Biological signal measurement device

Abstract

Provided is a biological signal measurement device capable of selecting a pair of electrodes suitable for electrocardiographic measurement from among a plurality of pairs of electrodes. The biological signal measurement device comprises: a band-like fixing member to be wound around a measurement subject; a plurality of pairs of electrodes disposed on the fixing member; a selection unit that, on the basis of a feature amount based on the absolute value of the maximum amplitude in the positive direction and the absolute value of the maximum amplitude in the negative direction when the potential of the baseline in an electrocardiogram waveform of the measurement subject acquired by each of the pairs of electrodes is used as the reference, selects a pair of measurement electrodes to be used for acquiring the electrocardiogram waveform, from among the pairs of electrodes; and a detection unit that detects characteristics of the electrocardiogram waveform by using the selected pair of measurement electrodes.

Description

Biosignal measurement device

[0001] The present invention relates to a biological signal measuring device.

[0002] Wearable biosignal measuring devices that are worn continuously on the body for an extended period of time and monitor electrocardiogram waveforms are known. Various products exist, ranging from medical devices such as 24-hour Holter electrocardiogram monitors to consumer devices such as smart watches. For example, Patent Literature 1 (JP-A-2005-102626) describes an electrocardiogram measuring device that contacts multiple electrodes with the upper arm, focuses on the amplitude of the R wave of the acquired electrocardiogram waveform, and selects a set of electrodes that maximizes the amplitude to be used to measure the electrocardiogram waveform.

[0003] Patent No. 5428889

[0004] Even if a pair of electrodes that maximizes the amplitude of the R wave in the electrocardiogram waveform is selected, the selected pair of electrodes may not measure the waveform information used for electrocardiogram analysis. For example, atrial fibrillation is detected by detecting the disappearance and inability to detect P waves and the irregularity of the R wave period, but there is a risk that the P wave will not be measured in the signal acquired by the pair of electrodes that maximizes the signal amplitude. Therefore, there is a risk that the selected pair of electrodes will not perform accurate electrocardiogram analysis.

[0005] One aspect of the disclosed technology aims to provide a biological signal measuring device that can select a set of electrodes suitable for electrocardiogram measurement from among multiple sets of electrodes.

[0006] One aspect of the disclosed technology is exemplified by the following biosignal measuring device: This biosignal measuring device includes a band-shaped fixing member wrapped around a subject, multiple sets of electrodes arranged on the fixing member, a selection unit that selects a set of measurement electrodes to be used to acquire an electrocardiogram waveform from the multiple sets of electrodes based on feature quantities based on absolute values ​​of maximum positive and negative amplitudes relative to a baseline potential of an electrocardiogram waveform of the subject acquired by each of the multiple sets of electrodes, and a detection unit that detects features of the electrocardiogram waveform using the selected set of measurement electrodes.

[0007] According to this biosignal measuring device, a set of measurement electrodes is selected based on the feature. By providing this feature, the biosignal measuring device can select a set of electrodes suitable for detecting features of an electrocardiogram waveform from multiple sets of electrodes. The feature detected by the detection unit may be, for example, an RRI, which is the interval between R-wave peaks in the electrocardiogram waveform, or the presence or absence of a P-wave. The feature may also be a value obtained by dividing the larger of the absolute value of the maximum amplitude in the positive direction and the absolute value of the maximum amplitude in the negative direction in the electrocardiogram waveform by the smaller of the absolute value of the maximum amplitude in the positive direction and the absolute value of the maximum amplitude in the negative direction in the electrocardiogram waveform, if the electrocardiogram waveform is adjusted so that the difference between the maximum and minimum amplitudes of each waveform included in the electrocardiogram waveform is constant. The feature may also be at least one of a first absolute value of the maximum amplitude in the positive direction and a second absolute value of the maximum amplitude in the negative direction in the electrocardiogram waveform. The selection section may select, as the pair of measurement electrodes, a pair of electrodes having a larger feature amount than other pairs of electrodes.

[0008] The biosignal measuring device may further include the following features: The selector selects the pair of measurement electrodes at predetermined intervals, and further includes a control unit that, when the same pair of electrodes is selected as the pair of measurement electrodes consecutively, stops the supply of power to the electrodes other than the pair of measurement electrodes. According to the biosignal measuring device, the supply of power to the electrodes other than the pair of measurement electrodes is stopped, thereby reducing the power consumption of the biosignal measuring device. Furthermore, when the same pair of electrodes is selected as the pair of measurement electrodes consecutively, there is a high probability that the same pair of electrodes will be selected again as the pair of measurement electrodes. Therefore, stopping the supply of power to the electrodes other than the pair of measurement electrodes is considered to have little effect on the measurement accuracy of electrocardiogram measurement.

[0009] The biosignal measuring device may further include the following feature: the selector receives a designation of the number of pairs of measurement electrodes to select, and selects the same number of pairs of measurement electrodes as the designation. A biosignal measuring device with such a feature can flexibly change the number of pairs of measurement electrodes according to the needs of the subject.

