WO2017179103A1

WO2017179103A1 - Oximetry sensor and oximetry apparatus

Info

Publication number: WO2017179103A1
Application number: PCT/JP2016/061707
Authority: WO
Inventors: 宏信前多; 晴雄山村
Original assignee: 株式会社フジタ医科器械
Priority date: 2016-04-11
Filing date: 2016-04-11
Publication date: 2017-10-19
Also published as: JPWO2017179103A1; JP6060321B1

Abstract

The purpose of the present invention is to provide an oximetry sensor capable of improving the reliability of information relating to sites differing in depth. This oximetry sensor is provided with: a pad attachable to a human body; a plurality of light sources which are disposed adjacent to but spaced from one another on the pad and emit near infrared radiation; a plurality of light-receiving elements which are disposed adjacent to but spaced from one another on the pad and arranged relative to a center common with the innermost one of the plurality of light sources in a one-to-one correspondence with the light sources, and receive transmitted light from the corresponding light sources; and a ROM unit which preliminarily measures transmitted light using a phantom and stores the result as a reference value as well as stores the amount of transmitted light received by the light receiving elements.

Description

Oxygen saturation measuring sensor and oxygen saturation measuring device

The present invention relates to an oxygen saturation measurement sensor and an oxygen saturation measurement device, and more particularly, to an oxygen saturation measurement sensor and an oxygen saturation for measuring oxygen saturation in blood in a living body in a non-invasive manner using near infrared rays. It relates to a measuring device.

The supply of oxygen by the breathing of the human body as a living body is carried and exchanged by circulating blood. Oxygen taken up by respiration is combined with hemoglobin (Hb) in the blood by gas exchange in the alveoli. Oxygen taken into the blood is sent to the whole body by arterial blood and taken into cells by capillaries.

Since the cells in each part survive due to oxygen in the blood, the oxygen state of the skull, especially the cerebral cortex, is measured in real time, especially during surgery such as the heart, or during heart massage due to cardiac arrest. Therefore, it is desirable to constantly check the state of brain cells.

As a method for measuring the oxygen state of the cerebral cortex, there is known an oxygen saturation measuring apparatus for measuring oxygen saturation in blood in a living body using a near-infrared ray by attaching a pad to the head of a human body. (For example, refer to Patent Document 1).

JP 2016-000240 A

By the way, the above-described conventional sensor uses a single light source and two photodetectors to subtract information on a shallow part from information on a deep part of the human head to obtain information on a deep part. In this case, the center (line) based on the separation distance between one light source and one photodetector is shifted from the center (line) based on the separation distance between one shared light source and the other photodetector. .

For this reason, the part where the near infrared light passes is different in the center between the deep position and the shallow position, and in the part where the blood vessel arrangement in the living body is different, it is difficult to say that information is accurate only in the deep part, and the reliability is low. was there.

In order to solve the above-described problems, an object of the present invention is to provide an oxygen saturation measuring sensor and an oxygen saturation measuring device capable of improving the reliability of information on parts having different depths. .

In order to achieve the above object, an oxygen saturation measurement sensor according to the present invention includes a pad that can be attached to a human body, a plurality of light sources that are arranged adjacent to the pad in a separated state and irradiate near infrared rays, and a pad. A plurality of light sources that are adjacent to each other in a separated state and are arranged so as to have a one-to-one correspondence with a plurality of light sources on the basis of a common center with a plurality of light sources, and receive transmitted light from the corresponding light sources. A light receiving element, and a ROM unit that measures light transmitted by the phantom in advance and stores it as a reference value and stores the amount of light received by the plurality of light receiving elements.

According to the present invention, since the centers (lines) of the separation distances between the plurality of light sources and the plurality of light receiving elements corresponding to the respective light sources on a one-to-one basis are the same, the reliability of the information on the parts having different depths Can be improved.

