Blood glucose level measuring device and blood glucose level measuring method

Abstract

To provide a blood glucose level measuring device and a blood glucose level measuring method capable of accurately measuring a blood glucose level of a living body.SOLUTION: A blood glucose level measuring device 1 includes: a light output unit 3 that outputs measurement light L to a living body 6; a light detection unit 4 that detects the measurement light L transmitted through the living body 6; a temporal phase difference calculation unit that calculates a temporal phase difference between an oxygenated hemoglobin waveform related to an oxygenated hemoglobin concentration of blood of the living body 6 and a deoxygenated hemoglobin waveform related to a deoxygenated hemoglobin concentration of the blood of the living body 6, based on a detection result of the light detection unit 4; a blood glucose level calculation unit that calculates a blood glucose level of the living body 6 based on the temporal phase difference; and a reliability estimation unit that estimates the reliability of the temporal phase difference. The reliability estimation unit estimates that the reliability of the temporal phase difference is lower as an SN ratio of the detection result of the light detection unit 4 is smaller.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a blood glucose level measuring device and a blood glucose level measuring method. [Background technology]

[0002] Known technology for measuring blood oxygen levels in living organisms includes, for example, the device described in Patent Document 1. The device described in Patent Document 1 prevents a decrease in the measurement accuracy of blood oxygen levels due to noise by appropriately setting the wavelengths of light emitted from multiple light sources. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-2167 Summary of the Invention [Problem to be solved by the invention]

[0004] However, noise can also affect the measurement accuracy of blood glucose level measuring devices, and there is a demand for improved blood glucose level measurement accuracy.

[0005] An object of the present invention is to provide a blood glucose level measuring device and a blood glucose level measuring method that are capable of measuring the blood glucose level of a living body with high accuracy. [Means for solving the problem]

[0006] The blood glucose measuring device of the present invention is [1] "a blood glucose measuring device for measuring a blood glucose level of a living organism, comprising: a light output unit that outputs light to the living organism; a light detection unit that detects the light output by the light output unit and transmitted through the living organism; a temporal phase difference calculation unit that calculates a temporal phase difference between an oxygenated hemoglobin waveform related to an oxygenated hemoglobin concentration in the blood of the living organism and a deoxygenated hemoglobin waveform related to a deoxygenated hemoglobin concentration in the blood of the living organism based on a detection result of the light detection unit; a blood glucose level calculation unit that calculates the blood glucose level of the living organism based on the temporal phase difference calculated by the temporal phase difference calculation unit; and a reliability estimation unit that estimates the reliability of the temporal phase difference calculated by the temporal phase difference calculation unit, wherein the reliability estimation unit estimates that the smaller the signal-to-noise ratio of the detection result of the light detection unit, the lower the reliability of the temporal phase difference."

[0007] In the blood glucose measuring device described in [1] above, the blood glucose level calculation unit calculates the blood glucose level of the living body based on the temporal phase difference between an oxygenated hemoglobin waveform relating to the oxygenated hemoglobin concentration in the blood of the living body and a deoxygenated hemoglobin waveform relating to the deoxygenated hemoglobin concentration in the blood of the living body. This allows the blood glucose level of the living body to be measured appropriately. Furthermore, the reliability estimation unit estimates that the reliability of the temporal phase difference is lower the smaller the signal-to-noise ratio of the detection result of the light detection unit. This makes it possible to calculate the blood glucose level taking the reliability of the temporal phase difference into consideration. Therefore, this blood glucose measuring device allows the blood glucose level of the living body to be measured accurately.

[0008] The blood glucose level measuring device of the present invention may be [2] "the blood glucose level measuring device according to the above [1], wherein the temporal phase difference calculating unit calculates a plurality of temporal phase differences, each of which is the temporal phase difference; the blood glucose level calculating unit calculates a plurality of blood glucose levels, each of which is the blood glucose level, based on the plurality of temporal phase differences; and calculates the sum of a sequence weighted for each of the plurality of blood glucose levels as a representative blood glucose level of the living body; the reliability estimating unit estimates the reliability of each of the plurality of temporal phase differences; and the blood glucose level calculating unit reduces the weight as the reliability of each of the plurality of temporal phase differences decreases." This allows weighting to be performed according to the reliability of the temporal phase differences, thereby enabling accurate measurement of the blood glucose level of the living body.

[0009] The blood glucose measuring device of the present invention may be [3] "the blood glucose measuring device according to the above [1] or [2], wherein the reliability estimation unit estimates that the temporal phase difference is highly reliable when the S / N ratio is greater than a predetermined threshold, and estimates that the temporal phase difference is unreliable when the S / N ratio is equal to or less than the threshold, and the threshold is determined based on the correlation between the error of the temporal phase difference and the S / N ratio and the allowable value for the error of the temporal phase difference." This allows the reliability of the temporal phase difference to be estimated efficiently.

[0010] The blood glucose measuring device of the present invention may be [4] "the blood glucose measuring device according to any one of the above [1] to [3], wherein the reliability estimating unit calculates the SN ratio based on a spectrum after fast Fourier transform of the detection result of the light detecting unit." This allows the SN ratio to be calculated with high accuracy.

