JPH04174648A - Oxygen saturation degree measuring device - Google Patents

Abstract

PURPOSE:To measure the oxygen saturation degree in the blood with high precision without being influenced by a variety of variation causes of the reflection light intensity in the blood by irradiating the light having different wave length into the blood and sampling the reflection light intensity of the light having the second wave length in the first cycle. CONSTITUTION:A probe 11 is inserted into a lung vein, and measures the oxygen saturation degree in the blood continuously. The probe 11 and a body are connected through an optical cable 28. At a part 16 where a light-electricity conversion part and a preamplifier are formed integrally, the reflection light supplied from the probe 11 is inputted, and an electric signal corresponding to the intensity of the input light is outputted. The light absorption characteristic of the hemoglobin which does not bond with oxygen is shown by 301, and the light absorption characteristic of the hemoglobin boded with oxygen is shown by 302. Accordingly, these two kinds of wave length light are irradiated into the blood, and the reflection light is detected, and the ratio is obtained, and the oxygen saturation degree in the blood can be obtained.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an oxygen saturation measurement device that measures oxygen saturation in blood by irradiating light into blood and measuring the intensity of the reflected light.

[Conventional technology]

In recent years, optical fibers have been incorporated into cardiac catheters, etc., and by irradiating light into the blood through this fiber, the oxygen saturation of mixed venous blood (
Systems that can monitor Sv02) have been developed. Monitoring of mixed venous blood oxygen saturation not only serves as a warning in the event of sudden changes in hemodynamics in post-operative patients, but also monitors the response to certain types of stress on the body, such as administration of drugs. It is thought that it will be useful for The problem when calculating oxygen saturation is that there are many factors other than oxygen saturation that can change the intensity of reflected light. It is necessary to keep the influence to a minimum.The fluctuations in reflected light intensity are caused by the measurement system, but fluctuations originating from the biological system are important.In order to continuously monitor blood, whole blood However, in addition to the light absorption characteristics of hemoglobin, it is necessary to take into account the light scattering of red blood cells, so it is impossible to theoretically determine oxygen saturation.Therefore, this monitor system First, blood is irradiated with two types of light of specific wavelengths, and backscattered light (reflected light) is detected from the blood. Here, the specific wavelength is the wavelength at which the absorption coefficients of oxygenated hemoglobin and deoxyhemoglobin are equal (805 nm; equiabsorptive wavelength)
This is the wavelength (660 nm) at which the difference in absorption coefficient between the two is large. Therefore, the reflected light intensity signal at 805 nm, which is the isoabsorption wavelength, is almost independent of oxygen saturation, and at 660 nm
Since the reflected light intensity signal changes in thickness depending on the oxygen saturation of hemoglobin, the oxygen saturation is calculated by comparing these two signals.

[Problem to be solved by the invention] The first processing method for continuous monitoring was developed in 1960 by P.
This is the process reported by o1any1 and others as shown by the following equation. Reflected light intensity of red light where A and B are constants. In this process, the ratio of the reflected light intensities of two wavelengths is calculated, so the effects of changes in blood flow velocity, blood cell size, etc. can be canceled out considerably. However, since the hematocrit value has different effects on the reflected light intensity of the two wavelengths, they cannot be canceled out even if their ratio is taken. Therefore, sufficient accuracy cannot be expected with this process. Therefore, in order to correct the hematocrit value, use the following formula: % Equation % Reflected light intensity of red light 10 Correction term 2 These correction terms 1 and 2 are constant values determined experimentally to minimize the influence of the hematocrit value. Also,
A" and Bo are also constants. This processing method is effective in monitoring using a sensor program unit fixed to the blood circuit, such as in extracorporeal circulation. However, mixed venous oxygen saturation monitors usually use the thermodilution method. (
It is used in the form of a catheter that measures heart rate, such as the so-called Swan-Ganz method, with added functions. That is, since measurements are made with an optical fiber incorporated into the catheter and placed in the pulmonary artery, such correction alone was insufficient. The present invention has been made in view of the above conventional example, and an object of the present invention is to provide an oxygen saturation measuring device that can accurately measure the oxygen saturation of blood without being affected by various fluctuation factors of the intensity of reflected light in the blood. With the goal. [Means for Solving the Problems] In order to achieve the above object, the oxygen saturation measuring device of the present invention has the following configuration. That is, an irradiation means that irradiates the blood with light of different first and second wavelengths, and a reflected light intensity of the light of the second wavelength is sampled in a first period, and an average value thereof is calculated. and a second calculation means that samples the reflected light intensities of the first and second wavelengths at a second period longer than the first period and calculates each average value. and a reference value determining means for determining a reference value from the average value of the reflected light intensity of the light of the second wavelength calculated by the second calculating means; and an oxygen saturation calculating means for calculating the oxygen saturation of the blood from the ratio of reflected light intensities of the first and second wavelengths of light and the reference value.

