eo ₁ + Ed ₁ Cd ′) _{^{'+ F)} 1/2 -Z 2}} = Ψ (Z 3 -Z 2) (20) equation (20) ^{_{from, Ed 1 2 Cd' 2 +}} Ed 1 Cd '(2Eo 1 + F) + Eo 1 (Eo 1 + F) - {Ψ (Z ₃ When ^{_{Z 2) + Z 2} 2}} = 0 Solving (21) (21), Cd '= { - B + (B 2 -4AC) 1/2} / 2A (22) where, A = Ed ₁ ^2: Constant (23) B = Ed ₁ (2Eo ₁ + F): constant (24) C = Eo ₁ (Eo ₁ + F) − ｛Ψ (Z ₃ −Z ₂ ) + Z ₂ ｝ ² (25) Cd ′ before dye injection Is Cd ₀ ′. Blood dye density D is expressed by _{D = (Cd '-Dd 0'} ) Hb (26). Therefore, if Ψ before dye injection is Ψ ₀ ,
The equation (25), before the dye injection C, that C _{0 is, C 0 = Eo 1 (Eo} 1 + F) - {Ψ 0 (Z 3 -Z 2) + Z 2} 2 (27) Therefore, Cd ₀ ' = {− B + (B ² −4AC ₀ ) ^1/2 } / 2A (28) From the equation (26), the blood pigment concentration D is expressed by the following equation. D = + ｛(B ² -4AC) ^1/2 − (B ² -4AC ₀ ) ^1/2 ｝ Hb / 2A (29)

Next, an apparatus based on the above principle will be described with reference to FIG.

The three-wavelength light source 1 has wavelengths of 805 nm, 890 nm, and 650 nm.
m It has three light emitting diodes for generating respective lights, and a scattering plate 2 for transmitting the light of the light emitting diodes. The scattering plate 2 has a scattering property close to a living tissue to be measured.

The light receiving section 3 is a circuit provided at an appropriate distance from the three-wavelength light source 1 and converts light from the three-wavelength light source 1 into an electric signal. The amplifier 4 is a circuit that amplifies an electric signal output from the light receiving unit 3. The A / D converter 6 is a circuit that converts a signal output from the amplifier 4 into a digital signal. The three-wavelength measurement control circuit 7 is a three-wavelength light source 1
It is a circuit that outputs a signal that causes two light emitting diodes to emit light sequentially at a predetermined timing. This signal is simultaneously supplied to the amplifier 4, the A / D converter 6, the storage circuit 9A, and the dimming ratio calculating circuit 10. The storage circuit 9A is A / D
This is a circuit for storing the intensity of the signal corresponding to each of the wavelengths λ ₁ , λ ₂ , and λ ₃ provided from the converter 6. The intensity ratio calculation storage circuit 9B is a circuit that calculates the ratio between the respective intensities stored in the storage circuit 9A and stores this. The extinction ratio calculation circuit 10 calculates a predetermined value from the signals corresponding to the wavelengths λ ₁ , λ ₂ , and λ ₃ provided from the A / D converter 6 and the intensity ratio stored in the intensity ratio calculation storage circuit 9B. It is a circuit that performs calculations.

The changeover switch 8 is a switch for switching the output of the A / D converter 6 to one of the storage circuit 9A and the dimming degree calculation circuit 10. The calibration / measurement switching control circuit 11 is a circuit that controls switching of the changeover switch 8.

The storage circuit 14 is a circuit for storing a calculation result calculated first after the changeover switch 8 is switched to the extinction ratio calculation circuit 10 side. The storage circuit 16 is a circuit for storing the hemoglobin concentration Hb when given. The dye density calculation circuit 15 is a circuit that performs a predetermined calculation based on the calculation result of the light attenuation ratio calculation circuit 10 and the values stored in the storage circuits 14 and 16 to calculate the blood dye density.

The display device 12 and the recorder 13 display and record the calculation results of the dye density calculation circuit 15, respectively.

Next, the operation of this embodiment will be described.

First, the operator places the light attenuating plate 15 between the three-wavelength light source 1 and the light receiving section 3. Here, the operator operates the calibration / measurement switching control circuit 11 to switch the changeover switch 8.
Is switched so that the A / D converter 6 and the storage circuit 9A are connected. Next, the operator causes the three-wavelength measurement control circuit 7 to start control. The three-wavelength light source 1, the storage circuit 9A, the extinction ratio calculation circuit 10, and the A / D converter 6 are controlled by control signals from the three-wavelength measurement control circuit 7. That is, the three-wavelength light source 1 uses the wavelengths λ ₁ (805 nm), λ ₂ (890 nm), λ ₃ (650 n
m) is generated at predetermined intervals. These lights pass through the light attenuation plate 15 and reach the light receiving section 3, where they are converted into electric signals. Then, the amplifier 4, the A / D converter 6, and the storage circuit 9A operate in synchronization with the lighting timing of the three-wavelength light source. At this time, the signals supplied to the storage means 9A correspond to Ie ₁ , Ie ₂ and Ie ₃ in the equation (4a). Storage circuit 9
A stores Ie ₁ , Ie ₂ , and Ie ₃ . The intensity ratio calculation storage circuit 9B obtains Ie ₃ / Ie from the storage contents of the storage circuit 9A.
₂ , Ie ₁ / Ie ₂ are calculated and stored.

