JP4385677B2 - Biological information measuring device - Google Patents

Description

  The present invention relates to a biological information measuring device that measures biological information such as oxygen saturation in blood.

2. Description of the Related Art Conventionally, a pulse oximeter is known as one of biological information measuring devices as a device capable of continuously measuring oxygen saturation in arterial blood in a non-invasive manner (see, for example, Patent Document 1). This pulse oximeter irradiates biological tissue with two different wavelengths of red light (for example, wavelength 660 nm) and infrared light (for example, wavelength 940 nm) in a time-sharing manner, and transmits transmitted light or reflected light of two different wavelengths. The oxygen saturation is measured based on the ratio of the obtained pulse wave component of absorbance. The reason for using red light and infrared light for the pulse oximeter is that, first, LED devices of these wavelengths are relatively inexpensive and readily available. Second, at each wavelength, the absorbance of oxygen hemoglobin and This is because the magnitude relationship between the absorbances of reduced hemoglobin is reversed and the measurement resolution can be increased.
Japanese Patent No. 3116255

  However, when infrared light (light with a wavelength near 940 nm) is used as irradiation light, transmitted light or reflected light is affected by noise caused by extraneous light such as natural light or indoor illumination light, so that oxygen saturation, which is biological information, is accurately determined. There is a problem that it cannot be measured. Especially in environments where the intensity or wavelength of external light changes, such as outdoors, it is difficult to remove noise components from infrared detection signals and extract only effective signal components, making accurate measurement difficult. is there.

  The present invention has been made in view of the above-described circumstances, and accurately measures biological information without being affected by external light even in an environment where external light changes such as outdoors. It is an object of the present invention to provide a biological information measuring device that can be used.

In order to achieve the above object, the present invention provides a living tissue including arterial blood flow with two wavelengths λ1 and λ2 having different wavelength ranges from about 400 nm to about 700 nm (where λ1> λ2), Light having a wavelength λ1 belonging to a wavelength region where the absorbance of oxyhemoglobin is smaller than the absorbance of reduced hemoglobin in the arterial blood flow, and wavelength λ2 belonging to a wavelength region where the absorbance of oxyhemoglobin is larger than the absorbance of reduced hemoglobin first and second light source for irradiating light, respectively, said wavelength .lambda.1, for each light .lambda.2, after being absorbance in the living tissue, receives the light reflected by the biological tissue including the blood flow light receiving means, a calculating means for calculating the two wavelengths .lambda.1, oxygen saturation based on the spectral signals of each of the absorbance .lambda.2 indicated by the light-receiving result of the light receiving means, wherein the wavelength .lambda.1, .lambda.2 A acceleration sensor for detecting the movement of the body part including the irradiation position of the light, before Symbol calculating means, the two wavelengths .lambda.1, from the spectrum signal of each of the absorbance .lambda.2, the frequency of the detection signal of the acceleration sensor Provided is a biological information measuring device characterized by subtracting a body motion spectrum signal calculated based on a component to calculate the oxygen saturation .

  According to this configuration, it is possible to detect biological information without being affected by the external light even in an environment where the external light changes such as outdoors.

  Here, when the wavelength is larger than about 700 nm, it is difficult to separate the external light and the detection light using the biological tissue as a light guide, and when the wavelength is smaller than about 400 nm, the absorption in the epidermis of the biological tissue is performed. Increases and it becomes difficult to obtain sufficient detection light. Therefore, it is possible to accurately measure biological information by using light having a wavelength belonging to a wavelength range from about 400 nm to about 700 nm.

  For example, the center wavelength of the first light source is about 660 nm, and the center wavelength of the second light source is about 470 nm.

  According to these desirable configurations, it is possible to improve the measurement and decomposition of biological information.

  Further, since the light receiving means is configured to receive the light reflected by the living tissue including the arterial blood flow, the light receiving means emits light having a wavelength that is relatively large in absorption by the living tissue (for example, a wavelength around 470 nm). Even when it is used, a sufficient amount of detection light can be obtained.

Contact name the calculating means may be configured to calculate the oxygen saturation and pulse rate as biological information.