[For use]

In the above configuration, light of different first and second wavelengths is irradiated into the blood, the reflected light intensity of the light of the second wavelength is sampled in a first cycle, and the average value is calculated. . Furthermore, the reflected light intensities of the lights of the first and second wavelengths are sampled at a second period longer than the first period, and each average value is calculated. A reference value is determined from the calculated average value of the reflected light intensity of the light of the second wavelength, and the blood oxygen saturation is determined from the ratio of the reflected light intensity of the first and second wavelength light and the reference value. It works to calculate.

【Example】

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. [Description of Oxygen Saturation Measuring Apparatus (Fig. 1)] Fig. 1 is a block diagram showing a schematic configuration of an oxygen saturation measuring apparatus 10 according to an embodiment. In the figure, reference numeral 11 denotes a catheter probe that is placed in a pulmonary artery or the like and is used to measure the intensity of light reflected in blood. 12 is a pulse timing circuit, and LED drive circuit 1
3 outputs a drive timing signal for the LEDs 14 (141 and 142), and also outputs a timing signal for sampling the intensity of reflected light from light of different wavelengths emitted from each LED to the sample/hold circuit 18. . Reference numeral 13 denotes an LED drive circuit, which drives one of the two LEDs 141 and 142 of the LED 14 to emit light according to a timing signal from the pulse timing circuit 12. 14 is a light emitting diode (L) that can output light with a wavelength of 660 nm and light with a wavelength of 800 nm.
ED), and here LED 141 (wavelength is 660n)
The LED 142 (wavelength: 805 nm) is comprised of two components: In this way, the lights of different wavelengths emitted from each LED are combined by an optical coupler, combined into one optical fiber, and sent to the probe 11. Note that by changing the driving voltage of LED l4, the wavelength of the output light can be changed between 660 nm and 805 nm.
If the LED can be changed between nm and
can be substituted with Reference numeral 15 denotes a connection portion such as a catheter that connects the probe 11 and the main body of the device, and an optical cable 28 is connected between the probe 11 and the main body.
connected with. Reference numeral 16 denotes a part in which a photoelectric conversion section and a preamplifier are integrated, which inputs reflected light from the probe 11 and outputs an electric signal corresponding to the intensity of the input light. A main amplifier 17 further amplifies the electrical signal from the photoelectric conversion section 16. Sample hold circuit 18
inputs the timing signal from the pulse timing circuit 12, and samples and holds the analog signal from the main amplifier section 17 in synchronization with the timing signal. Note that the light of each wavelength emitted from the LED 14 is controlled by a timing signal from the pulse timing circuit 12 so that the light of each wavelength does not overlap with each other in time, so the sample and hold circuit 18 adjusts the reflected light intensity for each wavelength. can be held independently. The signal sampled and held in this manner is outputted to the control section 20 after noise components are filtered by the filter circuit 19 . In the control section 20 , the analog signal from the filter circuit 19 is converted into a digital signal by the A/D converter 22 and input to the CPU circuit 21 . The control unit 20 inputs the timing signal 33.34 (35, 3f3) from the pulse timing circuit 12,
This makes it possible to determine which probe and which wavelength the digital signal input from the A/D converter 22 corresponds to is the reflected light intensity. Here, for example, the timing signal 33 indicates the input timing of the reflected light intensity for light with a wavelength of 660 nm, and the timing signal 34 indicates the input timing of the reflected light intensity for light with a wavelength of 805 nm. The second component is the CPU circuit, which includes a microprocessor, etc.
Control is performed according to control programs and various data stored in the OM24. 25 is an RA used as a work area for the CPU circuit and temporarily stores various data.
It is M. Reference numeral 23 denotes an operation section, which is operated by an operator and can input instructions for starting measurement and various functions. A display section 27 is driven by the display circuit 26 to display messages to the operator, measurement results, and the like. 28 is an external output circuit for outputting measurement data and the like to an external device such as a printer connected through eight external terminals, for example. 30 is a power supply circuit which inputs AClooV and creates various power supply voltages used in the device. 31 is a power supply circuit such as a switching regulator, which outputs various DC voltages as shown in the figure. A line filter 32 is provided on the power line and attenuates power noise input through the AC line. FIG. 2 is a diagram showing the probe 11 such as a catheter.
Figure (A) shows the front view, and Figure 2 (B) shows the tip of the catheter probe. In the figure, 201,2
