JP2019150104A - Pulse oximeter and blood characteristic measuring apparatus - Google Patents

Abstract

To provide a pulse oximeter capable od suppressing deterioration in SpOmeasurement accuracy due to variations in the wavelength of a light emitting device without measuring the wavelength of the light emitting device.SOLUTION: A pulse oximeter includes: a first table 401 in which a correspondence between a value equivalent to a light volume detected by a photodetector 122 and a peak wavelength is stored, and a value of the peak wavelength corresponding to a value equivalent to the light volume is output with the value equivalent to the light volume detected by the photodetector 122 as a reading address; a second table 402 in which a correspondence between the peak wavelength and an absorption coefficient is stored, and the absorption coefficient corresponding to the peak wavelength is output with the peak wavelength output from the first table 401 as a reading address; and an SpOcalculation unit 404 for calculating SpOusing the absorption coefficient and the value detected by the photodetector 122.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a pulse oximeter and a blood characteristic measurement device.

A pulse oximeter is widely used as a biological information measuring device capable of non-invasively measuring arterial blood oxygen concentration (hereinafter simply referred to as SpO ₂ or oxygen saturation). A pulse oximeter is a medical device that can noninvasively measure arterial oxygen saturation, which represents the ratio of oxygenated hemoglobin to total hemoglobin in arterial blood (see, for example, Patent Document 1).

  The pulse oximeter is configured to attach a probe to a measurement site such as a finger, a footpad or an earlobe. The probe is provided with a light emitting element such as an LED (Light Emitting Diode) and a photo detector such as a photodiode.

Then, by alternately emitting light emitting elements that emit red light and light emitting elements that emit near-infrared light, red light and near-infrared light are alternately irradiated toward the measurement site and transmitted through the measurement site. Or the light reflected from the measurement site is detected by a photodetector. In general, red light in SpO ₂ measurement is defined as 660 nm ± 5 nm, and near-infrared light is defined as 800 to 950 nm.

The pulse oximeter calculates SpO ₂ using a detection signal of transmitted light or reflected light obtained by a photodetector. Specifically, the fluctuation of the light detection level synchronized with the pulse of arterial blood is compared between the case of red light and the case of near infrared light, and SpO ₂ is calculated from the ratio. The pulse oximeter displays the calculated SpO ₂ on the display unit.

As a method for calculating the SpO ₂ , there is a method using a formula obtained from Lambert-Beer's law (formulation of absorption of light by a substance). Specifically, this calculation method obtains the value of SpO ₂ from the ratio “R” of the transmitted light amount of red light and near-infrared light and the extinction coefficients of hemoglobin and oxygenated hemoglobin at the respective wavelengths. (For example, refer nonpatent literature 1).

  Here, as described in Non-Patent Document 1, since LEDs used as light emitting elements have slightly different wavelengths for individual products (that is, there are individual differences), it is possible to calculate an accurate substance concentration. Therefore, it is necessary to prepare a calibration curve (calibration curve) of the substance concentration and absorbance at each LED wavelength before measurement.

In Non-Patent Document 1, the wavelength values of the red light LED and the near infrared light LED are stored in the memory of the pulse oximeter sensor, and the calibration curve is stored in the main body of the pulse oximeter. The main body reads the wavelength value of the sensor and selects the calibration curve. According to this configuration, it is considered that the use of the selected calibration curve can suppress a decrease in SpO ₂ measurement accuracy due to variations in the wavelength of the LED.

JP 2007-289462 A JP 2005-253478 A JP 2005-013273 A

Japan Intensive Medical Journal 2016; 23: 625-31. pp625-631

  By the way, in order to perform calibration as described in Non-Patent Document 1, it is assumed that the emission wavelength of the LED attached to the sensor of the pulse oximeter is accurately known.

  However, in order to accurately measure the wavelength of each LED that varies from individual to individual, a wavelength measuring device with a complicated configuration is required. Therefore, in practice, the wavelength of each LED is measured before the LED is attached to the pulse oximeter sensor. Further, the wavelength of each LED may be measured after the LED is attached to the sensor, but in any case, a measuring device having a complicated configuration is required.

  Thus, in order to perform the calibration as described in Non-Patent Document 1, a wavelength measuring device is required, and wavelength measurement using the wavelength measuring device must be performed for all LEDs. There is also annoyance that must be done.

  In particular, in a disposable pulse oximeter sensor, since it is often required to use an inexpensive LED, the wavelength of the LED may be deviated from the determined wavelength. In order to perform such calibration, it is necessary to measure the wavelengths of all LEDs, which is complicated.