It is a block diagram of the oxygen saturation measuring apparatus which concerns on one embodiment of this invention. FIG. 5 shows another oxygen saturation measurement sensor according to an embodiment of the present invention, wherein (A) is an explanatory diagram of a pad in which two light receiving elements are arranged in one light source, and (B) is a pair of light sources on the left and right sides; FIG. 6C is an explanatory diagram of pads in which light receiving elements are arranged, and FIG. 8C is an explanatory diagram of pads arranged in a one-to-one correspondence with a plurality of light sources and a plurality of light receiving elements at the same center (line). It is a graph which shows the relationship between the measurement voltage and measurement depth which use a water-containing cuvette and rubber | gum in the case of the separation distance of 40 mm. It is a graph which shows the relationship between the light reception intensity | strength which uses a cuvette with water and rubber | gum in the case of separation distance 40mm as a sample, and measurement depth. It is a graph which shows the relationship between the light reception intensity | strength which uses a cuvette with water and rubber | gum in the case of separation distance 30mm, and a measurement depth. It is a graph which shows the relationship between the light reception intensity | strength which uses a cuvette with water and rubber | gum in the case of separation distance 20mm, and a measurement depth. FIG. 2 shows a schematic configuration of a pad, where (A) is an explanatory diagram of a curved surface non-following type, and (B) is an explanatory diagram of a curved surface tracking type. It is explanatory drawing which shows the relationship between the cross-sectional structure of a human head, and sensor sensitivity. (A) is explanatory drawing of the cuvette used at the time of calibration curve creation, (B) is explanatory drawing of the phantom used at the time of calibration curve creation.

Next, an embodiment according to the present invention will be described with reference to the drawings.

As shown in FIG. 1, the oxygen saturation measuring apparatus 1 includes, for example, a sensor unit 2 and a main body unit 3 that are attached to the surface of the skull.

The sensor unit 2 includes a pad 21 that can be attached to a human body, and a plurality of

light sources

22A and 22B (hereinafter also referred to as “light source 22”) that are disposed adjacent to the pad 21 in a separated state and emit near-infrared rays. Arranged so as to correspond to the plurality of

light sources

22A, 22B on a one-to-one basis with the center P as a reference adjacent to the pad 21 in a separated state and shared with the innermost light source 22B among the plurality of

light sources

22A, 22B. A plurality of light receiving

elements

23A and 23B (hereinafter also referred to as “light receiving elements 23”) that receive the transmitted light from the plurality of

light sources

22A and 22B, and a ROM unit that measures the transmitted light by the phantom in advance and stores it as a reference value 24.

The plurality of

light sources

22A and 22B and the plurality of light receiving

elements

23A and 23B correspond one-to-one with the light source 22A and the light receiving element 23A, and between the light source 22B and the light receiving element 23B. In the following description, the combination of the light source (22A, 22B) and the light receiving element (23A, 23B) is also simply referred to as “sensor”. In this case, particularly when referring to the combination of the light source 22A and the light receiving element 23A, it is also referred to as “sensor A”, and when regarding the combination of the light source 22B and the light receiving element 23B, it is also referred to as “sensor B”.

In addition, the plurality of

light sources

22A and 22B and the plurality of light receiving

elements

23A and 23B are arranged such that the plurality of

light sources

22A and 22B are spaced apart by an equal distance on one side of the center P, and the plurality of light receptions are performed on the other side of the

center P. Elements

23A and 23B are spaced apart by an equal distance. Furthermore, the center p1 between the separation distance (center distance) between the light source 22A and the light source 22B and the center p2 between the separation distance (center distance) between the light receiving element 23A and the light receiving element 23B are at the center P. It is in a symmetrical position.

Therefore, the light source 22A and the light source 22B, the light source 22B and the light receiving element 23B, and the light receiving element 23A and the light receiving element 23B are arranged so that the respective separation distances (center distances) are all equal. At this time, the light source 22A and the light receiving element 23A having a long separation distance are set to have a separation distance (for example, 40 mm) so as to acquire information on a deep part of the skull. On the other hand, the light source 22B and the light receiving element 23B having a short separation distance are set to have a separation distance (for example, 20 mm) so as to acquire information on a shallow portion of the skull. In this embodiment, “deep / shallow” refers to a case where a pair of sensors is compared. In addition, for example, when one or more pairs of sensors are arranged, it is possible to obtain information of one or more intermediate depths equally dividing the deepest position and the shallowest position. it can. Note that the distance between the

light sources

22A and 22B and the

light receiving elements

23A and 23B varies depending on the size and thickness of the skull, such as for adults, middle-aged (children to adults), and children.

The light source 22A and the light source 22B use LEDs, and project, for example, near infrared rays having a predetermined wavelength 10 times per second per wavelength with a pulse of 0.2 mSec. The light receiving

elements

23A and 23B use photodiodes, detect oxyhemoglobin, deoxyhemoglobin, and near infrared rays of respective wavelengths corresponding to their cross points, and amplify the signals to calculate measured values. It has become. Therefore, the light source 22A and the light source 22B have wavelength characteristics of near infrared absorption spectrum characteristics, and are set to 805 nm at which the absorbances of oxygen hemoglobin and reduced hemoglobin substantially coincide with each other, 770 nm smaller than that, and 870 nm larger than that.

