JPH04332536A - Instrument for measuring oxygen in blood - Google Patents

Abstract

PURPOSE:To exactly measure the absolute oxygen quantity in blood. CONSTITUTION:Light emitting means 11 to 13 which emit light having a suitable wavelength respectively toward sections to be measured, a light receiving means 16 which receives the light transmitted through the section to be measured and converts this light to signals, signal forming means 28, 30, 40 which form the signals corresponding to the transmitted quantities of the respective light rays in accordance with the output signals of this light receiving means, and an arithmetic means 42 which calculates the concn. of the oxygen in the blood in accordance with the respective signals formed at the 1st time and the 2nd time in these signal forming means are provided.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring the amount of oxygen in blood.

0002

[Prior Art] Conventionally, in order to monitor the excess or deficiency of oxygen in the blood during or after surgery, the oxygen saturation level in the arterial blood is measured by shining light onto the subject's finger or the like from the outside. A device called a pulse oximeter has come to be provided. For example, in Japanese Patent Publication No. 53-26437, two types of light having different wavelengths are transmitted through pulsating blood, and based on the absorbance, the arterial blood oxygen saturation is determined, that is, the amount of oxyhemoglobin relative to the total amount of hemoglobin in the blood. The figure shows the calculation of the ratio of . According to such an oximeter, the oxygen saturation level in the blood can be easily measured without collecting blood from the subject.

0003

[Problems to be Solved by the Invention] Although the pulse oximeter described above can determine the oxygen saturation level, it cannot determine the absolute amount of hemoglobin or oxygen in the blood. Such absolute oxygen amount is also an important parameter in advancing medical care, and there is a desire to develop an apparatus that can accurately measure it.

[0004] In view of the above circumstances, an object of the present invention is to provide an apparatus that can accurately measure not only the oxygen saturation level in blood but also the absolute oxygen amount.

[0005]

[Means for Solving the Problems] The present invention provides a first light emitting means for emitting a first light having a wavelength that is absorbed by at least deoxyhemoglobin among deoxyhemoglobin and oxidized hemoglobin in blood, toward a measurement site. , a second light emitting means for emitting, toward a measurement site, second light having a wavelength different from the wavelength of the first light and absorbed by at least oxygenated hemoglobin among deoxyhemoglobin and oxyhemoglobin in blood; a third light emitting means for emitting third light having a wavelength that is not absorbed by the reduced hemoglobin and oxyhemoglobin but absorbed only by water, toward the measurement site; a light-receiving means for receiving the transmitted light and converting it into an electrical signal; and based on the output signal of the light-receiving means, signals corresponding to the transmitted amounts of the first light, the second light, and the third light are respectively generated. A blood oxygen amount is calculated based on a signal generating means to generate, each signal generated at a first time in this signal generating means, and each signal generated at a second time different from the first time. (Claim 1).

Here, the setting of the wavelength λi (i=1, 2, 3) of each light from the first light to the third light is, for example, shown in FIG.
This may be done by utilizing the relationship between the light wavelength and the light absorption coefficient of each substance as shown in a) and (b). That is, the wavelength λ1 of the first light is such that the absorption coefficient of at least deoxyhemoglobin is 0 among deoxyhemoglobin and oxyhemoglobin.
For example, about 600 nm or more and 1000 nm
The wavelength λ2 of the second light is set to a region where the absorption coefficient of at least oxyhemoglobin of deoxyhemoglobin and oxyhemoglobin is not 0, for example, a region of about 600 nm or more and 1100 nm or less. 3
The wavelength λ3 of the light may be set to a region where the absorption coefficient of water is not 0, for example, a region around 1200 nm or a region around 1450 nm. Further, it is desirable not to use a wavelength in a special region where the absorption coefficient of bilirubin is not 0, that is, a low wavelength.

Further, the light receiving means may be a single element that receives all of the transmitted light, or may be composed of a plurality of elements provided corresponding to each of the transmitted light. In the former case, the signal generating means may be configured to separate the output signal of the light receiving means into signals corresponding to transmitted light of each wavelength (claim 2).

[0008]

[Operation] According to the above device, the first to third lights are incident on a predetermined measurement site from each light emitting means, the transmitted light is received by the light receiving means, and a signal is generated based on the output signal of the light receiving means. A signal corresponding to the amount of transmission of each light from the first light to the third light is created by the creation means. Then, the blood oxygen amount is calculated based on each signal obtained at the first time and each signal obtained at a second time different from the first time.

[0009] The principle underlying the calculation of the blood oxygen amount described above is as explained below.

[0010] Now, assume that the wavelengths of the first light L1, the second light L2, and the third light L3 are λi (i=1, 2, 3). The transmitted light intensity when these lights L1 to L3 are irradiated onto the measurement site is related to the thickness of the arterial blood at that time, but since the thickness of the arterial blood changes over time in synchronization with the heartbeat, this When d(t) (t is time), the intensity of transmitted light at the first time t1 can be expressed by the following equation (Equation 1) according to Lambert Bear's law.