  Such a problem can occur widely in apparatuses that measure blood characteristics using a light emitting element in addition to a pulse oximeter.

The present invention has been made in consideration of the above points, and a pulse oximeter and blood characteristics capable of suppressing a decrease in SpO ₂ measurement accuracy due to variations in the wavelength of the light emitting element without measuring the wavelength of the light emitting element. Provide a measuring device.

One aspect of the pulse oximeter of the present invention is:
A light emitting element;
A photodetector for receiving the light of the light-emitting element transmitted or reflected through the measurement site;
A first table storing a correspondence between a value corresponding to a light amount detected by the photodetector and a peak wavelength;
A second table storing the correspondence between peak wavelength and extinction coefficient;
An SpO ₂ calculation unit for calculating SpO ₂ using the extinction coefficient and the value detected by the photodetector;
It comprises.

One aspect of the pulse oximeter of the present invention is:
A light emitting element;
A photodetector for receiving the light of the light-emitting element transmitted or reflected through the measurement site;
A table storing a correspondence relationship between a value corresponding to the amount of light detected by the photodetector and an extinction coefficient;
An SpO ₂ calculation unit for calculating SpO ₂ using the extinction coefficient and the value detected by the photodetector;
It comprises.

One aspect of the blood property measurement apparatus of the present invention is:
A light emitting element;
A photodetector for receiving the light of the light-emitting element transmitted or reflected through the measurement site;
A first table storing a correspondence between a value corresponding to a light amount detected by the photodetector and a peak wavelength;
A second table storing the correspondence between peak wavelength and extinction coefficient;
A blood characteristic calculator that calculates blood characteristics using the extinction coefficient and the value detected by the photodetector;
It comprises.

One aspect of the blood property measurement apparatus of the present invention is:
A photodetector for receiving the light of the light-emitting element transmitted or reflected through the measurement site;
A table storing a correspondence relationship between a value corresponding to the amount of light detected by the photodetector and an extinction coefficient;
A blood characteristic calculator that calculates blood characteristics using the extinction coefficient and the value detected by the photodetector;
It comprises.

According to the present invention, without measuring the wavelength of the light emitting element can realize a pulse oximeter that can suppress a decrease in SpO ₂ measurement accuracy due to variations in wavelength of the light emitting element. In addition, it is possible to realize a blood characteristic measuring apparatus that can suppress a decrease in measurement accuracy of blood characteristics due to variations in wavelength of light emitting elements without measuring the wavelength of the light emitting elements.

The perspective view which shows the state which mounted | wore the subject with the pulse oximeter Block diagram showing the configuration of the pulse oximeter The figure which shows the principal part structure for demonstrating the characteristic of the pulse oximeter of embodiment. Diagram showing the photosensitivity characteristics of a photodetector The figure which shows wavelength distribution of LED of red light and LED of near infrared light The figure which shows the structure of other embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  1 and 2 are diagrams showing an overall configuration of a pulse oximeter 10 according to the present embodiment. FIG. 1 is a perspective view showing a state in which a pulse oximeter 10 is mounted on a subject, and FIG. 2 is a block diagram showing a configuration of the pulse oximeter 10.

  The pulse oximeter 10 includes a probe unit 100 and a main body unit 200. The probe unit 100 and the main body unit 200 are connected via a cable 300. The probe unit 100 can be mounted on the subject's finger, and the main body unit 200 can be mounted near the wrist of the subject using a wristband (not shown).

  As shown in FIG. 2, the probe unit 100 of the pulse oximeter 10 is provided with a light emitting element 121 and a photodetector 122. In the present embodiment, the light emitting element 121 is an LED. The light emitting element 121 may be other than the LED. The light emitting element 121 emits red light (for example, red light with a peak wavelength of 660 [nm]) and first LED that emits near infrared light (for example, near infrared light with a peak wavelength of 940 [nm]). 2 LEDs.

  The photodetector 122 is configured by a photodiode, receives light of the light emitting element 121 that has passed through the finger, and outputs an electrical signal corresponding to the amount of received light (specifically, a current corresponding to the amount of light). Note that the photodetector 122 may be disposed not in the light transmission path from the finger but in the light reflection path from the finger, and the photodetector 122 may detect the reflected light from the finger.

The main body 200 obtains the subject's SpO ₂ and pulse based on the detection result obtained by the photodetector 122. This will be specifically described. The light emission driving unit 211 causes the first LED and the second LED of the light emitting element 121 to alternately emit light at a predetermined interval. Transmitted light or reflected light from the finger at that time is detected by the photodetector 122, subjected to photoelectric conversion, and input to the amplifying unit 212. The electric signal amplified by the amplifying unit 212 is output to the CPU 214 via the analog / digital conversion circuit (A / D) 213.

The CPU 214 includes a calculation unit 214a that calculates SpO ₂ and a pulse based on an electric signal from the A / D 213 by executing a predetermined program. Since this calculation method is a known technique as described in, for example, Patent Document 1 and Non-Patent Document 1, description thereof is omitted here. Further, the CPU 214 controls each part of the pulse oximeter 10. Specifically, the CPU 214 performs various settings based on an operation signal input from the operation unit 202. Further, the CPU 214 performs operation control of the light emission driving unit 211, display control of the display unit 201, and the like.

  In the present embodiment, the case where the photodetector 122 is provided on the probe unit 100 side has been described, but the photodetector 122 may be provided on the main body unit 200 side. In this case, in the probe unit 100, light transmitted or reflected through the measurement site (for example, a finger) may be incident on the cable 300 having the optical transmission path. Then, light may be detected (that is, photoelectrically converted) by the photodetector 122 provided on the output side of the cable 300, that is, on the main body 200 side.

  FIG. 3 is a diagram showing a main configuration for explaining the characteristics of the pulse oximeter 10 of the present embodiment.

The calculation unit 214a of the pulse oximeter 10 according to the present embodiment includes a first table 401, a second table 402, a storage unit 403, and an SpO ₂ calculation unit 404.

  The first table 401 stores the correspondence between the value corresponding to the amount of light detected by the photodetector 122 and the peak wavelength. From the first table 401, a value corresponding to the light amount detected by the photodetector 122 is used as a read address, and a peak wavelength value corresponding to the value corresponding to the light amount is output.

  The second table 402 stores the correspondence between the peak wavelength and the extinction coefficient. From the second table 402, the extinction coefficient corresponding to the peak wavelength is output using the peak wavelength output from the first table 401 as a read address.

  The extinction coefficient output from the second table 402 is stored in the storage unit 403.

  The first table 401 includes a red light table 401a and a near infrared light table 401b. Similarly, the second table 402 includes a table 402a for red light and a table 402b for near infrared light.

  The values in the first and second tables 401 and 402 are written by the manufacturer of the pulse oximeter 10 before the pulse oximeter 10 is shipped.

  Here, as described in the section of the problem to be solved by the above-described invention, the actual peak wavelength of the light emitting element (LED) 121 varies, and if this is directly measured, the wavelength measurement of a complicated configuration is performed. A device is necessary or troublesome. In consideration of this, in this embodiment, the actual peak wavelength of the light emitting element 121 is estimated from the detected light amount of the photodetector 122 instead of directly measuring the peak wavelength.

  This is based on the phenomenon that when the peak wavelength of the light emitting element 121 changes, the detected light quantity of the photodetector 122 changes accordingly.

  This will be described with reference to FIGS. As shown in FIG. 4, the light receiving sensitivity of the photodetector 122 changes according to the wavelength of the received light.

  On the other hand, FIG. 5 shows the wavelength distribution of a red LED and a near-infrared LED, and the wavelength distribution is a Gaussian distribution. Here, even if the peak wavelength of the red light LED is slightly shifted (specifically, even if there is a shift of about the product variation), the light amount (corresponding to the integral value of the wavelength distribution of the red light in FIG. 5). ) Hardly fluctuates. Similarly, even if the peak wavelength of the near-infrared LED is slightly shifted (specifically, even if there is a shift of product variation), the amount of light (the integrated value of the wavelength distribution of red light in FIG. 5) Corresponding) hardly fluctuate.

  Therefore, by referring to the light receiving sensitivity characteristic of the photodetector 122, the correspondence between the amount of light detected by the photodetector 122 and the peak wavelength can be uniquely determined. In the present embodiment, based on such an idea, the correspondence between the value corresponding to the amount of light detected by the photodetector 122 and the peak wavelength is determined and stored in the first table 401 in advance. In addition, the extinction coefficient corresponding to each peak wavelength is stored in advance in the second table 402.

  That is, this embodiment is based on the consideration that the peak wavelength of the light-emitting element 121 can be estimated based on the amount of light detected by the photodetector 122 without being directly measured. If the peak wavelength is known, an extinction coefficient appropriate for the peak wavelength can be selected.