Reference numeral 02 denotes an optical fiber cable, one of which is a fiber cable for light irradiation, and the other is a fiber cable for light incidence to take in the light that is reflected in the blood and then incident. This probe 11 is inserted into, for example, a pulmonary vein or the like, and continuously measures the oxygen saturation level of blood. FIG. 3 is a diagram for explaining the wavelength of light used in this embodiment. In FIG. 3, 301 shows the light absorption characteristics of hemoglobin not bound to oxygen, and 302 shows the light absorption characteristics of hemoglobin bound to oxygen. Then, 303 indicates the time when the difference between these two absorption properties becomes the largest, and 304 indicates the time when the difference between these two properties becomes "0", and the wavelengths corresponding to each of these are as follows.
The wavelengths are 660 nm and 805 nm, respectively. Therefore, each of these two wavelengths is irradiated into the blood,
By detecting the reflected light and taking the ratio, the oxygen saturation level in the blood can be determined. <Description of Operation> Before explaining the operation of this embodiment, the setting of a base level for eliminating the influence of scatterers other than blood (blood vessel walls, heart valves, etc.) contained in reflected light will be explained. First, it is assumed here that the intensity of reflected light from scatterers other than blood always acts to increase the intensity of reflected light at a wavelength of 805 nm. This is because, as described above, light with a wavelength of 805 nm does not depend on the intensity of reflected light in blood, and since the walls of blood vessels are nearly white, the reflectance of light is expected to be quite high. According to this assumption, the less the influence of scatterers other than blood, the less the reflected light intensity of 805 nm will be, and when the influence disappears, the reflected light intensity will be minimum. The minimum value of the reflected light intensity is used as the base level, and the oxygen saturation is calculated based on this. In the device of this example, the wavelength is 660 nm and the wavelength is 805 nm.
The reflected light intensity of each light of m is measured every 20 m seconds,
Oxygen saturation is calculated based on these. Below, wavelength 6
Let rl be the reflected light intensity of light with a wavelength of 60 nm, and r2 be the reflected light intensity of light with a wavelength of 805 nm. FIGS. 4(A) and 4(B) are flowcharts showing measurement processing in the oxygen saturation measurement apparatus of the embodiment, and a control program for executing this processing is stored in the ROM 24. This process starts when the power of the device is turned on. First, in step S1, the RAM area, counters, etc. to be described later are cleared, and various initial settings are made. In step S2, a switch is turned on to instruct calibration of the probe 11. See what happened. When the calibration switch is turned on, in order to maintain the compatibility of the probe used for measurement, the intensity of reflected light from the standard reflector is measured and these are designated as C1 and C2. Note that these values of C1 and C2 are average values of 21 points at 100 msec. This calibrates R1=r1/CI R2=r2/C2. Next, the process proceeds to step S3, and waits for the start switch to be turned on. When the start switch is turned on, the process proceeds to step S4, and starts measuring the reflected light intensity. When the measurement is started in step S4, the process proceeds to step SL2 in FIG. 4(B), where R1 and R2 are measured every 20 msec. In step S13, the counter is incremented by 1. This is to check whether the measurement has been performed 16 times in step S15. Next, the process proceeds to step S14, where an M1 filter is obtained as a calculation parameter. This will be explained in detail below. Now, if the measurement time is T, then T=0. 020Xt=0. Consider time coefficients S and t that are 320Xs. To explain this with reference to FIG. 5, one square is one block, and the time width is 320 m5. That is, the time coefficient t is 20m
5, the time factor S is every 320 m5. Further, "resetting" indicates the setting and final setting of R80, which will be described later. A solid line block with a curved line connected to a black circle indicates parameter calculation, and a connected dotted line indicates forwarding. ' Mn is the reflected light intensity signal R that is horizontally compared every 20 msec.
2 (wavelength: 805 nm), where n=t-2, provided that t≧4. In addition, "Min" is the moving average value of 21 points of the reflected light intensity signals R1 and R2 measured every 320 msec. Or, m=5-10.However, S≧20.Also, 2M
The subscript i (i=1.2) of 1I11 is the wavelength 660 nm
(i=1) and 805 nm (i=2). Furthermore, the time change of "M2m" of this moving average value "Min" is processed by a differential digital filter method. That is, "DMm'= (1/20)Σ (("M21.,
- "M2.-.k=1) /"M2. , )) where 16m' = t-224. However, t≧448, or m'=s-14, but S≧28. As a result, as is clear from FIG. 5, in order to perform the measurement at time t, the moving average values "Mlm," M2m from 1o block ago, and the moving average value "M2m differential value" from 14 blocks ago are used. It can be seen that DM,' is required. Therefore, each time these moving average values and their differential values are calculated, it is necessary to sequentially store the values and the corresponding times in the RAM 25. In this way, in step S14, when the average value of Ml for every 20 msec is calculated, the process proceeds to step S15, and 16 times Ml is calculated.
1 was calculated, i.e. 320 msec (1 block)
Check to see if it has passed. Otherwise, the process proceeds to step S19, but when 320 msec has elapsed, the process proceeds to step S16, where M2 filter calculation and M1 blocking are performed. This is the moving average value 2M1n every 320m5 mentioned above,