Also it includes an acceleration sensor for detecting the movement of the body part including the irradiation position of the wavelength .lambda.1, each light .lambda.2, before Symbol calculating means, the two wavelengths .lambda.1, from the spectrum signal of each of the absorbance of .lambda.2, the acceleration Since the oxygen saturation is calculated by subtracting the body motion spectrum signal calculated based on the frequency component of the detection signal of the sensor , the body motion component which is a noise component can be removed from the detection result, and the oxygen saturation can be calculated. It becomes possible to obtain more accurately.

  According to the present invention, there is provided a biological information measuring apparatus capable of accurately measuring biological information without being affected by the external light even in an environment where the external light changes such as outdoors. Is done.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing an external configuration of a pulse oximeter as an example of a biological information measuring apparatus according to the present embodiment, together with a mode of use thereof. As shown in this figure, the pulse oximeter 1 is provided on the apparatus main body 100 having a wristwatch structure and is mounted on the apparatus main body 100 and is wound around the user's arm from 12 o'clock in the wristwatch and fixed at 6 o'clock. And a wristband 103. On the upper surface of the apparatus main body 100, a liquid crystal display unit 108 is provided on which various information such as information related to biological information such as blood oxygen concentration and pulse rate and time are displayed. Is provided with a button switch 111 as input means used when inputting various information. Furthermore, a start / end button 116 is provided on the surface of the apparatus main body 100 (the surface on which the liquid crystal display unit 108 is provided). The start / end button 116 is used when the user instructs the pulse oximeter 1 to start or end the measurement of blood oxygen concentration or pulse rate.

  A connector part 105 is provided on the outer peripheral part in the 6 o'clock direction of the apparatus main body 100, and a connector piece 106 to which a biological sensor unit 102 for detecting biological information is connected is detachably attached to the connector part 105. It has been. That is, the pulse oximeter 1 functions as a wristwatch when the connector piece 106 is removed, and can function as a pulse oximeter that measures biological information when the connector piece 106 is attached. A biosensor unit 102 is connected to the connector piece 106 via a cable 101, and the biometric information of the user is detected by the biosensor unit 102. Specifically, the biosensor unit 102 is fixed near the base of the user's finger by the sensor fixing band 104, and detects biometric information (oxygen concentration and pulse wave) by irradiating the blood vessel with light. . The connector unit 105 is provided in the 3 o'clock direction of the wristwatch in the outer periphery of the apparatus main body 100 in order to prevent the user from coming into contact with the back of the hand and restricting the movement of the hand. Is desirable.

  FIG. 3 is a diagram schematically showing the configuration of the biosensor unit 102. As shown in this figure, the biosensor unit 102 includes a unit main body 102a including a sensor frame 1020, a back lid 1021 that closes the lower surface of the sensor frame 1020, and a glass plate 1023 that closes the upper surface. A circuit board 1026, two LEDs 1022 a and 1022 b mounted on the circuit board 1026, and a photodetector 1024 are incorporated in 102 a. In addition, a cable 101 is connected to the circuit board 1026, and a living body detection signal that is a detection signal from the photodetector 1024 is output to the apparatus main body 100 via the cable 101. In addition, power is supplied to the circuit board 1026 from a battery (not shown) built in the apparatus main body 100 via the cable 101.

  Here, the wavelength (center wavelength) of the LED 1022a is about 470 nm, a GaN-based (gallium-nitrogen-based) blue LED is used, and the wavelength (center wavelength) of the LED 1022b is about 660 nm, which is GaAlAs-based. A (gallium-aluminum-arsenic) red LED is used. The light emission surfaces of the LEDs 1022a and 1022b and the light receiving surface of the photodetector 1024 are opposed to the glass plate 1023, and the light emitted from each of the LEDs 1022a and 1022b toward the blood vessel is reflected by the blood vessel, and the amount of reflected light is It has a so-called reflection type structure that is transmitted through the glass plate 1023 and detected by the photodetector 1024. In general, when the wavelength is short, the absorption of light in the living body becomes strong, and the transmitted light passing through the finger is weak, so that it is difficult to measure biological information using this transmitted light. However, as described above, a configuration in which reflected light is detected allows a sufficient amount of light to be incident on the photodetector 1024 so that biological information measurement can be measured.