In practice, in the pulse oximeter 10, prior to the measurement of SpO ₂ , the light emitting element 121 emits light, and the light is detected by the photodetector 122. At that time, the first and second tables 401 and 402 are used. The red light absorption coefficient and the near infrared light absorption coefficient obtained in this way are stored in the storage unit 403.

  For example, when the amount of light detected by the photodetector 122 when the red light is emitted from the light emitting element 121 (actually the amount of light amplified by the amplification unit 212) is the amount of light X2, the first table 401 is used. "660" is output as the value of the peak wavelength, the extinction coefficient X2 is output as the extinction coefficient from the second table, and the extinction coefficient X2 is stored in the storage unit 403.

  If the light amount detected by the photodetector 122 when the near-infrared light is emitted from the light emitting element 121 (actually, the light amount amplified by the amplifying unit 212) is the light amount Y1, “750” is output as the peak wavelength value from the table 401, the extinction coefficient Y 1 is output as the extinction coefficient from the second table, and the extinction coefficient Y 1 is stored in the storage unit 403.

At the time of actual measurement of SpO ₂ , the SpO ₂ calculation unit 404 uses the red light absorption coefficient X 2 and the near infrared light absorption coefficient Y 1 stored in the storage unit 403, and the detection result by the photodetector 122. To calculate SpO ₂ . Incidentally, since the calculation of SpO ₂ using an extinction coefficient is a known technique described in Patent Document 1, Non-Patent Document 1, and the like, description thereof is omitted here.

As described above, according to the present embodiment, the correspondence between the value corresponding to the light amount detected by the photodetector 122 and the peak wavelength is stored, and the value corresponding to the light amount detected by the photodetector 122 is set. The first table 401 in which the peak wavelength value corresponding to the value corresponding to the light amount is output as the read address, and the correspondence relationship between the peak wavelength and the extinction coefficient are stored and output from the first table 401. SpO ₂ calculation for calculating SpO ₂ using the second table 402 in which the extinction coefficient corresponding to the peak wavelength is output using the peak wavelength as a read address, and the extinction coefficient and the value detected by the photodetector 122. The wavelength of the light emitting element 121 without measuring the wavelength of the light emitting element 121. The pulse oximeter 10 that can suppress a decrease in SpO ₂ measurement accuracy by key can be realized.

  The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the gist or main features thereof.

  In the above-described embodiment, the pulse oximeter 10 has been described as having the first and second tables 401 and 402. However, the present invention is not limited to this, and as shown in FIG. Two tables 401 and 402 may be combined into one table 501. The table 501 stores the correspondence between the value corresponding to the amount of light detected by the photodetector 122 and the extinction coefficient. From the table 501 (red light table 501a, near infrared light table 501b), a value corresponding to the light amount detected by the photodetector 122 is used as a read address, and an extinction coefficient corresponding to the value corresponding to the light amount is output. Is done. In other words, the tables 401 and 402 in the embodiment derive the extinction coefficient from the detected light amount with the peak wavelength interposed, but the table 501 in FIG. 6 directly derives the extinction coefficient from the detected light amount without interposing the peak wavelength. It has become.

  In the above-described embodiment, the case where the present invention is applied to a pulse oximeter has been described. However, the present invention is not limited to this, and the blood characteristic is measured using an extinction coefficient corresponding to the emission wavelength of the light emitting element. Widely applicable to measuring devices. For example, the present invention can also be applied to a hemoglobin A1c analyzer that analyzes the ratio of hemoglobin in blood bound to glucose non-invasively as described in Patent Document 2. Further, the present invention can be applied to a noninvasive blood sugar level measuring apparatus that measures a glucose concentration in a living body noninvasively as described in Patent Document 3.

  In short, a light-emitting element, a photodetector that receives light of the light-emitting element that has been transmitted or reflected through a measurement site, and a correspondence relationship between a value corresponding to the amount of light detected by the photodetector and a peak wavelength are stored. A blood characteristic calculation unit that calculates a blood characteristic using the table of 1, the second table storing the correspondence between the peak wavelength and the absorption coefficient, and the value detected by the absorption coefficient and the photodetector Thus, it is possible to realize a blood characteristic measuring apparatus capable of suppressing a decrease in blood characteristic measurement accuracy due to variations in the wavelength of the light emitting element without measuring the wavelength of the light emitting element.