[0011]

[Math 1]

Similarly, at a second time t1 different from the first time t1,
The transmitted light intensity at time t2 is expressed by the following equation (Math. 2).

[0013]

[Math 2]

[0014] Here, in proceeding with the calculation, a value Pi (i=1, 2, 3) shown by the following equation (Equation 3) is introduced.

[0015]

[Math 3]

Substituting the above two equations (Equation 1) (Equation 2) into this equation and setting d(t2)=d(t1)+Δd, we get
The above value Pi is as shown in the following equation (Equation 4).

[0017]

[Math 4]

Here, the wavelength λ3 of the third light L3 includes deoxyhemoglobin (Hb) and oxidized hemoglobin (HbO2).
Since a wavelength is selected that is not absorbed by both of 2), when i=3 in the above equation (4), the absorption coefficient εi (Hb) of deoxyhemoglobin and the absorption coefficient εi (HbO2) of oxidized hemoglobin are Both become 0. Therefore, by substituting these into the above equation (Equation 4) (see (Equation 1) for Xi) and squaring both sides, the following equation (Equation 5) can be obtained.
can be obtained.

[0019]

[Math 5]

Therefore, (Δd)2 is expressed by the following equation (Equation 6).

[0021]

[Math 6]

On the other hand, the wavelength λ1 of the first light L1
is set to be absorbed by at least deoxyhemoglobin among deoxyhemoglobin and oxidized hemoglobin, so in the above (Equation 4), the absorption coefficient ε1(H
b) is not necessarily 0, and the wavelength λ2 of the second light L2
is set to be absorbed by at least oxygenated hemoglobin out of deoxyhemoglobin and oxidized hemoglobin, so the absorption coefficient ε2(HbO2) is not necessarily zero. In this case, the following equation (Equation 7) is obtained from the above equation (Equation 4).

[0023]

[Math 7]

In this (Equation 7), each absorption coefficient εj(
Hb), εj(HbO2) are known values, each value P12,
P22 is a measured value obtained by the device of the present invention, and since (Δd)2 is expressed by the above equation (Equation 6), this equation (Equation 7) can be expressed as shown in the following equation (Equation 8). Blood concentration of each substance C (Hb), C (HbO2) [g/dl]
It becomes a simultaneous linear equation with unknowns.

[0025]

[Math. 8]

[0026] Therefore, by solving these simultaneous equations, the blood reduced hemoglobin concentration C (Hb) and the blood oxidized hemoglobin concentration C (HbO2) can be calculated. Specifically, both values are as follows.

[0027]

[Math. 9]

On the other hand, the amount of oxygen contained in blood (O2 content) is precisely the sum of O2 bound to hemoglobin in red blood cells and O2 dissolved in plasma. It is known that the O2 content [ml] contained in 100 ml (that is, 1 dl) of blood can be determined by the following equation (Equation 10).

[0029]

[Math. 10]

[0030] Here, PaO2 is the oxygen partial pressure at the arterial value. In addition, the amount of hemoglobin in the same equation (Equation 10) (
Blood total hemoglobin concentration) [g/dl] and oxygen saturation SaO2 [%] are expressed by the following equations (Equation 11) and (Equation 12), respectively.

[0031]

[Formula 11] (Hemoglobin amount [g/dl]) = C (Hb) +
C(HbO2)

[0032]

[Math. 12]

Therefore, these equations (Equation 11) (Equation 12)
By substituting the above equation (Equation 9) into , the above equation (Equation 1
The oxygen saturation and hemoglobin amount at 0) can be determined. Furthermore, the relationship between oxygen saturation SO2 (SaO2 in arterial blood) [%] and oxygen partial pressure PO2 (PaO2 in arterial blood) [Torr] is known as the oxygen dissociation curve as shown in Figure 5. If the saturation degree is known, the oxygen partial pressure PaO in equation (10) can be calculated from the above curve.
It is easy to find 2. Therefore, the O2 content in the blood can finally be determined based on the above equation (Equation 10).

Furthermore, in the case where the light receiving means is constituted by a single light receiving element (claim 2), the output signal thereof is
By separating the signals into signals corresponding to the amount of light transmitted with each wavelength, a signal that is the basis of calculation is created.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a blood oxygen amount measuring device according to an embodiment of the present invention.

This device includes a measurement probe 10 and an arithmetic control system 20. The measurement probe 10 has a shape that is fitted onto the test subject's measurement site (in this case, a finger) so as to cover it from the outside. A first light emitting element 11, a second light emitting element 12, and a third light emitting element 13 are provided at predetermined positions.
are arranged at positions close to each other, and a single light receiving element 16 is arranged at a position corresponding to the light emitting elements 11 to 13 on the other side.