  Next, as shown in FIG. 4, two transmission filters 1024 a and 1024 b having different transmission wavelength characteristics are attached so as to divide the light receiving surface of the photodetector 1024. The transmission filter 1024a transmits only light in the wavelength region of the LED 1022a (ie, near 470 nm), and the transmission filter 1024b transmits only light in the wavelength region of the LED 1022b (ie, near 660). With this configuration, it is possible to detect the amount of light in each wavelength region of the LEDs 1022a and 1022b by one photo detector 1024. When measuring biological information, the LEDs 1022a and 1022b alternately emit light in a time division manner, and the amount of reflected light detected by the light emission of the LED 1022a or LED 1022b is output to the apparatus main body 100 as a biological detection signal.

  Note that the glass plate 1023 is formed of a glass material having high transmission characteristics in at least the wavelength regions of the LEDs 1022a and 1022b (near 470 nm and 660 nm), and light in other wavelength regions is attached to the surface of the glass plate 1023. It is configured to be cut by an attached transmission filter (not shown), so that intrusion of extraneous light into the unit body 102a is prevented as much as possible, and noise due to extraneous light is prevented from being included in the photodetector 1024. . In this embodiment, since the LED 1024a that emits blue light having a wavelength of about 470 nm and the LED 1024b that emits red light having a wavelength of about 660 nm are used, it is possible to measure biological information without being affected by external light. This will be described in detail later in comparison with a conventional example.

  FIG. 5 is a block diagram showing a functional configuration of the pulse oximeter 1. In this figure, the CPU 130 controls the operation of each part of the pulse oximeter 1 and executes various arithmetic processing such as blood oxygen concentration arithmetic processing and pulse rate arithmetic processing based on the biological detection signal from the biological sensor unit 102. It functions as a control / calculation means. The ROM 132 is a rewritable memory such as an EEPROM (Electrically Erasable Programmable ROM), and stores a control program executed by the CPU 130 and various data. The RAM 134 is used as a work area for the CPU 130, and temporarily stores calculation results and various data by the CPU 130. The clock circuit 136 includes an oscillation circuit 1360 that outputs a clock signal having a predetermined frequency (for example, 32.768 kHz), and a frequency dividing circuit 1361 that divides the clock signal from the oscillation circuit 1360 and outputs a 1 Hz clock signal to the CPU 130. The CPU 130 performs a time measurement process based on a 1 Hz clock signal. The input unit 138 corresponds to the button switch 111 and the start / end button 116 described above, and outputs a signal corresponding to each button operation of the user to the CPU 130. The liquid crystal display unit 108 displays a screen according to the control of the CPU 130.

  The biological signal amplification circuit 120 amplifies the biological detection signal from the biological sensor unit 102 and outputs it to the A / D conversion circuit 122. The A / D conversion circuit 122 performs analog / digital conversion on the received biological detection signal and outputs it to the CPU 130 only while the control signal is input from the CPU 130. The CPU 130 captures the biological detection signal for a certain period, and performs FFT ( The frequency component of the living body detection signal is calculated by executing a (Fast Fourier Transform) process, and the biological spectrum signals Fsa and Fsb are obtained. Here, in order to individually detect the amount of reflected light corresponding to the two LEDs 1022a and 1022b included in the biosensor unit 102, the CPU 130 causes the LEDs 1022a and 1022b to alternately emit light in a time-sharing manner, and is detected when the LEDs 1022a emit light. The biological spectrum signal Fsa based on the biological detection signal and the biological spectrum signal Fsb based on the biological detection signal detected when the LED 1022b emits light are separately obtained.