[0010] The biological signal measuring device may further include the following feature: the detection unit detects atrial fibrillation based on the detected feature. A biological signal measuring device having such a feature can detect atrial fibrillation using the set of measurement electrodes selected by the selection unit.

[0011] According to the disclosed technology, a set of electrodes suitable for electrocardiographic measurement can be selected from a plurality of sets of electrodes.

[0012] FIG. 1 is a diagram showing an electrocardiograph according to an embodiment worn on the upper arm. FIG. 2 is a plan view of the electrocardiograph according to an embodiment. FIG. 3 is a perspective view of the electrocardiograph according to an embodiment. FIG. 4 is a block diagram showing an example of the functional configuration of a control main body. FIGS. 5A and 5B are diagrams illustrating electrocardiogram waveforms acquired by an acquisition unit. FIG. 6 is a diagram showing an example of a processing flow of electrode pair selection processing by an electrode selector in an embodiment. FIG. 7 is a block diagram showing an example of the functional configuration of a control main body according to a first modified example. FIG. 8 is a diagram showing an example of a processing flow of electrode pair selection processing by an electrode selector in the first modified example. FIG. 9 is a block diagram showing an example of the functional configuration of a control main body according to a second modified example. FIG. 10 is a diagram showing an example of an operation mode designation screen output by a mode control unit to an output unit in the second modified example. FIG. 11 is a diagram showing a first example of a processing flow of electrode pair selection processing by an electrode selector in the second modified example. FIG. 12 is a diagram showing an example of a correspondence between a cycle executed every 10 minutes and time. FIG. 13 is a diagram showing a second example of a processing flow of electrode pair selection processing by an electrode selector in the second modified example. Fig. 14 is a diagram showing an example of a process flow of electrocardiogram measurement when power-saving operation is started in Modification 2. Fig. 15 is a diagram showing an example of switching on and off the power-saving operation.

[0013] <Application Example> An application example of the present invention will be described. An electrocardiograph 1 according to this application example is a wearable electrocardiograph that is fixed by wrapping a band 10 around a measurement site of a subject, as shown in Fig. 1, for example. A plurality of electrodes 11 and a control main unit 12 are fixed to the band 10. Examples of measurement sites to which the band 10 is attached include the upper limbs (upper arm, forearm, wrist, hand, fingers), lower limbs (thigh, lower leg, ankle, foot, fingers), head, neck, chest, abdomen, earlobe, etc., and the measurement site is selected appropriately depending on the measurement algorithm, etc.

[0014] The electrocardiogram signal used to detect the characteristics of the electrocardiogram waveform is acquired using, for example, two electrodes 11 (one electrode pair). Three or more electrodes 11 are arranged side by side on the band 10, and a pair of electrodes 11 to be used for electrocardiogram measurement is selected by a pair selector 242 (see FIG. 4).

[0015] When the pair selector 242 selects pairs of electrodes 11, for example, potential differences are obtained for all pairs of electrodes 11 selected from the plurality of electrodes 11, and the potential differences are acquired as electrocardiogram signals. The pair selector 242 calculates feature quantities based on the absolute values ​​of the maximum amplitude in the positive direction and the maximum amplitude in the negative direction relative to the baseline potential in an electrocardiogram waveform that indicates time-series changes in the electrocardiogram signal, and selects pairs of electrodes 11 to be used for detecting features of the electrocardiogram waveform based on the calculated feature quantities. Hereinafter, detecting features of an electrocardiogram waveform is also referred to as electrocardiographic measurement. According to this application example, by using the feature quantities, a pair of electrodes suitable for detecting features of an electrocardiogram waveform can be selected from multiple pairs of electrodes.

[0016] <Embodiments> Hereinafter, embodiments will be described with reference to the drawings. Fig. 1 is a diagram showing an electrocardiograph 1 according to an embodiment worn on the upper arm. Fig. 2 is a plan view of the electrocardiograph 1 according to an embodiment. Fig. 3 is a perspective view of the electrocardiograph 1 according to an embodiment. Note that the electrocardiograph 1 is not limited to a device that performs only electrocardiographic measurements, and may also be a biosignal measuring device that measures biosignals other than electrocardiogram signals, such as blood pressure and blood oxygen concentration.

[0017] The electrocardiograph 1 of this embodiment is an upper arm electrocardiogram device that is worn on the user's upper arm (preferably the left upper arm close to the heart) and is used to measure electrocardiogram signals as biosignals.

[0018] The electrocardiograph 1 mainly comprises a band 10 , a plurality of electrodes 11 fixed to the band 10 , and a control unit 12 fixed to the band 10 .

[0019] The band 10 is a member (fixing member) for fixing the electrodes 11 in a state where they are pressed against the living body. In this embodiment, a strip-shaped band 10 made of a flexible and pliable material (e.g., chemical fiber, silicone, leather, etc.) is used. A fixing mechanism 13 is provided at the longitudinal end of the band 10. As shown in Figures 1 and 3, the electrocardiograph 1 can be worn on the upper arm by looping the band 10 and fastening it with the fixing mechanism 13. The fixing mechanism 13 may be any type of fastener, such as a hook and loop fastener, a hook, a connector, a button, or a magnet.

