JP2003093361A - Apparatus for detecting bioelectrical impedance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for calculating an erroneous impedance by detecting an abnormal condition in which contact of a living body with an electrode is incomplete or contact resistance is higher. SOLUTION: This apparatus is provided with the first reference resistance in a series connection with the living body and the second reference resistance in a parallel connection with the living body and a means for detecting the abnormal conditions in which the contact of the living body with the electrode is abnormal or the contact resistance is higher because of the potential of the first reference resistance and that the second reference resistance. According to the invention, an abnormal measurement can be easily and accurately detected and thus an apparatus that can perform an accurate measurement with proper applied electric current is now available for detecting the bioelectrical impedance, since the potential is detected when the reference resistance is made in series or in parallel connection with the living body, while the abnormal measurement is detected by an output from the means for detecting the potential of the reference resistance with the electric current that passed or did not pass the living body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bioimpedance detecting device for detecting bioimpedance.

[0002]

2. Description of the Related Art A bioimpedance detecting device detects the potential difference generated when a direct current or an alternating current is applied to a living body such as a human being or an animal to calculate the impedance of the living body. There are a two-terminal method in which the electrodes to be detected are the same and a four-terminal method in which the electrodes are separate. Since the same electrode is used for current application and voltage detection in the two-terminal method, the impedance including the contact resistance between the electrode and the living body and the impedance near the epidermis, which easily changes depending on the state of the outside air, is measured, and the body composition and other factors are reflected. Not very suitable for measuring deep impedance. Therefore, a known current is applied to the living body by a pair of electrodes for current application, and electrodes for voltage detection are arranged at arbitrary two points on the skin in the section where the current is flowing to detect the voltage between them. Therefore, in principle, the 4-terminal method is widely used because it is insusceptible to the influence of contact resistance and impedance near the skin.

Further, there is a body fat meter as a device using such a bioelectrical impedance detection device. In the conventional measurement of body fat, the density method, which measures the density of the human body and calculates the body fat percentage from the difference in specific gravity of fat and other tissues, was used as a standard measurement method by doctors and researchers. In this method, it is necessary to immerse the whole body in water in order to obtain the volume and specific gravity of the human body, and the physical load on the person to be measured is large and it is not used for home use.

Therefore, for home use, the bioimpedance, the light transmittance, and the ultrasonic reflectance and transmittance, which are said to have a correlation with the body fat percentage, are measured, and the measured values are measured by the density method described above. The indirect method of indirectly obtaining the body fat percentage by associating it with the measured body fat percentage is often used. In recent years, many household body fat percentage meters using bioimpedance have been released, for example, Japanese Patent Laid-Open No. 10-945.
As disclosed in Japanese Unexamined Patent Publication No. 30-35, an electrode is arranged on a weight scale to detect impedance between both feet to calculate the body fat percentage of the human body, and as disclosed in Japanese Unexamined Patent Publication No. 11-188016. There is one that grasps an electrode and detects the impedance between both arms to calculate the body fat percentage of the human body.

In order to realize such a body fat meter, Japanese Patent No. 28355656 has a plurality of reference resistors connected in series with a living body so that the current flowing through the living body and the current flowing through the reference resistor are the same. By changing the switch with a switch and detecting the voltages of the living body and the reference resistance with the same voltage detection circuit, the bioelectrical impedance can be accurately detected even if the current changes. FIG. 7 shows a block diagram of a conventional bioelectrical impedance detection device. The voltage signal formed by the 50 kHz sine wave oscillator 31 is converted into a constant current by the voltage-current converter 32, and the reference resistance 1 (33), the reference resistance 2 (34), the reference resistance 3 (35), and the human body 36. It flows in order. This current has the same current in all the elements because there is no branch in the path. The voltage across each of these elements is the switch 37.
Are connected to the differential amplifier 38 one element at a time by the rectifier 3
The high-frequency noise is cut by the LPF 40, converted into a digital signal by the analog-digital converter 41, and the MPU 42 calculates the impedance of the human body from the value of each element.

[0006]

In the conventional bioimpedance detecting device described above, the same current flows through the plurality of reference resistors and the human body, but even if the current waveform is distorted, the bioimpedance is detected based on the distorted current. Will be detected. In the case of the conventional example, in addition to a plurality of reference resistances and bioimpedance, a contact resistance between the electrode and the human body is added in series to the current path, and the voltage range of the current application circuit is more than the voltage drop due to all these resistances. Voltage range is required.

However, the contact resistance may be a very high value of several tens kΩ to several hundreds kΩ for a person with dry skin, and in such a case, the voltage operation range of the current application circuit is exceeded, and the power supply The portion exceeding the voltage range becomes flat and the correct sine waveform cannot be applied. However, even in such a case, a current with a distorted waveform flows through each element, and the bioimpedance corresponding to the situation is calculated. Considering the frequency component of the applied current at this time, the high frequency component of the part where the sine wave becomes flat is added to the 50 kHz sine wave, and the bioimpedance measured here is 50 kH.
It will have different properties than what is detected by the sine wave of z. When measuring bioimpedance, it is known that the value changes when the frequency to be measured changes. Due to the capacitance component of the cell membrane, the higher the frequency, the lower the impedance due to the capacitance component.

Therefore, there is a case where the correct bioelectrical impedance cannot be measured by applying an incorrect current, and there is a problem that an incorrect bioelectrical impedance is detected.

[0009]

In order to solve the above-mentioned problems, the present invention provides a pair of current applying electrodes for contacting a living body and applying a current to the contact portion, and a potential of the contact portion for contacting the living body. A pair of potential detection electrodes for detecting, a reference resistance whose resistance value is known, a current applying means for applying a current to the current application electrode or the reference resistance, and between the pair of potential detection electrodes or both ends of the reference resistance. Potential difference detecting means for detecting the potential difference between the current applying means, the current switching means for switching the current path applied by the current applying means between the current applying electrode and the reference resistance, and the potential difference detected by the potential detecting means as the potential detecting electrode. A potential switching means for switching between the reference resistance and a bioelectrical impedance detection means for detecting the bioelectrical impedance of the living body from the output of the potential difference detection means are provided, and the reference resistance is connected to the living body in series. With abnormality detecting means for detecting an abnormality from both potential and when connected with the case of the parallel.

According to the above invention, the potentials when the reference resistance is connected to the living body in series and in parallel are detected,
Anomalies in measurement are detected from the output of the potential difference detection means of the reference resistance due to the current that has passed through the living body and the current that does not pass through the living body. An impedance detection device can be realized.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A bioimpedance detecting device according to claim 1 of the present invention comprises a pair of current applying electrodes that contact a living body to apply a current to the contacting portion, and a potential of the contacting portion that contacts the living body. A pair of potential detection electrodes, a reference resistance whose resistance value is known, a current applying means for applying a current to the current application electrode or the reference resistance, and between the pair of potential detection electrodes or the reference resistance. A potential difference detecting means for detecting a potential difference between both ends, a current switching means for switching a current path applied by the current applying means between a current applying electrode and a reference resistor, and a potential difference detected by the potential detecting means for the potential detecting electrode. And a reference resistance, and a bioelectric impedance detection means for detecting the bioimpedance of the living body from the output of the potential difference detection means. To have an abnormality detecting means for detecting an abnormality from both potential and when connected in parallel when connected in series.

Then, the potentials when the reference resistance is connected to the living body in series and in parallel are detected and measured from the output of the potential difference detecting means of the reference resistance by the current passing through the living body and the current not passing through the living body. Since an abnormality is detected, it is possible to easily and accurately detect an abnormality in measurement.

In the bioimpedance detecting device according to claim 2 of the present invention, there are a plurality of reference resistors, at least one of which is connected in series with the living body and at least one of which is connected in parallel with the living body.

When using a plurality of reference resistors, it is possible to efficiently determine an abnormality by connecting at least one in parallel and at least one in series.

The bioimpedance detecting apparatus according to claim 3 of the present invention detects the potential both when the same reference resistance is connected in series to the living body and when it is connected in parallel.

Since the abnormality is detected using the potential when the same resistance is connected in series to the living body and the potential when the resistance is connected in parallel to the living body, accurate abnormality detection can be performed.

In the bioelectrical impedance detection apparatus according to claim 4 of the present invention, the abnormality detection means is a current application determination means for determining whether the current application means has normally applied the current to the living body.

Since it is possible to determine whether or not the current is correctly applied to the living body from the reference resistance connected in series to the living body or the reference resistance connected in parallel to the living body, it is possible to accurately detect the current application state. The correct bioimpedance can be detected by applying the correct current.

In the bioimpedance detecting apparatus according to claim 5 of the present invention, the current application determining means determines the potential difference between both ends of the reference resistance connected in series to the living body and the reference resistance connected in parallel to the living body. The state of current application to is determined.

Then, the current value flowing in the living body is calculated by the potential difference across the reference resistance connected in series to the living body,
Also, the original current value is calculated from the potential difference between both ends of the reference resistance connected in parallel to the living body, and it is possible to determine whether or not the current has been correctly applied to the living body by comparing the two, so the current application state can be accurately determined. it can.

In the bioimpedance detecting apparatus according to claim 6 of the present invention, the current application determining means calculates the amount of change in the potential of the reference resistance connected in series to the living body for a certain period of time to determine the state of current application to the living body. To judge.

When the amount of change in the potential difference between both ends of the reference resistor connected in series to the living body is large, it is determined that the current is not correctly applied to the living body, so that the current application state can be accurately determined.

In the bioelectrical impedance detection apparatus according to claim 7 of the present invention, the abnormality detection means is a contact detection means for detecting contact of the living body with the potential detection electrode or the current detection electrode.

Since the reference resistance connected in series to the living body or the reference resistance connected in parallel to the living body detects contact with the potential detection electrode or the current detection electrode of the living body,
Accurate contact detection is possible.