[0011] The blood glucose measuring device of the present invention may be [5] "the blood glucose measuring device according to the above [4], wherein the reliability estimating unit sets the period of the fast Fourier transform to an integer multiple of both the respiratory cycle and the cardiac cycle of the living body." This can improve the accuracy of the fast Fourier transform.

[0012] The blood glucose measurement method of the present invention is [6] "a blood glucose measurement method for measuring a blood glucose level of a living organism, comprising: a temporal phase difference calculation step for calculating a temporal phase difference between an oxygenated hemoglobin waveform relating to an oxygenated hemoglobin concentration in the blood of the living organism and a deoxygenated hemoglobin waveform relating to a deoxygenated hemoglobin concentration in the blood of the living organism based on a detection result of light transmitted through the living organism; a blood glucose level calculation step for calculating the blood glucose level of the living organism based on the temporal phase difference calculated in the temporal phase difference calculation step; and a reliability estimation step for estimating the reliability of the temporal phase difference calculated in the temporal phase difference calculation step, wherein in the reliability estimation step, it is estimated that the smaller the SN ratio of the light detection result, the lower the reliability of the temporal phase difference."

[0013] According to the blood glucose level measuring method described in [6] above, it is possible to measure the blood glucose level of a living body with high accuracy, similar to the blood glucose level measuring device described above.

[0014] The blood glucose level measuring method of the present invention may be [7] "the blood glucose level measuring method according to the above [6], further comprising a light outputting step of outputting the light to the living body, and a light detecting step of detecting the light outputted in the light outputting step and transmitted through the living body." This makes it possible to measure the blood glucose level of a living body with high accuracy, similar to the blood glucose level measuring device described above. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a blood glucose level measuring device and a blood glucose level measuring method that are capable of measuring the blood glucose level of a living body with high accuracy. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a conceptual diagram of a blood glucose level measuring device according to an embodiment. [Figure 2] 2 shows the detection results of the light detection unit shown in FIG. [Figure 3] FIG. 2 is a block diagram showing a functional configuration of the ECU shown in FIG. [Figure 4] 3 shows an oxygenated hemoglobin waveform and a deoxygenated hemoglobin waveform calculated based on the detection results shown in FIG. 2. [Figure 5] FIG. 5 is a schematic diagram of the oxygenated hemoglobin waveform and the deoxygenated hemoglobin waveform shown in FIG. 4. [Figure 6] FIG. 5 is a schematic diagram of the oxygenated hemoglobin waveform and the deoxygenated hemoglobin waveform shown in FIG. 4. [Figure 7] 5 shows spectra after fast Fourier transform of the oxygenated hemoglobin waveform and the deoxygenated hemoglobin waveform shown in FIG. 4. [Figure 8] 10 is a graph showing the correlation between the error in the temporal phase difference and the SN ratio. [Figure 9] FIG. 8 is a schematic diagram showing the cycle of the fast Fourier transform used to obtain the spectrum shown in FIG. 7. [Figure 10] 1 is a flowchart showing steps of a blood glucose level measurement method according to one embodiment. [Figure 11] FIG. 10 is a schematic diagram showing a period of a fast Fourier transform according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be omitted.

[0018] 1 is a cross-sectional view of a blood glucose level measuring device and a living body according to this embodiment. Fig. 1 is merely a conceptual diagram for explaining the function of the blood glucose level measuring device 1, and does not necessarily show an actual cross-section of the blood glucose level measuring device 1.

[0019] The blood glucose level measuring device 1 shown in Fig. 1 is, for example, a wearable device, a smartphone, or a pulse oximeter. Examples of wearable devices include a smart watch and a smart ring. In this embodiment, the blood glucose level measuring device 1 is a smart watch that has a function of measuring the blood glucose level of a living organism 6. The living organism 6 has a superficial tissue 61 and an internal tissue 62 that is located more internally than the superficial tissue 61. The surface 61a of the superficial tissue 61 is the surface of the skin of the living organism 6. The living organism 6 is, for example, a human body.

[0020] The blood glucose measuring device 1 measures the blood glucose level of a living organism 6. The blood glucose measuring device 1 comprises a main body 2, a light output unit 3, a light detection unit 4, and an ECU (Electronic Control Unit) 5. The main body 2 has a front face 2a and a back face 2b facing the opposite side to the front face 2a. The front face 2a functions as a display screen (display) that displays various information about the blood glucose measuring device 1. The blood glucose measuring device 1 is attached to the living organism 6 so that the back face 2b comes into contact with the skin of the living organism 6.

[0021] The light output unit 3 is provided in the main body 2. The light output surface of the light output unit 3 is exposed from the back surface 2b of the main body 2. The light output unit 3 has a light source that outputs measurement light L to the living body 6. The light source is, for example, a light emitting diode (LED), a laser diode (LD), or a superluminescent diode (SLD). The measurement light L is emitted from the back surface 2b. The measurement light L emitted from the light output unit 3 propagates inside the living body 6, and then is emitted from the living body 6 again. The light output unit 3 is controlled by the ECU 5.