In addition, as the role of the wavelength, the wavelength 770 nm and the wavelength 870 nm are used as the R / IR ratio in the calculation of the oxygen saturation by the combination thereof. On the other hand, the wavelength of 805 nm is used when measuring changes in the amount and concentration of the entire hemoglobin. That is, the wavelength of 805 nm is the wavelength where the extinction coefficient of human oxyhemoglobin / deoxyhemoglobin is equal and correlates with the total amount or concentration of hemoglobin regardless of the oxygen saturation, so it is used as an index of blood volume as a hemoglobin index To do. As a result, when measuring oxygen saturation, R / R is obtained by using two wavelengths 770 nm and 870 nm that have opposite extinction coefficients across the same extinction coefficient of human oxyhemoglobin and deoxyhemoglobin of wavelength 805 nm. From IR, it is possible to accurately measure oxygen saturation from low oxygen saturation to high oxygen saturation.

When the pad 21 is attached to the surface of the skull, the intensity of light decreases in inverse proportion to the square of the distance as the distance from the light source 22A to the light receiving element 23A and from the light source 22B to the light receiving element 23B increases. In addition, when the intensity of light is weak, the light passes near the scalp and skull near the shallow part of the cranium, and as the intensity increases, the light reaches the cerebral cortex at a deep part of the cranium.

The main unit 3 is connected to the sensor unit 2 in a circuit. The power unit 3A, a power control unit 3B that controls the voltage of the power unit 3A, an amplifier unit 3C that amplifies the measurement data, and a digital signal so that the data can be calculated. A / D conversion unit 3D for converting, arithmetic processing unit 3E for calculating data, screen display unit 3F for displaying data, storage unit 3G for storing data, and LEDs that are

light sources

22A and 22B of sensor unit 2 are driven and controlled. LED drive unit 3H, clock unit 3I for synchronizing pulse signals to LED drive unit 3H, input unit 3J for external operation, output for outputting data to the outside by wire (for example, USB) or wirelessly Part 3K.

When the power source unit 3A is switched, the main body unit 3 instructs the LED driving unit 3H to emit and receive light by the arithmetic processing unit 3E. Then, light of a predetermined wavelength is output from the two

light sources

22A and 22B of the sensor unit 2 while changing the intensity between strong and weak, and the transmitted light of the light is received by the two light receiving

elements

23A and 23B, respectively. To do.

The light reception signals by the

light receiving elements

23A and 23B are amplified by the amplifier unit 3C, and the amplified signal is converted into a digital signal by the A / D conversion unit 3D and input to the arithmetic processing unit 3E. The arithmetic processing unit 3E calculates the oxygen saturation rSO2 and the like in real time according to Bare Lambert's law from these light emission signals and light reception signals, and stores them in the storage unit 3G and displays them on the screen display unit 3F. Specifically, the arithmetic processing unit 3E measures the oxygen saturation rSO2 and hemoglobin index HbI of blood in the brain.

The case where the measuring apparatus having the above configuration is used will be described. First, the two

light sources

22A and 22B and the

light receiving elements

23A and 23B of the sensor unit 2 are mounted in contact with the surface of the skull. Thereafter, a light signal is output to the

light sources

22A and 22B to irradiate the inside of the skull. Then, the light transmitted through the skull is received by the

light receiving elements

23A and 23B, respectively. A light reception signal obtained by scattering and reflecting the blood mainly by hemoglobin is required with high accuracy. Thereafter, arithmetic processing is performed in the arithmetic processing unit.

The measuring apparatus 1 irradiates the skull with near-infrared light, and the amount of absorbed light is proportional to the concentration of incident light and solute. According to the Lambert-Beer law, the oxygen saturation level of hemoglobin in the brain region And measure changes in concentration. Using the difference in light absorption spectrum between oxyhemoglobin and deoxyhemoglobin, the absorbance is obtained from the light detected by the light receiving element through the skull at different wavelengths (770 nm and 870 nm), and the local oxygen saturation (rSO2 ).

Here, the information obtained by the sensor is information on the entire optical path of the paired light source (22A, 22B) and light receiving element (23A, 23B), and if the center is different, it is evaluated as accurate information on the center of the sensor. Cannot be performed or information with low reliability is obtained. In particular, since the arrangement of blood vessels varies depending on the site in a living body, this difference cannot be ignored.

