JP4196036B2 - Bioimpedance measurement device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention measures the impedance of a living body such as a body fat meter that calculates the body fat mass from the body impedance and body conditions such as height and weight by measuring the impedance of the living body by passing a high-frequency current through the living body. It is related with the apparatus which performs.
[0002]
[Prior art]
In general, as a method for measuring the amount of fat in the body, a method has been proposed in which the impedance between the ends of the body, such as between both hands, is measured by a four-terminal method, and the amount of fat in the body is calculated from body information such as height and weight. Yes.
[0003]
FIG. 5 is a block diagram showing a configuration of a conventional bioimpedance measuring apparatus. The bioimpedance is measured by generating a 50 kHz sine wave from the oscillator 1 and making the voltage of this sine wave constant by the voltage-current conversion means 2. This constant current is passed through the living body from between the electrodes 3a and 3b that are in contact with the living body. Then, the voltage between the electrodes 3a and 3b is taken out by the differential amplifier 4, the waveform is shaped by a filter circuit or the like, converted into direct current by the rectifier 5, and then the analog value is AD converted by the AD converter 6 as a digital numerical value. It is transmitted to the calculation unit 7 composed of a microcomputer. The computing unit 7 computes the bioelectrical impedance Z from the voltage signal.
[0004]
The bioelectrical impedance Z can be obtained by detecting the electrode voltage V when the current I is constant because the relationship between the bioelectrical current I and the electrode voltage V is Z = V / I. The amount of fat in the body is calculated from the bioelectrical impedance Z and body information such as height and weight.
[0005]
[Problems to be solved by the invention]
In the bioimpedance measuring apparatus having the conventional configuration, the output of the constant current source is affected by the output value due to a change in the ambient temperature or the like, and this change in the constant current causes a measurement error of the bioimpedance. In order to set the constant current source to a steady value, a great deal of labor is required such as reduction of external environmental fluctuations and improvement of the accuracy of the constant current source.
[0006]
[Means for Solving the Problems]
The present invention relates to a constant voltage source, a high frequency voltage generating means for generating a high frequency voltage from the constant voltage source, an electrode in contact with a living body, and a voltage divider for connecting the electrode in series and dividing the voltage of the high frequency generating means. Resistor, biological voltage detecting means for detecting the biological voltage between the electrodes, AD converting means for digitally converting the signal of the biological voltage detecting means, and AD using a constant voltage source as a reference voltage for the AD converting means Reference voltage means and calculation means for calculating the impedance of the living body from the signal of the living body voltage detecting means are provided.
[0007]
In the above means, the bioimpedance measuring apparatus can measure the impedance of the living body with higher accuracy without being affected by the environment such as temperature because the voltage of the bioimpedance at the time of measurement is obtained using a constant voltage source as the reference voltage of the AD converting means It is what you are trying.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The invention according to claim 1 of the present invention is a constant voltage source, a high frequency voltage generating means for generating a high frequency voltage from the constant voltage source, an electrode in contact with a living body, and the high frequency generating means connected in series with the electrode. A voltage dividing resistor for dividing the voltage of the living body, a living body voltage detecting means for detecting a living body voltage between the electrodes, an AD converting means for converting a signal of the living body voltage detecting means into digital, and a reference voltage of the AD converting means wherein those having an AD reference voltage means using a constant voltage source, and a calculating means for calculating the impedance of the living body from the signal of the living body voltage detecting means.
[0009]
In the above embodiment, the voltage is supplied from the constant voltage source by the high frequency generating means. This voltage is applied to the living body through the voltage dividing resistor and the electrode. The AD conversion means converts the voltage generated by the bioelectrical impedance into a digital value based on the voltage of the AD reference voltage means. Using this digital value, the computing means calculates the bioelectrical impedance. Therefore, since the constant voltage source applied to the living body is always detected to calculate the biological impedance, the accuracy of the biological impedance measurement can be improved.
[0010]
The invention according to claim 2 is in contact with a living body, a constant voltage source, high frequency voltage generating means for generating a high frequency voltage from the constant voltage source, voltage holding means for holding the voltage of the high frequency voltage generating means, and An electrode, a voltage dividing resistor connected in series with the electrode to divide the voltage of the high-frequency generating means, a biological voltage detecting means for detecting a biological voltage between the electrodes, and a signal from the biological voltage detecting means digitally AD converting means for converting, AD reference voltage means using the voltage held by the voltage holding means as a reference voltage of the AD converting means, and calculating means for calculating the impedance of the living body from the signal of the biological voltage detecting means It is provided .
[0011]
In the above embodiment, the voltage holding means holds the voltage of the high frequency voltage generating means and uses it as the reference voltage of the AD converting means. Therefore, since the bioelectrical impedance is calculated by always converting the analog value into a digital value based on the voltage applied to the living body, the measurement accuracy of the bioelectrical impedance can be improved.
[0012]
According to a third aspect of the present invention, there is provided the reference voltage switching means for switching the reference voltage of the AD reference voltage means by the voltage signal of the biological voltage detecting means according to any one of the first or second aspects. Is.
[0013]
In the above embodiment, the biological voltage Vz is detected using a predetermined reference voltage Vref. When the biological voltage Vz is smaller than the set value, a signal is transmitted from the calculation means to the reference voltage switching means, and the reference voltage switching means decreases the voltage of the AD reference voltage means. After the reference voltage Vref is switched, the biological voltage Vz is measured again, and the biological impedance Z is calculated from the biological voltage Vz. Therefore, even when the bioelectric voltage Vz is small, the reference voltage switching means can reduce the reference voltage Vref to increase the detection accuracy of the bioelectrical impedance.
[0014]
According to a fourth aspect of the invention, there is provided an amplification factor switching means for switching the amplification factor of the biological voltage detection means according to any one of the first or second aspects according to a voltage signal of the biological voltage detection means. Is.
[0015]
In the above embodiment, the biological voltage Vz is detected using a predetermined amplification factor. When the biological voltage Vz is smaller than the set value, a signal is transmitted from the calculation means to the amplification factor switching means, and the amplification factor switching means increases the amplification factor of the biological voltage detection means. After the amplification factor is switched, the biological voltage Vz is measured again, and the biological impedance Z is calculated from the biological voltage Vz. Therefore, when the biological voltage Vz is small, the amplification factor switching means increases the amplification factor, and the detection accuracy of the biological impedance can be improved.
[0016]
【Example】
The bioimpedance measuring apparatus of the present invention will be described below with reference to FIGS.
[0017]
(Example 1)
FIG. 1 is a block diagram showing the invention of Embodiment 1 of the bioimpedance measuring apparatus. A constant voltage source 10; high frequency voltage generating means 11 for generating a high frequency voltage from the constant voltage source 10; electrodes 12a and 12b in contact with a living body; and the electrodes 12a and 12b connected in series to the high frequency generating means 11 A voltage dividing resistor 13 for dividing the voltage, a biological voltage detecting means 14 for detecting a biological voltage between the electrodes 12a and 12b, an AD converting means 15 for converting the signal of the biological voltage detecting means 14 into digital, and this An AD reference voltage unit 16 that uses a constant voltage source as a reference voltage of the AD conversion unit 15 and a calculation unit 17 that calculates the impedance of the living body from the signal of the biological voltage detection unit 14 are provided.
[0018]
In the first embodiment, the high-frequency voltage generation means 11 generates a 50 kHz sine wave by the voltage of the constant voltage source 10. The voltage Vin causes a current I to flow between the voltage dividing resistor 13 and the electrodes 12a and 12b in contact with the living body. The electrodes 12a and 12b come into contact with the left and right hands of the body, and a current I flows between both hands. The biological voltage detection means 15 detects the voltage between the biological electrodes 12a and 12b generated by the current I with a differential amplifier. The voltage Vz of the biological voltage detection means 15 is determined by the current I from the sum of the impedance Zr of the voltage dividing resistor 13 and the biological impedance Z. The bioelectric voltage Vz is generated in the bioelectric impedance Z by this current I. The impedance Zr of the voltage dividing resistor 13 and the voltage Vin of the high-frequency voltage generation means 11 are predetermined set values, and the biological voltage Vz can be obtained from the above relationship. The reference voltage Vref of the AD conversion means 15 is supplied by the constant voltage of the constant voltage source 10. This reference voltage Vref is a reference voltage for converting an analog value into a digital value, and the voltage resolution per bit is determined by dividing by a set number of bits. That is, even if the voltage Vin varies, the biological voltage Vz and the reference voltage Vref both vary, so the digital value of the biological voltage Vz does not change. The calculation means 17 calculates the bioelectrical impedance Z from this digital value.
[0019]
In particular, in the first embodiment at this time, the reference voltage Vref of the AD conversion means 15 is supplied from the constant voltage source 10 and the fluctuation of the constant voltage source is absorbed in the digital value after AD conversion, thereby obtaining the biological voltage Vz. By detecting and calculating bioimpedance, highly accurate bioimpedance measurement can be realized.
[0020]
In the first embodiment, the frequency of the high frequency generating means 10 is 50 kHz, but the same effect can be obtained even at a frequency of 10 kHz to 500 kHz, and the frequency is not limited to a single frequency.
[0021]
(Example 2)
FIG. 2 is a block diagram showing a second embodiment of the bioimpedance measuring apparatus. This bioimpedance measuring apparatus is different from the first embodiment only in that the AD reference voltage means is provided with a voltage holding means for holding the voltage of the high-frequency voltage generating means, and other parts having the same configuration and effects are provided. Are denoted by the same reference numerals, detailed description thereof is omitted, and different points will be mainly described. Reference numeral 18 denotes voltage holding means for holding the voltage of the high frequency voltage generating means 11 in the AD reference voltage means 16.
[0022]
In the second embodiment, the voltage holding unit 18 peaks the high frequency voltage Vin from the diode and the capacitor with the sine wave signal of the high frequency voltage generating unit 11. This voltage is output to the reference voltage Vref of the AD conversion means 15. The biological voltage Vz is AD converted using this reference voltage Vref. That is, the biological voltage Vz can be detected by always detecting the output voltage of the high-frequency voltage generating means.
[0023]
As described above, according to the second embodiment, the sine wave voltage Vin at the time of measurement is detected and the bioelectrical impedance Z is determined, so that the influence of fluctuations in the constant voltage output can be reduced, and the measurement accuracy can be improved. A high impedance measuring device can be realized.
[0024]
(Example 3)
FIG. 3 is a block diagram showing a third embodiment of the bioimpedance measuring apparatus. This bioimpedance measuring device is different from the first embodiment only in that a reference voltage switching unit that switches an AD reference voltage unit according to a voltage signal of the bioelectric voltage detection unit is provided, and the other parts that have the same configuration and operational effects The same reference numerals are assigned to the components, and detailed description thereof is omitted, and different points will be mainly described. Reference numeral 19 is a reference voltage switching means for switching the AD reference voltage means 16 according to the voltage signal of the biological voltage detection means 14.
[0025]
In the third embodiment, the biological voltage Vz is detected using a predetermined reference voltage Vref. When the biological voltage Vz is smaller than the set value, a signal is transmitted from the calculation means 17 to the reference voltage switching means 19, and the reference voltage switching means 19 reduces the voltage of the AD reference voltage means 16. After the reference voltage Vref is switched, the biological voltage Vz is measured again, and the biological impedance Z is calculated from the biological voltage Vz. When the reference voltage Vref is reduced, the voltage resolution per bit is increased and the voltage detection accuracy is improved. By halving the reference voltage Vref from the set value, the voltage resolution is doubled. It is effective for measuring local bioimpedance and measuring local fat thickness, such as between the buttocks.
[0026]
As described above, according to the third embodiment, when the bioelectric voltage Vz is small, the reference voltage switching unit 19 can reduce the reference voltage Vref to increase the detection accuracy, thereby realizing a bioimpedance device with high measurement accuracy. it can.
[0027]
In an apparatus for measuring bioimpedance at a plurality of sites using a plurality of electrodes, the same effect can be obtained even when the reference voltage Vref is switched in conjunction with a signal for switching the electrodes when measuring a low impedance site.
[0028]
Example 4
FIG. 4 is a block diagram showing a fourth embodiment of the bioimpedance measuring apparatus. This bioimpedance measuring apparatus is provided with an amplifying means 20 for amplifying the signal of the bioelectric voltage detecting means 14 and an amplification factor switching means 21 for switching the amplification factor of the amplifying means 20 by the voltage signal of the bioelectric voltage detecting means 14. Only points differ from the first embodiment, and other parts having the same configuration and operational effects are denoted by the same reference numerals, detailed description thereof is omitted, and different points are mainly described. Reference numeral 20 denotes amplification means for amplifying the signal from the biological voltage detection means 14. Reference numeral 21 denotes amplification factor switching means for switching the amplification factor of the amplification means 20 according to the voltage signal of the biological voltage detection means 14.
[0029]
In the fourth embodiment, the biological voltage Vz is detected using a predetermined amplification factor. When the biological voltage Vz is smaller than the set value, a signal is transmitted from the computing unit 17 to the amplification factor switching unit 21 , and the amplification factor switching unit 21 increases the amplification factor of the biological voltage detection unit 14. After the amplification factor is switched, the biological voltage Vz is measured again, and the biological impedance Z is calculated from the biological voltage Vz. When the amplification factor is increased, the voltage resolution per bit is increased, and the voltage detection accuracy is improved. By doubling the amplification factor from the set value, the voltage resolution is doubled.
[0030]
As described above, according to the fourth embodiment, when the biological voltage Vz is small, the amplification factor switching unit 21 can increase the amplification factor to increase the detection accuracy, thereby realizing a bioimpedance device with high measurement accuracy. .
[0031]
【The invention's effect】
As described above, the invention according to claim 1 of the present invention is connected to a constant voltage source, high frequency voltage generating means for generating a high frequency voltage from the constant voltage source, an electrode in contact with a living body, and the electrode in series. A voltage dividing resistor for dividing the voltage of the high-frequency generating means, a biological voltage detecting means for detecting a biological voltage between the electrodes, an AD converting means for digitally converting a signal of the biological voltage detecting means, and the AD conversion and AD reference voltage means using the constant voltage source to the reference voltage means, the one having the from the signal of the living body voltage detecting means and calculating means for calculating the impedance of the living body, the reference voltage Vref of the AD converter constant voltage The constant voltage source fluctuation is absorbed into the digital value after AD conversion. Then, by detecting the bioelectric voltage Vz and calculating the bioelectrical impedance, it is possible to realize a highly accurate measurement of the bioelectrical impedance.
[0032]
The invention according to claim 2 is in contact with a living body, a constant voltage source, high frequency voltage generating means for generating a high frequency voltage from the constant voltage source, voltage holding means for holding the voltage of the high frequency voltage generating means, and An electrode, a voltage dividing resistor connected in series with the electrode to divide the voltage of the high-frequency generating means, a biological voltage detecting means for detecting a biological voltage between the electrodes, and a signal from the biological voltage detecting means digitally AD converting means for converting, AD reference voltage means using the voltage held by the voltage holding means as a reference voltage of the AD converting means, and calculating means for calculating the impedance of the living body from the signal of the biological voltage detecting means those having detects a sinusoidal voltage Vin at the time of measurement, because you have to determine the bioelectrical impedance Z, it can reduce the effect of a variation in the constant voltage, high measurement precision apparatus It can be current.
[0033]
According to a third aspect of the present invention, there is provided a reference voltage switching means for switching the AD reference voltage means by a voltage signal of the biological voltage detection means. When the biological voltage Vz is small, the reference voltage switching means is the reference voltage Vref. The detection accuracy can be increased by reducing the impedance, and a bioimpedance device with high measurement accuracy can be realized.
[0034]
According to a fourth aspect of the present invention, there is provided amplification means for amplifying a signal of the biological voltage detection means, and amplification factor switching means for switching the amplification factor of the amplification means by the voltage signal of the biological voltage detection means. When the biological voltage Vz is small, the amplification factor switching means 20 can increase the amplification factor to increase the detection accuracy, and a bioimpedance device with high measurement accuracy can be realized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a bioimpedance measuring apparatus according to a first embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of a bioimpedance measuring apparatus according to the second embodiment. FIG. 4 is a block diagram showing the configuration of the bioimpedance measuring apparatus in Example 4. FIG. 5 is a block diagram showing the configuration of the bioimpedance measuring apparatus in the conventional example. Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Constant voltage source 11 High frequency voltage generation means 12a Electrode 12b Electrode 13 Voltage dividing resistor 14 Biological voltage detection means 15 AD conversion means 16 AD reference voltage means 17 Calculation means 18 Voltage holding means 19 Reference voltage switching means 20 Amplification rate switching means

Claims (4)

A constant voltage source, a high frequency voltage generating means for generating a high frequency voltage from the constant voltage source, an electrode in contact with a living body, a voltage dividing resistor connected in series with the electrode and dividing the voltage of the high frequency generating means, a biological voltage detecting means for detecting a voltage of the living body between the electrodes, and the AD converting means for converting the signal of the biological voltage detecting means to a digital, AD reference voltage means using the constant voltage source to the reference voltage of the AD converter And a bioimpedance measuring apparatus comprising: a calculation means for calculating the impedance of the living body from the signal of the biological voltage detection means. A constant voltage source, a high frequency voltage generating means for generating a high frequency voltage from the constant voltage source, a voltage holding means for holding the voltage of the high frequency voltage generating means, an electrode in contact with a living body, and the electrode connected in series. A voltage dividing resistor for dividing the voltage of the high-frequency generating means, a biological voltage detecting means for detecting a biological voltage between the electrodes, an AD converting means for digitally converting a signal of the biological voltage detecting means, and the AD conversion A bioimpedance measuring apparatus comprising: an AD reference voltage means that uses a voltage held by the voltage holding means as a reference voltage of the means; and an arithmetic means for calculating the impedance of the living body from a signal of the biological voltage detecting means .   The bioimpedance measurement apparatus according to claim 1, further comprising a reference voltage switching unit that switches the AD reference voltage unit according to a voltage signal of the bioelectric voltage detection unit.   The bioimpedance measuring apparatus according to claim 1, further comprising an amplification factor switching unit that switches an amplification factor of the biological voltage detection unit according to a voltage signal of the biological voltage detection unit.

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