JP3422149B2 - Biological tissue oxygen monitor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention non-invasively measures changes in the oxidation / reduction state of hemoglobin and changes in blood volume in living tissue using near-infrared two-wavelength light. The present invention relates to a biological tissue oxygen monitor. 2. Description of the Related Art A living tissue is irradiated with a laser beam, reflected light from the living tissue is received, a change in oxygen or a change in blood volume is obtained based on the amount of the received light, and a guide for exercise is given to a user. There are devices such as an exercise monitor for giving and controlling an exercise load according to a user. In this type of apparatus, exercise intensity and exercise effect are determined based on changes in the oxidation / reduction state of hemoglobin that transports oxygen in living tissue, changes in blood volume, and the like. [0003] The hemoglobin and oxidized hemoglobin combined with oxygen (HbO _2), there are two states of reduced hemoglobin oxygen is not bound (Hb), the conventional apparatus, the HbO ₂ and Hb, and BV (blood volume)
Is calculated, that is, to obtain three parameters, laser light of three wavelengths is used as a light source. On the other hand, there is a device that uses a light emitting diode of near-infrared two wavelengths as a light source and measures and displays two parameters, Hb and BV, based on the amount of light received from a living tissue. [0004] However, an apparatus using three-wavelength laser light is a large stationary type light source using a laser light source. A compact, lightweight, battery-powered, portable device is desired. In an apparatus using a light emitting diode having two near-infrared wavelengths, the parameters of HbO ₂ are not measured and displayed, and the coefficients included in the arithmetic expressions of the parameters of Hb and BV are not specified. For this reason, there is a problem in the reliability of the parameters in order to more accurately determine the exercise intensity, the exercise effect, and the like. Accordingly, the present invention has been made in view of such a conventional problem, and has as its object to provide a portable and highly reliable biological tissue oxygen monitor. [0006] [Means for Solving the Problems] To achieve the above object, the biological tissue oxygen monitor of the present invention, the light emitting wave to the living tissue
Three light emitting diodes irradiating light of 760 nm long and living body
Light-emitting diode for irradiating tissue with light of emission wavelength 840 nm
A light-emitting element in which one of them is arranged in close proximity, a light-receiving element for receiving light reflected from the living tissue, and oxyhemoglobin (HbO ₂ ) in the living tissue based on the amount of light received by the light-receiving element. Calculating means for calculating a change in the state of reduced hemoglobin (Hb) and a change in blood volume (BV) by a linear function of the near-infrared two-wavelength absorbance change amount; Display means for displaying a change. [0007] The calculating means of the monitor uses the oxyhemoglobin (HbO) in the living tissue based on the amount of light received by the light receiving element.
Change and blood volume status ₂₎ and reduced hemoglobin (Hb) the change in the (BV), so calculated by a linear function of the near-infrared two-wavelength absorbance change, the light source is near-infrared two-wavelength light-emitting diode (light-emitting Three light emitting diodes with a wavelength of 760 nm
And one light emitting diode having an emission wavelength of 840 nm) , three parameters of HbO ₂ , Hb and BV can be calculated. Therefore, small, lightweight,
It is possible to provide a battery-powered portable monitor, improve the reliability of parameters, and perform more accurate motion determination and pointers. [0008] The present invention will be described below based on an embodiment. FIG. 1 shows a configuration block diagram of a biological tissue oxygen monitor according to the embodiment. This monitor includes a light-emitting element (light-emitting diodes LED ₁ and LED _{2 having} two near-infrared wavelengths) 1 for irradiating light to an arbitrary measurement site (tissue) of a living body,
A light receiving element (such as a photodiode) 2 for receiving light reflected from the measurement site, a light amount control circuit (LED drive circuit) 3 for controlling the amount of light emitted from the light emitting element 1, and a gain control for amplifying a signal from the light receiving element 2 A possible amplifier 4, an A / D conversion circuit 5 for converting the output of the amplifier 4 into a numerical value, and a memory used for storing data for controlling various parts, parameters of HbO ₂ , Hb, BV, etc., and arithmetic processing, etc. 6 and a CPU (arithmetic means) for controlling various parts, calculating parameters, and the like.