Next, the operator takes out the light attenuation plate 15, and
Instead, a living tissue 17 (a finger, an earlobe, or the like) to be measured is disposed between the three-wavelength light source 1 and the light receiving unit 3. Here, the operator operates the calibration / measurement switching control circuit 11 to switch the changeover switch 8 so that the A / D converter 6 and the extinction ratio calculation circuit 10 are connected. Next, the operator causes the three-wavelength measurement control circuit 7 to start control. From the A / D converter 6 in the same manner as in the irradiation light intensity measurement using the light attenuating plate 15,
Signals corresponding to It ₁ , It ₂ , It ₃ in (4a) are output to the dimming ratio calculating circuit 10.

The extinction ratio calculation circuit 10 stores Ie ₁ / Ie ₂ , Ie ₃ / Ie ₂ stored in the intensity ratio calculation storage circuit 9 B and It ₁ , It ₂ , It ₃ given from the A / D converter 6.
Is substituted into equation (4a) to calculate Ψ. The three-wavelength measurement control circuit 7 causes the three-wavelength light source 1 to periodically and repeatedly generate light of three wavelengths.

When the changeover switch 8 is switched to the extinction ratio calculation circuit 10 side, the storage circuit 14 first stores the extinction ratio calculation circuit 10.
Is calculated, that is, Ψ ₀ is stored.

The dye density calculating circuit 15 substitutes the [psi applied from the memory circuit 14 ₀ [psi for storing the memory circuit 16 Hb and attenuation are stored ratio calculation circuit 10 in the formula (29) ( Ψ ₀ is included in C ₀ in the formula, and Ψ is included in C in the formula).

Since the three wavelengths of light are sequentially and repeatedly irradiated on the living tissue 17 as described above, the dye density calculation circuit 15 performs the calculation each time, and the result is displayed on the display device 12 and the recorder.
Output to 13. Therefore, when a predetermined dye is injected into the blood of the living tissue 17 after the changeover switch 8 is switched to the dimming ratio calculating circuit 10 side, the temporal change of the dye concentration D, that is, the dye dilution curve is displayed on the display device 12. It is displayed and recorded by the recorder 13.

According to this embodiment, when measuring the irradiation light intensity, the light attenuating plate 15 is used, so that it can be measured by the same device as that for transmitting the living tissue 17 and measuring the light intensity. It is desirable that the light attenuating plate 15 has the same scattering degree for each wavelength of the light source. However, if there is a difference in the scattering degree, the difference is known, and the difference is calculated by the means for calculating the irradiation light intensity ratio. It suffices if a means for correction is included. In this example, the light of three wavelengths is irradiated in order. However, the light of three wavelengths is simultaneously irradiated to the light attenuating plate or the living tissue, and the respective transmitted light is simultaneously received and photoelectrically converted. Immediately Ie ₃ / Ie
_{2, Ie 2 / Ie 1,} It 3 / It 2, It 1 / It 2
May be obtained, and these may be stored and used in the calculation of equation (4a). If means for generating three wavelengths of light alternately at an extremely short cycle and receiving these lights and separating and reproducing the signals of the respective wavelengths is provided, the three wavelengths of light generated almost simultaneously can be processed. The same operation and effect as those in the case of performing the above are obtained.

Further, according to the present embodiment, since the light generated from the three-wavelength light source 1 is transmitted through the scattering plate, the light reduction rate does not differ between the shallow part and the deep part of the living tissue.

Further, according to the present embodiment, since the ratio of the irradiation light intensities is used, it is less affected by the measurement conditions. Further, according to the present embodiment, the irradiation intensity can be measured and stored in a timely manner, so that it is possible to prevent the light emitting section from being affected by aging or contamination.

In the above embodiment, the dye density calculation circuit 15
It is is used formula obtained by approximating the Ed ₃ = 0 (29), wherein without using approximation Ed ₃ = 0 (16) in Cd '
May be sequentially substituted by values that gradually increase from 0 by a predetermined amount, the value of the right side in each is obtained and compared with the left side Ψ, and the value of Cd ′ when the value exceeds the left side Ψ may be obtained.

In the above embodiments, the circuits for performing calculations and controls are independent circuits, but these calculations and controls may be performed by a computer.

[0040]

According to the present invention, accurate measurement can be performed even when the subject's pulsation is low, it is hardly affected by body movement, operation is easy, and measurement error is small.

[Brief description of the drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 3 wavelength light source 3 light receiving section 9A, 14, 16 storage circuit 9B intensity ratio calculation storage circuit 10 extinction ratio calculation circuit 15 dye density calculation circuit

Claims (2)

(57) [Claims] 1. Irradiating means for irradiating a tissue containing blood with light of three wavelengths, photoelectric conversion means for receiving light transmitted through the tissue and converting the light into an electric signal, irradiating light intensity of the light of three wavelengths, Or a storage unit for storing the irradiation light intensity ratio between them, and an irradiation light intensity of a combination of two wavelengths based on the contents stored in the storage unit and the transmitted light intensity obtained from the photoelectric conversion unit. The difference between the logarithm of the ratio and the logarithm of the transmitted light intensity ratio is determined, and the difference between the logarithm of the irradiation light intensity ratio and the logarithm of the transmitted light intensity ratio of the other two wavelength combinations is determined. And a dye concentration calculating means for calculating the concentration of a predetermined dye in blood by a relational expression between the light intensity and the degree of extinction due to light absorbed in blood. 2. An irradiation light intensity ratio is calculated based on the light intensity obtained by transmitting light generated from the irradiation means through a light attenuation plate having a known light attenuation characteristic and the characteristics of the light attenuation plate. 2. A dye dilution curve measuring apparatus according to claim 1, further comprising an irradiation light intensity ratio calculating means for storing the light intensity ratio in a storage means.