[0020] Multiple electrodes 11 (also called an electrode array) are embedded and fixed in the band 10 with the surface that comes into contact with the living body exposed on the inside (living body side) of the band 10. The multiple electrodes 11 are arranged in a row at equal intervals along the longitudinal direction of the band 10. This ensures that the electrodes 11 come into contact with different positions around the arm when the band 10 is wrapped around the arm. The number of electrodes 11 can be designed as desired. For the purpose of measuring electrocardiogram signals, at least two electrodes 11 (one electrode pair) are sufficient, but three or more electrodes 11 may be provided to improve the reliability and robustness of the measurement. In this embodiment, a configuration with six electrodes 11 is adopted.

[0021] The electrodes 11 are dry metal electrodes. Wet electrodes (gel electrodes, etc.) have problems such as the possibility of causing skin rash or itchiness when worn for a long period of time, and low durability and ease of maintenance, whereas the dry electrodes 11 do not have such problems. The electrocardiograph 1 of this embodiment is intended to be worn for a long period of time and to monitor electrocardiogram signals for 24 hours, so dry electrodes 11 are preferred.

[0022] The control main unit 12 is a processing unit that controls the electrocardiograph 1 and performs signal processing. The control main unit 12 has a structure in which a processor, memory, battery, and other circuits are mounted inside a case made of, for example, resin or metal. The control main unit 12 may also be provided with a physical switch and a display. Although not shown, the control main unit 12 and the multiple electrodes 11 are connected via signal lines.

[0023] (Control Main Unit) Fig. 4 is a block diagram showing an example of the functional configuration of the control main unit 12. The control main unit 12 includes an acquisition unit 22, an electrode selection unit 24, a storage unit 25, an output unit 26, and a detection unit 27. For example, a processor is disposed in the control main unit 12, and the processor executes a program stored in the storage unit 25 to realize each processing unit such as the acquisition unit 22, the electrode selection unit 24, the output unit 26, and the detection unit 27. In other words, the control main unit 12 can be considered a computer. Note that each processing unit such as the acquisition unit 22, the electrode selection unit 24, the output unit 26, and the detection unit 27 may be realized by a dedicated hardware circuit.

[0024] The acquisition unit 22 is a circuit that uses a differential amplifier to amplify potential differences between electrode pairs selected from the multiple electrodes 11 included in the electrocardiograph 1 and outputs the amplified potential differences as electrocardiogram signals. For example, when the electrode selector 24 selects pairs of electrodes 11, the acquisition unit 22 acquires potential differences for all pairs of electrodes 11 selected from the multiple electrodes 11 and outputs the amplified potential differences as electrocardiogram signals. The electrocardiogram signal is a signal that indicates the electrical activity of the heart. In this embodiment, electrode pairs are selected from the six electrodes 11 included in the electrocardiograph 1, resulting in a total of 15 electrode pairs. After the electrode selector 24 selects pairs of electrodes 11 to be used for electrocardiogram measurement, the acquisition unit 22 acquires potential differences between the selected pairs of electrodes 11 and outputs the amplified potential differences as electrocardiogram signals.

[0025] The electrode selector 24 selects a pair of electrodes 11 to be used for electrocardiogram measurement. The electrode selector 24 selects, for example, a pair of electrodes 11 from which an electrocardiogram signal suitable for detecting atrial fibrillation can be acquired. Atrial fibrillation is detected, for example, when the R-R interval (RRI), which is the interval between R-wave peaks, is irregular and no P waves are present in the electrocardiogram waveform. The electrode selector 24 includes a calculator 241 and a pair selector 242. The calculator 241 calculates a feature value related to the position of a baseline in the electrocardiogram waveform, which indicates time-series changes in the input electrocardiogram signal. The baseline is a straight line connecting the start point of a P wave and the start point of the next P wave in the electrocardiogram waveform. The position of the baseline in the electrocardiogram waveform is, for example, a straight line indicating a state in which no part of the heart is excited in the electrocardiogram waveform. The position of the baseline may be, for example, a straight line connecting the start point of a P wave and the start point of the next P wave when the electrocardiogram waveform is adjusted so that the difference between the maximum and minimum amplitudes of each waveform included in the electrocardiogram waveform is constant. The feature quantity related to the position of the baseline may be, for example, the position of a straight line in the electrocardiogram waveform that indicates a state in which no part of the heart is excited. The feature quantity related to the position of the baseline may also be the ratio of maximum amplitudes (baseline division ratio). The baseline division ratio is calculated, for example, by dividing the absolute value of the maximum positive amplitude by the absolute value of the maximum negative amplitude. The baseline division ratio may also be calculated by dividing the absolute value of the maximum positive amplitude by the absolute value of the maximum negative amplitude, whichever is greater, by the absolute value of the maximum positive amplitude or the absolute value of the maximum negative amplitude. The calculation unit 241 calculates the baseline division ratio for all pairs of electrodes 11. In the following description, a case in which the baseline division ratio is used as the feature quantity related to the position of the baseline will be described as an example.