7, a display circuit (display means) 8 for displaying parameters, displaying various instructions, and the like, and a switch 9 for transmitting ON / OFF of a power supply, a measurement start instruction, and other instructions to a monitor. The light emitting element 1 and the light receiving element 2 are integrally formed as an optical sensor section 10, as shown in FIG. Here, the optical sensor unit 10 includes a flexible belt 11 which can be attached for example to the body part, LED ₁ and L as a light emitting element 1 to the flexible belt 11
The ED ₂ and the light receiving element 2 are provided. LED
Each of the LED ₁ and the LED ₂ has a structure as shown in FIG. 3 (an enlarged plan view of a main part). That is, LED ₁ and LE
D ₂ has near-infrared emission wavelengths of 760 nm and 8 nm, respectively.
A total of four near-infrared LED chips of 40 nm (three of 760 nm and one of 840 nm) can measure the amount of received light in a well-balanced manner in consideration of the wavelength-dependent attenuation in living tissue. It is arranged as close as possible. In FIG. 3, reference numeral 12 denotes a glass epoxy substrate, and reference numeral 13 denotes a wire pattern. This L
ED ₁ and LED ₂ are both connected to the light amount control circuit 3. The light receiving element 2 receives the reflected light from the living tissue 20, and the received light signal is amplified by the amplifier 4. Next, the operation of the monitor configured as described above will be described with reference to the flow charts of FIGS. 4 and 5.
The feature of the monitor of the present invention is that three types of parameters of HbO ₂ , Hb and BV are calculated, and the other components are the same as those of the conventional device. Therefore, the description will be focused on the calculation of the parameters. First, automatic gain adjustment is performed in step (hereinafter abbreviated as ST) 1, and a measurement start instruction is input in ST 2. Next, measurement of the initial light receiving amounts I _{0 (760)} and I _{0 (840)} of the light receiving element for each of the near-infrared two-wavelength light (760 nm and 840 nm) by the light emitting diode, measurement of the dark value (dark), Calculation of the reference level and recording of the data are performed (ST3). Thereafter, measurement of the actual amount of received light, measurement of the dark value, and recording of the data are performed (ST4). Here, dark value (dark) are LED _1, L
This is the background light amount when all the EDs _{2 and the} like are turned off. In ST5, the absorbance (OD) is calculated. The absorbances at the emission wavelengths of 760 nm and 840 nm are obtained by the equations as described in ST5, respectively. After calculating the absorbance, in ST6, HbO ₂ , Hb, BV
Is calculated. Each parameter, Δ [HbO _2]: concentration change of oxygenated hemoglobin delta [Hb]: the concentration variation ΔBV deoxyhemoglobin: blood volume change Derutao.D. _840: amount of change in absorbance wavelength 840nm ΔO.D. ₇₆₀ : Assuming that the amount of change in absorbance at a wavelength of 760 nm is given by the following equation: Δ [HbO ₂ ] = ΔO.D. ₈₄₀ −0.66 ΔO.D. ₇₆₀ (1) Δ [Hb] = 0.58 (1.37ΔO.D. ₇₆₀ − ΔO.D. ₈₄₀ )... (2) ΔBV = 0.42 ΔO.D. ₈₄₀ +0.13 ΔO.D. ₇₆₀ ) (3) In the calculation of this parameter, Δ [HbO ₂ ] has been used as a parameter so far. The coefficients of 0.58, 1.37, 0.42, and 0.13 have been expressed as A and B, for example, in the arithmetic expressions of the parameters Δ [Hb] and ΔBV. But Δ [H
bO ₂ ], including all the coefficients of the arithmetic expressions (1) to (3), including the coefficients of the arithmetic expressions,
This is a major feature of the present invention. After calculating the three parameters in ST6,
Changes in these parameters, that is, changes in HbO ₂ , Hb, and BV are displayed (ST7). Thereafter, it is asked whether to end the calculation processing of these parameters (ST8). If YES, for example, an appropriate switch is operated. Finish the process,
When the process is continued, the switch is operated, and ST4 is performed.