For example, when the separation distance of the sensor A is 40 mm and the separation distance of the sensor B is 20 mm, the sensor A reflects information up to about 32 mm in the skull depth, and the sensor B reflects information up to about 16 mm in the skull height. Can be reflected. Therefore, if the arithmetic processing unit 3E subtracts the information of the sensor B from the information of the sensor A, it is possible to obtain information from about 16 mm shallow to 40 mm deep of the skull.

Here, as shown in FIG. 2A, in the known configuration in which the center (line) is different between one light source and two light receiving elements shown in the prior art, there is only one light source. When the distance to the light receiving element is 40 mm, which is the same as sensor A, and the distance to the other light receiving element close to the light source is 20 mm, the centers p3 and p4 are displaced by 10 mm. It was difficult to say that information with different depths was acquired, and the reliability was low.

Here, the fact that the depth of the part to be measured can be varied is known from experiments in which the separation distance of sensor A and the separation distance of sensor B are different. That is, since the light beam emitted from the light source (22A, 22B) immediately becomes scattered light, the path of light from the light source (22A, 22B) to the light receiving element (23A, 23B) is different (for example, in Monte Carlo simulation) Called Banana Shape). Generally, the deepest part of the light passing through is near the apex of an isosceles triangle. Considering this, the light receiving element of the sensor B is located immediately above the apex of the sensor A (separation distance 40 mm), which is different from the center (line) of the sensor B. In order to accurately obtain information on a shallow portion directly above the deep portion with a sensor when the separation distance is 40 mm, it is necessary to match the center of the sensor when the separation distance is 20 mm with the center of the sensor whose separation distance is 40 mm. In this way, by positioning a plurality of sensors having different separation distances, for example, the sensor B having a separation distance of 20 mm between the sensors A having a separation distance of 40 mm, and matching the centers thereof, it is possible to accurately Information on the shallow portion directly above can also be measured, so that it is possible to obtain more accurate information than information on only the deep portion.

The result obtained by subtracting the sensor B from the sensor A is information only for the deep part of the skull, but it is better if the whole including the shallow part of the skull can be known, so the deep part is targeted as the measurement channel. A separation distance of 40 mm and a separation distance of 20 mm for a shallow part are separately measured. It is preferable that the difference between the information of 40 mm and the information of 20 mm can be separately calculated as information only for a deep part. In the conventional method using one light source and two light receiving elements, only deep part information is used.

Fig. 3 to Fig. 6 show the experimental data for confirming the measurement depth according to the sensor separation distance. Of these experimental examples, FIG. 3 and FIG. 4 are examples in which a deep part of the skull with a separation distance of 40 mm is targeted, and a black rubber sheet and a cuvette containing water (described later) are inserted under the sensor. Experimental data confirming how deep the detection signal can be detected is shown. As a result, when the separation distance between the light source and the light receiving element is 40 mm (FIGS. 3 and 4), the depth of 28 mm to 32 mm can be confirmed as the detection limit. Similarly, it has been found that depths from 70% to a maximum of 80% of the distance between the light source and the light receiving element can be detected at a separation distance of 30 mm (FIG. 5) and 20 mm (FIG. 6).

Therefore, as shown in FIG. 2C, the

light sources

22A and 22B and the

light receiving elements

23A and 23B are configured in a pair, and the separation distance between the sensor A (the light source 22A and the light receiving element 23A) is 40 mm, and the sensor B ( The distance between the light source 22B and the light receiving element 23B) is set to 20 mm, and the respective irradiation and light reception are operated alternately so that the sensor A can acquire information up to the deep part of the skull and the sensor B can acquire information about the shallow part of the skull. did. Since the two centers (center line P) of these sensors A and B are the same, information having different depths can be independently acquired at the same measurement site. Here, if information on the shallow part is subtracted from information on the deep part, information on only the deep part can be obtained. The same measurement site is not the same measurement site in a strict sense because the depth is different, but here the center (center line P) of the sensor A and the sensor B provided on the pad 21 is the same. For this reason, the measurement site is substantially the same in the sense of measurement in the vicinity of the center.

Therefore, when the centers p3 and p4 are shifted as shown in FIG. 2A or when the centers p5 and p6 are shifted as shown in FIG. It is not the same measurement site. In each of the configurations shown in FIGS. 2 (A) to 2 (C), the information obtained by the light when the cranium is the target is the solvent in the portion where the light projected from the light source to the light receiving element has passed through the cranium. The information of the part that has not passed through the skull is not reflected.

Since the light path from the light source to the light receiving element is considered to have a shape called a banana shape by Monte Carlo simulation, the farthest part is the apex of an equilateral triangle connecting the light source, the light receiving element, and the inside of the skull And coincides with the center (center line P) of the separation distance between the light source and the light receiving element.