[0022] The wavelength range of the measurement light L is, for example, from the red wavelength region of visible light to the near-infrared region (670 nm to 2500 nm). That is, the light output unit 3 outputs measurement light L included in the range from the red wavelength region of visible light to the near-infrared region. The light output unit 3 outputs measurement light L, for example, with different wavelengths. In this case, the light output unit 3 has multiple (for example, three) light sources. The first light source outputs measurement light L having a wavelength of, for example, 735 nm, the second light source outputs measurement light L having a wavelength of, for example, 810 nm, and the third light source outputs measurement light L having a wavelength of, for example, 850 nm. Note that the light output unit 3 may have a single light source that outputs probe light (for example, white light) containing mutually different wavelength components.

[0023] The light detection unit 4 is provided in the main body 2. The light detection unit 4 is separated from the light output unit 3. The light detection surface of the light detection unit 4 is exposed from the rear surface 2b of the main body 2. The light detection unit 4 has a light detection element that detects measurement light (transmitted light) L output from the light output unit 3 and transmitted through the living body 6. The light detection element is, for example, a photodiode (PD). The light detection unit 4 also has a preamplifier that amplifies the photocurrent output from the light detection element, and an A / D conversion circuit that converts the signal amplified by the preamplifier into a digital signal. The light detection unit 4 may have a CCD image sensor or a CMOS image sensor. The light detection unit 4 transmits a signal related to the intensity of the measurement light L to the ECU 5.

[0024] 2, the light detection unit 4 detects at least first data D1 and second data D2. The first data D1 is, for example, a change over time in the intensity of transmitted light when measurement light L having a first wavelength passes through the living body 6 and enters the light detection unit 4, and the second data D2 is, for example, a change over time in the intensity of transmitted light when measurement light L having a second wavelength passes through the living body 6 and enters the light detection unit 4. Each of the first data D1 and the second data D2 periodically fluctuates over time. Note that the respective periods of the first data D1 and the second data D2 approximately coincide with the cardiac cycle of the living body 6.

[0025] The ECU 5 is provided in the main body 2. The ECU 5 is an electronic control unit having a CPU (Central Processing Unit) and a storage unit such as a ROM (Read Only Memory) or a RAM (Random Access Memory). In the ECU 5, for example, a program stored in the storage unit is executed by the CPU. The ECU 5 calculates the blood glucose level of the living body 6, the pulse rate of the living body 6, the oxygen saturation concentration of the living body 6, etc. based on the signal transmitted from the light detection unit 4 (the detection result of the light detection unit 4). FIG. 3 is a block diagram showing the functional configuration of the ECU 5. As shown in FIG. 3, the ECU 5 includes a time phase difference calculation unit 51, a reliability estimation unit 52, and a blood glucose level calculation unit 53.

[0026] 4, the temporal phase difference calculation unit 51 calculates an oxygenated hemoglobin waveform P1 and a deoxygenated hemoglobin waveform P2 based on the detection results of the light detection unit 4. The oxygenated hemoglobin waveform P1 is data related to the oxygenated hemoglobin (OHb) concentration in the blood of the living body 6, and the deoxygenated hemoglobin waveform P2 is data related to the deoxygenated hemoglobin (HHb) concentration in the blood of the living body 6. The temporal phase difference calculation unit 51 calculates the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2 by performing spectroscopic calculation processing based on, for example, the Modified Beer-Lambert (MBL) method on the first data D1 and the second data D2.

[0027] Specifically, the temporal phase difference calculation unit 51 calculates the temporal relative change in oxygenated hemoglobin (ΔO2Hb) and the temporal relative change in deoxygenated hemoglobin (ΔHHb) based on the difference between the intensity of the first data D1 at the first time and the intensity of the first data D1 at the second time (the temporal change in the intensity of the first data D1), the difference between the intensity of the second data D2 at the first time and the intensity of the second data D2 at the second time (the temporal change in the intensity of the second data D2), the respective absorption coefficients of oxygenated hemoglobin and deoxygenated hemoglobin for the first data D1, and the respective absorption coefficients of O2Hb and HHb for the second data D2. The temporal phase difference calculation unit 51 continues to calculate ΔO2Hb and ΔHHb at predetermined time intervals (for example, approximately 16 milliseconds). The change in ΔO2Hb over time is the oxygenated hemoglobin waveform P1 shown in Figure 4, and the change in ΔHHb over time is the deoxygenated hemoglobin waveform P2 shown in Figure 4. The concentration index on the vertical axis in Figure 4 is, for example, a volume concentration index (concentration × optical path length).