Among the three light emitting elements 11 to 13, the first light emitting element 11 is one that emits light having a wavelength at which at least deoxyhemoglobin of deoxyhemoglobin and oxidized hemoglobin in blood is absorbed, The second light emitting element 12 is one that emits light having a wavelength at which at least oxyhemoglobin among the deoxyhemoglobin and oxyhemoglobin is absorbed. On the other hand, the third light emitting element 13 is one that emits light having a wavelength that is not absorbed by either the deoxyhemoglobin or oxyhemoglobin and is absorbed only by water. Note that when setting each wavelength, it is desirable to exclude from the target a special region (low wavelength region) that is absorbed by bilirubin.

[0038] The light receiving element 16 is connected to the light emitting elements 11 to 16.
It is configured to receive the light emitted from 13 and transmitted through the measurement site, and to convert it into an electrical signal and output it.

The calculation control system 20 includes a power supply section 22, a light emitting element drive section 24, a timing generation section 26, an I/V conversion section 28, a signal separation circuit 30, an A/D conversion section 40, a calculation control section 42, and a display. (output means) 44.

The light emitting element driving section 24 outputs a drive signal to the four light emitting elements 11 to 13 to cause them to emit light. The timing generating section 26 outputs a timing signal to the light emitting element driving section 24 and each sample hold section 31 to 33 described below, and more specifically, it outputs a timing signal to the light emitting element driving section 24 at a predetermined timing. By outputting a signal, each light emitting element 11 to 13 is turned on in a time-division manner, and in synchronization with this, each light emitting element 11 is turned on.
A timing signal is outputted to operate the sample hold units 31 to 33 corresponding to 13.

The lighting cycle of each of the light emitting elements 11 to 13 is set to be sufficiently shorter than a heartbeat, so that lighting is performed many times per heartbeat cycle.

The I/V converter 28 converts the photocurrent output from the light receiving element 16 into an analog voltage. The signal separation circuit 30 separates the output signal of the I/V converter 28 into three signals corresponding to the wavelengths λ1 to λ3 of the transmitted light of the light emitting elements 11 to 13, respectively. Three sample hold sections 31 to 33 and low pass filter sections 35 to 13 respectively corresponding to
It is equipped with 37. Each of the sample and hold sections 31 to 33 samples and holds the output of the I/V conversion section 28 while the corresponding light emitting elements 11 to 13 are turned on, based on the output timing signal of the timing generation section 26, The low-pass filter sections 35 to 37 create photoplethysmogram signals for each wavelength based on the outputs of the corresponding sample and hold sections 31 to 33, respectively.

The A/D converter 40 receives the output control signal from the arithmetic control section 42 and performs analog-to-digital conversion on the outputs of the respective low-pass filter sections 35 to 37. The arithmetic control section 42 includes the timing generation section 26
It outputs a control signal to the A/D converter 40 to control the same, and calculates the amount of oxygen in the blood based on the output signal of the A/D converter 40. More specifically, the A/D converter 40 is controlled to perform analog-to-digital conversion on the outputs of each of the low-pass filter sections 35 to 37 at a first time t1 and a second time t2 different from this, and Based on the converted value, the amount of blood oxygen is calculated based on the calculation formula described in the section of the above-mentioned operation, and the calculation result is displayed on the display section 44.

Note that the first time t1 and the second time t2 are set, for example, when a predetermined time Δt has elapsed from the first time t1 at which the analog-to-digital conversion was first performed. The next analog-to-digital conversion may be performed at the second time t2, or
Alternatively, after the first time t1, the second time t2 is a point in time when the output of one channel of the low-pass filter sections 35 to 37 increases or decreases by more than a predetermined value due to a change in the thickness of arterial blood. You may also do so. Thereby, it is possible to ensure a sufficient output difference between both times t1 and t2.

Next, the operation of this device will be explained.

First, with the measurement probe 10 attached to the test subject's measurement site (in this case, a finger), the timing generator 26 transmits the light emission timing to the light emitting element drive unit 24 as shown in the upper half of FIG. A signal is output, and based on this signal, first light, second light, and third light having different wavelengths are emitted from each light emitting element 11 to 13 intermittently and out of phase with each other toward the measurement site. are respectively incident. The transmitted light is received by the light receiving element 16 all at once, converted into an electrical signal, and then input to the signal separation circuit 30 through the I/V converter 28. The input signal at this time is, for example, as shown in FIG. 3(a).