Here, the configuration of the pad 21 will be described. When the pad 21 is intended for the cranium, the pasting portion is basically a curved surface. Therefore, as shown in FIG. 7A, a printed circuit board 4 is employed for mass production, and a chip-like light source 22 and a light receiving element 23 are placed on the surface of the substrate 4 and soldered. Furthermore, since the surfaces of the light source 22 and the light receiving element 23 are separated from the printed board 4 by the thickness of each element, the surface of the element is finished to be entirely flush with the foamed rubber 5. At this time, it is an essential condition that the element is in close contact with the living body H. That is, the light cannot be detected unless the light emitting surface and the light receiving surface of each element are directed on the printed circuit board 4, and the living body H is a curved surface. Therefore, the element is difficult to be in close contact with the curved surface of the living body H. It will cause an error.

Therefore, as shown in FIG. 7B, when mounting the light source 22 and the light receiving element 23, a hole having the same size as the light source 22 and the light receiving element 23 is made in the printed circuit board 4. Are made flush with the base surface (copper foil surface) of the printed circuit board 4 and the foamed rubber 5 is provided on the back surface side of the printed circuit board 4 to ensure followability (adhesion) to the curved surface of the living body H. And stable measurement results can be obtained.

Next, with reference to FIG. 8, a measurement example in which information in the skull is measured independently from a deep place to a shallow place, at a shallow place and a deep place will be described.

Sensor unit 2 can measure the amount of hemoglobin and oxygen saturation in blood inside living body H using near infrared rays. From the above experimental results, the sensor has a depth that can be monitored from 70% to 80% of the separation distance. On the other hand, as shown in FIG. 8, it is said that the thickness of the skull in the case of an adult is about 8 mm to 10 mm, and the thickness from the epidermis to the skull is about 5 mm to 8 mm.

Here, in order to measure only the information outside the skull, it is only necessary to measure information from a depth of 13 mm to 18 mm, so if 70% to 80% is within the monitorable range, the sensor separation distance is 18.5 mm. 25.7 mm, or 16.2 mm to 22.5 mm. In addition, when the thickness of the skull (8 to 10 mm) is taken into consideration, it is considered that information in the skull is not included if the distance of light transmission and reception is 20 mm.

Therefore, as shown in FIG. 8, information obtained by a sensor having a separation distance of 40 mm includes information on the inside and outside of the cranium. Therefore, information on the light transmission / reception 20 mm outside the skull is obtained from the information obtained when the separation distance is 40 mm. If deducted, it is considered that the information is only in the cranium.

From the experimental results, when elements having the same characteristics are used, the signal of the light receiving element (23A) of the sensor having a separation distance of 40 mm is more affected by absorption and scattering than the signal of the light receiving element (23B) of the 20 mm sensor. It is necessary to increase the amplification factor by about 40 times. From this, when calculating the amount of absorption by hemoglobin, the separation distance of 40 mm has a larger absorption amount, so if the R / IR ratio is calculated after subtracting the absorption amount of the separation distance of 20 mm from the absorption amount of the separation distance of 40 mm, Only the deep oxygen saturation can be calculated.

If you want to evaluate the blood flow only in the muscle by deleting the information of the shallow part to the subepidermal fat layer other than the intracranial information, the distance in the depth direction to the muscle is 12-20 mm, the epidermis and the fat layer When the thickness up to 6 mm is considered, a combination of a separation distance of 10 mm and a separation distance of 30 mm is optimal for optimal muscle blood flow measurement.

Specifically, since the amount of light absorption Kλ is determined by Log 10 (1000 / measurement voltage), the measurement voltage with a separation distance of 40 mm is used as it is, and the measurement voltage with a separation distance of 20 mm is multiplied by an amplification factor of 40 times to obtain the difference. Is the deep part of the skull. Log 10 (1000 / measurement voltage) in the above equation is equivalent to 1000 times when the voltage of the light source (22A, 22B) is calculated back from the voltage measured by the light receiving element (23A, 23B) using a logarithmic graph from the experimental result. Therefore, it was adopted in the calculation formula. The light absorption in the deep part is
KD = log 10 (1000/40 mm) −log 10 (1000 / (20 mm × 40))
Ask for.

The oxygen saturation can be obtained from the R / IR ratio according to the theory described above from the light absorption obtained in this manner. The hemoglobin index is a value in which the amount of absorption is directly correlated with HbI as a relative value. In this way, by aligning the center position and independently obtaining the upper part in the depth direction, blood flow information of a target region can be selectively obtained by applying these ideas to other than the skull. .