[0028] The temporal phase difference calculation unit 51 calculates the temporal phase difference (hereinafter simply referred to as "temporal phase difference") between the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2. FIG. 5 is a schematic diagram of the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2 shown in FIG. 4. The temporal phase difference calculation unit 51 calculates the time difference between a first characteristic point C1 of the oxygenated hemoglobin waveform P1 and a second characteristic point C2 of the deoxygenated hemoglobin waveform P2 as the temporal phase difference Δθ. In this embodiment, the first characteristic point C1 is a bottom point of the oxygenated hemoglobin waveform P1, and the second characteristic point C2 is a bottom point of the deoxygenated hemoglobin waveform P2. The first characteristic point C1 may be, for example, a peak point or a notch point of the oxygenated hemoglobin waveform P1, and the second characteristic point C2 may be, for example, a peak point or a notch point of the deoxygenated hemoglobin waveform P2. In this embodiment, the methods disclosed in Japanese Patent No. 6846152, for example, are used to calculate the temporal phase difference Δθ.

[0029] 6, the detection result of the light detection unit 4 may contain noise, and as a result, at least one of the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2 (the deoxygenated hemoglobin waveform P2 in FIG. 6) may also contain noise. In such a case, for example, extraction of the second feature point C2 of the noisy deoxygenated hemoglobin waveform P2 may become unstable, which may result in a decrease in the accuracy of calculation of the temporal phase difference Δθ. This tendency is particularly noticeable when the amplitude of the noise is at the same level as the temporal phase difference Δθ.

[0030] The reliability estimation unit 52 estimates the reliability of the temporal phase difference Δθ calculated by the temporal phase difference calculation unit 51. The reliability estimation unit 52 estimates that the reliability of the temporal phase difference Δθ increases as the S / N ratio of the detection result of the photodetection unit 4 increases (as the noise level of the detection result of the photodetection unit 4 decreases). The reliability estimation unit 52 estimates that the reliability of the temporal phase difference Δθ decreases as the S / N ratio of the detection result of the photodetection unit 4 decreases (as the noise level of the detection result of the photodetection unit 4 increases).

[0031] The reliability estimation unit 52 calculates the signal-to-noise ratio of the detection result of the photodetector 4 based on the spectrum after fast Fourier transform (FFT) of the detection result of the photodetector 4. The fast Fourier transform of the detection result of the photodetector 4 may be either a direct fast Fourier transform applied to the detection result of the photodetector 4 or an indirect fast Fourier transform applied to parameters calculated from the detection result of the photodetector 4. In this embodiment, the reliability estimation unit 52 applies fast Fourier transform to each of the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2, as shown in Fig. 7. The first spectrum F1 shown in Fig. 7 is the power spectrum after fast Fourier transform of the oxygenated hemoglobin waveform P1, and the second spectrum F2 is the power spectrum after fast Fourier transform of the deoxygenated hemoglobin waveform P2.

[0032] The first spectrum F1 includes a first main peak Pm1 and a first noise floor N1. The first main peak Pm1 is the peak with the smallest frequency among the main peaks in the first spectrum F1. The first main peak Pm1 is a peak (heartbeat frequency peak) corresponding to the pulse of the living body 6. The first noise floor N1 is a region in the first spectrum F1 that has a frequency higher than the frequency of the first main peak Pm1 and an intensity lower than the intensity of the first main peak Pm1. The intensity of the first noise floor N1 is, for example, the average intensity of the frequency range in the first spectrum F1 that is considered to be noise.

[0033] The second spectrum F2 includes a second main peak Pm2 and a second noise floor N2. The second main peak Pm2 is the peak with the smallest frequency among the main peaks of the second spectrum F2. The second main peak Pm2 is a peak (heartbeat frequency peak) corresponding to the pulse of the living body 6. The second noise floor N2 is a region of the second spectrum F2 that has a frequency higher than the frequency of the second main peak Pm2 and an intensity lower than the intensity of the second main peak Pm2. The intensity of the second noise floor N2 is, for example, the average intensity of a frequency range of the second spectrum F2 that is considered to be noise. The first spectrum F1 and the second spectrum F2 shown in FIG. 7 are normalized so that the first main peak Pm1 of the first spectrum F1 and the second main peak Pm2 of the second spectrum F2 coincide with each other.

[0034] The reliability estimation unit 52 recognizes the first difference W1 between the first main peak Pm1 and the first noise floor N1 as the S / N ratio of the first spectrum F1 (the S / N ratio of the detection result of the photodetector 4), and recognizes the second difference W2 between the second main peak Pm2 and the second noise floor N2 as the S / N ratio of the second spectrum F2 (the S / N ratio of the detection result of the photodetector 4). The reliability estimation unit 52 estimates that the reliability of the temporal phase difference Δθ increases as the S / N ratio of the first spectrum F1 (first difference W1) and the S / N ratio of the second spectrum F2 (second difference W2) increase. The reliability estimation unit 52 estimates that the reliability of the temporal phase difference Δθ decreases as the S / N ratio of the first spectrum F1 and the S / N ratio of the second spectrum F2 decrease.

[0035] In this embodiment, the reliability estimation unit 52 estimates that the temporal phase difference Δθ is highly reliable when both the SNR of the first spectrum F1 and the SNR of the second spectrum F2 are greater than a predetermined threshold, and estimates that the temporal phase difference Δθ is unreliable when at least one of the SNR of the first spectrum F1 and the SNR of the second spectrum F2 is equal to or less than the threshold. The threshold is determined based on, for example, the correlation between the error in the temporal phase difference Δθ and the SNR and the allowable error value of the temporal phase difference Δθ.

