JP5110277B2 - Body composition estimation device and body composition estimation method - Google Patents

Description

  The present invention relates to a body composition estimation apparatus, and more particularly to a body composition estimation apparatus and a body composition estimation method used for estimating body composition such as a body fat state and body water distribution of a subject based on a bioelectrical impedance method.

  Conventionally, for example, in Patent Documents 1 to 4 and the like, various body composition estimation apparatuses for estimating body composition such as the body fat state and body water distribution of a subject based on the bioelectrical impedance method have been proposed. Specifically, Patent Document 1 discloses a body composition estimation device using the body composition estimation method described below.

That is, in the body composition estimation apparatus described in Patent Document 1, bioelectrical impedance is measured when a plurality of currents having different frequencies are applied. From the obtained bioelectrical impedance at a plurality of frequencies, an impedance locus is calculated by using the least square method. A bioelectrical impedance R0 when the frequency of the subject's body is 0 and a bioelectrical impedance R∞ when the frequency is ∞ are calculated from the impedance locus. Then, the body composition of the subject's body is estimated from the bioelectrical impedances R0 and R∞.
JP 2000-316829 A Japanese Patent Laid-Open No. 9-154829 JP 2003-116805 A Japanese Patent No. 3984332

  The measured value of the electrical impedance of the subject's body varies greatly depending on the posture of the subject when measuring the electrical impedance and the contact state between the subject's body and the electrode of the body composition estimation apparatus. For this reason, when the subject's posture is not preferable, or when a part of the subject's body is in contact with a metal member such as a frame of the bed, the electrical impedance may not be measured accurately.

  However, in the body composition estimation apparatus disclosed in Patent Document 1, even when the electrical impedance is not accurately measured, the body composition is estimated and the estimated body composition is output. In this case, since the body composition is estimated based on inaccurate electrical impedance, the obtained body composition estimation value is also inaccurate. Therefore, if such an inaccurate body composition estimated value is output, the body composition may be misidentified.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide an electrical characteristic estimation device that can suppress the body composition of a subject from being misidentified.

  For example, Patent Document 2 discloses a method for displaying an impedance locus on a screen together with an estimated body composition value. Patent Document 3 discloses a technique for displaying a change in impedance locus in real time. According to these techniques, the subject or the diagnostician cannot see whether the accurate measurement has been performed by looking at the displayed impedance locus.

  However, in these techniques, since it is left to the subjective judgment of the subject or measurer to determine whether or not an accurate measurement has been performed, it is difficult to make a quantitative judgment. The judgment of whether or not it has been made will be different. In addition, it is difficult for a subject who is not used to using the electrical characteristic estimation apparatus to determine whether normal measurement has been performed from the impedance trajectory.

  The body composition estimation apparatus according to the present invention estimates the body composition of a subject. The body composition estimation apparatus according to the present invention includes an electrical impedance measurement unit, an impedance locus calculation unit, a determination unit, a notification unit, and a body composition estimation unit. The electrical impedance measurement unit generates a plurality of probe currents having different frequencies, applies the probe current of each frequency to the subject's body, and measures the electrical impedance of the subject's body. The impedance locus calculation unit calculates an impedance locus from the electrical impedance at each frequency measured by the electrical impedance measurement unit. The determination unit determines whether there is no abnormality in the measurement of the electrical impedance based on at least one of the distribution of the electrical impedance with respect to the impedance locus at each measured frequency and the size of the impedance locus. The notification unit notifies the abnormality when the determination unit determines that there is an abnormality. The body composition estimation unit estimates the body composition of the subject from the impedance locus when at least the determination unit determines that there is no abnormality.

In a specific aspect of the present invention, determination unit Sigma] e ^{(f) 2,} is' Sigma] e obtained by ^{(f) 2} or the following formula ^{(2) '' (f)} 2 Σe obtained by the following equation (1), It is determined that there is an abnormality in the measurement of electrical impedance when the threshold value is larger than a predetermined threshold value.
Σe ′ (f) ² = Σ {e (f) / r} ² (1)
Σe ″ (f) ² = Σ {e (f) / h} ² (2)
However,
e (f): distance in a predetermined direction between the electrical impedance and the impedance locus at the frequency (f),
r: radius of impedance locus,
h: height of subject,
It is.

  In another specific aspect of the present invention, the determination unit determines that there is an abnormality in the measurement of electrical impedance when the frequency at the point where the reactance is minimum in the impedance locus is outside a predetermined range.

  In yet another specific aspect of the present invention, the determination unit divides the electrical impedance R∞ when the frequency of the probe current calculated from the impedance locus is ∞ by the electrical impedance R0 when the frequency of the probe current is 0. When the value R∞ / R0 obtained is outside the predetermined range, it is determined that there is an abnormality in the measurement of the electrical impedance.

  In a specific aspect of the present invention, the determination unit determines that there is an abnormality in the measurement of electrical impedance even when the frequency at the point where reactance is minimum is not within a predetermined range in the impedance locus. It may be.

  In this case, the determination unit is obtained by dividing the electrical impedance R∞ when the frequency of the probe current calculated from the impedance locus is ∞ by the electrical impedance R0 when the frequency of the probe current is 0. Even when the value R∞ / R0 is outside the predetermined range, it may be determined that there is an abnormality in the measurement of the electrical impedance.

  In a specific aspect or another specific aspect of the present invention, the determination unit determines the electrical impedance R∞ when the frequency of the probe current calculated from the impedance locus is ∞ as the frequency of the probe current is 0. Even when the value R∞ / R0 obtained by dividing by the electric impedance R0 is outside the predetermined range, it may be determined that there is an abnormality in the measurement of the electric impedance.

  In the body composition estimation unit according to the present invention, the body composition estimation unit may estimate the body composition of the subject only when the determination unit determines that there is no abnormality.