Next, a method for obtaining a calibration curve will be described. When accurately assessing the non-invasive blood oxygen saturation level or the standard for measuring changes in blood volume, measure the oxygen saturation level of the blood accurately and measure with the CO oximeter. It is preferable to measure blood and accurately evaluate the consistency of any device value with the CO oximeter value.

At this time, when adjusting the blood to an arbitrary oxygen saturation, for example, when raising the oxygen saturation of the blood, the blood is exposed to air, and when reducing the oxygen saturation of the blood, dithionite as a reducing agent. Reduction with sodium (Na ₂ S ₂ O ₄ ). In addition, since hemoglobin is concentrated in the whole blood state, light is absorbed, so blood (whole blood) is diluted 3 times with physiological saline and used (the maximum density of blood vessels in vivo is Cerebrovascular, calculated to be about 30%). The blood of the brain exists in capillaries and the like, and the concentration seen from the whole tissue is about 54 ml / min with respect to 100 g brain tissue, and the hemoglobin concentration seen from the brain tissue is about 5 g / dl. Therefore, in the above measurement, blood was diluted to about 1/3 with heparin physiological saline.

If, when measuring oxygen saturation, tonated blood with known oxygen saturation can be created, a calibration curve for sensor calibration can be created using that blood. Using the same element as the actual sensor, the tonated blood was filled in a cuvette with a thickness of about 1 mm, the voltage of the received light signal was measured at two different wavelengths, and the absorbance from the measured voltage was Bear Lambert. Calculate from the law. If the ratio (R / IR) of each light absorption amount is known for each oxygen saturation of tonated blood, the calibration curve for the relationship between oxygen saturation and R / IR can be obtained by connecting R / IR points.

The R / IR absorption ratio is measured by filling the tonated blood (measurement and confirmation of oxygen saturation and hemoglobin concentration using a CO oximeter) in a cuvette 6 as shown in FIG. In a dark state where no external light enters, the sensor having the light source 22 and the light receiving element 23 of the same wavelength to be used can measure the light absorption characteristics for each wavelength of each light.

As shown in FIG. 9 (B), the cuvette 6 was positioned directly below the

sensors

22 and 23, and the cuvette 6 was sandwiched between hams 7 or the like simulating a living body. The tonated blood was finely made from 0% to 100%, and a calibration curve was created from the measurement result of each. Thus, in order to measure the oxygen saturation, the measured value is not a theoretical value but a more practical reproducible value.

(Other conditions)
The blood uses a cuvette 6 with a thickness of around 1 mm for standard oxygen saturation measurements. The blood inside the cuvette 6 is checked for oxygen saturation with a CO oximeter before and after the measurement. Oxygen saturation is made every 5% from 0% to 100% and measured 10 times or more each time. From these measurement results, the R / IR ratio is calculated by wavelength, and a curve of oxygen saturation and correlation of the CO oximeter is created. The sensor element to be used satisfies the same specification as that actually used as a product, or a device to be evaluated is used. As described above, the wavelengths used are 770 nm, 805 nm, and 870 nm.

Next, a configuration example of a phantom for determining the reference value will be described. The reference value at this time is a non-invasive reference value for the oxygen saturation and the amount of hemoglobin in the living body, and needs to be a reference value that can accurately evaluate the blood information in the living body. .

In general, it is known that a living body is a strongly scattering substance for light. Although the scattering coefficient and the diffusion coefficient can be measured, the living body constantly changes, so it is difficult to always maintain a constant state. On the other hand, some resins have the same scattering, diffusion, and absorption coefficient as living organisms, so select those with the same optical characteristics as living organisms and overlay them in multiple layers like living organisms. Made up a phantom.

(Configuration of phantom (calibrator))
The phantom has optical characteristics similar to those of, for example, the forehead of the adult, the skull, and the cortex, by alternately combining resin plates having the same scattering and absorption characteristics as the living body. The actual structure is as follows:
-One surface of absorbing plate 0.5t-5 scattering plates 2t below it-1 sheet of absorbing plate 0.5t below it-6 sheets of scattering plate 2t below it-1 sheet of polished aluminum plate 1t below- Under this, one foamed rubber plate 5t was stored in a light-shielded black metal case.

Also, the scattering plate to be used is a well-known light fixture cover, and a point light source with strong light diffusivity was selected. Since a living body is known as a strong scatterer and light cannot travel straight, it is desirable to select a material that can obtain the same effect. The absorption plate is positioned between the surface and the surface of a substance that absorbs light, such as melanin. The scattering plate and the light absorption plate are combined as described above, and placed in a light-shielding box to avoid external light.