[0036] 8 is a graph showing the correlation between the error in the temporal phase difference Δθ and the S / N ratio. In this embodiment, the correlation is calculated by numerical calculation. Specifically, a predetermined noise is first added to both the first spectrum F1 and the second spectrum F2 (noise-free spectra), and then the differences in the temporal phase difference Δθ before and after the addition of the noise are calculated multiple times (e.g., 1000 times). Next, the standard deviation of the multiple differences is calculated as the error in the temporal phase difference Δθ. Next, while the noise level is changed, multiple errors in the temporal phase difference Δθ corresponding to multiple S / N ratios are calculated.

[0037] The first correlation R1 shown in Fig. 8 is the correlation between the error (1σ) of the temporal phase difference Δθ and the S / N ratio, and the second correlation R2 shown in Fig. 8 is the correlation between the error (3σ) of the temporal phase difference Δθ and the S / N ratio. In this embodiment, the S / N ratio corresponding to the intersection of the first correlation R1 and the allowable value T for the error in the temporal phase difference Δθ is the first threshold value S1, and the S / N ratio corresponding to the intersection of the second correlation R2 and the allowable value T is the second threshold value S2. The first threshold value S1 is smaller than the second threshold value S2. The allowable value T for the error in the temporal phase difference Δθ is calculated using a blood glucose calculation formula described below, for example, based on the allowable value for the measurement error of the blood glucose level (for example, the ISO recommended value).

[0038] The reliability estimation unit 52 estimates that the temporal phase difference Δθ is highly reliable when both the SN ratio of the first spectrum F1 and the SN ratio of the second spectrum F2 are greater than the first threshold S1 or the second threshold S2, and estimates that the temporal phase difference Δθ is unreliable when at least one of the SN ratios of the first spectrum F1 and the second spectrum F2 is equal to or less than the first threshold S1 or the second threshold S2. When both the SN ratios of the first spectrum F1 and the second spectrum F2 are greater than the first threshold S1, the probability that the temporal phase difference Δθ is highly reliable is 68%. When both the SN ratios of the first spectrum F1 and the SN ratios of the second spectrum F2 are greater than the second threshold S2, the probability that the temporal phase difference Δθ is highly reliable is 99.7%. The reliability estimation unit 52 can adopt either the first threshold S1 or the second threshold S2 depending on the required blood glucose measurement accuracy, etc. The first correlation R1 and the second correlation R2 may be stored in advance in a storage unit of the blood glucose level measuring device 1.

[0039] The reliability estimation unit 52 sets the above-mentioned fast Fourier transform period to an integer multiple of both the respiratory cycle and the cardiac cycle of the living body 6. FIG. 9 is a schematic diagram showing the fast Fourier transform period. FIG. 9 shows an oxygenated hemoglobin waveform P1 and a respiratory waveform B of the living body 6. The respiratory waveform B increases as the living body 6 inhales and then decreases as the living body 6 exhales. The period of the respiratory waveform B (the respiratory cycle of the living body 6) is several times the period of the oxygenated hemoglobin waveform P1 (the cardiac cycle of the living body 6). The entire oxygenated hemoglobin waveform P1 changes according to the respiratory waveform B, and the bottom point of the oxygenated hemoglobin waveform P1 overlaps with the respiratory waveform B. In other words, a swell component formed by the respiratory cycle of the living body 6 is superimposed on the oxygenated hemoglobin waveform P1.

[0040] To ensure the accuracy of the fast Fourier transform of the oxygenated hemoglobin waveform P1, the amplitude of the start point Ps of the oxygenated hemoglobin waveform P1 used in the fast Fourier transform must match the amplitude of the end point Pe. If the period of the fast Fourier transform is an integer multiple of both the respiratory cycle and the cardiac cycle of the living body 6, that is, if a region of the oxygenated hemoglobin waveform P1 corresponding to an integer multiple of both the respiratory cycle and the cardiac cycle of the living body 6 is extracted, the amplitude of the start point Ps of the oxygenated hemoglobin waveform P1 will likely match the amplitude of the end point Pe. The reliability estimation unit 52 extracts a region of the oxygenated hemoglobin waveform P1 that is an integer multiple of the period of the respiratory waveform B, using the intersection of the oxygenated hemoglobin waveform P1 with the respiratory waveform B as the start point Ps, and performs the fast Fourier transform on the extracted region. In this embodiment, the reliability estimation unit 52 determines the intersection of the bottom point of the respiratory waveform B and the bottom point of the oxygenated hemoglobin waveform P1 as the start point Ps or end point Pe of the oxygenated hemoglobin waveform P1. That is, the reliability estimation unit 52 extracts a region between two adjacent intersections of the oxygenated hemoglobin waveform P1 and performs a fast Fourier transform on the region. The reliability estimation unit 52 also performs a fast Fourier transform on the deoxygenated hemoglobin waveform P2 at a similar cycle.