In the bioimpedance detecting apparatus according to claim 8 of the present invention, the contact detecting means detects contact with the potential detecting electrode or the current detecting electrode of the living body based on the potential difference between both ends of the reference resistance connected in series to the living body. Used for.

If the living body is not in contact with either one of the electrodes, the correct current does not flow through the reference resistance connected in series to the living body, and the potential difference that should be generated does not occur. Therefore, this is detected. Accurate contact detection is possible.

In the bioimpedance detecting apparatus according to claim 9 of the present invention, the contact detecting means calculates the variation of the potential of the reference resistance connected in series to the living body for a certain period of time to detect the potential detection electrode or the current of the living body. Used to detect contact with electrodes.

When the living body is not in contact with either one of the electrodes of the living body, a constant current does not flow through the reference resistance connected in series to the living body, and the measured value greatly varies.
By detecting this, accurate contact can be detected.

In the bioimpedance detecting apparatus according to claim 10 of the present invention, the contact detecting means uses the potential of the reference resistance connected in series to the living body and the potential of the reference resistance connected in parallel to the living body. It is used to detect contact with the potential detection electrode or the current detection electrode.

When the living body does not come into contact with either one of the current applying electrodes, a correct current does not flow in the reference resistance connected in series to the living body, but is correct in the reference resistance connected in parallel to the living body. Since a current flows, the contact of the living body with the electrode can be accurately detected from the relationship of the values of these reference resistances.

According to an eleventh aspect of the bioelectrical impedance detection device of the present invention, the contact detection means has a range of potentials that the reference resistances connected in series to the living body should have from the potentials of the reference resistances connected in parallel to the living body. It has a potential range calculating means for calculating, and when the potential of the reference resistance connected in series is within the range calculated by the potential range calculating means, it is determined that the living body is in contact with the potential detecting electrode or the current detecting electrode.

Then, the voltage range of the reference resistance connected in series to the living body is predicted from the voltage drop when the correct constant current originally applied to the living body is applied to the reference resistance connected in parallel to the living body, and the range is predicted. Since it is determined that the living body has come into contact with the electrode only when entering, the contact can be accurately detected.

According to a twelfth aspect of the bioimpedance detecting device of the present invention, the contact detecting means has a potential of a reference resistance connected in parallel to the living body from a potential of the reference resistance connected in series to the living body for a certain period of time. When the variation of the potential of the reference resistance connected in series within a certain time is within the range calculated by the variation range calculation means, the living body has a potential detection electrode or a current. It is determined that the detection electrode has been contacted.

From the variation of the potential difference between both ends when the correct constant current originally applied to the living body is applied to the reference resistance connected in parallel to the living body, the output variation range of the potential difference of the reference resistance connected in series to the living body. Since it is determined that the living body has contacted the electrode only when entering the range,
The contact can be detected accurately.

In the bioimpedance detecting device according to claim 13 of the present invention, the bioimpedance detecting means is configured such that the potential of the reference resistance connected in parallel to the living body and the potential of the reference resistance connected in series to the living body and the potential detection electrode. Has a calculation means for calculating the impedance of the living body by substituting the potential of the body into a predetermined calculation formula, and the contact detection means is detected when the living body is not in contact with the current application electrode or the potential detection electrode. The contact of the living body with the current applying electrode or the potential detecting electrode is detected by using the potential of the reference resistance connected in series to the living body and the output of the potential detecting means.

Then, when the living body is not in contact with the electrode, the output of the reference resistance connected in parallel to the living body to which the correct current is applied and the reference resistance connected in series to the living body to which the correct current is not applied It is possible to detect the contact with the electrode of the living body accurately by calculating the bioelectrical impedance from the output of it can.

According to a fourteenth aspect of the present invention, the bioelectrical impedance detecting device brings the reference resistance connected in series to the living body and the potential detecting electrode close to the circuit into contact with the living body after the other potential detecting electrode.

Since it is possible to prevent the noise signal from the living body as an antenna from being directly applied to the potential detection circuit, it is possible to realize contact detection with less influence of noise.

In the bioimpedance detecting device according to the fifteenth aspect of the present invention, the value of the reference resistance connected in series to the living body is larger than the value of the reference resistance connected in parallel to the living body.

Since the contact of the living body with the electrode is detected from the potential difference of the resistance having a large value, it is possible to realize the contact detection which is hardly affected by noise.

In the bioimpedance detecting apparatus according to claim 16 of the present invention, when the current application determining means determines that the measurement current is not correctly applied to the living body, the subject is instructed to take measures to reduce the contact resistance. To do.

Since the state of high contact resistance is detected and the subject is instructed together with countermeasures, the bioimpedance can be correctly measured even in the case of abnormally high contact resistance.

[0043]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a block diagram of a bioimpedance detecting apparatus in Embodiment 1 of the present invention, and FIG. 2 is an external view of the apparatus. In the present embodiment, an example of a body fat meter that detects the bioelectrical impedance of the human body and calculates the body fat mass is shown. In the figure, 1 to 4 are electrodes that are brought into contact with the epidermis of the living body 5 for electrical conduction, and among these, 1, 3
Are current application electrodes for applying a current to the living body 5, and 2 and 4 are potential detection electrodes for detecting a potential difference of the living body 6.