[0026] 5A and 5B are diagrams illustrating electrocardiogram waveforms acquired by the acquisition unit 22. The vertical axis of each of FIGS. 5A and 5B illustrates potential difference (mV), and the horizontal axis illustrates time (seconds). The electrocardiogram waveform acquired by the acquisition unit 22 varies depending on the electrode pair used for measurement. FIGS. 5A and 5B are electrocardiogram waveforms measured by the acquisition unit 22 using different electrode pairs. The amplitude of the R wave, which indicates the maximum amplitude of the electrocardiogram waveform, is larger in FIG. 5A than in FIG. 5B, while the amplitude of the P wave, which is used for detecting atrial fibrillation, is larger in FIG. 5B than in FIG. 5A. In other words, when considering the detection of atrial fibrillation, the waveform of FIG. 5B is more preferable than the waveform of FIG. 5A. Furthermore, the baseline division ratio of the waveform of FIG. 5B is larger than that of the waveform of FIG. 5A. As a result of observing the electrocardiogram waveforms of many subjects in subject experiments, the inventors have found that the lower the baseline of an electrocardiogram waveform is below the QRS wave, the larger the amplitude of the P wave tends to be. The baseline division ratio is an index that increases as the baseline is lower than the QRS wave.

[0027] The pair selector 242 selects a pair of electrodes 11 to be used for electrocardiogram measurement based on the baseline division ratio calculated by the calculator 241. For example, the pair selector 242 selects the pair of electrodes 11 having the largest calculated baseline division ratio as the pair of electrodes 11 to be used for electrocardiogram measurement. The pair selector 242 stores information indicating the selected pair of electrodes 11 in the storage unit 25. The pair selector 242 also stores electrocardiogram signals acquired by the selected pair of electrodes 11 in the storage unit 25. The storage unit 25 is a non-volatile memory.

[0028] The output unit 26 is, for example, a liquid crystal display (LCD), a plasma display panel (PDP), an inorganic electroluminescence (EL) panel, or an organic EL panel. The output unit 26 displays, for example, information indicating the pair of electrodes 11 selected by the pair selection unit 242 and an electrocardiogram waveform indicating time-series changes in the electrocardiogram signal acquired by the acquisition unit 22. For example, a touch panel that detects touch operations by the user's finger or the like may be superimposed on the output unit 26. By superimposing a touch panel on the output unit 26, the electrocardiograph 1 can provide the user with an intuitive operating environment.

[0029] The detector 27 detects features of the electrocardiogram signal from the electrocardiogram signal stored in the memory 25 and detects atrial fibrillation based on the detected features. The detector 27 causes the output unit 26 to output the atrial fibrillation detection result.

[0030] (Selection of a pair of electrodes 11) Fig. 6 is a diagram showing an example of a processing flow of a process of selecting a pair of electrodes 11 by the electrode selector 24 in the embodiment. In the example illustrated in Fig. 6, the electrode selector 24 selects one pair of electrodes 11. Hereinafter, an example of a processing flow of a process of selecting a pair of electrodes 11 by the electrode selector 24 in the embodiment will be described with reference to Fig. 6.

[0031] In step S1, the electrode selector 24 acquires the electrocardiogram signal acquired by the acquirer 22. In step S2, the calculator 241 calculates a baseline splitting ratio. In step S3, the pair selector 242 selects a pair of electrodes 11 to be used for electrocardiogram measurement based on the baseline splitting ratio calculated in step S2. The pair selector 242 stores information indicating the selected pair of electrodes 11 in the storage unit 25. Thereafter, the electrocardiogram signal acquired by the selected electrodes 11 is stored in the storage unit 25, and the detector 27 detects atrial fibrillation using the electrocardiogram signal stored in the storage unit 25.

[0032] If a pair of electrodes 11 is selected based on the maximum amplitude of the waveform of an electrocardiogram signal, there is a risk that a pair of electrodes 11 that acquires an electrocardiogram signal with a large maximum amplitude (amplitude of the R wave) but a small amplitude of the P wave, such as the waveform of Fig. 5A, will be selected. According to this embodiment, by using the baseline division ratio, a pair of electrodes 11 that can acquire an electrocardiogram signal in which the P wave appears more clearly can be selected as a pair of electrodes 11 to be used for electrocardiogram measurement.

[0033] <First Modification> In the processing by the control main body 12 described in the embodiment, processing to remove noise components from the electrocardiogram signal acquired by the acquisition unit 22 is not performed. Therefore, if the subject wearing the electrocardiograph 1 is not standing still but is moving, noise is included in the electrocardiogram signal acquired by the acquisition unit 22, and it may be difficult to calculate the baseline division ratio with high accuracy. In the first modification, a modification is described in which processing to remove noise from the electrocardiogram signal acquired by the acquisition unit 22 is further performed. The same components as in the embodiment are assigned the same reference numerals, and their description is omitted. The first modification will be described below with reference to the drawings.

[0034] 7 is a block diagram showing an example of the functional configuration of a control unit 12A according to the first modification. The control unit 12A differs from the control unit 12 according to the embodiment in that it further includes a signal processing unit 23.

[0035] The signal processing unit 23 performs AD conversion and filtering of the electrocardiogram signal acquired by the acquisition unit 22. The signal processing unit 23 outputs the AD converted and filtered electrocardiogram signal to the electrode selection unit 24. The signal processing unit 23 has an extraction unit 231 and a filter unit 232. The extraction unit 231 extracts a normally acquired electrocardiogram signal from the electrocardiogram signal output by the acquisition unit 22. Examples of normally acquired electrocardiogram signals include a signal that is not saturated and a signal that does not have consecutive "0s." The length of the extracted electrocardiogram signal is, for example, 10 seconds.

[0036] The filter unit 232 removes high-frequency noise and low-frequency noise from the electrocardiogram signal extracted by the extraction unit 231 to increase the signal-to-noise ratio. High-frequency noise can be caused by, for example, myoelectric potential or power supply noise present around the subject. Low-frequency noise can be caused by, for example, displacement of the electrodes 11 due to the subject's movement. The filter unit 232 is, for example, a band-pass filter. The signal processing unit 23 outputs the electrocardiogram signal processed by the extraction unit 231 and the filter unit 232 to the electrode selection unit 24.

[0037] 8 is a diagram showing an example of a processing flow of the selection process of a pair of electrodes 11 by the electrode selector 24 in the first modified example. Hereinafter, an example of the processing flow of the selection process of a pair of electrodes 11 by the electrode selector 24 in the first modified example will be described with reference to FIG.

[0038] In step S21, the extraction unit 231 extracts a normal signal from the electrocardiogram signal read in step S1. In step S22, the filter unit 232 removes high-frequency noise and low-frequency noise from the signal extracted in step S21 to increase the signal-to-noise ratio.

[0039] In the processing illustrated in Figure 8, noise is removed by the processing of the signal processing unit 23 in step S22, so even if the subject wearing the electrocardiograph 1 is moving freely, the baseline division ratio can be calculated with high accuracy, and ultimately, pairs of electrodes 11 can be selected with high accuracy.

[0040] <Second Modification> In the embodiment and first modification described above, specification of an operation mode, such as the number of pairs of electrodes 11 used for electrocardiogram measurement or the frequency of selection of pairs of electrodes 11, was not accepted. In the second modification, a modification in which specification of these operation modes is accepted will be described. The same components as those in the embodiment and first modification are assigned the same reference numerals, and description thereof will be omitted. The second modification will be described below with reference to the drawings.

[0041] 9 is a block diagram showing an example of the functional configuration of a control unit 12B according to the second modification. The control unit 12B differs from the control unit 12A according to the first modification in that it further includes a mode control unit 21.

[0042] The mode control unit 21 receives from the user a designation of an operation mode related to electrocardiogram measurement. The operation mode includes, for example, designation of whether or not to select a pair of electrodes 11 to be used for electrocardiogram measurement, the frequency of selecting a pair of electrodes 11, whether or not to save power, the number of pairs of electrodes 11 to be selected, and the criteria for selecting pairs of electrodes 11.

[0043] The mode control unit 21 may, for example, output an operation mode designation screen to the output unit 26 and accept the designation of the operation mode from the user. Fig. 10 is a diagram showing an example of the operation mode designation screen that the mode control unit 21 outputs to the output unit 26 in the second modified example. The operation mode designation screen shown in Fig. 10 displays the following items: "Electrode selection," "Selection frequency," "Power saving," "Number of selected pairs," and "Selection criteria." In the operation mode designation screen shown in Fig. 10, for example, the selected parameter is indicated by coloring the background of the selected value.

[0044] In the "Electrode Selection" item, whether or not to select electrodes 11 is specified. When "Yes" is specified in the "Electrode Selection" item, a pair of electrodes 11 to be used for electrocardiogram measurement is selected by processing exemplified in FIG. 11 , which will be described later. When "No" is specified in the "Electrode Selection" item, for example, a default pair of electrodes 11 is used for electrocardiogram measurement. Information indicating the default pair of electrodes 11 is stored in the storage unit 25, for example, when the electrocardiograph 1 is manufactured.

[0045] The "selection frequency" item specifies how often to select a pair of electrodes 11. If "10 min" is specified in the "selection frequency" item, the selection of a pair of electrodes 11 is performed once every 10 minutes. If "30 min" is specified in the "selection frequency" item, the selection of a pair of electrodes 11 is performed once every 30 minutes. The period from one selection of an electrode 11 to the next is also referred to as "one cycle."

[0046] The "power saving" item specifies whether or not to enable the power saving mode. When "Yes" is specified in the "power saving" item, the power saving mode is executed. In the power saving mode, for example, when the same pair of electrodes 11 is selected for two consecutive cycles, a power saving operation is initiated in which the supply of power to electrodes other than the selected pair of electrodes 11 is turned off for four cycles. When four cycles have ended since the start of the power saving operation, the supply of power to all electrodes 11 is resumed, and a new pair of electrodes 11 to be used for electrocardiogram measurement is selected by the pair selector 242. When "No" is specified in the "power saving" item, the power saving mode is not executed.

[0047] The "number of selected pairs" field specifies the number of pairs of electrodes 11 to be used for electrocardiogram measurement. When "1" is specified in the "number of selected pairs" field, the pair selector 242 selects one pair of electrodes 11 to be used for electrocardiogram measurement. When "3" is specified in the "number of selected pairs" field, the pair selector 242 selects three pairs of electrodes 11 to be used for electrocardiogram measurement.

[0048] The "selection criteria" field specifies a criterion for selecting a pair of electrodes 11. When "low baseline" is selected in the "selection criteria," a pair of electrodes 11 having a low baseline (large baseline division ratio) in the waveform of an electrocardiogram signal is preferentially selected as a pair of electrodes 11 to be used for electrocardiogram measurement. When "high-low baseline" is selected in the "selection criteria," a pair of electrodes 11 having a low baseline (large baseline division ratio) in the waveform of an electrocardiogram signal and a pair of electrodes 11 having a high baseline (small baseline division ratio) are selected as pairs of electrodes 11 to be used for electrocardiogram measurement. For example, when the "number of selected pairs" is "1" and the "selection criteria" is "high-low baseline," the pair selector 242 may select one pair of electrodes 11 having the largest baseline division ratio and one pair of electrodes 11 having the smallest baseline division ratio, i.e., two pairs of electrodes 11 in total.

[0049] Fig. 11 is a diagram showing a first example of a processing flow of a process for selecting a pair of electrodes 11 by the electrode selector 24 in the second modified example. In the processing flow illustrated in Fig. 11, it is assumed that, for example, the operation mode illustrated in Fig. 10 has been specified. That is, it is assumed that the operation mode is specified as follows: "Yes" for "Electrode Selection," "10 min" for "Selection Frequency," "No" for "Power Saving," "3" for "Number of Selected Pairs," and "Low Baseline" for "Selection Criteria."

[0050] In step S3A, the pair selector 242 selects pairs of electrodes 11 to be used for electrocardiogram measurement, the number of pairs being the "number of selected pairs" accepted by the mode controller 21. Here, the three pairs of electrodes 11 to be used for electrocardiogram measurement are selected in descending order of the baseline position, i.e., in descending order of the baseline division ratio.

[0051] Since "10 min" is specified as the "selection frequency", the processes of steps S1, S21, S22, S2 and S3A are repeatedly executed every 10 minutes.

[0052] FIG. 12 is a diagram illustrating an example of the correspondence between a cycle executed every 10 minutes and time. FIG. 12 illustrates the items "Time" and "Cycle." In FIG. 12 , for example, it is assumed that measurement by the control main unit 12 begins at 11:38:40. In this case, the control main unit 12 waits without starting measurement until 11:39:59. Then, at 11:40:00, the control main unit 12 executes the processes of steps S1, S21, S22, S2, and S3 to select a pair of electrodes 11 to be used for electrocardiographic measurement, and performs electrocardiographic measurement using the selected pair of electrodes 11. Subsequently, at 11:50:00, the control main unit 12 executes the processes of steps S1, S21, S22, S2, and S3 to reselect a pair of electrodes 11 to be used for electrocardiographic measurement, and performs electrocardiographic measurement using the reselected pair of electrodes 11. The same applies after 11:50.

[0053] Next, a process when "Yes" is selected for "Power saving" as an operation mode will be described. Fig. 13 is a diagram showing a second example of the process flow of the selection process of a pair of electrodes 11 by the electrode selector 24 in the second modified example. In the second example, it is assumed that "Yes" is specified for "Electrode selection," "10 min" for "Selection frequency," "Yes" for "Power saving," "1" for "Number of selected pairs," and "Low baseline" for "Selection criteria" as the operation mode.

[0054] In step S31, the mode control unit 21 determines whether the same pair of electrodes 11 has been selected in consecutive cycles by the pair selection unit 242. If the same pair of electrodes 11 has been selected in consecutive cycles (YES in step S31), the process proceeds to step S32. If the same pair of electrodes 11 has not been selected in consecutive cycles (NO in step S32), the process ends.

[0055] In step S32, the mode control unit 21 starts a power saving operation. When the power saving operation starts, the supply of power to the electrodes 11 other than the pair of electrodes 11 selected in step S31 is stopped.

[0056] Fig. 14 is a diagram showing an example of a process flow for electrocardiogram measurement when power-saving operation is started in Modification 2. Hereinafter, an example of a process flow for electrocardiogram measurement when power-saving operation is started in Modification 2 will be described with reference to Fig. 14 .