The measurement principle of oxygen saturation utilizes the fact that two different types of light are absorbed and attenuated by hemoglobin in the living body. According to Bear Lambert's law, the degree of attenuation is proportional to the amount of hemoglobin contained in the optical path. If the amount of oxygenated hemoglobin is HbO ₂ and the amount of deoxygenated hemoglobin is HbR, the oxygen saturation can be expressed as (HbO ₂ / (HbO ₂ + HbR)) × 100%. When the oxygen saturation is 50%, HbO ₂ and HbR are equal. From the absorbance curves for HbO ₂ and HbR, the two hemoglobins show the same extinction coefficient at a wavelength of 805 nm. If the wavelength that shows the same extinction coefficient is selected across the 805 nm wavelength, the R / IR ratio on the phantom (if the degree of absorption of the two infrared rays is the same according to Bare-Lambert's law, the amount of each hemoglobin is The oxygen saturation is 50% at 1.0. Even when the absorption coefficient of the wavelength to be used is different, correction is possible by multiplying the ratio of the absorption coefficient by the R / IR ratio.

(Proof that phantom calibration is possible)
The oxygen saturation is 50% when the ratio of oxy and deoxyhemoglobin is 1.0. Since the oxygen saturation is calibrated to 50% when R / IR is 1.0 on the phantom, the extinction coefficient of the near-infrared wavelength is as follows.
HbO2: 770 = 0.150 805 = 0.196 870 = 0.248
Hb: 770 = 0.350 805 = 0.196 870 = 0.168
Absorption coefficient ε = 0.434K K: Absorbance Absorbance at each wavelength is as follows.
HbO2: 770 = 0.346 805 = 0.369 870 = 0.571
Hb: 770 = 0.806 805 = 0.369 870 = 0.387
In Bear Lambert's law, K = εcd where c: concentration of solvent d: optical path length Absorbance at a certain wavelength is as follows.
Kλ = (rSO2 × KHbO2 + (1-rSO2) × KHb) cd
When calculating the absorbance of each wavelength used,
R = K770 = (rSO2 × 0.346 + (1-rSO2) × 0.806) cd
IR = K870 = (rSO2 × 0.571 + (1-rSO2) × 0.387) cd
R / IR = (0.806-0.46rSO2) / (0.387 + 0.194rSO2)
Here, if R / IR = A, A (0.387 + 0.194rSO2) = (0.806-0.46rSO2)
When rSO2 is obtained, rSO2 = (0.806-0.387A) / (0.46 + 0.194A)
It becomes. The theoretical value of A = R / IR when rSO2 changes from 0% to 100% is as follows.
rSO2 = 0% 0 = 0.806-0.387A A = 2.083
rSO2 = 100% 0.46 + 0.194A = 0.806-0.387A
A = 0.346 / 0.581 = 0.596
When rSO2 = 50%, the absorbance is calculated with rSO2 = 0.5 at each wavelength.
Since Kλ = (rSO2 × KHbO2 + (1-rSO2) × KHb) cd, K770 = (0.5 × 0.346 + 0.5 × 0.806) cd = 0.576cd
K870 = (0.5 × 0.571 + 0.5 × 0.387) cd = 0.479 cd
from now on,
R / IR = A = 1.2025
It becomes.

Theoretically, the absorbance at each wavelength when rSO2 = 50% is as described above. The absorbance of R = K770 is 0.576 cd, the absorbance of IR = K870 is 0.479 cd, and the absorbance of R increases.

Therefore, the measurement voltage having a wavelength of 770 nm is corrected by multiplying the absorbance ratio = 1.2525. As a result, the absorbance becomes 0.479 cd for K770 and 0.479 cd for K870,
R / IR = 1: 1 and can be corrected to 50%.

