JP7432454B2 - Oxygen saturation measuring device - Google Patents

Description

The present invention relates to an oxygen saturation measuring device.

Patent Document 1 discloses an oxygen saturation measurement device that measures oxygen saturation based on two types of pulse wave signals transmitted or reflected through living tissue. This oxygen saturation measuring device employs the following calculation method so that it can accurately measure oxygen saturation even when noise due to the body movement of the test subject is mixed into the pulse wave signal. That is, this oxygen saturation measuring device separates the above two types of pulse wave signals into a plurality of frequency bands, and calculates the attenuation ratio for each separated frequency band. Then, this oxygen saturation measurement device selects a candidate frequency band (for example, a frequency band with the minimum attenuation ratio) based on the obtained attenuation ratio, and calculates the oxygen saturation level from the attenuation ratio in the selected frequency band. Calculate saturation.

JP2007-83021A

However, with this calculation method, it is necessary to calculate the attenuation ratio for all frequency bands and compare the calculated values, which tends to increase the processing load and required storage space, so it is recommended to simplify the configuration. is required.

In order to solve at least one of the above-mentioned problems, the present invention aims to provide a technique that can realize oxygen saturation measurement with a simple configuration while suppressing the influence of noise caused by body movements.

The oxygen saturation measuring device of the present invention includes a light emitting section, a light receiving section, a generating section, a candidate value calculating section, and a determining section. The light emitting unit emits a plurality of lights having different wavelengths toward the living tissue. The light receiving section receives a plurality of lights that have passed through or been reflected from the living tissue. The generation unit generates frequency spectra corresponding to each of the plurality of lights by performing time-frequency conversion to convert an electrical signal based on the light received by the light receiving unit into a frequency signal for each of the plurality of lights. The candidate value calculation unit calculates candidate values of oxygen saturation corresponding to each of the plurality of peaks from the amplitude values at the plurality of peaks identified according to a predetermined peak identification method in all frequency bands or a specific frequency band of the frequency spectrum. Calculate. The determination unit determines the maximum value of the candidate values calculated by the candidate value calculation unit as the oxygen saturation level.

This oxygen saturation measurement device can calculate oxygen saturation based on the amplitude value of the peak in the frequency spectrum. Additionally, the peak in the frequency spectrum may also occur when noise is mixed into the electrical signal due to the body movement of the measurement target, but the oxygen saturation calculated based on the amplitude value of the peak due to noise is a relatively small value. It's easy to become. Therefore, this oxygen saturation measurement device calculates oxygen saturation candidate values corresponding to each of the plurality of peaks from the amplitude values at the plurality of peaks, and determines the maximum value of these candidate values as the oxygen saturation. I try to do that. Therefore, this oxygen saturation measuring device can measure oxygen saturation with high accuracy even when noise is generated due to body movement. Furthermore, after generating the frequency spectrum, this oxygen saturation measurement device calculates only the oxygen saturation candidate values that correspond to the amplitude values of the portion where the peak occurs. This is simplified compared to a configuration in which candidate values for are calculated and compared. Therefore, this oxygen saturation measuring device can measure oxygen saturation while suppressing the influence of noise due to body movement with a simple configuration.

The specific frequency band may have a lower limit frequency of 0.50 Hz or more and an upper limit frequency of 3.33 Hz or less. The candidate value calculation unit may identify a peak in a specific frequency band.

According to this configuration, since peaks are identified in a specific frequency band, processing load and required storage area can be reduced compared to a configuration in which peaks are identified in all frequency bands. Moreover, this oxygen saturation measuring device has a lower limit frequency of 0.50 Hz or higher and an upper limit frequency of 3.33 Hz or lower in the specific frequency band, so it is possible to effectively exclude frequencies that are unnecessary for pulse measurement. . Therefore, this oxygen saturation measuring device can measure oxygen saturation while suppressing the influence of noise due to body movement with an even simpler configuration.

The above peak identification method sequentially calculates the increase width of adjacent amplitude values in the frequency spectrum in the direction where the frequency increases or decreases, and defines the peak when the increase width changes from a positive value to a negative value. It may also be a method of specifying.

According to this configuration, a peak can be identified by simply calculating the rise width of the amplitude value in order and detecting the part where the value changes from a positive value to a negative value, thereby simplifying the processing required to identify the peak. .

The oxygen saturation measurement device may include a communication unit that communicates with an external device. The communication unit may output information indicating the oxygen saturation level determined by the determination unit to an external device.

According to this configuration, the oxygen saturation measured by the oxygen saturation measurement device can be output to an external device.

In addition, in this specification, descriptions using "more than" shall include the lower limit value, and descriptions using "less than" shall include the upper limit value. For example, the description "10 or more" shall include "10", and the description "20 or less" shall include "20".

According to the present invention, measurement of oxygen saturation while suppressing the influence of noise due to body movement can be realized with a simple configuration.

FIG. 1 is a block diagram conceptually illustrating the electrical configuration of the oxygen saturation measuring device according to the first embodiment. FIG. 2 is a flowchart illustrating the flow of oxygen saturation measurement processing performed by the oxygen saturation measurement device of the first embodiment. FIG. 3 is an explanatory diagram showing an example of a waveform of a frequency spectrum. FIG. 4 is a block diagram conceptually illustrating the electrical configuration of the oxygen saturation measuring device according to the second embodiment.

1. First embodiment 1-1. Configuration of Oxygen Saturation Measuring Device The oxygen saturation measuring device 1 shown in FIG. First drive section 10, second drive section 12, selection section 14, amplifier circuit 15, A/D converter 16, bandpass filter 17, demodulation circuit 18, control section 22, storage section 24, display section 26, and operation section 28.

The first light emitting section 2 and the second light emitting section 4 correspond to an example of a light emitting section, and are configured as, for example, a light emitting element such as an LED, and emit light having different wavelengths toward the living tissue B. For example, the first light emitting section 2 emits red light, and the second light emitting section 4 emits infrared light.

The light receiving section 6 is configured as a photodiode, for example, and receives the light emitted from the first light emitting section 2 and the second light emitting section 4 and transmitted through the biological tissue B (for example, a finger). The light received by the light receiving section 6 is converted into an electric signal according to the intensity of the light by the light receiving section 6, amplified by the amplifier circuit 15, converted from an analog signal to a digital signal by the A/D converter 16, and then passed through a bandpass filter. The signal is band-limited by 17, demodulated by demodulation circuit 18, and input to control section 22.

The first driving section 10 is configured as, for example, an LED driving circuit, and drives the first light emitting section 2 so that the first light emitting section 2 emits light. The second driving section 12 is configured as, for example, an LED driving circuit, and drives the second light emitting section 4 so that the second light emitting section 4 emits light.

The selection unit 14 is configured, for example, as a timing generation circuit, and alternately outputs timing signals to the first drive unit 10 and the second drive unit 12 in accordance with instructions from the control unit 22. Thereby, the selection section 14 causes the first light emitting section 2 and the second light emitting section 4 to emit light alternately. The selection unit 14 also outputs the timing signal to the demodulation circuit 18. Thereby, the demodulation circuit 18 can specify the light emission timing of each of the first light emitting section 2 and the second light emitting section 4.

The bandpass filter 17 is configured as a filter circuit such as a digital filter, and removes frequency components outside a specific frequency band. The specific frequency band is preferably a band wider than a frequency corresponding to a general human pulse (0.66 Hz or more and 2.50 Hz or less) from the viewpoint of excluding frequencies other than pulses. For example, the lower limit frequency of the specific frequency band is preferably 0.50 Hz or more, more preferably 0.60 Hz or more. Further, the upper limit frequency of the specific frequency band is preferably 3.33 Hz or less, more preferably 3.00 Hz or less.

The demodulation circuit 18 demodulates the input electrical signal. The demodulation circuit 18 determines whether the electrical signal input from the light receiving section 6 is based on the light from the first light emitting section 2 or the second light emitting section 4 based on the timing signal input from the selection section 14 . Determine whether it is an electrical signal based on light. Then, the demodulation circuit 18 individually demodulates the electrical signal based on the light from the first light emitting section 2 and the electrical signal based on the light from the second light emitting section 4.

The control unit 22 corresponds to an example of a generation unit, a candidate value calculation unit, and a determination unit, and is configured as, for example, a CPU. The storage unit 24 is configured as a memory such as ROM or RAM, for example. The display unit 26 is configured as a display device such as a liquid crystal display, and is used to display the measurement results of oxygen saturation level and the like. The operation unit 28 is configured as a button, for example, and is used for setting processing in the control unit 22 and the like.

The control section 22 can control the operation of the selection section 14 to cause the first light emitting section 2 and the second light emitting section 4 to emit light at a predetermined timing. The light emitted by the first light emitting section 2 and the second light emitting section 4 passes through the living tissue B, is received by the light receiving section 6, and is converted into an electrical signal, which is then sent to the amplifier circuit 15, the A/D converter 16, and the bandpass filter. 17 and the demodulation circuit 18 to the control unit 22 .

The control unit 22 performs time-frequency conversion to convert an electrical signal based on the light received by the light receiving unit 6 into a frequency signal for each of the plurality of lights received by the light receiving unit 6, thereby converting the frequency corresponding to each of the plurality of lights. Generate a spectrum. Specifically, the control unit 22 generates the first frequency spectrum FSR by performing time-frequency conversion to convert an electrical signal based on the light emitted by the first light emitting unit 2 into a frequency signal. Further, the control unit 22 generates the second frequency spectrum FSIR by performing time-frequency conversion to convert an electrical signal based on the light emitted by the second light emitting unit 4 into a frequency signal. The control unit 22 performs, for example, FFT (Fast Fourier Transform) as time-frequency transformation.

The control unit 22 identifies peaks in all frequency bands or in a specific frequency band of the frequency spectrum according to a predetermined peak identifying method. In this embodiment, since the band is limited to a specific frequency band by the bandpass filter 17, the entire frequency band of the frequency spectrum and the specific frequency band are synonymous. The control unit 22 identifies a peak in one of the two frequency spectra (for example, the second frequency spectrum FSIR).

In the peak identification method, for example, in a frequency spectrum, the increase width of adjacent amplitude values is calculated in order in the direction where the frequency increases or decreases, and the peak is determined when the increase width changes from a positive value to a negative value. This is a method for specifying.

However, peaks that meet the exclusion conditions may be excluded from the identified peaks. The exclusion condition may be, for example, "the peak frequency is outside a specific frequency band (for example, 0.50 Hz or more and 3.33 Hz or less)".

Furthermore, the exclusion condition may be "in a case where a plurality of peaks are identified, the peak has a frequency corresponding to a harmonic of the frequency of other peaks". Note that the harmonics do not need to be exactly an integral multiple of the frequency of other peaks, and should include an error range. For example, what satisfies the following formula (1) may be the second harmonic for the frequency FX, and what satisfies the following formula (2) may be the third harmonic with respect to the frequency FX.
FX x 2 x (1 - α) <"2ndharmonic"< FX x 2 x (1 + α) ... Formula (1)
FX×3×(1-α)<“3rd harmonic”<FX×3×(1+α)...Formula (2)
α is a predetermined value, for example 0.05.

In addition, the exclusion condition is ``When peaks exceeding the specified number are identified, peaks whose amplitude value (for example, the amplitude value in the second frequency spectrum FSIR) is less than the upper specified number (for example, 3) It may be “to be”.

In addition, for example, in the case of a device with a pulse intensity PI (min) of about 0.1%, the exclusion condition is ``a peak whose amplitude value (for example, the amplitude value in the second frequency spectrum FSIR) is less than a predetermined lower limit value. It may be "something".

The control unit 22 extracts the amplitude value of each peak identified according to the peak identification method. More specifically, the control unit 22 identifies the frequency of each peak identified according to the peak identification method, and extracts the amplitude value at each peak frequency in each of the two frequency spectra.

The control unit 22 uses the extracted amplitude values to calculate candidate values of oxygen saturation corresponding to each of the peaks. Oxygen saturation is calculated, for example, by the following equation (3).
Oxygen saturation = A x R ² + B x R + C ... Formula (3)
A, B, and C are values determined by the type of oxygen saturation measuring device. For example, A=-12, B=-12, and C=170, and the following equation (3)' may be used.
Oxygen saturation = -12 x R ² -12 x R + 170...Formula (3)'
R is calculated by the following equation (4).
R=(Red(Fn)/Red(F0))/(IR(Fn)/IR(F0))...Formula (4)
Red (Fn) is the amplitude value of the peak frequency Fn in the first frequency spectrum FSR. Red (F0) is the amplitude value when the frequency is 0 Hz in the first frequency spectrum FSR. IR(Fn) is the amplitude value of the peak frequency Fn in the second frequency spectrum FSIR. IR (F0) is an amplitude value at a frequency of 0 Hz in the second frequency spectrum FSIR.
In other words, equation (3) is a quadratic function with R as a variable.
The control unit 22 calculates a candidate value of oxygen saturation by substituting the extracted amplitude value into the above equation (3) for each peak frequency.

The control unit 22 identifies the maximum value from among the candidate oxygen saturation values according to a predetermined maximum value identification method. The maximum value identification method, for example, extracts the maximum value and the value whose difference from the maximum value is within a predetermined error range as the maximum value group, and if only one value is extracted in the maximum value group, it is used as the maximum value. If two or more are extracted, the candidate value calculated based on the maximum amplitude value (for example, the maximum amplitude value in the second frequency spectrum FSIR) is specified as the maximum value. be.

The control unit 22 determines the maximum value specified according to the maximum value identification method as the oxygen saturation level. The control unit 22 causes the display unit 26 to display information indicating the determined oxygen saturation level.

1-2. Oxygen Saturation Measurement Process The oxygen saturation measurement process performed by the control unit 22 will be described with reference to the flowchart of FIG. The oxygen saturation measurement process is a process for measuring the oxygen saturation of the biological tissue B. The control unit 22 starts the oxygen saturation measurement process when a predetermined start condition is satisfied. The start condition may be, for example, "the start operation is performed using the operation unit 28 while the power is on", or it may be another condition.

When the oxygen saturation measurement process is started, the control unit 22 performs light emission control to cause the first light emitting unit 2 and the second light emitting unit 4 to emit light alternately (S11). The control unit 22 instructs the selection unit 14 to cause the first light emission unit 2 and the second light emission unit 4 to emit light alternately, so that the selection unit 14 causes the first drive unit 10 and the second drive unit 12 to alternately operate. The first light emitting section 2 and the second light emitting section 4 are driven to emit light alternately. The light emitted by the first light emitting section 2 and the second light emitting section 4 passes through the living tissue B and is received by the light receiving section 6. The light received by the light receiving section 6 is converted into an electric signal according to the intensity of the light by the light receiving section 6, amplified by the amplifier circuit 15, converted from an analog signal to a digital signal by the A/D converter 16, and then passed through a bandpass filter. The signal is band-limited by 17, demodulated for each light emitting source by demodulation circuit 18, and input to control section 22.

The control unit 22 generates a frequency spectrum as shown in FIG. 3 by subjecting the input digital signal to FFT (time-frequency transformation) (S12). That is, the control unit 22 generates the first frequency spectrum FSR by performing FFT on the electric signal based on the light emitted by the first light emitting unit 2. Further, the control unit 22 generates the second frequency spectrum FSIR by performing FFT on the electrical signal based on the light emitted by the second light emitting unit 4.

The control unit 22 identifies a peak in the frequency spectrum (for example, second frequency spectrum FSIR) generated in S12 (S13). Moreover, peaks corresponding to the exclusion conditions are excluded from the identified peaks. As a result, in the example shown in FIG. 3, three peaks, peaks P1, P2, and P3, are identified.

After identifying the peaks, the control unit 22 extracts the amplitude values of the peaks P1, P2, and P3 for each of the first frequency spectrum FSR and the second frequency spectrum FSIR (S14). Specifically, the control unit 22 specifies frequencies F1, F2, and F3 of peaks P1, P2, and P3 in the second frequency spectrum FSIR. Then, the control unit 22 extracts amplitude values FR1, FR2, FR3 at frequencies F1, F2, F3 in the first frequency spectrum FSR, and extracts amplitude values FIR1, FIR2 at frequencies F1, F2, F3 in the second frequency spectrum FSIR. , FIR3 is extracted.

After extracting the amplitude values of the peaks, the control unit 22 uses the extracted amplitude values to calculate candidate values of oxygen saturation corresponding to each of the peaks (S15). Specifically, the control unit 22 calculates R by substituting the amplitude value FR1 into Red(Fn) and the amplitude value FIR1 into IR(Fn) in the above equation (4), and converts this R into the equation Substituting into (3), a candidate value C1 of oxygen saturation is calculated. Further, the control unit 22 calculates R by substituting the amplitude value FR2 into Red(Fn) and the amplitude value FIR2 into IR(Fn) in the above equation (4), and calculates R by using the equation (3). The candidate value C2 of oxygen saturation is calculated by substituting C2 into C2. Furthermore, the control unit 22 calculates R by substituting the amplitude value FR3 into Red(Fn) and the amplitude value FIR3 into IR(Fn) in the above equation (4), and calculates R by using the equation (3). A candidate value C3 of oxygen saturation is calculated by substituting C3 into C3.

After calculating the candidate value of oxygen saturation, the control unit 22 specifies the maximum value from among the candidate values C1, C2, and C3 according to the maximum value specifying method described above (S16). The control unit 22 determines the maximum value specified in S16 as the oxygen saturation level (S17). As a result of extensive studies, the inventors discovered that when oxygen saturation is calculated based on peaks due to body movement noise, the oxygen saturation becomes smaller than the actual value. Therefore, by identifying the maximum value from among the candidate values and determining it as the oxygen saturation, it is possible to exclude the oxygen saturation based on the peak due to body movement noise and obtain the true oxygen saturation. After determining the oxygen saturation, the control unit 22 causes the display unit 26 to display information indicating the oxygen saturation (for example, a numerical value indicating the oxygen saturation).

1-3. Effects The oxygen saturation measuring device 1 described above produces, for example, the following effects.
The oxygen saturation measuring device 1 can calculate oxygen saturation based on the amplitude value of the peak in the frequency spectrum. In addition, peaks in the frequency spectrum can also occur when noise is mixed into the electrical signal due to the body movement of the measurement target, but the oxygen saturation calculated based on the amplitude value of the peak due to noise tends to be a relatively small value. . Therefore, this oxygen saturation measuring device 1 calculates oxygen saturation candidate values corresponding to each of the plurality of peaks from the amplitude values at the plurality of peaks, and calculates the maximum value among them that is specified according to the maximum value identification method. It is determined as oxygen saturation. Therefore, this oxygen saturation measurement device 1 can measure oxygen saturation with high accuracy even when noise is generated due to body movement. Moreover, after generating the frequency spectrum, this oxygen saturation measuring device 1 calculates only the oxygen saturation candidate values corresponding to the amplitude values of the portion where the peak occurs. This is simplified compared to a configuration in which candidate values for degrees are calculated and compared. Therefore, the oxygen saturation measuring device 1 can measure oxygen saturation while suppressing the influence of noise due to body movement with a simple configuration.