[0041] The blood glucose level calculation unit 53 calculates the blood glucose level of the living organism 6 based on the temporal phase difference Δθ calculated by the temporal phase difference calculation unit 51. The blood glucose level calculation unit 53 calculates the blood glucose level of the living organism 6 using the formula G=α×Δθ-β, where G is the blood glucose level of the living organism 6, Δθ is the temporal phase difference, and α and β are coefficients determined according to the glucose metabolic capacity and the measurement site of the living organism 6. In this embodiment, the methods disclosed in Japanese Patent No. 6846152, for example, are used as blood glucose level calculation methods.

[0042] The blood glucose level calculation unit 53 calculates a representative blood glucose level of the living body 6. Specifically, the temporal phase difference calculation unit 51 calculates, for example, a first temporal phase difference Δθ1 and a second temporal phase difference Δθ2 as the plurality of temporal phase differences. The reliability estimation unit 52 estimates, for example, the reliability of the first temporal phase difference Δθ1 and the reliability of the second temporal phase difference Δθ2 as the reliability of each of the plurality of temporal phase differences. The blood glucose level calculation unit 53 calculates a plurality of blood glucose levels based on the plurality of temporal phase differences. For example, the blood glucose level calculation unit 53 calculates a first blood glucose level G1 based on the first temporal phase difference Δθ1 and a second blood glucose level G2 based on the second temporal phase difference Δθ2.

[0043] The blood glucose level calculation unit 53 calculates the sum of a sequence of weighted first blood glucose levels G1 and second blood glucose levels G2 as the representative blood glucose level G of the living body 6. The blood glucose level calculation unit 53 calculates the representative blood glucose level of the living body 6 using, for example, the formula G = G1 × f1 + G2 × f2. Here, G is the representative blood glucose level, G1 is the first blood glucose level, G2 is the second blood glucose level, f1 is the first weight, and f2 is the second weight. That is, the blood glucose level calculation unit 53 assigns a first weight f1 to the first blood glucose level G1 and a second weight f2 to the second blood glucose level G2. The blood glucose level calculation unit 53 assigns smaller weights as the reliability of the temporal phase difference decreases. For example, when the reliability of the first temporal phase difference Δθ1 is smaller than the reliability of the second temporal phase difference Δθ2, the blood glucose level calculation unit 53 assigns a smaller first weight f1 than the second weight f2. For example, when the reliability of the first temporal phase difference Δθ1 is equal to or greater than the reliability of the second temporal phase difference Δθ2, the blood glucose level calculator 53 sets the first weight f1 to be equal to or greater than the second weight f2.

[0044] The blood glucose level calculation unit 53 may set either the first weight f1 or the second weight f2 to zero. That is, the blood glucose level calculation unit 53 may discard either the first blood glucose level G1 or the second blood glucose level G2. The blood glucose level calculation unit 53 may discard the blood glucose level calculated based on the unreliable temporal phase difference as described above.

[0045] Next, the blood glucose measurement method of this embodiment will be described. As shown in Fig. 10, in the blood glucose measurement method of this embodiment, first, measurement light L is output to the living body 6 (step S1). Step S1 corresponds to a light output step. Next, the measurement light L output in step S1 and transmitted through the living body 6 is detected (step S2). Step S2 corresponds to a light detection step. Next, based on the detection result of the measurement light L transmitted through the living body 6, a temporal phase difference Δθ between the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2 is calculated (step S3). Step S3 corresponds to a temporal phase difference calculation step. In step S3 of this embodiment, a first temporal phase difference Δθ1 and a second temporal phase difference Δθ2 are calculated. Next, the reliability of each of the first temporal phase difference Δθ1 and the second temporal phase difference Δθ2 calculated in step S3 is estimated (step S4). Step S4 corresponds to a reliability estimation step. In step S4, it is estimated that the smaller the signal-to-noise ratio of the detection result of the measurement light L, the lower the reliability of the temporal phase difference.

[0046] Next, the blood glucose level of the living body 6 is calculated based on the temporal phase difference calculated in step S3 (step S5). In this embodiment, in step S3, a first blood glucose level G1 is calculated based on the first temporal phase difference Δθ1, and a second blood glucose level G2 is calculated based on the second temporal phase difference Δθ2. Next, the sum of the weighted sequences of the first blood glucose level G1 and the second blood glucose level G2 is calculated as the representative blood glucose level of the living body 6 (step S6). In step S6, the sum of the first blood glucose level G1 (G1×f1) to which the first weight f1 is assigned and the second blood glucose level G2 (G2×f2) to which the second weight f2 is assigned is calculated. In step S6, for example, if the reliability of the first temporal phase difference Δθ1 is smaller than the reliability of the second temporal phase difference Δθ2, the first weight f1 is made smaller than the second weight f2, and for example, if the reliability of the first temporal phase difference Δθ1 is equal to or greater than the reliability of the second temporal phase difference Δθ2, the first weight f1 is made equal to or greater than the second weight f2. Steps S5 and S6 correspond to blood glucose level calculation steps.

