Body fat measuring instrument

Details Body fat measuring instrument Body fat measuring instrument

2001-05-18

2003-05-20

Jeffery, John A. (Department: 3742)

Surgery

Diagnostic testing

Measuring electrical impedance or conductance of body portion

Reexamination Certificate

active

06567692

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a body fat measuring device for measuring the amount of fat in a human body.
BACKGROUND ART
The body composition of a human body is made up of muscles, bones, fat and others. The value of impedance of a human body containing a large amount of fat components differs from that of a human body containing a large amount of muscle components. More specifically, bio-impedance has such a nature that as fat components increase, the value of impedance increases and as components containing water increase, the value of impedance drops. When obtaining the amount of fat contained in the body composition by utilizing this nature, the following method is usually taken: Electrodes are attached to dermal surfaces at distal sites of the body such as the tips of fingers of right and left hands, the tiptoes of right and left feet, and the soles of right and left feet. An alternate current or voltage having a frequency of about several tens of KHz to 100 KHz is applied to these electrodes to measure the impedance of the body composition present between the distal sites. Then, the amount of body fat is calculated from the value of impedance thus obtained and personal data such as age, sex and height.
In recent years, the amount of fat contained in the body composition has been considered to be an index for health care and attracted the attention of ordinary people a great deal. Accordingly, demands toward body fat measuring devices for family or personal use have been increasingly growing. With such a background, there have been developed and sold a variety of inexpensive body fat measuring devices capable of measuring the amount of body fat with easy operation.
Known body fat measuring devices generally employ the measuring method called “the two terminal method” (the two electrode method) or the measuring method called “the four terminal method” (the four electrode method), and measure the amount of body fat in the body composition by measuring, in an easy way, body inter-distal-site impedance (i.e., the impedance between discrete distal sites of the body to which electrodes are attached) or body composition impedance that excludes the composition of the body at the distal sites.
FIG.
9
(
a
) is a measurement principle diagram illustrating the principal of measurement of body composition impedance by a body fat measuring device which utilizes the conventional two terminal method and FIG.
9
(
b
) is a circuit diagram for explaining the measurement principle. This body fat measuring device
100
comprises two electrodes
101
a
,
101
b
on its top surface. The two electrodes
101
a
,
101
b
are connected to a constant current circuit
102
and a patient steps on the measuring device
100
with one foot placed on the electrode
101
a
and the other foot on the electrode
101
b
, so that a constant current Ic is supplied to the human subject from the constant current circuit
102
. The constant current circuit
102
is comprised of (i) an operational amplifier
103
for outputting the constant current Ic and (ii) a reference resistor
104
having a given value Rs for controlling the circuit so as to allow the operational amplifier
103
to output the constant current Ic. The electrodes
101
a
,
101
b
are connected to a voltage measurement circuit
105
and a voltage V generated between the electrodes
101
a
,
101
b
in a condition in which the constant current Ic is applied thereto is measured by the voltage measurement circuit
105
. The voltage measurement circuit
105
comprises (i) an operational amplifier
106
for outputting the voltage V generated between the electrodes
101
a
,
101
b
in response to a voltage signal released from the electrodes
101
a
,
101
b
; (ii) input resistors
107
a
,
107
b
for the operational amplifier
106
; and (iii) a resistor
108
for a negative feedback circuit.
In the thus-arranged body fat measuring device
100
, where the body inter-distal-site impedance is Zo, the contact impedance between the electrode
101
a
and the dermal surface of a foot of the human subject is RX
1
, the contact impedance between the electrode
101
b
and the dermal surface of another foot is RY
1
, the relationship represented by the following equation exists between the impedances Zo, RX
1
, RY
1
, the constant current Ic, and the voltage V.
(
RX
1
+
Zo+RY
1
)·
Ic=V
That is,
Zo+RX
1
+
RY
2
=
V/Ic
Herein, if the sum of the contact impedances RX
1
, RY
1
(RX
1
+RY
1
) is much smaller than the body inter-distal-site impedance Zo, in other words, if Zo+RX
1
+RY
2
≈Zo, the body inter-distal-site impedance Zo can be obtained.
By performing calculation based on the body inter-distal-site impedance Zo thus obtained and personal data such as the age, sex and height of the patient which have been input to the body fat measuring device
100
beforehand, the amount of body fat can be obtained. It should be noted that the body inter-distal-site impedance Zo is obtained by combining body distal site surrounding composition impedance to body composition impedance.
Next, a body fat measuring device using the conventional four terminal method will be explained. FIG.
10
(
a
) is a diagram showing the measurement principal of a body composition impedance in a body fat measuring device which utilizes the conventional four terminal method and FIG.
10
(
a
) is a circuit diagram for explaining the measurement principle. The body fat measuring device
110
comprises four electrodes
111
a
,
111
b
,
112
a
and
112
b
on the top surface thereof. A patient steps on the measuring device
110
with one foot placed on the electrodes
111
a
,
112
a
and the other foot on the electrodes
111
b
,
112
b
. The electrodes
111
a
,
111
b
are connected to a constant current circuit
113
, and when the patient puts one foot on the electrode
111
a
and the other on the electrode
111
b
, a current Id is supplied to the human subject from the constant current circuit
113
.
The electrodes
112
a
,
112
b
are connected to a voltage measurement circuit
114
and a voltage generated between the electrodes
112
a
,
112
b
when the constant current Id is applied thereto is measured. Herein, the constant current circuit
113
is comprised of (i) an operational amplifier
115
for outputting the constant current Id and (ii) a reference resistor
116
having a given value Rs for controlling the circuit so as to allow the operational amplifier
115
to output the constant current Id. The voltage measurement circuit
114
is comprised of (i) an operational amplifier
117
for outputting the voltage V generated between the electrodes
112
a
,
112
b
in response to a voltage signal released from the electrodes
112
a
,
112
b
; (ii) input resistors
118
a
,
118
b
for the operational amplifier
117
; and (iii) a resistor
119
for a negative feedback circuit.
In the thus-arranged body fat measuring device
110
, where the body composition impedance to be measured is Zi, the contact impedances between the electrodes
111
a
,
111
b
,
112
a
,
112
b
and the dermal surfaces of the feet of the human subject are RX
1
, RY
1
, RX
2
and RY
2
, respectively, the resistance values of the input resistors
118
,
118
b
of the operational amplifier
117
are set to be sufficiently higher than the contact impedances RX
2
, RY
2
, whereby the constant current Id to be supplied between the electrodes
111
a
,
111
b
will not flow into the operational amplifier
117
and the amplification factor of the operational amplifier
117
will not be affected even if the contact impedances RX
2
, RY
2
fluctuate. Accordingly, a voltage generated between virtual intersections P and Q in the body, that is, the voltage V generated at both ends of the body composition impedance Zi excluding the contact impedances and body distal site surrounding composition impedances can be measured by the voltage measurement circuit
114
. Zi is calculated from the equation Zi=V/Id based on the voltage V thus obtained and the constant curren

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