Further, 6 is a first reference resistance connected in series to the living body, 7 is a second reference resistance connected in parallel to the living body, and 8 is an applied waveform forming a current waveform used for measuring the bioelectrical impedance. Forming means, 9 is a current applying means for applying the waveform formed by the applied waveform forming means 8 to the living body 5 or two reference resistors, and 10 is a living body to which a current is applied by the current applying means 9, or a potential difference between the reference resistors. , 11 is a current switching means for switching the target to which the current of the current applying means 9 is applied, 12 is two potential switching means (12a, 12b) for switching the target of the potential difference detected by the potential difference detecting means 10, Reference numeral 13 is a signal processing means for rectifying and amplifying the output of the potential difference detected by the potential difference detecting means 10, and 14 is A for changing the output of the signal processing means by AD.
D conversion means, 15 is a bioimpedance detection means for calculating the impedance of the living body from the output of the AD conversion means 14 when connected to the living body and two reference resistors, and 16 is a current application electrode of the living body from the output of the AD conversion means 14. Contact detection means for detecting contact with the potential difference detection electrode, 17 is AD
Current application determination means, which is an abnormality detection means for detecting the state of the current applied to the living body from the output of the conversion means 14, 18 is an input means for inputting the physical characteristics of the subject, and 19 is a measurement start for instructing the start of measurement. Instructing means, 20 is a display means for displaying the measurement result, and 21 is a control means for controlling the overall operation.

Here, the current switching means 11 uses the 4ch analog multiplexer 4052 and is controlled by the control means 21 and connected in series to the living body 5 and the first reference resistor 6.
And one of the paths (0ch, 2ch) passing through and the path (1ch) passing only the second reference resistor 7 connected in parallel to the living body, and connected to the current applying means 9.
On the other hand, the potential switching means 12 is also 4ch like the current switching means.
A potential difference (2 ch) between two potential detection electrodes connected to the living body 5 under the control of the control means 21 using two analog multiplexers 4052 and a potential difference (0 ch) between both ends of the first reference resistor 6 and the second One of three potential differences (1ch) at both ends of the reference resistor 7 is selected and connected to the potential difference detecting means 10. The current applying means 9 is composed of an operational amplifier 22 and a current value adjusting resistor 23.
The ut terminal 22a is connected to the current applying electrode 1, while the negative terminal 22b of the operational amplifier is connected from the applied waveform forming means 8 via the current value adjusting resistor 23 and also to the current applying electrode 3, and the + of the operational amplifier is added. The terminal 22c is set to the DC voltage of the waveform formed by the applied waveform forming means 8, whereby a constant current circuit including the living body is constructed and 2
An AC constant current that is uniquely determined by the output signal formed by the applied waveform forming unit 8 and the current value adjusting resistor 23 is applied between the two current applying electrodes 1 and 3 regardless of the biological impedance. The applied waveform forming means 8 is 50 kHz
The sine wave waveform of is output as a voltage signal, and the current applying means 9 applies it as a constant current of 500 μA to the living body or the reference resistance.

In this embodiment, the bioelectrical impedance between both legs of a human being and the right upper limb is measured,
The current applying electrode 3 and the potential detecting electrode 4 are formed on the measuring table 24, and the subject rides on the measuring table so that both feet are in contact with each other, and the current applying electrode 1 and the voltage detecting electrode 2 are connected to the grip portion 2.
It is configured in 5 and is held by the right palm and brought into contact with it. The current application electrode 3 and the potential detection electrode 4 installed on the measurement table 24 are separated into two, one for each leg, but they are electrically connected and have the same potential. Further, the bioelectrical impedance detection means has a storage means 15a and a calculation means 15b, and three AD conversion means 1 obtained by connecting the bioelectrical impedance to the living body and two reference resistors.
The output of 4 is sequentially stored in the storage means 15a, and the calculation means 15
The bioelectrical impedance is calculated by substituting the value stored in the storage unit 15a in b into a predetermined calculation formula. In the present embodiment, the first reference resistor 6 is 1000
Ω, the second reference resistor 7 is a resistor having a value of 100Ω, and the bioimpedance detecting means has a bioimpedance measuring range of 100 to 1000Ω.

Next, the operation and action of the above configuration will be described. FIG. 3 shows the output of the AD conversion means 14. First, after inputting the physical information such as the height, weight, and sex of the subject from the input means 18, when the measurement start instruction means 19 is pressed to instruct the measurement start, the bioimpedance measurement state is set. Here, the 50 kHz sine wave waveform formed by the applied waveform forming means 8 is output to the voltage application circuit 9, but the subject is not on the measurement table 24.
When the person does not ride on the body or the grip 25 is not gripped, the circuit between the living body 5 and the current applying means 9 is not closed, so that the current applying circuit 9 applies the current to the living body 50.
The sine wave current of kHz 500 μA does not flow in the living body and the first reference resistor even if the current switching means 11 is in a position where the current flows in the living body 5 and the first reference resistor 6 connected in series to the living body. .

On the other hand, this current flows through the second reference resistor 7 connected in parallel to the living body when the current switching means 11 is in a position where a current is passed through the second reference resistor 7. Figure 3
The output of the signal processing means 13 at this time is shown in (a). In the figure, a, b, and c are outputs that appear when the electrodes are normally contacted, where a is a second reference resistance, b is a living body, and c is a first reference resistance.

As shown in the figure, the output value when connected to the second reference resistor 7 (◯ in the figure) is stable in the vicinity of a, whereas when it is connected to the potential difference detection electrode (Δ in the figure). Shows that the output is larger than b as well as c, and the resistance value is large in the open state. When connected to the first reference resistor 6 (□ in the figure), the output value is small and drops to around a. The price is also slightly fluctuating. Next, when the user holds the grip 25 and stands on the measuring table 24, the circuit of the current applying means 9 is closed and the living body 5 is closed.
Then, the current also flows through the first reference resistor 6.

The output of the signal processing means at this time is shown in FIG. 3B. The output is stable in the vicinity of a normal value for all of the living body, the first reference resistance, and the second reference resistance. The contact detecting means detects the presence or absence of contact of the human body with the electrode by using the signal change before and after such contact with the electrode.

The presence / absence of contact is determined to be non-contact if any of the following conditions is satisfied. (1)
The output of the signal processing means 14 for the first reference resistor 6 is not within the determined range. (2) The variation of the output of the signal processing unit 14 with respect to the first reference resistor 6 for a certain period of time is not within the determined range. (3) First reference resistor 6
And the result calculated by the bioelectrical impedance calculation means 15 based on the second reference resistance 7 and the output of the AD conversion means 14 of the living body 5 is not within the determined range. Of the above,
Regarding (1) and (2), the value changes when the living body does not contact at least one of the current applying electrodes,
The contact is determined by using the large variation. In case of (1), 1000 of the two reference resistors
The side with a large resistance value of Ω is connected in series with the living body, but if there is no contact with the living body, it will be in a short state, and if it comes in contact there will be a large potential difference output due to a large resistance The detection sensitivity can be increased. Regarding (3), the impedance of the living body 5 and the output value of the first reference resistor 6 are not correct values, and the living body has a large value and the reference resistance has a small value. The measured bioresistance value is 10 times or more as large as the normal measurement range.

This state is shown in FIG. The horizontal axis of the figure shows the output of the signal processing means 13, and the vertical axis shows the resistance value. FIG. 4A shows a case where the living body 5 normally contacts the current applying electrode and the potential detecting electrode, and the first reference resistance 6 is plotted at the point A1 and the second reference resistance is plotted at the point B1. A straight line L connecting the points A1 and B1 is a conversion formula for converting the output of the signal processing means 13 into a resistance value, and when there is a living body C1, 450 is derived from this straight line.
Calculated as Ω. FIG. 4B shows the case where the living body 5 is not placed on the grip measuring table 23 only in the grip portion 24, whereas the second reference resistance 7 is plotted at the same position B2 as in FIG. 4A. , Because the first reference resistor 6 has a low output,
A straight line L ′ that is plotted at a position A2 that is moved to the left by a distance larger than that of (a) and has a completely different appearance from the straight line L of FIG. 4A is connected. Furthermore, since the output of the living body 5 also becomes a large impedance in the open state, it moves to the right opposite to the first reference resistance 6, and if this value is substituted as it is, it will be plotted at the position of C2 ′ and calculated. Is a value far from the normal range (-7 in the figure).
Since it is calculated as 200Ω), the presence or absence of contact can be determined very clearly by using this value.

As can be seen from the position of C2 'in FIG. 4 (b), when the living body 5 is not in proper contact with the four electrodes, the output itself of the signal processing means 13 when the living body is connected measures the impedance. Since it is out of the range, it is possible to detect the contact of the living body with the electrode only by using this. However, in the case of the method (3), the output difference due to the contact of the electrodes is extremely large, and even if noise or the like occurs, the output range corresponding to the human body cannot be reached, and the electrode of the living body can be easily and accurately detected. Can detect contact.

Under the conditions (1) and (2), both are within a certain range for determination, but in the present embodiment, this range is the second reference resistance connected in parallel to the living body. It is determined using the output of 7. Since the first reference resistor 6 and the second reference resistor 7 are known, and the connected current applying unit 9, potential difference detecting unit 10 and signal processing unit 13 are the same, the second reference resistor 7 serves as the potential difference detecting unit. When the first reference resistor 6 is connected to the potential difference detecting means 10, the current state and the outline of the circuit characteristics of the potential difference detecting means 10 and the signal processing means 13 are obtained from the output of the signal processing means 13 when connected. The output of the signal processing means 13 can be predicted. Further, the variation in the output of the signal processing means 13 also changes each time due to the state of noise at the time of measurement, etc. Therefore, in order to eliminate the influence of noise, the signal processing means 13 of the signal processing means 13 when connected to the second reference resistor 7 is eliminated. From the output variation, it is possible to predict the output variation of the signal processing means when the living body contacts the electrode and is connected to the first reference resistor 6.

In order to realize such a structure, the contact detecting means 16 of this embodiment changes the output of the signal processing means 13 when the potential difference switching means 12 is connected to the second reference resistor 7 from the potential difference switching means 12. Of the potential difference range calculating means 16a for calculating the output range of the signal processing means 13 when the potential difference switching means 12 is connected to the second reference resistor 7, and the signal processing means 13 when the potential difference switching means 12 is connected to the second reference resistance 7. It has a variation range calculation means 16b for calculating the variation range of the output of the signal processing means 13 when the potential difference switching means 12 is connected to the first reference resistor 6 from the variation of the output, and is used for abnormality determination. In addition to these two outputs, the output of 15b is used to make the determination in (3), and the abnormality determination output means 16c
Outputs the determination result to the control means 21.

When the living body 5 comes into contact with the electrode of the measuring table 24 and the electrode of the grip 25, the contact detecting means 1 as described above.
6 detects the contact, then the current application determination means determines the state of the current applied to the living body, and when the measured current of 50 kHz 500 μA is correctly applied to the living body, the bioelectrical impedance detection means detects the bioelectrical impedance. Transition. The operation of the current state determination by the current application determination means is shown below.

When the living body comes into contact with the measuring table 23 and the electrodes of the grip portion 24, the current applying circuit of the current applying means 9 is closed and the current is applied to the living body 5 and the first reference resistor 6. At this time, in addition to the living body 5 and the first reference resistor 6, the contact resistances of the current applying electrodes 1 and 3 are connected in series to the current applying unit 9. This contact resistance has a value of several tens when the skin condition of the living body is dry or swollen.
It is known that it will be extremely large from kΩ to several hundred kΩ,
When the contact resistance is large, the voltage drop during that period is large, and it is necessary to secure the power supply voltage of the current applying means at a voltage higher than the voltage drop. When a voltage drop of more than the power supply voltage occurs, the waveform of the portion exceeding the power supply voltage range becomes a cut waveform as shown in FIG. 5B, and FIG.
Since the measured current having a swing width of 50 kHz and 500 μA as shown in (3) cannot be correctly applied, and the swing width of the applied current becomes small, the bioimpedance is relatively underestimated. Furthermore, this effect is not limited to the swing width, but also affects the frequency characteristics. FIG. 6 shows the frequency characteristics of the current applied to the living body by the current applying means. Figure 6 (a)
In the case of normal application, the component of 50 kHz is extremely large, and its harmonic is considerably smaller than 50 kHz.

On the other hand, FIG. 6 (b) shows the frequency component when the upper and lower parts are cut off, but the higher harmonic component appears largely due to the upper and lower part being cut off. When detecting bioimpedance, it is known that the value changes depending on the measurement frequency.This is because the biological tissue is an aggregate of cells and the cell membrane encapsulating the cells has a capacitive component. The low-frequency current passes through the extracellular fluid surrounding the outside of the cell and a high impedance is detected, whereas
In the case of a high-frequency current, the current passes through the cell membrane, and the current flows not only in the extracellular fluid but also in the intracellular fluid inside the cell, and a low impedance is detected. In this way, since the meaning of the impedance detected by changing the frequency component of the measurement current also changes, it is not possible to detect the correct bioimpedance even if the signal due to such measurement current is detected,
Even if the body fat is obtained based on this, an accurate body fat amount cannot be calculated. Therefore, it is desirable to configure the current applying means 9 with a high power supply voltage that does not exceed the power supply voltage even if the contact resistance increases, but when a measurement current of 500 μA is passed, for example, the contact resistance at one electrode is 10 kΩ. If so, the voltage drop at that portion becomes 5V, and if there are two locations, the contact resistance alone reaches 10V. This is 10 times the sum of the voltage drop due to the maximum value 1000Ω in the measurement range of the living body 5 and 1000Ω of the first reference resistance, which is 1v, and it is not economical to increase the power supply voltage due to the contact resistance. On the other hand, the contact resistance decreases by more than 1/10 just by squeezing the electrode strongly or by lightly sprinkling water on the skin of the contact part. Therefore, the current application state is detected and the subject is instructed to lower the contact resistance. With such a configuration, it is possible to realize an economical and accurate bioelectrical impedance measuring device without requiring a large high power supply voltage assuming an extremely large contact resistance.

In the present embodiment, the potential switching means 12 determines the potential switching means 12 from the absolute value and the variation of the output of the signal processing means 13 when the potential switching means 12 is connected to the second reference resistor 7 connected in parallel to the living body. The absolute value and variation range of the output of the signal processing means 13 when connected to the first reference resistor 6 connected in series to the living body are predicted, and the absolute value and variation of the output of the first reference resistance 6 are actually predicted. If it is within the predicted range, it is judged that the current is correctly applied, the bioelectrical impedance is detected, and if either one of the absolute value and the variation is not within the predicted range, hold firmly It gives instructions to reduce contact resistance by sprinkling water on it. With such a configuration, it is possible to prevent inaccurate detection of bioimpedance due to the influence of contact resistance without increasing the power supply voltage.

In the present embodiment, the electrode 1 connected to the out terminal 22a of the operational amplifier of the current applying means 9 is connected to the electrode of the grip 25, but this is the grip 25.
First grasp the electrode of the
This is because it is often the case that measurement is performed by contacting the electrode of. The first contacting electrode is brought to the out terminal side 22a of the operational amplifier of the current application circuit in order to reduce the influence of noise when the contact detection means detects the contact of the human body. If the electrodes to be contacted first are on the side of 3 and 4, the living body and the potential difference detecting means are connected when detecting the potential difference between both ends of the first reference resistor 7, and the living body becomes an antenna and picks up noise, It is input to the signal processing means. On the other hand, if the living body comes into contact with the sides 1 and 2 first,
The electrode of is connected to the second reference resistor 7, which is connected in parallel to the living body, the circuit is closed regardless of the contact of the living body, and is not affected by noise. The noises added to the potential difference detecting means are also small because they are distant from each other.

Therefore, in order to reduce the influence of noise, the electrode to be contacted first is o of the operational amplifier of the current application circuit.
The ut terminal 22a side, that is, the electrode that is not connected to the reference resistance connected in series to the living body is not affected by noise caused by the living body.

In the above embodiment, one of the two different reference resistances is connected in series to the living body and the other is connected in parallel to the living body. However, one reference resistance is switched by the switching means and connected in series to the living body. The abnormality may be detected from the output when connected in parallel with when connected to. In this case, in the normal case, the same output can be obtained regardless of the connection state, so that the abnormality can be easily and accurately detected.

Further, although two reference resistors are used in the above embodiment, a configuration using two or more reference resistors may be used, at least one of which is connected in series to the living body,
In addition, at least one may be connected to the living body in parallel.

In the above embodiment, the body fat percentage meter using the bio-impedance detecting device has been described. However, the bio-impedance detecting configuration can be used independently and can be used in the body fat percentage meter. It is not limited to. Further, in addition to the body fat percentage, it may be applied to a measuring device in a physiological state that can be measured by using bioelectrical impedance such as body water content.

Further, in the above embodiment, the bioimpedance and the body fat percentage of the human body as a living body are obtained, but the same applies not only to the human body but also to animals and the like. Further, not limited to a living body, the application is possible as long as the impedance near the electrode is likely to change and may become extremely large.

According to the above-mentioned invention, it is possible to realize a bioimpedance detecting device capable of detecting contact or detecting a current application state and performing a correct measurement with a correct applied current. As a result, the bioimpedance is used to measure the characteristics of the human body, such as the amount of body fat and It can be applied to devices that measure body water content, etc.

[0068]

As described above, according to the bioelectrical impedance detection device of the present invention, the potentials when the reference resistance is connected in series to the living body and when the reference resistance is connected in parallel are detected, and the current passing through the living body and the living body are detected. Since the measurement abnormality is detected from the output of the reference resistance potential detection means due to the current not passing through,
It is possible to realize a bioimpedance detecting device that can easily and accurately detect a measurement abnormality and can perform a correct measurement with a correct applied current. As a result, it can be applied to a device that measures the characteristics of the human body, such as the amount of body fat and the amount of body water, using the bioelectrical impedance.

[Brief description of drawings]

FIG. 1 is a block diagram of a bioelectrical impedance detection device according to a first embodiment of the present invention.

[Fig. 2] External view of the device

FIG. 3 (a) is an output diagram of the signal processing unit of the same apparatus when the living body is not in contact with the electrode, and (b) is an output diagram of the signal processing unit of the same apparatus when the living body is in contact with the electrode.

FIG. 4 (a) is a conceptual diagram of a bioimpedance calculation when the living body of the bioimpedance detecting means of the device is in contact with the electrode. Of bioimpedance calculation

FIG. 5A is a current waveform diagram when the current application circuit of the device is normal, and FIG. 5B is a current waveform diagram when the contact resistance of the current application circuit of the device is abnormally large.

FIG. 6A is a frequency analysis diagram of a current waveform of a current application circuit of the same device in a normal case. FIG. 6B is a frequency analysis diagram of a current waveform of a current application circuit of the device in an abnormally large contact resistance.

FIG. 7 is a block diagram of a bioelectrical impedance detection device in a conventional example.

[Explanation of symbols]

1, 3 Current application electrodes 2, 4 Voltage detection electrodes 5 Human body (living body) 6 First reference resistance (reference resistance connected in series to living body) 7 Second reference resistance (reference resistance connected in parallel to living body) ) 9 current application means 10 potential difference detection means 11 current switching means 12 potential difference switching means 15 bioelectrical impedance calculation means 16 contact detection means (abnormality detection means) 16a potential difference range calculation means 16a variation range calculation means 17 current application determination means (abnormality detection means) )

Continued front page    (72) Inventor Masatsugu Inoue             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Makoto Hirano             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Kazutoshi Nagai             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Hiroyuki Ogino             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 4C027 AA06 EE01

Claims (16)

[Claims] 1. A pair of current applying electrodes that come into contact with a living body to apply a current to a contact portion, a pair of potential detection electrodes that come into contact with the living body to detect the potential of the contact portion, and resistance values are known. A reference resistance, a current application means for applying a current to the current application electrode or the reference resistance, a potential difference detection means for detecting a potential difference between the pair of potential detection electrodes or both ends of the reference resistance, and the current application means. Current switching means for switching the path of the applied current between the current application electrode and the reference resistance, potential switching means for switching the potential difference detected by the potential detection means between the potential detection electrode and the reference resistance, and the output of the potential difference detection means From the bioelectrical impedance detection means for detecting the bioelectrical impedance of the living body, different from both potentials when the reference resistance is connected to the living body in series and in parallel. A bioimpedance detecting device having an abnormality detecting means for detecting a normal state. 2. The bioelectrical impedance detection device according to claim 1, wherein there are a plurality of reference resistors, at least one of which is connected to a living body in series, and at least one of which is connected to the living body in parallel. 3. The bioelectrical impedance detection device according to claim 1, which detects a potential difference both when the same reference resistance is connected to a living body in series and when it is connected in parallel. 4. The bioelectrical impedance detection device according to claim 1, wherein the abnormality detection means is a current application determination means for determining whether or not the current application means has normally applied the current to the living body. 5. The current application determination means determines the current application state to the living body from the potential difference between both ends of the reference resistance connected in series to the living body and the reference resistance connected in parallel to the living body. The bioimpedance detecting device described. 6. The current application determining means determines the current application state to the living body by calculating the variation of the potential or the potential difference of the reference resistance connected in series to the living body for a certain period of time.
The bioimpedance detection device according to item 1. 7. The bioelectrical impedance detection device according to claim 1, wherein the abnormality detection unit is a contact detection unit that detects contact of the living body with the potential detection electrode or the current detection electrode. 8. The contact detecting means calculates a potential difference between both ends of a reference resistance connected in series to a living body and uses it for detecting contact with a potential detecting electrode or a current detecting electrode of the living body.
The bioimpedance detection device according to item 1. 9. The contact detecting means is used to detect the contact of the potential or the current detection electrode of the living body by calculating the variation of the potential or the potential difference of the reference resistance connected in series to the living body for a certain period of time. 7. The bioelectrical impedance detection device according to 7. 10. The contact detection means uses the potential difference between reference resistances connected in series to the living body and the potential difference between reference resistances connected in parallel to the living body to detect the contact with the potential detection electrode or the current detection electrode of the living body. The bioelectrical impedance detection device according to claim 7, which is used for detection. 11. The contact detection means has a potential difference range calculation means for calculating a range of potential difference that a reference resistance connected in series to a living body should have from a potential difference between reference resistances connected in parallel to the living body, and connected in series. The bioelectrical impedance detection device according to claim 10, wherein when the potential of the reference resistance thus determined is within the range calculated by the potential difference range calculation means, it is determined that the living body has contacted the potential detection electrode or the current detection electrode. 12. A variation in which the contact detection means calculates a range of variation in potential or potential difference for a certain period of time that the reference resistance connected in series to the living body should have from the potential or potential difference of the reference resistance connected in parallel to the living body. Having a range calculation means, when the variation of the potential or the potential difference of the reference resistance connected in series for a certain period of time is within the range calculated by the variation range calculation means, the living body contacts the potential detection electrode or the current detection electrode. The bioelectrical impedance detection device according to claim 10, wherein the determination is performed. 13. The bioelectrical impedance detection means substitutes a potential difference between reference resistors connected in parallel with the living body, a potential difference between reference resistors connected in series with the living body, and a potential difference between potential detection electrodes into a predetermined calculation formula. And a calculation means for calculating the impedance of the living body, and the contact detection means is a potential difference between a reference resistance connected in series to the living body detected when the living body is not in contact with the current application electrode or the potential detection electrode. The bioelectrical impedance detection device according to claim 7, wherein contact of the living body with the current application electrode or the potential detection electrode is detected using the output of the potential detection means and the potential difference of the reference resistance connected in parallel to the living body. 14. The living body according to at least one of claims 7 to 13, wherein a potential detection electrode which is connected in series with the living body in series with a potential detection electrode in circuit is brought into contact with the living body after the other potential detection electrode. Impedance detection device. 15. The value of the reference resistance connected in series to the living body is larger than the smallest resistance value among the reference resistances connected in parallel to the living body. Bioimpedance detection device. 16. The test subject is instructed to take measures to reduce the contact resistance when the current application determination means determines that the measurement current is not correctly applied to the living body. Bioimpedance detection device.