  The biological detection signal, that is, the biological spectrum signals Fsa and Fsb includes information indicating oxygen saturation and pulse rate in the blood as biological information. More specifically, when light is emitted toward the finger from the LEDs 1022a and 1022b, this light reaches the blood vessel, and part of it is absorbed by hemoglobin (oxygenated hemoglobin, reduced hemoglobin) in the blood and partly reflected. The light reflected from the living body (blood vessel) is received by the photodetector 1024, and the change in the amount of received light corresponds to the change in blood volume caused by the pulse wave of blood.

  Specifically, when the blood volume is large, the absorption of light in hemoglobin increases, so that the reflected light becomes weak, while when the blood volume decreases, the reflected light becomes strong. Therefore, if the change in the reflected light intensity is monitored by the photodetector 1024, the pulse can be detected from the pulsation cycle of the reflected light intensity (that is, the biological spectrum signals Fsa and Fsb).

Although the detailed description is omitted, the oxygen saturation SpO ₂ (Saturation Pulse Oxygen) is a pulse wave of absorbance with respect to light of the wavelength of the LED 1022a (in this embodiment, 480 nm) as shown in the following equation (1). It is obtained from the intensity ratio between the component ACa and the pulse wave component ACb of the absorbance with respect to the light of the wavelength of the LED 1022b (6600 nm in this embodiment).

Oxygen saturation SpO ₂ = f (ACb / ACa) (1)
However, the function f is a predetermined function determined by the absorbance at each wavelength of the LEDs 1022a and 1022b.

Since there is a variation in sensitivity depending on the light emission intensity of the light emitting elements (LEDs 1022a, 1022b) and the wavelength of the light receiving element (photodetector 1024), the pulse wave component AC of the absorbance is actually expressed as shown in the following equation (2). A more accurate oxygen saturation SpO ₂ is obtained by dividing and normalizing by a direct current component DC (a component including variations in emission intensity of light emitting elements, absorption of body tissues, variations in performance of electric circuits, etc.). .

Oxygen saturation SpO ₂ = f ((ACb / DCb) / (ACa / DCa)) (2)
When the above equation (2) is expressed using the biological spectrum signals Fsa and Fsb, the pulse wave components ACa and ACb correspond to the spectral components Fsah and Fsbh having the maximum power among the spectral components included in the biological spectrum signals Fsa and Fsb. Since the direct current components DCa and DCb correspond to the spectral components Fsao and Fsbo having a frequency of “0 Hz”, the following equation (3) is obtained.

Oxygen saturation SpO ₂ =
f ((Fsbh / Fsbo) / (Fsah / Fsao)) (3)
FIG. 6 is a diagram schematically showing the relationship between the value of {(ACb / DCb) / (ACa / DCa)} and the oxygen saturation SpO _{2 in} the above equation (2). As shown in this figure, the value of {(ACb / DCb) / (ACa / DCa)} and the oxygen saturation SpO ₂ are approximately proportional, and the value of {(ACb / DCb) / (ACa / DCa)} Accordingly, the oxygen saturation level SpO ₂ is uniquely identified. Therefore, in this embodiment, the value of {(ACb / DCb) / (ACa / DCa)} (more specifically, the value of (Fsbh / Fsbo) / (Fsah / Fsao)) and the oxygen saturation SpO ₂ If table data (not shown) indicating the correspondence relationship is stored in the ROM 132 in advance and the value of {(ACb / DCb) / (ACa / DCa)} is calculated, the oxygen saturation SpO ₂ is calculated based on the table data. It has a specific configuration. Thereby, since it is not necessary to calculate the functional expression shown in the above expression (2) or (3), the oxygen saturation SpO ₂ can be quickly identified, and the power consumption by this calculation can be reduced. It becomes.

Note that the oxygen saturation SpO ₂ is not obtained from the above equation (3) based on the frequency analysis value, but the AC component (pulse wave amplitude) and DC are calculated from the biological detection signal waveform (A / D conversion value) from the photodetector 1024. The component may be obtained, and the oxygen saturation SpO2 may be obtained directly using the above equation (2).