[0047] As described above, in the blood glucose level measuring device 1 of this embodiment, the blood glucose level calculating unit 53 calculates the blood glucose level of the living organism 6 based on the temporal phase difference Δθ between the oxygenated hemoglobin waveform P1 relating to the oxygenated hemoglobin concentration in the blood of the living organism 6 and the deoxygenated hemoglobin waveform P2 relating to the deoxygenated hemoglobin concentration in the blood of the living organism 6. This allows the blood glucose level of the living organism 6 to be measured appropriately. Moreover, the reliability estimating unit 52 estimates that the reliability of the temporal phase difference Δθ decreases as the S / N ratio of the detection result from the light detecting unit 4 decreases. This makes it possible to calculate the blood glucose level taking the reliability of the temporal phase difference Δθ into consideration. Therefore, the blood glucose level measuring device 1 allows the blood glucose level of the living organism 6 to be measured accurately.

[0048] The blood glucose level calculation unit 53 calculates a first blood glucose level G1 based on the first temporal phase difference Δθ1 and calculates a second blood glucose level G2 based on the second temporal phase difference Δθ2. The blood glucose level calculation unit 53 calculates the sum of a series of weighted sequences for the first temporal phase difference Δθ1 and the second temporal phase difference Δθ2 as the representative blood glucose level of the living body 6. The reliability estimation unit 52 estimates the reliability of each of the first temporal phase difference Δθ1 and the second temporal phase difference Δθ2. The blood glucose level calculation unit 53 assigns a smaller weight as the reliability of the temporal phase difference decreases. This allows weighting to be performed according to the reliability of the temporal phase difference, enabling the blood glucose level of the living body 6 to be measured with high accuracy.

[0049] The reliability estimation unit 52 estimates that the temporal phase difference Δθ is highly reliable when both the SNR of the oxygenated hemoglobin waveform P1 and the SNR of the deoxygenated hemoglobin waveform P2 are greater than a first threshold S1 or a second threshold S2, and estimates that the temporal phase difference Δθ is unreliable when at least one of the SNR of the oxygenated hemoglobin waveform P1 and the SNR of the deoxygenated hemoglobin waveform P2 is equal to or less than the first threshold S1 or the second threshold S2. The first threshold S1 or the second threshold S2 is determined based on the correlation between the error in the temporal phase difference Δθ and the SNR and the allowable value T for the error in the temporal phase difference Δθ. This allows the reliability of the temporal phase difference Δθ to be estimated efficiently.

[0050] The reliability estimation unit 52 calculates the SN ratio based on the spectrum after fast Fourier transform of the detection result of the light detection unit 4. This makes it possible to calculate the SN ratio with high accuracy.

[0051] The reliability estimation unit 52 sets the period of the fast Fourier transform to an integer multiple of both the respiratory cycle and the cardiac cycle of the living body 6. This makes it possible to improve the accuracy of the fast Fourier transform.

[0052] According to the blood glucose level measuring method of this embodiment, like the blood glucose level measuring device 1, it is possible to measure the blood glucose level of the living body 6 with high accuracy.

[0053] Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment.

[0054] In the embodiment, the reliability estimation unit 52 performed the fast Fourier transform using the intersection of the bottom point of the respiratory waveform B and the bottom point of the oxygenated hemoglobin waveform P1 as the start point Ps of the oxygenated hemoglobin waveform P1, but the reliability estimation unit 52 may also perform the fast Fourier transform using any intersection point of the oxygenated hemoglobin waveform P1 with the respiratory waveform B as the start point Ps, as shown in Fig. 11. In this case as well, the amplitude of the start point Ps and the end point Pe of the oxygenated hemoglobin waveform P1 tend to match, ensuring the accuracy of the fast Fourier transform.

[0055] In the embodiment, the reliability estimation unit 52 calculates the S / N ratio of the light detection unit 4 by performing a fast Fourier transform on each of the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2, but the reliability estimation unit 52 may calculate the S / N ratio of the light detection unit 4 by performing a fast Fourier transform on each of the first data D1 and the second data D2.

[0056] In the embodiment, the ECU 5 is provided in the main body 2, but the ECU 5 does not have to be provided in the main body 2. The ECU 5 may be provided in, for example, a server that can communicate with the main body 2. In this case, the main body 2, the light output unit 3, the light detection unit 4, and the ECU 5 are each component of the blood glucose measurement system.

[0057] The light detection unit 4 may detect third data in addition to the first data D1 and the second data D2. The temporal phase difference calculation unit 51 may calculate multiple (three) temporal phase differences based on the first data D1, the second data D2, and the third data. The blood glucose level calculation unit 53 may calculate the blood glucose level of the living body 6 based on, for example, the average value of the three temporal phase differences.

[0058] The blood glucose level calculation unit 53 may calculate the change over time of the representative blood glucose level G. When a low-reliable representative blood glucose level G calculated based on a low-reliable temporal phase difference exists among the representative blood glucose levels G at each time, the blood glucose level calculation unit 53 may discard the low-reliable representative blood glucose level G. In this case, the blood glucose level calculation unit 53 may use representative blood glucose levels G before and after the low-reliable representative blood glucose level G to complement the representative blood glucose level at the time corresponding to the low-reliable representative blood glucose level G. The blood glucose level calculation unit 53 may, for example, calculate the average value of the representative blood glucose levels G before and after the low-reliable representative blood glucose level G as the representative blood glucose level at the time corresponding to the low-reliable representative blood glucose level G.

[0059] The blood glucose level calculation unit 53 may calculate the blood glucose level multiple times and calculate the average of the multiple blood glucose levels as the representative blood glucose level G. If the reliability of each temporal phase difference is relatively low, the blood glucose level calculation unit 53 may increase the number of times to calculate the blood glucose level. This ensures the measurement accuracy of the representative blood glucose level G even if the multiple temporal phase differences used to calculate the representative blood glucose level G include a temporal phase difference with relatively low reliability.

[0060] The ECU 5 may further include a notification unit as a functional component. The notification unit displays the reliability of the blood glucose level together with the blood glucose level on the display screen of the main body 2. The notification unit 55 may, for example, display on the display screen of the main body 2 an icon indicating the change over time of the representative blood glucose level G and the magnitude of the reliability of the representative blood glucose level G at each time (reliability of the temporal phase difference). [Explanation of symbols]

[0061] 1...blood glucose level measuring device, 3...light output unit, 4...light detection unit, 6...biological body, 51...temporal phase difference calculation unit, 52...reliability estimation unit, 53...blood glucose level calculation unit, F1...first spectrum, F2...second spectrum, L...measurement light, P1...oxygenated hemoglobin waveform, P2...deoxygenated hemoglobin waveform, S1...first threshold, S2...second threshold, T...tolerance value, Δθ...temporal phase difference.

Claims

1. A blood glucose level measuring device for measuring a blood glucose level of a living body, a light output unit that outputs light to the living body; a light detection unit that detects the light output from the light output unit and transmitted through the living body; a temporal phase difference calculation unit that calculates a temporal phase difference between an oxygenated hemoglobin waveform relating to the oxygenated hemoglobin concentration of the blood of the living body and a deoxygenated hemoglobin waveform relating to the deoxygenated hemoglobin concentration of the blood of the living body based on the detection result of the light detection unit; a blood glucose level calculation unit that calculates the blood glucose level of the living body based on the temporal phase difference calculated by the temporal phase difference calculation unit; a reliability estimation unit that estimates the reliability of the temporal phase difference calculated by the temporal phase difference calculation unit, The reliability estimation unit estimates that the reliability of the temporal phase difference is lower as the signal-to-noise ratio of the detection result of the light detection unit is lower.

2. the temporal phase difference calculation unit calculates a plurality of temporal phase differences, each of which is the temporal phase difference; the blood glucose level calculation unit calculates a plurality of blood glucose levels, each of which is the blood glucose level, based on the plurality of temporal phase differences, and calculates a sum of a sequence of weighted numbers for each of the plurality of blood glucose levels as a representative blood glucose level of the living body; the reliability estimation unit estimates a reliability of each of the plurality of temporal phase differences; The blood glucose level measuring device according to claim 1 , wherein the blood glucose level calculating section reduces the weight as the reliability of each of the plurality of temporal phase differences decreases.

3. the reliability estimation unit estimates that the temporal phase difference is highly reliable when the S / N ratio is greater than a predetermined threshold, and estimates that the temporal phase difference is unreliable when the S / N ratio is equal to or less than the threshold; The blood glucose measuring device according to claim 1 , wherein the threshold value is determined based on a correlation between the error in the temporal phase difference and the S / N ratio, and an allowable value for the error in the temporal phase difference.

4. The blood glucose measuring device according to claim 1 , wherein the reliability estimating section calculates the S / N ratio based on a spectrum after a fast Fourier transform of the detection result of the light detecting section.

5. The blood glucose measuring device according to claim 4 , wherein the reliability estimating section sets the period of the fast Fourier transform to an integer multiple of both a respiratory cycle and a cardiac cycle of the living body.

6. A blood glucose measurement method for measuring a blood glucose level of a living body, comprising: a time phase difference calculation step of calculating a time phase difference between an oxygenated hemoglobin waveform relating to the oxygenated hemoglobin concentration of the blood of the living body and a deoxygenated hemoglobin waveform relating to the deoxygenated hemoglobin concentration of the blood of the living body based on the detection result of the light transmitted through the living body; a blood glucose level calculation step of calculating the blood glucose level of the living body based on the temporal phase difference calculated in the temporal phase difference calculation step; a reliability estimating step of estimating reliability of the temporal phase difference calculated in the temporal phase difference calculating step, The blood glucose level measuring method, wherein the reliability estimating step estimates that the reliability of the temporal phase difference is lower as the signal-to-noise ratio of the light detection result is lower.

7. a light output step of outputting the light to the living body; The blood glucose level measuring method according to claim 6 , further comprising: a light detecting step of detecting the light output in the light outputting step and transmitted through the living body.

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