[0057] In step S41, the acquisition unit 22 acquires an electrocardiogram signal using the pair of electrodes 11 stored in the storage unit 25. In step S42, the electrocardiogram signal filtered by the filter unit 232 in step S22 is stored in the storage unit 25. The detection unit 27 detects, for example, the presence or absence of atrial fibrillation using the electrocardiogram signal stored in the storage unit 25. After the processing from step S41 to step S42 has been repeated a predetermined number of cycles (for example, four cycles), the processing proceeds to step S43. In step S43, power supply to all of the electrodes 11 is resumed.

[0058] FIG. 15 is a diagram illustrating an example of switching the power-saving operation on and off. In FIG. 15 , as in FIG. 12 , it is assumed that electrocardiogram measurement started at 11:38:40. In FIG. 15 , the items "Time," "Cycle," "Selected Pair," and "Power Saving" are illustrated. Since "Time" and "Cycle" are the same as in FIG. 12 , their description will be omitted. "Selected Pair" illustrates information indicating the pair of electrodes 11 selected by the pair selection unit 242. In the example of FIG. 15 , a unique ID is assigned to each pair of electrodes 11, and "Selected Pair" illustrates the ID indicating the pair of electrodes 11. "Power Saving" illustrates whether or not the power-saving operation is being performed. In "Power Saving," "ON" illustrates that the power-saving operation is being performed, and "OFF" illustrates that the power-saving operation is not being performed.

[0059] 15 , the same pair of electrodes 11 is selected consecutively from the second cycle to the third cycle. Therefore, power saving operation is performed for four cycles from the fourth cycle to the seventh cycle, and power supply is stopped to the electrodes 11 other than the pair of electrodes 11 indicated by ID "7." In the eighth cycle, power supply to all electrodes 11 is resumed, and the pair selection unit 242 selects a pair of electrodes 11.

[0060] According to the second modification, electrocardiogram measurement can be performed in an operation mode that suits the subject's preference, since the mode control unit 21 accepts the operation mode designation. Furthermore, in the second modification, when the power saving mode is turned on, power supply to the electrodes 11 other than the pair of electrodes 11 selected in successive cycles is stopped, thereby reducing the power consumption of the electrocardiograph 1.

[0061] Furthermore, in the power-saving mode, if the same pair of electrodes 11 is selected for two consecutive cycles, the power-saving operation is initiated, and the supply of power to the electrodes 11 other than the selected pair of electrodes 11 is stopped. If the same pair of electrodes 11 is selected for two consecutive cycles, there is a high probability that the same pair of electrodes 11 will continue to be selected because the subject's posture is stable, etc. Therefore, even if the power-saving operation is initiated when the same pair of electrodes 11 is selected for two consecutive cycles, it is considered that the impact on the measurement accuracy of electrocardiogram measurement by the electrocardiograph 1 is small.

[0062] <Other Modifications> In the above-described embodiments and modifications, the baseline division ratio has been used as a feature quantity related to the baseline position. However, other values ​​may be used as the feature quantity related to the baseline position. For example, the feature quantity related to the baseline position may be a value obtained by dividing the larger of the absolute value of the maximum amplitude in the positive direction and the absolute value of the maximum amplitude in the negative direction by the smaller of the absolute value of the maximum amplitude in the negative direction when the baseline potential of the electrocardiogram waveform is used as a reference. Furthermore, for example, when the difference between the maximum and minimum amplitudes of each waveform included in the electrocardiogram waveform is adjusted to be constant, the feature quantity related to the baseline position may be the difference between the absolute value of the maximum amplitude in the positive direction and the absolute value of the maximum amplitude in the negative direction in the electrocardiogram waveform. Furthermore, for example, the feature quantity related to the baseline position may be the average amplitude of the P wave, R wave, S wave, and Q wave in the electrocardiogram waveform.

[0063] The embodiments and modifications disclosed above can be combined with each other.