  By the way, when the user is exercising or the like, the biological spectrum signals Fsa and Fsb include frequency components corresponding to body movement (that is, movement of the arm). Therefore, in order to measure biological information (oxygen saturation, pulse) more accurately, it is necessary to remove body motion components from the biological spectrum signals Fsa and Fsb. Therefore, the pulse oximeter 1 according to the present embodiment includes a body motion sensor 140 that detects body motion, as shown in FIG. The body motion sensor 140 includes an acceleration sensor for detecting repeated movements of arm swings associated with walking as user body motions. The body motion sensor 140 including an acceleration sensor is built in the apparatus main body 100, detects the acceleration of the user's arm swing, and outputs it to the body motion signal amplification circuit 142 as a body motion signal.

  The body motion signal amplification circuit 142 amplifies the body motion signal and outputs the amplified body motion signal to the A / D conversion circuit 122. As described above, the A / D conversion circuit 122 performs analog / digital conversion on the body movement signal and outputs the signal to the CPU 130 only while the control signal is input from the CPU 130. That is, the A / D conversion circuit 122 alternately receives the biological detection signal from the biological signal amplification circuit 120 and the body movement signal from the body movement signal amplification circuit 142 at regular intervals (that is, time division), and analog / digital. It converts and outputs to CPU130. When the body motion signal converted into the digital signal is captured for a certain period, the CPU 130 calculates the frequency component of the body motion signal by executing the FFT process to obtain the body motion spectrum signal Ft. Then, the CPU 130 obtains the oxygen saturation by subtracting the body motion spectrum signal Ft in order to remove the body motion component from the biological spectrum signals Fsa and Fsb.

  FIG. 7 is a flowchart showing the procedure of the biological information measurement process. As shown in this figure, when the CPU 130 of the pulse oximeter 1 detects that the start / end button 116 is operated by the user and a measurement start instruction is made (step S1: Yes), the CPU 130 of the pulse oximeter 1 sends the A / D conversion circuit 122. A control signal is output and operated, and each of the LEDs 1022a and 1022b and the body motion sensor 140 of the biological sensor unit 102 is operated exclusively (time-division), and the biological detection signal based on the light emission of the LED 1022a and the LED 1022b The living body detection signal based on the light emission and the body motion signal are taken in a time division manner (step S2).

  Next, the CPU 130 performs FFT processing on each of the living body detection signal and the body motion signal, and calculates each of the biological spectrum signals Fsa and Fsb and the body motion spectrum signal Ft (step S3). Then, the CPU 130 subtracts the body motion spectrum signal Ft from each of the biological spectrum signals Fsa and Fsb in order to remove the body motion component from the biological spectrum signals Fsa and Fsb (step S4), and the subtracted biological spectrum signal Fsa. Based on Fsb, the oxygen saturation and the pulse rate (ie, biological information) are calculated (step S5).

FIG. 8 is a flowchart showing the procedure of the biological information calculation process. First, in order to obtain the oxygen saturation SpO ₂ using the above equation (3), the CPU 130 uses the biological spectrum signals Fsa and Fsb as the spectral components Fsao and Fsbo having the frequency “0 Hz”, the spectral component Fsah having the maximum power, Fsbh (step S50), and from these spectral components Fsao, Fsbo, Fsah, and Fsbh, the value of (Fsbh / Fsbo) / (Fsah / Fsao), that is, the absorbance ratio of each of the two wavelengths is calculated ( Step S51). Then, the CPU 130 specifies the oxygen saturation SpO ₂ corresponding to the calculated absorbance ratio with reference to the table data stored in the ROM 132 (step S52). Here, the oxygen saturation SpO ₂ is obtained from the above equation (3) based on the frequency analysis value. However, the present invention is not limited to this, and the biological detection signal waveform (A / D conversion value) from the photodetector 1024 is used. An AC component (pulse wave amplitude) and a DC component may be obtained, and the oxygen saturation SpO2 may be directly obtained using the above equation (2).

  Next, the CPU 130 calculates the pulse rate by the following equation (4) using the fact that the frequency of the spectrum components Fsah and Fsbh having the maximum power among the biological spectrum signals Fsa and Fsb indicates the pulse (step S53).