This is to calculate the differential value. Here, the block corresponds to one square in FIG. 5 mentioned above, and its number is indicated by j. Here, in order to block Ml, ' Mn is calculated at 16 points. This value is compared with "M2m" and used to calculate the judgment parameter MM as described later, so data up to block number j=10, that is, t-175, must be saved as shown in FIG. In addition, when creating blocks of "Mim" and "DMm", the correspondence between these subscripts m and mo and the block number j is "Mi Bj; j=s-, k=m, m- 1-
"DMMBj;j=s-ni',ni'=m,m
' -1 As described above with reference to FIG. 5, in order to calculate the oxygen saturation at time t, block number j =
14 data "MfB+4" is used. This is "DMs+' which has the largest block number j among the calculation parameters.
This is because j=14. Therefore, the block data “MIBj” and “M2Bj” are j=10 to 14 (10
14 blocks) are updated and stored sequentially. Next, the base level for correcting oxygen saturation, which is a feature of this embodiment described above, will be explained. This base level is the block data “M2B” mentioned above.
j and the judgment parameters (MM, DM, MB
) is calculated from. As mentioned above, this base level is for eliminating the influence of reflected light from sources other than blood (such as the walls of blood vessels), and is based on the assumption mentioned above.
The reflected light intensity when the reflected light intensity of m is the minimum is taken as the base level. These determination parameters will be explained below. ■Judgment parameter MM This parameter is determined by the ratio between 'Mn and 'M2m, but when shown in correspondence to one block (block 10 here), MMBlo = Max ['Mt-+ts/'' M2B
+a, 'Mt-+go/"M2B!.l Here, Max [X, Yl is the maximum absolute value from X to Y. The judgment parameter MM is calculated from the value of the above equation, M M = O
; ABS(1-MMB,.)≦0.14MM=l
; ABS(1-MMBlo)>0.14. Note that 0.14 is a threshold value here. ■Judgment parameter DM This judgment parameter is determined by DM8.4 (differential value of M2si of 14 blocks), DM =
O; ABS("DMB+4) ≦0.02
DM=l; ABS("DMB14)>0
．． It becomes 02. Note that 0.14 is a threshold value here. ■Judgment parameter MB This judgment parameter MB is the ratio of "M2R,4 to the base level, but both parameters depend on oxygen saturation. Therefore, in order to compare, Since it is necessary to convert to the value of , we will convert it to the value when the oxygen saturation is 80%.And if these are MB0 and B2O, then MB=0; 0.9≦M80/B80≦1.0MB =
1; 1.0<M80/B80≦1.1MB=2.
1.1<M80/880≦1.35MB=3. 0.5
≦M80/B80<0.9MB=4. 1.35<M
80/B80≦1.8M B = 5; M
80/B80 < 0.5MB = 6, 1.8
<M80/880. Note that each of these threshold values is a value here. By the way, MB0 is obtained by the following formula. M80= ” M2R, 4X (1+zl X (0,
8-0,01X 5O2)). Note that zl is a constant, and Sow is oxygen saturation (%). This MB0 is stored and stored sequentially in blocks in the same way as each calculation value described above.
Update. In this way, the first base level B is determined. This is based on the above-mentioned calculation parameter "M2m m=10~1
Calculated from the average value up to 4. Returning to the flowchart of FIG. 4 again, once M2k of blocks 10 to 14 is calculated and the first base level B is determined, the process proceeds from step S17 to step S18, but until then, steps 818 and S19 are skipped. In step S18, the data reading flag is turned on, and in step S19, the timer waits for a predetermined time to elapse.When this data reading flag is turned on, the process proceeds from step S5 in FIG. 4 to step S6, and the oxygen saturation is determined. When calculating this oxygen saturation, this base level B
Since the oxygen saturation also depends on the oxygen saturation, it is necessary to correct the oxygen saturation by setting the base level to 880 when the oxygen saturation is 80%. However, at this stage, the oxygen saturation cannot be calculated using the regular processing method (a feature of this embodiment), so the oxygen saturation is measured using the following equation. SO, : Σai level etc. are used to improve the accuracy of oxygen saturation. This formula is shown below: Sow = Ibi xRd' 1=O Rd = (Bd-di)/(Bd
” M2B,,)X (1+W+t xwi)
-d2)Bd =B80X (1+zlX
(0,01XSO2-0,08))Wr”O;
” M2Bz−Bd≦0Wr= fl
BS(2M2B14-Bd)/Bd); ” M2
B+4-Bd>O W, = -0,06; 100≦5O2W, =-0
,005xSOt+0.04;O≦SO□100w,
= 0.0. a ;0 <SO2
Note that bi, zl, di, and fl in these above equations are constants, and the numerical values used to calculate W3 are provisional coefficients. Once the oxygen saturation has been calculated in this manner, the process proceeds to step S7 to check for errors, and the calculation result is displayed on the display section 27 in step S8. In step S9, the information is output to, for example, a connected printer. Next, the case of updating this base level B80 will be explained. There are three possible conditions for updating this base level: 0M80 and the current base level are compared, and when all 25 points are greater than 880, the base level B80 is updated. B80=0.04ΣM80j j=14 Note that M80j is the average value when the oxygen saturation level corresponding to block number j is 80%. ■Judgment parameter M for block number j = 14 to 38
M and DM are all “0”, and the judgment parameter M
The base level is updated when B (j=14) is "0". B 80 = M80 ■ Judgment parameter M for block number j = 14 to 38
M and DM are all “0”, and the judgment parameter M
When B (j=14) is "1", the base level is updated. B80=B80+0.5XM80 Note that 0.5 is a coefficient. As explained above, according to this embodiment, by correcting oxygen saturation based on the base level, it is possible to remove the influence of reflected light from sources other than blood, which has the effect of accurately measuring oxygen saturation. There is.