  Further, a photodetector that receives the light of the light emitting element that has been transmitted or reflected through the measurement site, a table that stores a correspondence relationship between a value corresponding to the amount of light detected by the photodetector and an extinction coefficient, and the extinction coefficient And a blood characteristic calculation unit for calculating blood characteristics using the values detected by the photodetectors, the wavelength variation of the light emitting element is similarly measured without measuring the wavelength of the light emitting element. The blood characteristic measuring device which can suppress the fall of the measurement accuracy of the blood characteristic by this can be realized.

  Incidentally, various conventional methods can be adopted as a method of calculating blood characteristics by the blood characteristic calculator. For example, blood characteristics may be calculated using scattered light in addition to the extinction coefficient and the value detected by the photodetector. The blood characteristic to be calculated may be the ratio of hemoglobin in blood bound to glucose as in Patent Document 2, or may be the glucose concentration in the living body as in Patent Document 3, or any other value. In short, the configuration using the table of the present invention can be widely applied to devices that measure blood characteristics using an extinction coefficient corresponding to the emission wavelength of the light emitting element.

The present invention is widely applicable to pulse oximeters and blood characteristic measuring devices that measure SpO ₂ and blood characteristics using an extinction coefficient corresponding to the emission wavelength.

DESCRIPTION OF SYMBOLS 10 Pulse oximeter 100 Probe part 121 Light emitting element 122 Photo detector 200 Main body part 214a Arithmetic part 300 Cable 401 1st table 401a, 402a, 501a Red light table 401b, 402b, 501b Near infrared light table 402 2nd table Table 403 Storage unit 404 SpO ₂ calculation unit 501 Table

Claims (10)

A light emitting element;
A photodetector for receiving the light of the light-emitting element transmitted or reflected through the measurement site;
A first table storing a correspondence between a value corresponding to a light amount detected by the photodetector and a peak wavelength;
A second table storing the correspondence between peak wavelength and extinction coefficient;
An SpO ₂ calculation unit for calculating SpO ₂ using the extinction coefficient and the value detected by the photodetector;
A pulse oximeter comprising: From the first table, a value corresponding to the light amount detected by the photodetector is used as a read address, and a peak wavelength value corresponding to the value corresponding to the light amount is output.
From the second table, the peak wavelength output from the first table is used as a read address, and an extinction coefficient corresponding to the peak wavelength is output.
The pulse oximeter according to claim 1. A storage unit for storing the extinction coefficient output from the second table;
Prior to the measurement of SpO ₂ , the storage unit stores extinction coefficients obtained using the light emitting element, the photodetector, and the first and second tables,
The SpO ₂ during the measurement, the SpO ₂ calculator calculates the SpO ₂ using the extinction coefficients stored in the storage unit,
The pulse oximeter according to claim 1 or 2. Each of the first and second tables has a table for red light and a table for near infrared light,
The pulse oximeter according to any one of claims 1 to 3. A light emitting element;
A photodetector for receiving the light of the light-emitting element transmitted or reflected through the measurement site;
A table storing a correspondence relationship between a value corresponding to the amount of light detected by the photodetector and an extinction coefficient;
An SpO ₂ calculation unit for calculating SpO ₂ using the extinction coefficient and the value detected by the photodetector;
A pulse oximeter comprising: From the table, a value corresponding to the light amount detected by the photodetector is used as a read address, and an extinction coefficient corresponding to the value corresponding to the light amount is output.
The pulse oximeter according to claim 5. A storage unit for storing the extinction coefficient output from the table;
Prior to the measurement of SpO ₂ , the storage unit stores an extinction coefficient obtained using the light emitting element, the photodetector, and the table,
The SpO ₂ during the measurement, the SpO ₂ calculator calculates the SpO ₂ using the extinction coefficients stored in the storage unit,
The pulse oximeter according to claim 5 or 6. Each of the tables has a table for red light and a table for near infrared light,
The pulse oximeter according to any one of claims 6 to 7. A light emitting element;
A photodetector for receiving the light of the light-emitting element transmitted or reflected through the measurement site;
A first table storing a correspondence between a value corresponding to a light amount detected by the photodetector and a peak wavelength;
A second table storing the correspondence between peak wavelength and extinction coefficient;
A blood characteristic calculator that calculates blood characteristics using the extinction coefficient and the value detected by the photodetector;
A blood characteristic measuring device comprising: A photodetector for receiving the light of the light-emitting element transmitted or reflected through the measurement site;
A table storing a correspondence relationship between a value corresponding to the amount of light detected by the photodetector and an extinction coefficient;
A blood characteristic calculator that calculates blood characteristics using the extinction coefficient and the value detected by the photodetector;
A blood characteristic measuring device comprising:

Images