[0064] <Supplementary Note 1> A biosignal measuring device (1) comprising: a band-shaped fixing member (10) wrapped around a subject; multiple sets of electrodes (11) arranged on the fixing member; a selection unit (242) that selects a set of measurement electrodes to be used to acquire an electrocardiogram waveform from the multiple sets of electrodes based on feature quantities based on absolute values ​​of the maximum amplitude in the positive direction and the maximum amplitude in the negative direction relative to a baseline potential of an electrocardiogram waveform of the subject acquired by each of the multiple sets of electrodes; and a detection unit (27) that detects features of the electrocardiogram waveform using the selected set of measurement electrodes. <Supplementary Note 2> The biosignal measuring device (1) according to Supplementary Note 1, wherein the feature quantities include a value obtained by dividing the larger of the absolute value of the maximum amplitude in the positive direction and the absolute value of the maximum amplitude in the negative direction in the electrocardiogram waveform by the smaller of the absolute value of the maximum amplitude in the positive direction and the absolute value of the maximum amplitude in the negative direction. <Supplementary Note 3> The biosignal measuring device (1) according to Supplementary Note 1 or 2, wherein the electrocardiogram waveform is adjusted so that a difference between a maximum amplitude and a minimum amplitude of each waveform included in the electrocardiogram waveform is constant, and the feature amount includes a difference between the absolute value of the maximum amplitude in the positive direction and the absolute value of the maximum amplitude in the negative direction in the electrocardiogram waveform. <Supplementary Note 4> The biosignal measuring device (1) according to any one of Supplementary Notes 1 to 3, wherein the electrocardiogram waveform is adjusted so that a difference between a maximum amplitude and a minimum amplitude of each waveform included in the electrocardiogram waveform is constant, and the feature amount includes at least one of a first absolute value of the maximum amplitude in the positive direction and a second absolute value of the maximum amplitude in the negative direction in the electrocardiogram waveform. <Supplementary Note 5> The biosignal measuring device (1) according to any one of claims 1 to 4, wherein the selector (242) selects an electrode pair whose feature amount is larger than that of other electrode pairs as the measurement electrode pair. <Supplementary Note 6> The biological signal measuring device (1) according to any one of Supplementary Notes 1 to 5, wherein the characteristics include at least one of an RRI, which is the interval between peaks of R waves in the electrocardiogram waveform, and the presence or absence of a P wave in the electrocardiogram waveform.<Supplementary Note 7> The biological signal measuring device (1) according to any one of Supplements 1 to 6, further comprising a control unit (21) that selects the pair of measurement electrodes at predetermined intervals and stops supplying power to the electrodes (11) other than the pair of measurement electrodes when the same pair of electrodes (11) is consecutively selected as the pair of measurement electrodes. <Supplementary Note 8> The biological signal measuring device (1) according to any one of Supplements 1 to 7, wherein the selection unit (242) receives a designation of the number of pairs of measurement electrodes to select and selects the same number of pairs of measurement electrodes as the received number. <Supplementary Note 9> The biological signal measuring device (1) according to any one of Supplements 1 to 8, wherein the detection unit detects atrial fibrillation based on the detected features.

[0065] DESCRIPTION OF SYMBOLS 1. Electrocardiograph 10. Band 11. Electrode 12. Control unit 12A. Control unit 12B. Control unit 13. Fixing mechanism 21. Mode control unit 22. Acquisition unit 23. Signal processing unit 24. Electrode selection unit 25. Storage unit 26. Output unit 27. Detection unit 231. Extraction unit 232. Filter unit 241. Calculation unit 242. Pair selection unit

Claims

1. A biosignal measuring device comprising: a band-shaped fixing member wrapped around a subject; multiple sets of electrodes arranged on the fixing member; a selection unit that selects a set of measurement electrodes to be used for acquiring an electrocardiogram waveform from the multiple sets of electrodes based on features based on the absolute value of the maximum amplitude in the positive direction and the absolute value of the maximum amplitude in the negative direction when the baseline potential of the electrocardiogram waveform of the subject acquired by each of the multiple sets of electrodes is taken as a reference; and a detection unit that detects features of the electrocardiogram waveform using the selected set of measurement electrodes.

2. The biosignal measuring device of claim 1, wherein the feature value includes a value obtained by dividing the greater of the absolute value of the maximum amplitude in the positive direction in the electrocardiogram waveform and the absolute value of the maximum amplitude in the negative direction by the smaller of these values.

3. The biosignal measuring device of claim 1, wherein the electrocardiogram waveform is adjusted so that the difference between the maximum amplitude and the minimum amplitude of each waveform contained in the electrocardiogram waveform is constant, and the feature value includes the difference between the absolute value of the maximum amplitude in the positive direction in the electrocardiogram waveform and the absolute value of the maximum amplitude in the negative direction.

4. The biosignal measuring device of claim 1, wherein the electrocardiogram waveform is adjusted so that the difference between the maximum amplitude and the minimum amplitude of each waveform contained in the electrocardiogram waveform is constant, and the feature value includes at least one of a first absolute value of the maximum amplitude in the positive direction in the electrocardiogram waveform and a second absolute value of the maximum amplitude in the negative direction.

5. The biosignal measuring device according to claim 1, wherein the selection unit selects, as the measurement electrode pair, an electrode pair having a larger feature amount than other electrode pairs.

6. The biosignal measuring device according to claim 1, wherein the characteristics include at least one of an RRI, which is the interval between peaks of R waves in the electrocardiogram waveform, and the presence or absence of a P wave in the electrocardiogram waveform.

7. The biosignal measuring device of claim 1, further comprising a control unit that selects the pair of measurement electrodes at a predetermined interval and stops the supply of power to the electrodes other than the pair of measurement electrodes when the same pair of electrodes is consecutively selected as the pair of measurement electrodes.

8. The biosignal measuring device according to claim 1, wherein the selection unit receives a designation of the number of pairs of measurement electrodes to be selected, and selects the number of pairs of measurement electrodes equal to the received number.

9. The biosignal measuring device according to any one of claims 1 to 8, wherein the detection unit detects atrial fibrillation based on the detected features.

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