【Effect of the invention】

As explained above, according to the present invention, there is an effect that the oxygen saturation level of blood can be measured with high accuracy without being affected by various fluctuation factors of the intensity of reflected light in blood.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the schematic configuration of the oxygen saturation measurement device of the example. Figure 2 (A) and (B) are external views of the probe of the example. Figure 3 is oxyhemoglobin and deoxyhemoglobin in blood. Figure 4 is a flowchart showing the measurement process in the oxygen saturation measuring device of the example, and Section 5 shows the differences in the absorbance of the oxygen saturation measuring device of the example according to the wavelength of light. FIG. 3 is a diagram showing blocking and reference blocks. In the figure, 10...Oxygen saturation measuring device, 11...Probe, 12...Pulse timing circuit, 13...L
ED drive circuit, 14...LED, 15...connection part,
16... Photoelectric conversion section, 17... Main amplifier section, 1
8... Sample hold circuit, 19... Filter circuit, 20... Control unit, 21... CPU circuit, 22...
...A/D converter, 23...operation unit, 24...
ROM, 25... RAM, 27... Display, 28.
...It is an optical fiber. Tsubohiro;・ Figure 2 (B) Figure 3 Figure 4 (A)

Claims (3)

[Claims] (1) Irradiation means for irradiating light of different first and second wavelengths into the blood, sampling the reflected light intensity of the light of the second wavelength in a first cycle, and calculating the average value thereof. a first calculation means for calculating, and a second calculation for sampling the reflected light intensities of the lights of the first and second wavelengths in a second period longer than the first period, and calculating each average value. means, a reference value determining means for determining a reference value from an average value of the reflected light intensity of the light of the second wavelength calculated by the second calculating means; An oxygen saturation measuring device comprising: an oxygen saturation calculation means for calculating the oxygen saturation of the blood based on a ratio of reflected light intensities of lights of first and second wavelengths and the reference value. (2) Differentiating means for calculating the differential value of the average value of the reflected light intensity of the light of the second wavelength calculated by the second calculating means, and the average calculated by the first and second calculating means. 2. The oxygen saturation measuring device according to claim 1, further comprising determining means for determining whether to update the reference value based on each of the values and the differential value. (3) The oxygen saturation measuring device according to claim 1, wherein the first wavelength is 660 nm and the second wavelength is 805 nm.