Pulse rate (beats / minute)
= Frequency of power maximum component Fsah of biological spectrum signal × 60 (4)
Or
Pulse rate (beats / minute)
= Frequency of power maximum component Fsbh of biological spectrum signal × 60 ·· (4 ′)
Note that the pulse rate can be calculated using any of the biological spectrum signals Fsa and Fsb obtained corresponding to each of the LEDs 1022a and 1022b. Accordingly, the pulse rate may be calculated using any one of the biological spectrum signals, and the average value of the pulse rates calculated for each of the biological spectrum signals Fsa and Fsb is calculated in order to reduce the error. You may do it.

  Returning to FIG. 7 again, the CPU 130 displays the oxygen saturation and the pulse rate calculated in step S5 on the liquid crystal display unit 108 (step S6: see FIG. 9), and notifies the user of the measurement result. Then, the CPU 130 determines whether or not there is an instruction to end the biological information measurement by the user's operation of the start / end button 116 (step S7). If the determination result is No, the biological information measurement is continued. In order to carry out, while returning the processing procedure to step S2, if the determination result is Yes, the CPU 130 ends the biological information measurement processing. In the biometric information calculation process described above, the biometric information is calculated in the order of oxygen saturation and pulse rate. However, it is needless to say that the configuration may be such that the pulse rate and oxygen saturation are calculated in this order.

  In this embodiment, instead of the conventional infrared light, by using the LED 1022a that irradiates blue light (center wavelength 480 nm), more accurate biological information measurement can be achieved without being affected by external light. ing. Hereinafter, the result of the performance test performed on the configuration of the present embodiment will be described in comparison with the conventional configuration.

  As shown in FIG. 10, this performance test is performed with one arm of the subject U placed in the dark room and the other arm exposed to extraneous light, and the reference pulse oximeter is placed on the arm in the dark room. Two test pulse oximeters 1Ea and 1Eb are attached to the arm to which 1R is attached and illuminated by external light. The reference pulse oximeter 1R uses two wavelengths of red light (center wavelength: about 660 nm) and infrared light (center wavelength: about 940 nm) as light to irradiate the living tissue. The test pulse oximeter 1Ea uses light having a center wavelength of about 480 nm and light having a center wavelength of about 660 nm (this embodiment) as light of two wavelengths, and the test pulse oximeter 1Eb includes Light having a center wavelength of about 940 nm and light having a center wavelength of about 660 nm (conventional configuration) are used. However, each of the test pulse oximeters 1Ea and 1Eb has substantially the same configuration except that the wavelength of the light source is different, and factors other than the light source wavelength do not affect the test result. Further, the two test pulse oximeters 1Ea and 1Eb are attached at the same time, and the biosensor unit is attached to different fingers (for example, the index finger and the middle finger).

  In such a test environment, first, the measurement was performed after stopping the irradiation of external light. FIG. 11 is a diagram showing the relationship between the oxygen saturation SpO2 obtained from the reference pulse oximeter 1R and the absorbance ratio of two wavelengths for each of the test pulse oximeters 1Ea and 1Eb. As shown in this figure, when there is no influence of extraneous light, a linear correlation is found with the measured value of the reference pulse oximeter 1R regardless of which test pulse oximeter 1Ea, 1Eb is used. In both cases, it is understood that there is no hindrance in the measurement of biological information.

  Next, FIG. 12 shows the result obtained when the external light is irradiated. As shown in this figure, the test pulse oximeter 1Ea using the wavelength of the present embodiment as a light source has a linear correlation with the reference pulse oximeter 1R, as in the case of no external light irradiation. Although it has a relationship, in the test pulse oximeter 1Eb having the conventional configuration, the correlation with the reference pulse oximeter 1R is broken, and it is understood that accurate biological information cannot be measured.

  This is because, of the extraneous light, light having a wavelength region of about 700 nm or more (that is, light having a longer wavelength than near-infrared light) reaches the photodetector 1024 using the finger as a light guide. As a result, in the conventional configuration using light with a wavelength of 940 nm, noise due to extraneous light is included in the photodetector 1024, and as shown in FIG. 12, the measured values vary. On the other hand, most of the extraneous light having a wavelength region of about 700 nm or less does not reach the photodetector 1024 because most of it is absorbed by the living tissue when passing through the finger. Therefore, by using light in a wavelength region of about 700 nm or less, biological information can be measured without being affected by extraneous light.