  The body composition estimation method according to the present invention is a method for estimating the body composition of a subject, and includes an electrical impedance measurement step, an impedance locus calculation step, a determination step, a notification step, and a body composition estimation step. Yes. The electrical impedance measurement step is a step of generating a plurality of probe currents having different frequencies, applying the generated probe currents of the respective frequencies to the subject's body, and measuring the electrical impedance of the subject's body. The impedance locus calculation step is a step of calculating an impedance locus from the electrical impedance at each frequency measured in the electrical impedance measurement step. The determination step is a step of determining whether or not there is no abnormality in the measurement of the electrical impedance based on at least one of the distribution of the electrical impedance with respect to the impedance locus at various measured frequencies and the size of the radius of the impedance locus. The notification step is a step of notifying that there is an abnormality when it is determined that there is an abnormality in the determination step. The body composition estimation step is a step of estimating the body composition of the subject from the impedance locus when it is determined that there is no abnormality at least in the determination unit.

  According to the present invention, the determination unit automatically determines whether or not there is an abnormality in the measurement of electrical impedance. When it is determined that there is an abnormality in the measurement of electrical impedance, the notification unit notifies the abnormality. Therefore, it can suppress that a test subject misidentifies a body composition.

(Bioelectrical impedance method)
Prior to describing the embodiment of the present invention, the principle of the bioelectrical impedance method used in the body composition estimation apparatus of the following embodiment will be described.

  The bioelectrical impedance method is a method for estimating body composition such as body water distribution, body fat percentage, and body fat mass of a subject from bioelectrical impedance. Bioelectrical impedance consists of the body's resistance to the current carried by ions in the body and the reactance associated with various types of polarization processes created by cell membranes, tissue interfaces, or non-ionized tissues.

Capacintas, which is the reciprocal of reactance, mainly causes a time delay in the current and creates a phase shift. This phase shift can be quantified geometrically as the electrical phase angle, which is the arctangent of the ratio of reactance to resistance. The magnitude of the bioelectrical impedance Z is defined as Z ² = R ² + X ² where R is resistance and X is reactance.

  The bioelectric impedance Z, resistance R, reactance X, and electrical phase angle Φ have frequency dependency. When the current frequency is very low, the bioelectrical impedance Z at the cell membrane-tissue interface is very high. For this reason, current does not flow through the cell membrane or tissue interface, but only through the extracellular fluid. Therefore, the measured bioelectrical impedance Z is substantially equal to the resistance R.

  As the frequency of the current increases, the current flows through the cell membrane and tissue interface. For this reason, the reactance X is increased and the phase angle Φ is increased. However, when the frequency of the current exceeds the critical frequency fc, the capacitive performance of the cell membrane and the tissue interface is lost. For this reason, when the frequency of the current exceeds the critical frequency fc, the reactance X decreases. When the current frequency becomes very high, the bioelectrical impedance Z again becomes substantially equal to the resistance R again. The “critical frequency” refers to the frequency at which the reactance is maximized.

  FIG. 3 is an electrical equivalent circuit diagram of the human body. As shown in FIG. 3, the equivalent circuit of the human body is configured by a parallel circuit of a circuit in which a cell membrane capacitance Cmk and an intracellular fluid resistance Rik are connected in series and an extracellular fluid resistance Re.

  When the current frequency is low, the current flows mainly in the extracellular space. For this reason, the impedance Z is substantially equal to the extracellular fluid resistance Re. On the other hand, when the frequency of the current is high, the current substantially passes through the cell membrane. For this reason, the cell membrane capacitance Cm is considered to be substantially short-circuited. Therefore, when the frequency of the current is high, the impedance Z is substantially equal to the combined resistance Ri · Re / (Ri + Re). Here, Cm and Ri mean the combined capacity and combined resistance of Cmk and Rik as a whole tissue.

  Therefore, the extracellular fluid resistance Re can be obtained by applying a low-frequency current and measuring the electrical impedance of the subject's body. Further, the intracellular fluid resistance Ri is obtained from Z = Ri · Re / (Ri + Re) from the obtained extracellular fluid resistance Re and the electrical impedance of the subject's body when a high-frequency current is applied. Can do. Then, the body composition value of the subject can be estimated based on the obtained intracellular fluid resistance Ri and extracellular fluid resistance Re. In addition, the estimation method of a test subject's body composition is not specifically limited, A conventionally well-known method can be used.

  In the present specification, “body composition” refers to all data related to body composition. For example, “body composition” includes the amount of body composition, the ratio of a particular composition to the body, the distribution of the particular composition to the body, and the like. The “composition” is a composition of the body, and specific examples of the composition include water, intracellular fluid, extracellular fluid, protein, fat, calcium content and the like. Specific examples of the body composition include body fat percentage, weight of fat contained in the subject's body, slow fat body weight, body water distribution, bone density, and the like. Specific examples of body water distribution include intracellular fluid volume, extracellular fluid volume, and body water volume. The amount of water in the body is the sum of the amount of intracellular fluid and the amount of extracellular fluid.

(First embodiment)
-Configuration of body composition estimation device 1-
Next, the body composition estimation apparatus 1 according to the first embodiment shown in FIGS. 1 and 2 will be described. As shown in FIG. 2, the body composition estimation device 1 is a device for estimating the body composition of the body E of the subject. As shown in FIG. 1, the body composition estimation apparatus 1 includes a CPU (central processing unit) 10, a current detection unit 20, a signal output unit 30, a voltage detection unit 40, a recording unit 62, and an input unit 63. The speaker 64, the display unit 65, the surface electrodes Lc and Hc, and the surface electrodes Lp and Hp are provided.

  The CPU 10 includes an impedance locus calculation unit 11, an impedance calculation unit 12, a determination unit 13, a body composition estimation unit 15, and a notification unit 14. The impedance calculation unit 12, the current detection unit 20, the signal output unit 30, and the voltage detection unit 40 of the CPU 10 constitute an electrical impedance measurement unit 50.

  First, the electrical impedance measurement unit 50 will be described with reference to FIGS. 1 and 2. The electrical impedance measurement unit 50 generates a plurality of probe currents having different frequencies, applies the probe currents of the respective frequencies to the body E of the subject, and causes the probe currents of the respective frequencies to flow through the body E of the subject. The electrical impedance of the body E of the subject is measured.

  The signal output unit 30 causes the multi-frequency current Ib to flow through the subject's body E in accordance with an instruction from the CPU 10. The signal output unit 30 includes a PIO (parallel interface) 31, a measurement signal generator 32, and an output buffer 33. The measurement signal generator 32 outputs a measurement signal (current) Ia to the output buffer 33 at predetermined intervals in accordance with an instruction from the CPU 10 performed via the PIO 31. The period in which the measurement signal generator 32 outputs the measurement signal Ia can be set to, for example, about 800 nsec. The measurement signal Ia is a signal that changes as needed at predetermined frequency intervals within the predetermined period. The measurement signal Ia may change at a frequency interval of 15 kHz in the range of 1 kHz to 400 kHz, for example. Alternatively, it may be a measurement signal including many frequency components such as an M-sequence signal disclosed in Japanese Patent Laid-Open No. 10-14898.

  The output buffer 33 outputs the input measurement signal Ia to the surface electrode Hc as a multi-frequency current Ib while maintaining a constant current state. As shown in FIG. 2, the surface electrode Hc is attached to the right back H of the subject's body E at the time of measurement. Thereby, the multi-frequency current Ib flows through the body E of the subject. Note that the current value of the multi-frequency current Ib is not particularly limited. The current value of the multi-frequency current Ib can be set to, for example, about 100 to 800 μA.

  The surface electrode Hc is paired with the surface electrode Lc. The surface electrode Lc is attached to the right instep L. As shown in FIG. 1, the surface electrode Lc is connected to the current detection unit 20. The current detection unit 20 detects the multi-frequency current Ib flowing through the body E of the subject, converts the multi-frequency current Ib into a voltage, and then outputs the obtained voltage signal Vb.

  As shown in FIG. 1, the current detection unit 20 includes an I / V converter 24, a BPF 23, an A / D converter 22, and a sampling memory 21. The I / V converter 24 is a current / voltage converter. As shown in FIG. 2, the I / V converter 24 detects a multi-frequency current Ib flowing between the surface electrode Hc and the surface electrode Lc and converts it into a voltage Vb. The I / V converter 24 outputs the obtained voltage Vb to the BPF 23.

  The BPF 23 is a band pass filter. The BPF 23 cuts an unnecessary band signal from the voltage signal Vb and outputs the cut signal to the A / D converter 22. Note that the passband of the BPF 23 can be appropriately selected according to the specifications of the body composition estimation apparatus 1. The pass band of the BPF 23 can be set to about 1 kHz to 800 kHz, for example.

  The A / D converter 22 converts the analog voltage Vb into a digital voltage signal Vb in accordance with a digital conversion instruction from the CPU 10. The digital voltage signal Vb is stored in the sampling memory 21 as current data Vb for each frequency of the measurement signal Ia.

  The sampling memory 21 transmits the digital voltage signal Vb temporarily stored for each frequency of the measurement signal Ia to the CPU 10 in response to the request of the CPU 10. Specifically, the digital voltage signal Vb is transmitted to the impedance calculation unit 12 in the CPU 10. The sampling memory 21 and the sampling memory 41 to be described later can be configured by, for example, SRAM.

  Thus, the digital voltage signal Vb is input to the impedance calculation unit 12 by the signal output unit 30 and the current detection unit 20.

  On the other hand, the digital voltage signal Vp is input from the voltage detector 40 to the impedance calculator 12.

  As shown in FIG. 1, the voltage detection unit 40 includes a differential amplifier 44, a BPF 43, an A / D converter 42, and a sampling memory 41.

  As shown in FIG. 2, the differential amplifier 44 detects a voltage Vp between the surface electrode Hp attached to the subject's right back H and the surface electrode Lp attached to the rear leg L. As shown in FIG. 1, the differential amplifier 44 outputs the detected voltage Vp to the BPF 43.

  The BPF 43 cuts a signal in a predetermined band from the input voltage signal Vp and outputs the cut signal to the A / D converter 42. Note that the passband of the BPF 43 can be appropriately selected according to the specifications of the body composition estimation apparatus 1. The pass band of the BPF 43 can be set to about 1 kHz to 800 kHz, for example.

  The A / D converter 42 converts the analog voltage Vp into a digital voltage signal Vp in accordance with a digital conversion instruction from the CPU 10. The digital voltage signal Vp is stored in the sampling memory 41 for each frequency of the measurement signal Ia.

  The sampling memory 41 transmits the temporarily stored digital voltage signal Vp to the CPU 10 in response to the request of the CPU 10. Specifically, the digital voltage signal Vp is transmitted to the impedance calculation unit 12 in the CPU 10.

  The impedance calculator 12 calculates the electrical impedance of the body E of the subject from the input digital voltage signals Vb and Vp. The impedance calculation unit 12 outputs the calculated electrical impedance to the impedance locus calculation unit 11, the determination unit 13, and the body composition estimation unit 15.

  The impedance locus calculation unit 11 calculates the center coordinates and radius of the impedance locus from the electrical impedance at each frequency input from the impedance calculation unit 12. Further, the impedance trajectory calculation unit 11 further calculates the resistance R∞ when the probe current frequency is ∞, the resistance R0 when the probe current frequency is 0, R∞ / R0, and the critical frequency fc. calculate. The impedance locus calculation unit 11 outputs the impedance locus, R∞, R0, and R∞ / R0, the critical frequency fc, and the electrical impedance calculated in step S1 to the determination unit 13 and the body composition estimation unit 15. .

  The impedance locus is calculated using the least square method. The resistances R∞ and R0 can be calculated by obtaining the intersection between the calculated impedance locus and the reactance X = 0. The critical frequency fc can be calculated from the frequencies corresponding to the measured electrical impedance values located on the left and right sides of the point where the reactance becomes the smallest in the impedance locus.

  FIG. 6 is a graph showing an ideal impedance locus. The horizontal axis of the graph shown in FIG. 6 is resistance R, and the vertical axis is reactance X. The data indicated by dots in FIG. 6 are measured electrical impedance values at each frequency. In FIG. 6, the data is measured when the dot D is applied with the current having the highest frequency. In FIG. 6, dot E is data measured when a current having the lowest frequency is applied.

  The impedance trajectory is a curve calculated so as to fit the electrical impedance measurement value of each frequency. Usually, the impedance locus is a Cole-Cole arc.

  As described above, when the frequency is very low and very high, the reactance X is substantially zero and the electrical impedance Z is substantially equal to the resistance R. For this reason, as shown in FIG. 6, among the intersections of the impedance locus and X = 0, the larger resistance is the resistance R0 when the frequency is 0, and the smaller resistance is when the frequency is ∞. Resistance R∞.

  The determination unit 13 illustrated in FIG. 1 determines whether there is no abnormality in the electrical impedance measurement based on at least one of the distribution of the electrical impedance measurement value at each frequency with respect to the impedance locus and the radius of the impedance locus. When it is determined that there is no abnormality in the electrical impedance measurement, the determination unit 13 outputs an OK signal indicating “no abnormality” to the body composition estimation unit 15 and the notification unit 14. On the other hand, when it is determined that there is an abnormality in the electrical impedance measurement, the determination unit 13 outputs an NG signal indicating “abnormality” to the body composition estimation unit 15 and the notification unit 14.

  The notification unit 14 does nothing when the OK signal is input, and notifies the subject or the operator of the body composition estimation apparatus 1 of the abnormality when the NG signal is input. An abnormality notification method is not particularly limited. For example, the abnormality may be notified by a method of outputting an abnormality notification sound from the speaker 64, a method of displaying an abnormality in the electrical impedance measurement on the display unit 65, or a method of combining them.

  The body composition estimation unit 15 estimates the body composition based on the measured electrical impedance value and the impedance locus, and the subject information input from the input unit 63 configured by a keyboard or the like. The body composition estimation unit 15 estimates the body composition at least when an OK signal is input. The body composition estimation unit 15 may estimate the body composition only when an OK signal is input, or the body composition is estimated both when an OK signal is input and when an NG signal is input. It may be estimated. In the present embodiment, a case where the body composition is estimated only when an OK signal is input will be described as an example.

  The body composition estimation unit 15 outputs the estimated body composition to the display unit 65. The display unit 65 displays the estimated body composition. When an NG signal is output from the determination unit 13 to the notification unit 14, it is displayed that the estimation of the body composition has been stopped, assuming that there is an abnormality in the electrical impedance measurement.

  The body composition estimation unit 15 also outputs the estimated body composition to the recording unit 62. The recording unit 62 records the estimated body composition. The recording unit 62 can be configured by a RAM, a ROM, a hard disk, or the like.

In addition, the specific estimation method of a body composition is not specifically limited, A conventionally well-known method can be used. For example, body water content can be estimated by regression analysis. Specifically, it is assumed that a conductor portion of a human body, that is, a body moisture portion is a cylinder having a length L and a cross-sectional area S. In that case, the resistance of the conductor portion of the human body is proportional to the length L and inversely proportional to the cross-sectional area S. Therefore, when R = ρL / S and deformation occurs, S = ρL / R. Substituting this into the volume V = LS, the volume V of the conductor part of the human body is estimated as ρL ² / R. Therefore, the body water content (TBW) can be estimated by TBW = α + βL ² / R. Here, α and β are statistically determined constants. Moreover, the accuracy of the estimated body water content can be improved by adding human body characteristic data such as height to the above formula. Specifically, the body water content (TBW) can be estimated more accurately by TBW = α + βL ² / R + γW + δAGE, so that the body water content can be estimated more accurately. Here, W is weight and AGE is age.

  A lean mass (FFM) can also be estimated by the same method.

-Operation of body composition estimation apparatus 1-
Next, the operation of the body composition estimation apparatus 1 will be described mainly with reference to FIGS. 4 and 5 and FIG.

(1) Measurement of electrical impedance (step S1)
As shown in FIG. 4, first, in step S1, the electrical impedance of the body E of the subject is measured. Step S1 includes step S1-1, step S1-2, and step S1-3. In step S1-1, the voltage Vb is detected. Specifically, the multi-frequency current Ib is caused to flow from the signal output unit 30 shown in FIG. The current detector 20 detects the multi-frequency current Ib that has flowed through the body E of the subject. The detected multi-frequency current Ib is converted into a voltage Vb by the I / V converter 24. As for the voltage Vb, a voltage signal in an unnecessary band is cut in the BPF 23, and further converted into a digital voltage signal Vb in the A / D converter 22. The digital voltage signal Vb is temporarily stored in the sampling memory 21 and then output to the impedance calculation unit 12 in the CPU 10 in response to a request from the CPU 10.

  As shown in FIG. 4, step S1-2 is performed in parallel with step S1-1. In S1-2, the voltage Vp is detected. Specifically, when the probe current Ib is supplied from the signal output unit 30 shown in FIG. 1, the differential amplifier 44 detects the voltage Vp between the surface electrode Hp and the surface electrode Lp. From the detected voltage Vp, an unnecessary band voltage signal is cut in the BPF 43 and further converted into a digital voltage signal Vp in the A / D converter 42. The digital voltage signal Vp is temporarily stored in the sampling memory 41, and then output to the impedance calculation unit 12 in the CPU 10 in response to a request from the CPU 10.

  As shown in FIG. 4, step S1-3 is performed following step S1-1 and step S1-2. In step S <b> 1-3, from the digital voltages Vb and Vp output to the impedance calculator 12, the impedance calculator 12 calculates an electrical impedance when a probe current of each frequency is applied. Specifically, when the measurement signal includes many frequency components such as an M-sequence signal, first, Fourier transform processing is performed on the voltages Vb and Vp that are functions of time. As a result, Vp (f) and Vb (f) which are functions of the frequency are obtained. When the measurement signal is a signal whose frequency changes from time to time, Vp (f) and Vb (f) are directly measured as a function of the frequency, so this processing is unnecessary. Subsequently, the voltages Vp (f) and Vb (f) are averaged, and then the electrical impedance Z (f) = Vp (f) / Vb (f) for each frequency is calculated.

(2) Measurement of impedance locus (step S2)
The calculated electrical impedance Z (f) of each frequency is output from the impedance calculator 12 to the impedance locus calculator 11 as shown in FIG. Then, the impedance locus calculation unit 11 calculates the center coordinates and radius of the impedance locus (step S2). Further, in step S2, from the calculated impedance locus, resistance R∞ when the frequency of the probe current is ∞, resistance R0 when the frequency of the probe current is 0, R∞ / R0, and the critical frequency fc is calculated. The impedance locus calculated in step S2, R∞, R0, and R∞ / R0, the critical frequency fc, and the electrical impedance calculated in step S1 are output to the determination unit 13.

(3) Judgment whether or not there was any abnormality in the measurement of electrical impedance (step S10), estimation of body composition (step S3), notification, and cancellation of estimation (step S4)
Next, as shown in FIG. 4, in step S10, it is determined by the determination unit 13 shown in FIG. 1 whether or not there is an abnormality in the impedance measurement. In step S10, whether or not there is an abnormality in the measurement of the electrical impedance is determined based on at least one of the distribution of the electrical impedance with respect to the impedance locus at each frequency and the radius of the impedance locus.

  If it is determined in step S10 that there is no abnormality in the impedance measurement, the process proceeds to step S3 as shown in FIG. In step S <b> 3, body composition estimation is performed by the body composition estimation unit 15.

  Specifically, the body composition estimation unit 15 reads a body composition estimation program recorded in the recording unit 62. The body composition estimation unit 15 uses the body composition estimation program, the electrical impedance Z (f) and the impedance locus, and human body characteristic data such as the subject's height, weight, sex, and age, which are input from the input unit 63, Based on the above, the human body composition of the body E of the subject is estimated. The body composition estimation unit 15 outputs the estimated human body composition to the display unit 65. Thereby, the estimated body composition is displayed together with the human body characteristic data of the subject. The estimated body composition is also output to the recording unit 62 and recorded in the recording unit 62.

  On the other hand, if it is determined in step S10 that there is an abnormality in the measurement of electrical impedance, the process proceeds to step S4 as shown in FIG. In step S <b> 4, the determination unit 13 outputs an abnormality signal indicating that it has been determined that there is an abnormality in impedance measurement to the notification unit 14. The notification unit 14 notifies the subject and the operator of the body composition estimation apparatus 1 that there is an abnormality in impedance measurement. Note that the method of notifying abnormality is not particularly limited. For example, the abnormality may be notified by outputting a notification sound from the speaker 64. Moreover, you may alert | report an abnormality by displaying on the display part 65 that there was abnormality in an impedance measurement. In the present embodiment, when the determination unit 13 determines that there is an abnormality in the impedance measurement, the estimation of the body composition is stopped.

(4) Details of Step S10 Next, a process of determining whether or not there is an abnormality in the impedance measurement of Step S10 will be described in detail with reference mainly to FIG.

  In this embodiment, as shown in FIG. 5, step S10 includes step S10-1, step S10-2, and step S10-3. Steps S <b> 10-1 and S <b> 10-2 are steps for determining whether or not there is an abnormality in the electrical impedance measurement based on the distribution of the electrical impedance measurement values at each frequency with respect to the impedance locus. On the other hand, step S10-3 is a step of determining whether there is no abnormality in the electrical impedance measurement based on the size of the radius of the impedance locus.

  Specifically, step S10-1 is a step of judging whether or not there is no abnormality in the electrical impedance measurement by evaluating the variation of the impedance measurement value at each frequency with respect to the impedance locus. Step S10-2 is a step of determining whether there is no abnormality in the electrical impedance measurement by evaluating the bias of the distribution of the impedance measurement value at each frequency with respect to the impedance locus using the critical frequency fc as an index. Step S10-3 is a step of determining whether there is no abnormality in the electrical impedance measurement based on whether the magnitude of the impedance locus is within the normal range with R∞ / R0 as an index.

  In the present embodiment, an example in which step S10-1, step S10-2, and step S10-3 are performed in this order will be described. However, the present invention is not limited to this configuration. Step S10-1, step S10-2, and step S10-3 may be performed in any order.

  In the present embodiment, as shown in FIG. 5, first, in step S10-1, it is determined whether there is no abnormality in the electrical impedance measurement by evaluating the variation of the impedance measurement value at each frequency with respect to the impedance locus. Specifically, a distance e in a predetermined direction between the electrical impedance Z (f) measured at the frequency (f) and the impedance locus is calculated. The distance e may be, for example, a distance in the radial direction of the impedance locus between the electrical impedance and the impedance locus, or may be a distance in the horizontal axis direction or the vertical axis direction. For example, in the radial direction, the distance between the measured electrical impedance Z (f) and the impedance locus can be expressed as follows using the distance d (f) between the Z (f) and the center of the impedance locus and the radius r. .

e (f) = d (f) -r
Next, a square sum Σe (f) ² of the calculated distance e is obtained. Then, it is determined whether or not the calculated Σe (f) ² is larger than a predetermined threshold value. If Σe (f) ² is smaller than a predetermined threshold value, it is determined that there is no abnormality in the impedance locus, and the process proceeds to step S10-2. On the other hand, when Σe (f) ² is larger than a predetermined threshold value, it is determined that there is an abnormality in the impedance locus, and the process proceeds to step S4.

Here, a predetermined threshold value for Σe (f) ² can be appropriately set according to the purpose and use of the body composition estimation apparatus 1. For example, the square of the value of 5 to 10% of the radius of the impedance locus of a normal healthy person may be multiplied by the number of measurement frequency points of electrical impedance.
Further, Σe ′ (f) ² is obtained by inputting the calculated distance e and the radius r of the impedance locus into the following equation (1).
Σe ′ (f) ² = Σ {e (f) / r} ² (1)
However,
e (f): distance in a predetermined direction between the electrical impedance and the impedance locus at the frequency (f),
r: radius of impedance locus,
It is.

Then, it is determined whether or not the calculated Σe ′ (f) ² is larger than a predetermined threshold value. When Σe ′ (f) ² is smaller than a predetermined threshold value, it is determined that there is no abnormality in the impedance locus, and the process proceeds to step S10-2. On the other hand, when Σe ′ (f) ² is larger than a predetermined threshold value, it is determined that there is an abnormality in the impedance locus, and the process proceeds to step S4.

Here, a predetermined threshold value for Σe ′ (f) ² can be appropriately set according to the purpose and use of the body composition estimation apparatus 1. For example, the square of the value of 5 to 10% of the radius of the impedance locus may be multiplied by the number of measurement frequency points of electrical impedance.

  In the above equation (1), e (f) is divided by r because the size of the body E of the subject is taken into consideration. The radius r of the impedance locus varies greatly depending on the size (length and cross-sectional area) of the body E of the subject. For this reason, the magnitude of e (f) varies greatly depending on the height of the subject. By setting e (f) / r, a uniform determination can be made regardless of the size of the body E of the subject. That is, by using the above formula (1), it is possible to accurately evaluate whether or not the electrical impedance measurement is possible in both cases where the height of the subject is large and small.

In the above formula (1), e (f) is divided by r, but e (f) may be divided by the height h of the subject. That is, according to the following mathematical formula (2), it may be determined whether there is no abnormality in the impedance locus depending on whether the obtained Σe ″ (f) ² is larger than a predetermined threshold value.
Σe ″ (f) ² = Σ {e (f) / h} ² (2)
However,
e (f): distance in a predetermined direction between the electrical impedance and the impedance locus at the frequency (f),
r: radius of impedance locus,
h: height of subject,
It is.

  In step S10-2, it is determined whether or not the critical frequency fc calculated by the impedance locus calculating unit 11 shown in FIG. 1 is outside a predetermined range. If it is determined that the critical frequency fc is within a predetermined range, it is determined that there is no abnormality in the critical frequency fc, and the process proceeds to step S10-3. On the other hand, when the critical frequency fc is outside the predetermined range, it is determined that there is an abnormality in the critical frequency fc, and the process proceeds to step S4.

  Usually, a healthy person has a critical frequency fc of around 50 kHz. However, there are individual differences in the critical frequency fc. For this reason, the lower limit of the critical frequency fc is preferably about 5 to 20 kHz, and the upper limit is preferably 90 to 150 kHz. That is, in step S10-2, it is preferable that a range of about 5 to 150 kHz to about 20 to 90 kHz is determined as an allowable range of the critical frequency fc.

  In step S10-3, it is determined whether R∞ / R0 is within a predetermined range. If it is determined that R∞ / R0 is within a predetermined range, as shown in FIG. 5, assuming that there is no abnormality in the value R∞ / R0 and there is no abnormality in the impedance measurement, step S10 is performed. End and proceed to step S3. On the other hand, when the value R∞ / R0 is outside the predetermined range, it is assumed that there is an abnormality in R∞ / R0, and the process proceeds to step S4.

  Usually, in the case of a healthy person, the value R∞ / R0 is about 0.6 to 0.8 (60% to 80%). For this reason, in step S10-3, the allowable range of R∞ / R0 can be set to about 0.85 to 0.9 or less.

  In the present embodiment, only an example of determining only the value R∞ / R0 will be described in step S10-3. However, whether R∞ and R0 are within an appropriate range together with the value R∞ / R0. You may make it judge. That is, when R∞ or R0 is abnormally large or abnormally small, it may be determined that there is an abnormality in the measurement of electrical impedance.

  As described above, in this embodiment, it is determined in step S10 whether or not there is no abnormality in impedance measurement. If it is determined that there is an abnormality in the impedance measurement, the abnormality is notified in step S4. For this reason, even when the accurate measurement of the electrical impedance is not performed, it is possible to prevent the body composition of the subject from being misidentified by the subject or the operator of the body composition estimation apparatus 1.

  Further, in the present embodiment, since step S10-1 is performed, when a disturbance such as an electrode contact failure occurs and an impedance measurement value varies with respect to the impedance locus, an inaccurate body composition is estimated. This can be suppressed.

  FIG. 7 is a graph showing electrical impedance measurement values and impedance trajectories obtained when there is no abnormality in electrical impedance measurement. As shown in FIG. 7, when there is no abnormality in the electrical impedance measurement, the electrical impedance measurement values at each frequency are arranged almost on the Cole-Cole locus. Thus, the electrical impedance measurements at each frequency are arranged approximately on the impedance trajectory.

  However, when a disturbance such as an electrode contact failure occurs, electrical impedance measurement values at each frequency may not be neatly arranged on the Cole-Cole rail. FIG. 8 shows an example. In the case shown in FIG. 8, the measured electrical impedance values at each frequency show a distribution that is significantly different from the Cole-Cole locus. For this reason, an impedance locus that is far from the distribution of the measured electrical impedance values is calculated. Therefore, the accurate body composition of the subject's body E cannot be estimated using the electrical impedance measurement values shown in FIG. However, in the conventional body composition estimation apparatus as shown in Patent Document 1, the body composition of the subject's body E is estimated even in such a case.

On the other hand, in the present embodiment, as shown in FIG. 8, when the variation of the electrical impedance measurement value at each frequency with respect to the impedance locus is large, Σe ′ (f) ² obtained by the above equation (1) becomes large. In step S10-1, it is determined that there is an abnormality in impedance measurement. For this reason, the estimation of the body composition is stopped and the abnormality is notified. Therefore, it is suppressed that the misidentification of the body composition of the body E of a test subject arises.

  Further, in the present embodiment, since step S10-2 is performed, when a disturbance such as an electrode contact failure occurs, and an electrical impedance measurement value is distributed unevenly with respect to the impedance locus, an inaccurate body composition is estimated. It can be suppressed.

  As shown in FIG. 7, when the measurement of the electrical impedance is normally performed, the electrical impedance measurement values are distributed relatively uniformly on the impedance locus. However, when a disturbance such as an electrode contact failure occurs, as shown in FIGS. 9 and 10, the measured impedance values are distributed in a part of the impedance locus. Then, an accurate impedance locus cannot be calculated, and as a result, it is difficult to estimate an accurate body composition of the body E of the subject.

  On the other hand, in this embodiment, in step S10-2, it is determined whether or not the critical frequency fc is within a predetermined range. As shown in FIGS. 9 and 10, when the impedance measurement values are distributed in a part of the impedance locus, the critical frequency fc becomes extremely large or extremely small. Specifically, when the electrical impedance measurement value is biased to the R0 side as shown in FIG. 9, the frequency corresponding to the electrical impedance measurement value located near the minimum point of the impedance locus becomes large. Therefore, the critical frequency fc becomes extremely large. On the other hand, as shown in FIG. 10, when the electrical impedance measurement value is biased to the R∞ side, the frequency corresponding to the electrical impedance measurement value located near the minimum point of the impedance locus becomes small. Therefore, the critical frequency fc becomes extremely small. Therefore, it is determined that there is an abnormality in the impedance measurement in step S10-2. As a result, the estimation of the body composition is stopped and the abnormality is notified. Therefore, it is suppressed that the misidentification of the body composition of the body E of a test subject arises.

  For example, when the measurement of electrical impedance is performed at a frequency of 2.5 kHz to 350 kHz for a total of 140 times every 2.5 kHz, the critical frequency fc is about 115 kHz when the electrical impedance measurement values are distributed as shown in FIG. Become. As shown in FIG. 10, the critical frequency fc is zero when the measured electrical impedance is distributed. This is because there is no measured value of electrical impedance near the minimum point of the impedance locus. In the case shown in FIG. 12, the critical frequency fc is about 5 kHz. In the case shown in FIG. 13, the critical frequency fc is about 20 kHz. In the case shown in FIG. 14, the critical frequency fc is about 50 kHz. In the case shown in FIG. 15, the critical frequency fc is about 90 kHz. In the case shown in FIG. 16, the critical frequency fc is about 150 kHz. Thus, normally, when the critical frequency fc is in the vicinity of 50 kHz, the electrical impedance measurement values are particularly uniformly distributed with respect to the impedance trajectory.

  Moreover, in this embodiment, since step S10-3 is performed, when a disturbance such as the subject's body E touching a metal occurs and a short circuit occurs, it is suppressed that an incorrect body composition is estimated. be able to.

  As shown in FIG. 7, when the measurement of electrical impedance is performed normally, R∞ / R0 is about 0.7 (70%). However, when a short circuit occurs due to the subject's body E coming into contact with metal, R∞ / R0 becomes very small, and the impedance locus may become very small as shown in FIG. This is because the resistance when the frequency is 0 and the resistance when the frequency is ∞ are close to each other due to a short circuit caused by a metal having substantially no frequency selectivity. When R∞ / R0 falls outside the predetermined range due to the occurrence of a short circuit in this way, an accurate impedance locus is not calculated, and the body composition of the subject's body E cannot be accurately estimated, which is inaccurate. There is a risk that a correct body composition is output.

  On the other hand, in the present embodiment, in step S10-3, it is determined whether R∞ / R0 is within a predetermined range. For this reason, when R∞ / R0 is out of the predetermined range due to a short circuit or the like, the estimation of the body composition is stopped and an abnormality is notified. Therefore, it is suppressed that the misidentification of the body composition of the body E of a test subject arises.

  Thus, according to the present embodiment, when a short circuit occurs due to poor contact of the electrodes or the subject's body E contacting a conductor such as metal, the estimation of the body composition is stopped and an abnormality occurs. Since it is notified, it is suppressed effectively that the misidentification of the body composition of the test subject's body E arises.

(Second Embodiment)
In the said 1st Embodiment, when it was judged that there was abnormality in the measurement of an electrical impedance in step S10, the case where estimation of a body composition was stopped was demonstrated. However, the present invention is not limited to this. For example, the body composition may be estimated even when it is determined in step S10 that there is an abnormality in the measurement of electrical impedance.

  Hereinafter, the estimation process of the body composition in this embodiment will be described with reference to FIG. In the description of the present embodiment, constituent elements having substantially the same functions are described with reference numerals common to the first embodiment, and description thereof is omitted.

  In the second embodiment, as shown in FIG. 17, when it is determined in step S10 that there is an abnormality in the measurement of electrical impedance, the process proceeds to step S5. In step S5, the body composition is estimated, and then in step S6, the abnormality notification is displayed together with the body composition estimated on the display unit 65 shown in FIG.

  Thus, even if the estimated body composition is displayed when it is determined that there is an abnormality in the measurement of electrical impedance, if the estimated body composition is displayed together with the abnormality notification, the subject or body It becomes difficult for the operator of the composition estimation apparatus 1 to mistake the body composition.

(Modification)
In the first embodiment, the case where all of step S10-1, step S10-2, and step S10-3 are performed in step S10 has been described as an example. However, it is not always necessary to perform all of step S10-1, step S10-2, and step S10-3 in step S10.

  For example, as shown in FIGS. 18-20, you may perform only any one of step S10-1, step S10-2, and step S10-3. Further, as shown in FIGS. 21 and 22, two of step S10-1, step S10-2, and step S10-3 may be performed.

It is a block diagram of the body composition estimation apparatus which concerns on 1st Embodiment. It is a conceptual diagram showing the use condition of a body composition estimation apparatus. It is an equivalent circuit schematic of a test subject's body. It is a flowchart showing the body composition estimation process in 1st Embodiment. It is a detailed flowchart of step S10 in 1st Embodiment. It is a graph which illustrates an impedance locus. It is a graph which illustrates an electrical impedance measurement value and impedance locus when measurement of electrical impedance is completed normally. It is a graph which illustrates an electrical impedance measured value and an impedance locus when there is an abnormality in the measurement of electrical impedance. It is a graph which illustrates an electrical impedance measured value and an impedance locus when there is an abnormality in the measurement of electrical impedance. It is a graph which illustrates an electrical impedance measured value and an impedance locus when there is an abnormality in the measurement of electrical impedance. It is a graph which illustrates an electrical impedance measured value and an impedance locus when there is an abnormality in the measurement of electrical impedance. It is a graph which illustrates an electrical impedance measurement value and impedance locus when a critical frequency is 5 kHz when a measurement of electrical impedance is performed at a frequency of 2.5 kHz to 350 kHz for a total of 140 times every 2.5 kHz. . It is a graph which illustrates an electrical impedance measurement value and impedance locus when a critical frequency is 20 kHz when a measurement of electrical impedance is performed at a frequency of 2.5 kHz to 350 kHz for a total of 140 times every 2.5 kHz. . It is a graph which illustrates an electrical impedance measurement value and an impedance locus when a critical frequency is 50 kHz when a measurement of electrical impedance is performed at a frequency of 2.5 kHz to 350 kHz for a total of 140 times every 2.5 kHz. . It is a graph which illustrates an electrical impedance measurement value and impedance locus when a critical frequency is 90 kHz when measurement of electrical impedance is performed at a frequency of 2.5 kHz to 350 kHz for a total of 140 times every 2.5 kHz. . It is a graph which illustrates an electrical impedance measurement value and impedance locus in case a critical frequency is 150 kHz, when a measurement of electrical impedance is carried out at a frequency of 2.5 kHz to 350 kHz for a total of 140 times every 2.5 kHz. . It is a flowchart showing the body composition estimation process in 2nd Embodiment. It is a flowchart showing the body composition estimation process in the modification 1. It is a flowchart showing the body composition estimation process in the modification 2. 10 is a flowchart showing a body composition estimation step in Modification 3. It is a flowchart showing the body composition estimation process in the modification 4. 10 is a flowchart showing a body composition estimation step in Modification 5.

Explanation of symbols

1 ... Body composition estimation device 10 ... CPU
DESCRIPTION OF SYMBOLS 11 ... Impedance locus | trajectory calculation part 12 ... Impedance calculation part 13 ... Judgment part 14 ... Notification part 15 ... Body composition estimation part 20 ... Current detection part 21 ... Sampling memory 22 ... A / D converter 23 ... BPF
24 ... I / V converter 30 ... Signal output unit 31 ... PIO
32 ... Measurement signal generator 33 ... Output buffer 40 ... Voltage detector 41 ... Sampling memory 42 ... A / D converter 43 ... BPF
44 ... Differential amplifier 50 ... Electrical impedance measuring unit 62 ... Recording unit 63 ... Input unit 64 ... Speaker 65 ... Display unit

Claims (5)

A body composition estimation device for estimating the body composition of a subject,
An electrical impedance measurement unit that generates a plurality of probe currents having different frequencies, applies the probe current of each frequency to the body of the subject, and measures the electrical impedance of the body of the subject;
An impedance locus calculating unit for calculating an impedance locus from the electrical impedance at each frequency measured by the electrical impedance measuring unit;
A determination unit that determines whether there is no abnormality in the measurement of the electrical impedance based on at least one of the distribution of the electrical impedance at each measured frequency with respect to the impedance locus and the size of the impedance locus;
An informing unit for informing the abnormality when it is determined that there is an abnormality in the determination unit;
A body composition estimation unit for estimating the body composition of the subject from the impedance locus when it is determined that there is no abnormality at least in the determination unit;
With
The determination unit, Sigma] e ^{(f) 2,} 'Sigma] e obtained by ^{(f) 2} or the following formula ^(2)''(f) 2 Σe obtained by the following equation (1) is, than a predetermined threshold A body composition estimation device that determines that there is an abnormality in the measurement of the electrical impedance when it is large;
Σe ′ (f) ² = Σ {e (f) / r} ² (1)
Σe ″ (f) ² = Σ {e (f) / h} ² (2)
However,
e (f): distance in a predetermined direction between the electrical impedance and the impedance locus at the frequency (f),
r: radius of impedance locus,
h: height of subject,
It is.   2. The determination unit according to claim 1, wherein the determination unit determines that the measurement of the electrical impedance is abnormal even when a frequency at a point where reactance is minimum in the impedance locus is outside a predetermined range. Body composition estimation device.   The determination unit obtains a value R obtained by dividing the electrical impedance R∞ when the frequency of the probe current calculated from the impedance locus is ∞ by the electrical impedance R0 when the frequency of the probe current is 0. The body composition estimation apparatus according to claim 1 or 2, wherein it is determined that there is an abnormality in the measurement of the electrical impedance even when ∞ / R0 is outside a predetermined range.   The body composition estimation apparatus according to claim 1, wherein the body composition estimation unit estimates the body composition of the subject only when it is determined that there is no abnormality in the determination unit. A method for estimating the body composition of a subject,
An electrical impedance measuring step of generating a plurality of probe currents having different frequencies and applying the probe current of each frequency to the body of the subject to measure the electrical impedance of the subject's body;
An impedance locus calculating step of calculating a impedance locus from the electrical impedance at each frequency measured in the electrical impedance measuring step;
A determination step of determining whether or not there is no abnormality in the measurement of the electrical impedance based on at least one of a distribution of the electrical impedance at each measured frequency with respect to the impedance locus and a size of the impedance locus;
A notification step of notifying the abnormality when it is determined that there is an abnormality in the determination step;
A body composition estimation step of estimating the body composition of the subject from the impedance locus when it is determined that there is no abnormality in at least the determination step ;
With
The determination step, Sigma] e ^{(f) 2,} 'Sigma] e obtained by ^{(f) 2} or the following formula ^(2)''(f) 2 Σe obtained by the following equation (1) is, than a predetermined threshold A body composition estimation method for determining that there is an abnormality in the measurement of the electrical impedance when it is large;
Σe ′ (f) ² = Σ {e (f) / r} ² (1)
Σe ″ (f) ² = Σ {e (f) / h} ² (2)
However,
e (f): distance in a predetermined direction between the electrical impedance and the impedance locus at the frequency (f),
r: radius of impedance locus,
h: height of subject,
It is.

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