And the same processing is repeated to calculate and display three types of parameters. By the way, as described above, the present invention
The feature is to calculate and display three kinds of parameters of O ₂ , Hb, and BV. The process of obtaining the above-mentioned arithmetic expressions (1) to (3) for giving these parameters will be described below. There are devices that calculate and output two parameters of Hb and BV using near-infrared two-wavelength light, but theoretically calculate three kinds of parameters of HbO ₂ , Hb, and BV using near-infrared two-wavelength light. That is, the specific arithmetic expression is obtained by experiments based on a known theory. First, wavelength λ ₁ = 7 as near-infrared two-wavelength light
The light intensity with respect to the wavelength of the LED of 60 nm and the LED of wavelength λ ₂ = 840 nm is as shown in FIG. FIG. 7 shows a result obtained by measuring the linearity of the amount of light when the LEDs having the wavelengths λ ₁ and λ ₂ are used as the light source by transmission measurement using ink as an absorber having a known absorption coefficient. FIG. 7 shows the change in absorbance at wavelengths of 760 nm and 840 nm with respect to the ink concentration. It can be seen that good linearity was obtained in each case. In addition, the measurement stability during the operation of the battery was examined. The change in absorbance after 6 hours of measurement was ± 0.22% at a wavelength of 760 nm and ± 0.2% at a wavelength of 840 nm.
It is 74%, the measurement is stable after 6 hours, and there is no problem in the measurement. Since BV can be obtained from the sum of HbO ₂ and Hb, the unknown to be obtained is H
bO ₂ and Hb. If two wavelengths are applied to this, the equation can be solved. That is, the equation is as follows. _{ΔO.D. 840 = k 1 Δ [HbO} 2] + k 1 'Δ [Hb] ΔO.D. 760 = k 2 Δ [HbO 2] + k 2' Δ [Hb] ΔBV = Δ [HbO 2] + Δ [Hb From these equations, the following equations are derived. Δ [HbO ₂ ] = k ｛ΔO.D. ₈₄₀ − (k ₁ ′ / k ₂ ′) ΔO.D. ₇₆₀ ｝ (4) Δ [Hb] = k (k ₂ / k ₂ ′) ｛ (K ₁ / k ₂ ) ΔO.D. ₇₆₀ −ΔO.D. ₈₄₀ ｝ (5) k = k ₂ ′ / (k ₁ k ₂ ′ −k ₁ ′ k ₂ ) ≡1 where unknown Are k ₁ ′ / k ₂ ′, k ₁ / k ₂ , k ₂ /
k ₂ ′, and these coefficients become meaningful values having no dimensions because the absorption coefficient and the optical path length are canceled in calculation. However, since the coefficient k is affected by the optical path length, a meaningful value cannot be given, and is set to 1 for convenience. An experimental apparatus as shown in FIG. 8 was used to experimentally determine these unknown coefficients. In this apparatus, a polyethylene container 40 having a diameter of 9 cm having a stirrer / heater 41 was charged with 800 ml of a solution containing yeast under the conditions shown in FIG. Further, oxygen O ₂ having a concentration of 100% was introduced into the container 40 by an oxygen cylinder 42 via a valve 43, for example. The probe 31 of the monitor 30 of the present invention was attached to the side of the container 40, and the monitor 30 was connected to the personal computer 44. However, the probe 31 is configured such that the optical sensor unit 10 including the LED ₁ , the LED ₂ having the wavelength of 760 nm and the wavelength 840 nm, and the light receiving element 2 is a probe. This experiment was performed with two types of scattering intensity. The scattering intensity was measured by measuring the optical path length based on the Lambert-Beer rule using ink as an absorber having a known absorption coefficient.
It was set by determining the concentration of intralipid (milk) so that DPF (Differential Pathlength Factor) was 3 and 6. This substantially covers the range of scattering intensity in living tissue. The amount of blood was changed with these two scatterer concentrations, and the diffuse reflection light amount was measured by the monitor of the present invention. However, from the viewpoint of examining a case where the change in blood volume is large, such as during exercise, the blood volume change width is set to about 0 to 2.5% in hematocrit with respect to the tissue volume. FIG. 9 is a graph showing the relationship between the blood concentration and each coefficient (intralipid, 1%, 30%) based on the experimental results. As is clear from FIG. 9, each coefficient is not always a constant value, and a result varying by absorption and scattering was obtained. Therefore, each coefficient was calculated based on the time of rest (hematocrit 1% based on the total tissue amount), and each coefficient was determined as an average value when the scattering intensity was high and when the scattering intensity was low. The results are shown in the table of FIG. According to the table shown in FIG. 10, k ₁ ′ / k ₂ ′ = 0.66 k ₁ / k ₂ = 1.37 k ₂ / k ₂ ′ = 0.58. Substituting into 4) and (5), HbO ₂ , Hb, BV parameter calculation formula (1)
To (3) are obtained. FIG. 11 shows the result of a measurement example (intralipid, 1%) by the monitor of the present invention using the obtained arithmetic expressions (1) to (3) in relation to blood concentration and change in absorbance. FIG.