  However, since light having a wavelength region of about 400 nm or less is almost absorbed by the skin surface, the light does not reach the blood vessels, and measurement itself becomes difficult. Therefore, when measuring biological information by irradiating a living tissue including arterial blood and receiving reflected light or transmitted light, light belonging to a wavelength range of about 400 nm to about 700 nm may be selected. It becomes. Therefore, in the present embodiment, an LED having a center wavelength of about 470 nm and an LED having a wavelength of about 660 nm are used so that biological information can be detected without being affected by external light.

Incidentally, as shown in FIGS. 11 and 12, in the test pulse oximeter 1Ea corresponding to the configuration of the present embodiment, the measured value has a linear correlation with the reference pulse oximeter 1R. The inclination is smaller than that of the conventional configuration (see FIG. 11), and the resolution of the oxygen saturation SpO ₂ measurement is inferior to that of the conventional configuration. Therefore, in the present embodiment, as shown in FIG. 13, in order to obtain the same resolution as the conventional configuration, the inclination of the measurement result obtained by the test pulse oximeter 1Ea of the configuration of the present embodiment is corrected, and the inclination Has increased. FIG. 14 is a diagram illustrating a result obtained by adding the above correction to the result obtained when the external light is irradiated. As shown in this figure, the test pulse oximeter 1Ea having the configuration of the present embodiment has a linear correlation with the reference pulse oximeter 1R, and has a large inclination, which is influenced by external light. It can be seen that measurement with good resolution is possible.

As described above, according to the present embodiment, since the wavelength of light irradiating the living tissue including arterial blood is set to about 470 nm and about 660 nm, even if it is used outdoors, external light is used. The biological information can be measured accurately without being affected by the above. Further, since the reflected light is received instead of the light that passes through arterial blood, the photodetector 1024 can obtain a sufficient amount of received light even when light having a short wavelength is used as the irradiation light. Furthermore, the measurement resolution can be improved because the linear relationship between the measured value obtained using these wavelengths and the oxygen saturation is corrected to increase its slope.
<Modification>
The above-described embodiments are merely examples of the present invention, and can be arbitrarily modified within the scope of the present invention. Accordingly, various modifications will be described below.
(Modification 1)
In the above-described embodiment, light having a wavelength of about 470 nm and light having a wavelength of about 660 nm are used as light to irradiate the living tissue, but the present invention is not limited to this. That is, as shown in FIG. 17, any light can be used as long as it belongs to a wavelength range of about 400 nm to about 700 nm, so that it is not affected by extraneous light and is absorbed by living tissue. Biological information can be measured without being affected by the above.

Here, in order to improve the measurement resolution, light having a wavelength (for example, wavelength 660 nm) in which the absorbance of oxyhemoglobin is smaller than the absorbance of reduced hemoglobin in the arterial blood flow in the wavelength range of about 400 nm to about 700 nm. On the contrary, it is desirable to use light having a wavelength (for example, a wavelength of 470 nm) at which the absorbance of oxyhemoglobin is greater than the absorbance of reduced hemoglobin. In other words, when the first wavelength is λ1, the second wavelength is λ2, the absorbance of reduced hemoglobin in the arterial blood flow at wavelengths λ1 and λ2 is λiHb, and the absorbance of oxyhemoglobin is λiHbO ₂ (where i = 1, 2),
(Λ1Hb / λ1HbO ₂ ) / (λ2Hb / λ2HbO ₂ ) ≦ 0.15
(For example, λ1 = 660 nm, λ2 = 470 nm).