Furthermore, since this oxygen saturation measurement device 1 identifies peaks in a specific frequency band, it is possible to reduce processing load and required storage space compared to a configuration that identifies peaks in all frequency bands. . Moreover, this oxygen saturation measurement device 1 has a lower limit frequency of 0.50 Hz or more and an upper limit frequency of 3.33 Hz or less in the specific frequency band, so it is possible to effectively exclude frequencies unnecessary for pulse measurement. can. Therefore, this oxygen saturation measurement device 1 can realize measurement of oxygen saturation while suppressing the influence of noise due to body movement with an even simpler configuration.

Furthermore, according to this oxygen saturation measuring device 1, a peak can be identified simply by sequentially calculating the rise width of the amplitude value and detecting the part where the value changes from a positive value to a negative value. The processing required for this can be simplified.

2. Second Embodiment The oxygen saturation measurement device 201 of the second embodiment differs from the oxygen saturation measurement device 1 of the first embodiment in that it can communicate with an external device 250 having a display unit 252, and the other configurations are as follows. It has the same configuration as the oxygen saturation measuring device 1 of the first embodiment. Note that the same configurations as in the first embodiment will be described using the same reference numerals.

The oxygen saturation measuring device 201 of the second embodiment further includes a communication section 30. The communication unit 30 is configured as a communication interface including a communication module such as a LAN chip, for example. The control unit 22 can communicate with the external device 250 via the communication unit 30 by wireless communication such as Bluetooth (registered trademark) communication. For example, after determining the oxygen saturation in the oxygen saturation measurement process described in the first embodiment, the oxygen saturation measuring device 201 transmits information indicating the determined oxygen saturation (for example, a numerical value indicating the oxygen saturation) to an external device. Output toward 250.

The external device 250 is configured as a terminal device such as a smartphone, and includes a display section 252 and a communication section 254. The display unit 252 is configured as a display device such as a liquid crystal display, for example. The communication unit 254 is configured as a communication interface including a communication module such as a LAN chip, and wirelessly communicates with the communication unit 30 of the oxygen saturation measuring device 201. When the external device 250 acquires the information indicating the oxygen saturation from the oxygen saturation measuring device 201, the external device 250 causes the display unit 252 to display information indicating the oxygen saturation (for example, a numerical value indicating the oxygen saturation).

According to this oxygen saturation measurement device 201, it is possible to display the oxygen saturation measured by the oxygen saturation measurement device 201 on the display section 252 of the external device 250.

<Other embodiments>
The present invention is not limited to the embodiments described above and illustrated in the drawings; for example, the following embodiments are also included within the technical scope of the present invention. Furthermore, various features of the embodiments described above and the embodiments described below may be combined in any combination that does not contradict each other.

In the first embodiment and the second embodiment, the light receiving section 6 is configured to receive light emitted from the first light emitting section 2 and the second light emitting section 4 and transmitted through the biological tissue B. Also, the light emitted from the second light emitting section 4 and reflected from the living tissue B may be received.

In the first embodiment and the second embodiment, the bandpass filter is a digital filter, but it may be arranged as an analog filter closer to the light receiving section 6 than the A/D converter 16.

In the first embodiment and the second embodiment, the oxygen saturation measuring device 1, 201 has a configuration in which a bandpass filter is provided, but the configuration may be such that the bandpass filter is not provided. When configured without a bandpass filter, the oxygen saturation measuring device 1, 201 may be configured to identify peaks in all frequency bands of the frequency spectrum, or may be configured to identify peaks in a specific frequency band. .