In this signal separation circuit 30, as shown in FIG.
Since the sample-and-hold timing signal is output to , each sample-and-hold unit 31 to 33 samples and holds only a portion of the input signal that corresponds to the transmitted light emitted by each light emitting element 11 to 13. Therefore, for example, the output signal of the sample hold section 31 becomes as shown in FIG. 3(b). Each output signal is sent to the low-pass filter sections 35 to 37.
As shown in Fig. 3(c), A/
The signal is input to the D converter 40. Therefore, the waveforms of these signals correspond to the wavelengths λ1 to λ3 of each light.

[0048] These signals are A/D converted at a preset first time t1 and a second time t2, and are taken into the arithmetic control section 42. Based on these signals, the arithmetic control unit 42 calculates the above-mentioned equations (Equation 9), (Equation 10), and (Equation 10).
Calculate the amount of hemoglobin, oxygen saturation, and even the absolute amount of oxygen in the blood (O2 content) using Equation 11) and (Equation 12),
These values are displayed on the display section 44.

[0049] According to such a device, it is possible not only to measure oxygen saturation as in the conventional method, but also to accurately measure the absolute amount of oxygen in the blood, thereby providing more valuable data. be able to.

In this embodiment, all the transmitted light from the first light to the third light is received by a single light receiving element 16, but a plurality of light receiving elements each receiving each light individually are used. It is also possible to include a light receiving element and calculate the blood oxygen amount based on the output signal of each light receiving element. In this case,
There is no need for means for separating signals as in the above embodiments. However, if all the light is received by a single light receiving element 16 as in the above embodiment, the structure can be simplified and costs can be reduced.

[0051]

As described above, the present invention emits light having appropriate wavelengths toward the measurement site, receives the transmitted light, and creates a signal corresponding to the amount of transmitted light for each wavelength. Since the amount of blood oxygen is calculated based on each signal obtained at the first time and the second time, it is not only possible to measure the blood oxygen saturation level as in the conventional method, but also to measure the absolute amount of oxygen. It has the effect of being able to measure accurately and provide more valuable data.

Furthermore, according to the device according to claim 2, the light receiving means is constituted by a single light receiving element, which receives all the transmitted light, so that the structure of the device can be simplified and the cost can be reduced. This has the effect of reducing costs.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of a blood oxygen amount measuring device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing a light emission timing signal and a sample hold timing signal output from a timing generation section in the above device.

FIG. 3 (a) is a waveform diagram showing the output signal of the I/V conversion section in the above device, (b) is a waveform diagram showing the output signal of the sample hold section corresponding to the first light emitting element in the same device; c) is a waveform diagram showing an output signal of the low-pass filter section corresponding to the first light emitting element.

[Figure 4] (a) is a graph showing the relationship between light wavelength and the light absorption coefficient of each substance in the short wavelength region, and (b) is a graph showing the relationship between light wavelength and the light absorption coefficient of each substance in the long wavelength region. This is a graph showing.

FIG. 5 is a graph showing an oxygen dissociation curve showing the relationship between oxygen saturation and oxygen partial pressure in blood.

[Explanation of symbols]

10 Measurement probe 11 First light emitting element (first light emitting means) 12 Second light emitting element (second light emitting means) 13 Third light emitting element (third light emitting means) 16 Light receiving element (light receiving means) 20 Arithmetic control system 24 Light emitting element Drive section (light emitting means) 26 Timing generation section 28 I/V conversion section (signal creation means) 30 Signal separation circuit (signal creation means) 40 A/D converter (signal creation means) 42 Arithmetic control section (calculation means)

Claims (2)

[Claims] Claim 1: A first light source that emits a first light having a wavelength that is absorbed by at least deoxyhemoglobin among deoxyhemoglobin and oxyhemoglobin in blood toward a measurement site.
and a second light emitting means that emits, toward a measurement site, a second light having a wavelength different from the wavelength of the first light and absorbed by at least oxygenated hemoglobin among deoxyhemoglobin and oxyhemoglobin in blood. and third light emitting means for emitting third light having a wavelength that is not absorbed by deoxyhemoglobin and oxyhemoglobin in blood but is absorbed only by water, towards the measurement site, and a third light emitting means emitted from these light emitting means. , a light receiving means that receives the light transmitted through the measurement site and converts it into an electrical signal, and based on the output signal of this light receiving means, corresponds to the transmitted amount of the first light, the second light, and the third light, respectively. a signal generating means for generating a signal, each signal generated at a first time in the signal generating means and the first signal;
1. A blood oxygen amount measuring device comprising: calculation means for calculating a blood oxygen amount based on each signal created at a second time different from the time of the first step. 2. The blood oxygen amount measuring device according to claim 1, wherein the light receiving means is constituted by a single light receiving element that receives all of the transmitted light, and the output signal of the light receiving means is transmitted to the first light receiving element. A blood oxygen amount measuring device characterized in that the signal generating means is configured to separate the signals into signals corresponding to the transmitted amounts of the light, the second light, and the third light, respectively.