By using light of these wavelengths, the slope in the linear relationship between the measured value and the oxygen saturation can be made relatively large, thereby increasing the measurement resolution. As described above, even in this configuration, when the measurement resolution is inferior to the conventional configuration, the resolution can be improved by correcting the inclination.
(Modification 2)
In the above-described embodiment, the configuration in which the pulse oximeter 1 is mounted near the base of the finger and irradiates light to the blood vessel in the vicinity of the pulse oximeter 1 has been described.
(Modification 3)
In the above-described embodiment, light having two wavelengths is received in a time division manner using one photodetector 1024, and biological information is calculated based on the light reception result. It is good also as a structure which uses one photo detector for every. Thereby, it is not necessary to drive the LED or the like in a time division manner, and the arithmetic processing is facilitated.
(Modification 4)
In the above-described embodiment, the body motion sensor 140 is used to remove the body motion component from the light reception result (biological detection signal) received by the photodetector 1024. However, the present invention is not limited to this. That is, instead of the body motion sensor 140, an expected pseudo body motion component may be stored in the ROM 132 in advance, and the body motion component may be removed from the light reception result (biological detection signal) using this. Note that if the user is used only when the user is in a resting state, the body motion component included in the light reception result (biological detection signal) can be substantially ignored, so there is no need to provide a configuration for removing the body motion component.

It is a figure which shows the external appearance structure of the pulse oximeter which concerns on embodiment of this invention. It is a figure which shows the aspect of mounting | wearing with the biosensor unit. It is a sectional side view which shows typically the structure of the biosensor unit. It is a top view which shows typically the structure of the biosensor unit. It is a block diagram which shows the functional structure of the pulse oximeter. It is a figure which shows the relationship between the measured value of the pulse oximeter, and oxygen saturation. It is a flowchart which shows the procedure of a biometric information measurement process. It is a flowchart which shows the procedure of a biometric information calculation process. It is a figure which shows the aspect which alert | reports biometric information to a user. It is a figure which shows the experimental condition of the comparison experiment of the structure of this invention, and a conventional structure. It is a figure which shows the measurement result of the structure of this invention, and a conventional structure when there is no irradiation of extraneous light. It is a figure which shows the measurement result of the structure of this invention, and a conventional structure in case there exists irradiation of external light. It is a figure for demonstrating correction | amendment with respect to the measurement result of the structure of this invention. It is a figure which shows the result of having correct | amended the measurement result of the structure of this invention when there exists irradiation of external light. It is a figure which shows the relationship between the wavelength of light, and the molecular extinction coefficient (absorbance) of each of reduced hemoglobin and oxyhemoglobin.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Pulse oximeter (biological information measuring device), 102 ... Biosensor unit, 130 ... CPU, 140 ... Body motion sensor, 1022a, 1022b ... LED, 1024 ... Photo detector.

Claims (3)

Biological tissue including arterial blood flow has two wavelengths λ1, λ2 (where λ1> λ2) having different wavelength ranges from about 400 nm to about 700 nm, and is oxidized more than the absorbance of reduced hemoglobin in the arterial bloodstream. First and second light sources for irradiating light of wavelength λ1 belonging to a wavelength region where the absorbance of hemoglobin is small and light of wavelength λ2 belonging to a wavelength region where the absorbance of oxyhemoglobin is larger than the absorbance of reduced hemoglobin, respectively. When,
A light receiving means for receiving light reflected by the biological tissue including the arterial blood flow after being absorbed by the biological tissue with respect to each of the wavelengths λ1 and λ2 .
Arithmetic means for calculating oxygen saturation based on spectral signals of absorbance at each of the two wavelengths λ1 and λ2 indicated by the light reception result of the light receiving means;
An acceleration sensor that detects the movement of the body part including the irradiation part of each light of the wavelengths λ1 and λ2,
Before SL calculating means, the calculating two wavelengths .lambda.1, from the spectrum signal of each of the absorbance .lambda.2, the oxygen saturation by subtracting the body motion spectrum signal calculated based on the frequency component of the detection signal of the acceleration sensor A biological information measuring device.   The biological information measuring apparatus according to claim 1 or 2, wherein a center wavelength of the first light source is about 660 nm, and a center wavelength of the second light source is about 470 nm. Said first and second light source, the biological information measuring apparatus according to claim 1 or 2, characterized disposed on the user's finger can be fixed sensor fixing band.

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