In the first embodiment and the second embodiment, the formula for calculating the oxygen saturation level is formula (3), but another formula may be used. For example, if the formula calculates the oxygen saturation based on the amplitude value of the peak (the amplitude value of the first frequency spectrum FSR and the amplitude value of the second frequency spectrum FSIR), another calculation formula known in the art (for example, The calculation formula disclosed in Publication No. 7-327964) may be employed. In addition, in the first and second embodiments, the formula for calculating oxygen saturation is a quadratic function as shown in formula (3) above, but it is not limited to a quadratic function, and may also be a linear function, for example. good. Even if a different calculation formula is adopted, candidate values for oxygen saturation are calculated based on the peak amplitude values (amplitude values of the first frequency spectrum FSR and amplitude values of the second frequency spectrum FSIR), and these By determining the maximum value among these as the oxygen saturation, the true oxygen saturation can be measured.

In the first and second embodiments, from the viewpoint of stability, the peak is identified from the second frequency spectrum FSIR in which the absorbance change of oxyhemoglobin is relatively small, but the peak is identified from the first frequency spectrum FSR. It is also possible to have a configuration in which

In the second embodiment, the oxygen saturation measuring device 201 and the external device 250 communicate wirelessly, but they may also communicate via wire.

It should be noted that the embodiments disclosed herein are illustrative in all respects and should not be considered restrictive. The scope of the present invention is not limited to the embodiments disclosed herein, and includes all modifications within the scope indicated by the claims or within the scope equivalent to the claims. is intended.

1,201...Oxygen saturation measuring device 2...First light emitting part (light emitting part)
4...Second light emitting section (light emitting section)
6... Light receiving unit 22... Control unit (generation unit, candidate value calculation unit, determination unit)
30...Communication unit 250...External device 252...Display unit B...Biological tissue FSR...First frequency spectrum (frequency spectrum)
FEIR…Second frequency spectrum (frequency spectrum)
P1, P2, P3...peak F1, F2, F3...peak frequency

Claims (3)

a light emitting part that emits multiple lights of different wavelengths toward living tissue;
a light receiving unit that receives the plurality of lights transmitted or reflected by the living tissue;
a generation unit that generates frequency spectra corresponding to each of the plurality of lights by performing time-frequency conversion to convert an electrical signal based on the light received by the light receiving unit into a frequency signal for each of the plurality of lights;
Candidate values for calculating oxygen saturation candidate values corresponding to each of the plurality of peaks from amplitude values at a plurality of peaks identified according to a predetermined peak identification method in all frequency bands or a specific frequency band of the frequency spectrum. A calculation section,
and a determination unit that determines the maximum value of the candidate values calculated by the candidate value calculation unit as the oxygen saturation level ,
The peak identification method sequentially calculates the increase width of the adjacent amplitude values in the frequency spectrum in the direction where the frequency increases or decreases, and when the increase width changes from a positive value to a negative value. is a method of identifying the peak as the peak,
The candidate value calculation unit calculates R from the following equation (4) using the amplitude value of each of the peaks identified according to the peak identification method, and substitutes each calculated R into equation (3). An oxygen saturation measurement device that calculates the candidate value of oxygen saturation.
Oxygen saturation = A x R ² + B x R + C ... Formula (3)
R=(Red(Fn)/Red(F0))/(IR(Fn)/IR(F0))...Formula (4)
A, B, and C are values determined by the type of oxygen saturation measuring device.
Red (Fn) is the amplitude value of the peak frequency Fn in the first frequency spectrum FSR.
Red (F0) is the amplitude value when the frequency is 0 Hz in the first frequency spectrum FSR.
IR(Fn) is the amplitude value of the peak frequency Fn in the second frequency spectrum FSIR.
IR (F0) is an amplitude value at a frequency of 0 Hz in the second frequency spectrum FSIR. The specific frequency band is a frequency band with a lower limit frequency of 0.50 Hz or more and an upper limit frequency of 3.33 Hz or less,
The oxygen saturation measuring device according to claim 1, wherein the candidate value calculation unit specifies the peak in the specific frequency band. Equipped with a communication section that communicates with external devices,
The oxygen saturation measurement device according to claim 1 or 2 , wherein the communication unit outputs information indicating the oxygen saturation determined by the determination unit to the external device .

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