According to No. 1, there is almost no crosstalk and the measurement is performed with good linearity. FIG. 12 shows the results of measurement examples of the occlusion test with the arm in relation to time and changes in absorbance. In venous occlusion, the blood volume (BV) increases, and the amount of oxyhemoglobin (HbO ₂ ) and reduced hemoglobin (Hb) increases accordingly. In total occlusion, the blood volume does not change, a decrease in oxyhemoglobin and an increase in reduced hemoglobin are observed, and it is possible to separately measure changes in the state of oxidized and reduced hemoglobin and changes in blood volume in the living body. You can check. According to the biological tissue oxygen monitor of the present invention, as described above, the states of oxyhemoglobin (HbO ₂ ) and reduced hemoglobin (Hb) in the biological tissue are based on the amount of light received by the light receiving element. Changes in blood volume and blood volume (BV)
The light source is a near-infrared two-wavelength light emitting diode (emission wavelength) because it is calculated by a linear function of the near-infrared two-wavelength absorbance change amount.
Three light emitting diodes of 760 nm and emission wavelength of 840 nm
Despite a light emitting diode 1), HbO
The three parameters of ₂ , Hb and BV can be calculated. Therefore, a portable monitor that is small, light, and battery-driven can be provided. In addition, the calculation formula of each parameter of HbO ₂ , Hb, and BV is obtained from an experiment in which scattering in a living body is varied to two types in a living tissue model within a range that can actually exist, and the blood volume is also greatly varied. Therefore, the reliability of parameters is improved as compared with the conventional method in which the change width of the blood volume is obtained without changing the scattering and the change width of the blood volume is small. It can be carried out.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration block diagram of a biological tissue oxygen monitor according to one embodiment. FIG. 2 is a diagram showing an optical sensor unit including a light emitting element and a light receiving element in the monitor. FIG. 3 is an enlarged plan view of a main part of an optical sensor unit including a light emitting element and a light receiving element in the monitor. FIG. 4 is a flowchart showing the operation of the monitor (parameter calculation processing). FIG. 5 is a flowchart following FIG. 4; FIG. 6 is a diagram showing the relationship between the wavelength of a light-emitting diode having two near-infrared wavelengths (760 nm and 840 nm) and light intensity. FIG. 7 is a diagram illustrating a relationship between an ink concentration and a change in absorbance with respect to light emission of a light-emitting diode having two near-infrared wavelengths (760 nm and 840 nm). FIG. 8 is a schematic configuration diagram of an experimental apparatus used for obtaining an arithmetic expression of a parameter. FIG. 9 is a diagram showing the relationship between the blood concentration and each coefficient of the parameter calculation formula based on the test results obtained by the test device. FIG. 10 is a diagram showing values of respective coefficients obtained from an experiment result by the experiment apparatus. FIG. 11 is a diagram showing a measurement example using the monitor of the present invention in relation to a blood concentration and a change in absorbance. FIG. 12 is a diagram showing a result of an occlusion test on an arm using the monitor of the present invention in a relationship between time and a change in absorbance. [Description of Signs] 1 Light-emitting element 2 Light-receiving element 7 CPU (arithmetic means) 8 Display circuit (display means) LED ₁ LED with a wavelength of 760 nm and 840 nm LED ₂ LED with a wavelength of 760 nm and 840 nm

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-88340 (JP, A) JP-A-6-38948 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 5/145

Claims (1)

(57) [Claim 1] Irradiation of light having an emission wavelength of 760 nm to a living tissue
Light emitting diode and light emission wavelength 840n for living tissue
m and a single light emitting diode that emits light of
The light emitting element disposed, the light receiving element for receiving the reflected light from the living tissue, and the state of oxyhemoglobin (HbO ₂ ) and reduced hemoglobin (Hb) in the living tissue based on the amount of light received by the light receiving element. Calculation means for calculating the change and the change in blood volume (BV) by a linear function of the near-infrared two-wavelength absorbance change amount, and display means for displaying the calculated change in the oxidation / reduction state and the change in the blood volume. A biological tissue oxygen monitor, comprising: