JP2025161158A - Blood glucose level measuring device and blood glucose level measuring method - Google Patents

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

The present invention relates to a blood glucose level measuring device and a blood glucose level measuring method.

One known technology for measuring blood oxygen levels in living organisms is the device described in Patent Document 1. The device described in Patent Document 1 prevents a decrease in the accuracy of blood oxygen level measurements caused by noise by appropriately setting the wavelengths of light emitted from multiple light sources.

Japanese Patent Application Laid-Open No. 2016-2167

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

The present invention aims to provide a blood glucose level measuring device and blood glucose level measuring method that can accurately measure blood glucose levels in a living body.

The blood glucose measuring device of the present invention is [1] "a blood glucose measuring device for measuring the 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 the oxygenated hemoglobin concentration of the blood of the living organism and a deoxygenated hemoglobin waveform related to the deoxygenated hemoglobin concentration of the blood of the living organism based on the detection results 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 reliability of the temporal phase difference decreases as the signal-to-noise ratio of the detection results of the light detection unit decreases."

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 the oxygenated hemoglobin waveform related to the oxygenated hemoglobin concentration in the blood of the living body and the deoxygenated hemoglobin waveform related 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 decreases as the signal-to-noise ratio of the detection result of the light detection unit decreases. 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.

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

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

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

The blood glucose measuring device of the present invention may be [5] "the blood glucose measuring device described in [4] above, wherein the reliability estimation 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.

The blood glucose measurement method of the present invention is [6] "a blood glucose measurement method for measuring the 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 the oxygenated hemoglobin concentration in the blood of the living organism and a deoxygenated hemoglobin waveform relating to the deoxygenated hemoglobin concentration in the blood of the living organism based on the 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 the reliability estimation 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."

The blood glucose measurement method described in [6] above makes it possible to accurately measure the blood glucose level of a living body, similar to the blood glucose measurement device described above.

The blood glucose level measurement method of the present invention may be [7] "the blood glucose level measurement method described in [6] above, further comprising a light output step of outputting the light to the living body, and a light detection step of detecting the light output in the light output step and transmitted through the living body." This makes it possible to accurately measure the blood glucose level of a living body, similar to the blood glucose level measurement device described above.

The present invention provides a blood glucose level measuring device and a blood glucose level measuring method that can accurately measure blood glucose levels in a living body.

1 is a conceptual diagram of a blood glucose level measuring device according to an embodiment. 2 shows the detection results of the light detection unit shown in FIG. 1. FIG. 2 is a block diagram showing a functional configuration of the ECU shown in FIG. 1 . 3 shows an oxygenated hemoglobin waveform and a deoxygenated hemoglobin waveform calculated based on the detection results shown in FIG. 2 . 5 is a schematic diagram of the oxygenated hemoglobin waveform and the deoxygenated hemoglobin waveform shown in FIG. 4. 5 is a schematic diagram of the oxygenated hemoglobin waveform and the deoxygenated hemoglobin waveform shown in FIG. 4. 5 is a spectrum after fast Fourier transform of the oxygenated hemoglobin waveform and the deoxygenated hemoglobin waveform shown in FIG. 4. 10 is a graph showing the correlation between the error in the temporal phase difference and the S/N ratio. FIG. 8 is a schematic diagram showing the period of the fast Fourier transform for obtaining the spectrum shown in FIG. 7 . 1 is a flowchart showing steps of a blood glucose level measurement method according to one embodiment. FIG. 10 is a schematic diagram showing a period of a fast Fourier transform according to a modified example.

Embodiments of the present invention will now be described in detail with reference to the drawings. Note that identical or equivalent parts in each drawing will be designated by the same reference numerals, and duplicate explanations will be omitted.

Figure 1 is a cross-sectional view of a blood glucose level measuring device and a living body according to this embodiment. Figure 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.

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 smart watches and smart rings. In this embodiment, the blood glucose level measuring device 1 is a smart watch that has the 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 deeper inside the living organism 6 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.

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 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.

The light output unit 3 is provided on 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), laser diode (LD), or 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 again from the living body 6. The light output unit 3 is controlled by the ECU 5.

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). In other words, the light output unit 3 outputs measurement light L within the range from the red wavelength region of visible light to the near-infrared region. The light output unit 3 outputs measurement light L with, for example, 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 with a wavelength of, for example, 735 nm, the second light source outputs measurement light L with a wavelength of, for example, 810 nm, and the third light source outputs measurement light L with a wavelength of, for example, 850 nm. Note that the light output unit 3 may also have a single light source that outputs probe light (for example, white light) containing different wavelength components.

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 back 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 also have a CCD image sensor or a CMOS image sensor. The light detection unit 4 sends a signal related to the intensity of the measurement light L to the ECU 5.

As shown in FIG. 2, the light detection unit 4 detects at least first data D1 and second data D2. The first data D1 is, for example, the 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, the 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 second data D2 fluctuates periodically over time. Note that the respective periods of the first data D1 and second data D2 approximately match the cardiac cycle of the living body 6.

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 ROM (Read Only Memory) or 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). Figure 3 is a block diagram showing the functional configuration of the ECU 5. As shown in Figure 3, the ECU 5 includes a temporal phase difference calculation unit 51, a reliability estimation unit 52, and a blood glucose level calculation unit 53.

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 ( _O2Hb ) 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.

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 ΔO ₂ Hb over time is the oxygenated hemoglobin waveform P1 shown in Fig. 4, and the change in ΔHHb over time is the deoxygenated hemoglobin waveform P2 shown in Fig. 4. The concentration index on the vertical axis in Fig. 4 is, for example, a volume concentration index (concentration × optical path length).

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 the first characteristic point C1 of the oxygenated hemoglobin waveform P1 and the 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 the bottom point of the oxygenated hemoglobin waveform P1, and the second characteristic point C2 is the bottom point of the deoxygenated hemoglobin waveform P2. The first characteristic point C1 may be, for example, a peak point or notch point of the oxygenated hemoglobin waveform P1, and the second characteristic point C2 may be, for example, a peak point or notch point of the deoxygenated hemoglobin waveform P2. In this embodiment, the methods used to calculate the temporal phase difference Δθ are those disclosed in, for example, Japanese Patent No. 6846152.

As shown in FIG. 6, the detection results 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 (deoxygenated hemoglobin waveform P2 in FIG. 6) may also contain noise. In such cases, 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 calculating 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.

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 optical detection unit 4 increases (as the noise level of the detection result of the optical detection 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 optical detection unit 4 decreases (as the noise level of the detection result of the optical detection unit 4 increases).

The reliability estimation unit 52 calculates the signal-to-noise ratio of the detection results of the optical detection unit 4 based on the spectrum after a fast Fourier transform (FFT) of the detection results of the optical detection unit 4. The fast Fourier transform of the detection results of the optical detection unit 4 may be a direct fast Fourier transform applied to the detection results of the optical detection unit 4, or an indirect fast Fourier transform applied to parameters calculated from the detection results of the optical detection unit 4. In this embodiment, the reliability estimation unit 52 applies a 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 the fast Fourier transform of the oxygenated hemoglobin waveform P1, and the second spectrum F2 is the power spectrum after the fast Fourier transform of the deoxygenated hemoglobin waveform P2.

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 corresponding to the pulse of the living body 6 (heartbeat frequency peak). 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.

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 corresponding to the pulse of the living body 6 (heartbeat frequency peak). 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 the 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.

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 optical detection unit 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 optical detection unit 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.

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

Figure 8 is a graph showing the correlation between the error in the temporal phase difference Δθ and the S/N ratio. In this embodiment, this correlation is calculated by numerical calculation. Specifically, a predetermined amount of noise is first added to both the first spectrum F1 and the second spectrum F2 (noise-free spectra), and then the difference in the temporal phase difference Δθ before and after the addition of the noise is calculated multiple times (e.g., 1,000 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.

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 tolerance T for the error in the temporal phase difference Δθ is the first threshold S1, and the S/N ratio corresponding to the intersection of the second correlation R2 and the tolerance T is the second threshold S2. The first threshold S1 is smaller than the second threshold S2. The tolerance T for the error in the temporal phase difference Δθ is calculated using the blood glucose calculation formula described below, for example, based on the tolerance for blood glucose measurement error (e.g., the ISO recommended value).

The reliability estimation unit 52 estimates that the temporal phase difference Δθ is highly reliable when both the S/N ratio of the first spectrum F1 and the S/N 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 low reliable when at least one of the S/N 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 S/N ratio of the first spectrum F1 and the S/N ratio of 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 S/N ratio of the first spectrum F1 and the S/N ratio 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 the memory unit of the blood glucose measuring device 1.

The reliability estimation unit 52 sets the above-mentioned fast Fourier transform period to an integer multiple of both the respiratory cycle and cardiac cycle of the living body 6. Figure 9 is a schematic diagram showing the fast Fourier transform period. Figure 9 shows an oxygenated hemoglobin waveform P1 and a respiratory waveform B of the living body 6. The respiratory waveform B is a waveform that 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 in accordance with the respiratory waveform B, and the bottom point of the oxygenated hemoglobin waveform P1 overlaps with the respiratory waveform B. In other words, an undulation component composed of the respiratory cycle of the living body 6 is superimposed on the oxygenated hemoglobin waveform P1.

To ensure the accuracy of the fast Fourier transform of the oxygenated hemoglobin waveform P1, it is necessary for the amplitudes of the start point Ps and end point Pe of the oxygenated hemoglobin waveform P1 used in the fast Fourier transform to match. When the period of the fast Fourier transform is an integer multiple of both the respiratory cycle and cardiac cycle of the living body 6, that is, when a region of the oxygenated hemoglobin waveform P1 corresponding to an integer multiple of both the respiratory cycle and cardiac cycle of the living body 6 is extracted, the amplitudes of the start point Ps and end point Pe of the oxygenated hemoglobin waveform P1 tend to match. 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. In other words, the reliability estimation unit 52 cuts out the region between two adjacent intersections of the oxygenated hemoglobin waveform P1 and performs a fast Fourier transform on it. The reliability estimation unit 52 also performs a fast Fourier transform on the deoxygenated hemoglobin waveform P2 at a similar cycle.

The blood glucose level calculation unit 53 calculates the blood glucose level of the living body 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 body 6 using the formula G = α × Δθ - β, where G is the blood glucose level of the living body 6, Δθ is the temporal phase difference, and α and β are coefficients determined according to the glucose metabolic capacity of the living body 6 and the measurement site. In this embodiment, the methods disclosed in Japanese Patent No. 6846152, for example, are used to calculate blood glucose levels.

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, as multiple temporal phase differences, for example, a first temporal phase difference Δθ1 and a second temporal phase difference Δθ2. The reliability estimation unit 52 estimates, as the reliability of each of the multiple temporal phase differences, for example, the reliability of the first temporal phase difference Δθ1 and the reliability of the second temporal phase difference Δθ2. The blood glucose level calculation unit 53 calculates multiple blood glucose levels based on the multiple 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.

The blood glucose level calculation unit 53 calculates the representative blood glucose level G of the living body 6 as the sum of a sequence weighted for the first blood glucose level G1 and the second blood glucose level G2. 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 x f1 + G2 x 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. In other words, 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, if 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, 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 blood glucose level calculation unit 53 sets the first weight f1 to be equal to or greater than the second weight f2.

The blood glucose level calculation unit 53 may set either the first weight f1 or the second weight f2 to zero. In other words, 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 a blood glucose level calculated based on an unreliable temporal phase difference as described above.

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 the 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 the light detection step. Next, the temporal phase difference Δθ between the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2 is calculated based on the detection result of the measurement light L transmitted through the living body 6 (step S3). Step S3 corresponds to the 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 the 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.

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 weighted sequences for 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 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.

As described above, in the blood glucose level measuring device 1 of this embodiment, the blood glucose level calculation 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. Furthermore, the reliability estimation unit 52 estimates that the reliability of the temporal phase difference Δθ decreases as the signal-to-noise ratio of the detection result of the light detection 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.

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 sequence weighted for each of 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.

The reliability estimation unit 52 estimates that the temporal phase difference Δθ is highly reliable if both the S/N ratio of the oxygenated hemoglobin waveform P1 and the S/N ratio of the deoxygenated hemoglobin waveform P2 are greater than the first threshold S1 or the second threshold S2, and estimates that the temporal phase difference Δθ is low reliable if at least one of the S/N ratios of the oxygenated hemoglobin waveform P1 and 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 S/N ratio, 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.

The reliability estimation unit 52 calculates the S/N ratio based on the spectrum after fast Fourier transform of the detection results from the light detection unit 4. This allows the S/N ratio to be calculated with high accuracy.

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 improves the accuracy of the fast Fourier transform.

The blood glucose measurement method of this embodiment makes it possible to accurately measure the blood glucose level of a living body 6, similar to the blood glucose measurement device 1.

The above describes one embodiment of the present invention, but the present invention is not limited to the above-described embodiment.

In the embodiment, the reliability estimation unit 52 performed a 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. However, as shown in FIG. 11, the reliability estimation unit 52 may also perform a fast Fourier transform using any intersection point of the oxygenated hemoglobin waveform P1 with the respiratory waveform B as the start point Ps. In this case, too, 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.

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. However, the reliability estimation unit 52 may also 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.

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, for example, in 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 each constitute a part of the blood glucose measurement system.

The light detection unit 4 may detect third data in addition to the first data D1 and second data D2. The temporal phase difference calculation unit 51 may calculate multiple (three) temporal phase differences based on the first data D1, second data D2, and 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.

The blood glucose level calculation unit 53 may calculate the change in the representative blood glucose level G over time. If a low-reliability representative blood glucose level G calculated based on a low-reliability 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-reliability representative blood glucose level G. In this case, the blood glucose level calculation unit 53 may use the representative blood glucose levels G before and after the low-reliability representative blood glucose level G to complement the representative blood glucose level at the time corresponding to the low-reliability 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-reliability representative blood glucose level G as the representative blood glucose level at the time corresponding to the low-reliability representative blood glucose level G.

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 the blood glucose level is calculated. 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.

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 unit 2. The notification unit 55 may, for example, display on the display screen of the main unit 2 an icon indicating the change in the representative blood glucose level G over time and the magnitude of the reliability of the representative blood glucose level G at each time (reliability of the temporal phase difference).

1...blood glucose level measuring device, 3...light output unit, 4...light detection unit, 6...living 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 (7)

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. 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. 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. The blood glucose measuring device of claim 1, wherein the reliability estimation unit calculates the S/N ratio based on a spectrum after a fast Fourier transform of the detection result of the light detection unit. The blood glucose measurement device of claim 4, wherein the reliability estimation 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. 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. 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.