By correcting in this way, the measured value in the actual machine becomes rSO2 = 50% when R / IR = 1, which matches the theoretical value. If this correction is performed even at 0% and 100%, the respective light absorption ratios A = R / IR are as follows. The calculation formula (theoretical value) of rSO2 is as described above.
rSO2 = (0.806-0.387A) / (0.46 + 0.194A)
So, if A for correction is multiplied by 1.2525 in this equation, when rSO2 is 0% and 100%,
At 0%, (0.806-0.387 × 1.2025A) = 0
A = 1.732
At 100%, (0.46 + 0.194 × 1.2025A) = (0.806−0.387 × 1.2025A)
A = 0.495
It becomes. The equation of the calibration curve based on the theoretical value corrected in this way is as follows.
A <1 rSO2 = 100 × (1.495-A) /0.99 100-50%
A> 1 rSO2 = 100 × (1.732-A) /1.464 50-0%

When different wavelengths are used, the extinction coefficient ε for oxy and deoxyhemoglobin at each wavelength is known, so that the numerical value is applied to the following equation and recalculated.
Absorption coefficient ε = 0.434K K: Absorbance

By the way, such an oxygen saturation measuring device 1 and an oxygen saturation measuring sensor 2 can be applied to all cases that require numerical values related to oxygen saturation and hemoglobin amount based on hemoglobin change information by near infrared light. it can.

(Brain protection during surgery)
For example, when there is a state where blood does not go to the brain temporarily due to circulatory arrest in cardiac surgery or carotid artery blockage in brain surgery, the oxygen saturation measurement sensor 2 is attached to the forehead part to Information on blood oxygen saturation and blood volume can be acquired, and it is possible to easily grasp whether or not it is in a dangerous state, which can be useful for brain protection and prevention of brain damage.

(Cardiopulmonary arrest <resuscitation by AED>)
When cardiopulmonary arrest occurs at room temperature, the oxygen saturation of the blood in the brain rapidly decreases, causing loss of consciousness. In this case, of course, since there is no pulsation, the pulse oximeter cannot be used. The oxygen saturation measurement sensor 2 using the near infrared can measure the oxygen saturation and HbI without any problem if blood is present.

Therefore, for example, if cardiopulmonary resuscitation is attempted by so-called chest compression for heart massage and heartbeat is resumed using AED, the oxygen saturation rises from 40% to 60%. Knowing the oxygen saturation at the time of contact with the injured person also makes it possible to know the possibility of rehabilitation.

(Brain hemorrhage)
In the above-described blood oxygen saturation measurement of only deep brain tissue, information on intracranial hemorrhage is subtracted and cannot be obtained as information. In contrast, the oxygen saturation measurement sensor 2 described above can reflect information on all hemoglobins in the optical path through which the near infrared light has passed. Normally, blood exists only in blood vessels, but for example, in the case of subarachnoid hemorrhage or intracranial hemorrhage, hemoglobin overflows outside the blood vessel, so the amount of hemoglobin in the measurement optical path is extraordinarily large in the blood vessel. From the phantom reference HbI value, it can be easily determined whether or not there is bleeding.

As described above, the oxygen saturation measurement sensor according to the present invention has an effect of improving the reliability of information on parts having different depths, and is non-invasive using near infrared rays. It is useful for oxygen saturation measuring sensors and oxygen saturation measuring devices in general for measuring oxygen saturation in blood.

2 Sensor unit (oxygen saturation measurement sensor)
21 Pad 22 Light source (22A, 22B)
23 Light receiving element (23A, 23B)
24 ROM
3 Main unit 3E Arithmetic processing unit

Claims

A pad that can be attached to the human body,
A plurality of light sources arranged adjacent to the pad in a separated state and irradiating near infrared rays;
Arranged so as to have a one-to-one correspondence with the plurality of light sources on the basis of a center that is adjacent to the pad in a separated state and common to the innermost of the plurality of light sources, and transmits from the corresponding plurality of light sources A plurality of light receiving elements for receiving light; and
ROM section for measuring the transmitted light by the phantom in advance and storing it as a reference value;
An oxygen saturation measurement sensor comprising:
The plurality of light sources and the plurality of light receiving elements are:
The plurality of light sources are arranged equidistantly on one side of the center,
The plurality of light receiving elements are spaced apart by an equal distance on the other side of the center,
2. The oxygen saturation measuring sensor according to claim 1, wherein:
It consists of a sensor part and a body part.
The sensor unit is
A pad that can be attached to the human body,
A plurality of light sources arranged adjacent to the pad in a separated state and irradiating near infrared rays;
Arranged so as to have a one-to-one correspondence with the plurality of light sources on the basis of a center that is adjacent to the pad in a separated state and common to the innermost of the plurality of light sources, and transmits from the corresponding plurality of light sources A plurality of light receiving elements for receiving light; and
ROM section for measuring the transmitted light by the phantom in advance and storing it as a reference value;
With
The body part is
An arithmetic processing unit that calculates the actual absorbance based on the received light value and the reference value related to the received light amount stored in the ROM, and calculates the oxygen state of the living body in accordance with the Bare-Lambert law in comparison with the reference value An oxygen saturation measuring device comprising: