Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2002-03-04
2004-04-20
Deb, Anjan K. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S691000, C324S715000, C600S547000
Reexamination Certificate
active
06724200
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for measuring the bioelectrical impedance of a living body in which the bioelectrical impedance can be determined by making a weak current of high-frequency flow from one to the other selected point in the living body, and by determining the weak current of high-frequency flowing through the current passage between the opposite selected points and the voltage appearing between another two selected points in the current passage in which the weak current flows.
2. Prior Art
Composition assessment of a selected portion of a living body in terms of its bioelectrical impedance is known from the magazine, “The American Journal of Clinical Nutrition”, 41(4)810-817 1985, “Assessment of fat-free mass using bioelectrical impedance measurement of the human body”. Also, an apparatus for analyzing the composition in a selected portion of a living body in terms of the bioelectrical impedance appearing in the selected portion is described in the magazine, “Journal of Applied Physiology VOL77 NO.1, Segmental bioelectrical analysis: theory and application of a new technique”. Specifically, the bioelectrical impedance is determined by making electric current of high-frequency flow between the opposite terminal points of both hands and both feet and by measuring the voltage appearing between another two selected points in the current passage in which the weak current flows. A similar apparatus is disclosed in Japanese Patent Application Laid-Open No.10-510455.
In such a conventional bioelectrical impedance gauge a weak current of high-frequency is made to flow in a living body; and the voltage appearing across a given length of current path in which the weak current flows is determined, as seen from FIG.
5
.
Referring to
FIG. 5
, one terminal end of a load Z, which represents a portion selected in a living body, is connected both to the proximal end Ta
1
of a high-frequency current supplying cable C
1
and to the proximal end Ta
4
of a voltage-measuring cable C
4
whereas the other terminal end of the load Z is connected both to the proximal end Ta
2
of another high-frequency current supplying cable C
2
and to the proximal end Ta
3
of another voltage-measuring cable C
3
. Each cable C
1
, C
2
, C
3
or C
4
has its stray capacitance Cs
1
, Cs
2
, Cs
3
or Cs
4
appearing between the cable and the ground. These stray capacitances will have an adverse effect on the measurement.
Different currents appearing on the current supplying side of the impedance gauge of
FIG. 5
are given as follows:
I
1
=I
2
+Is
1
where I
1
stands for the electric current flowing from the impedance gauge to the high-frequency current supplying cable C
1
(the current being measured by a current detector); I
2
stands for the electric current passing through the proximal end Ta
1
of the high-frequency current supplying cable C
1
; and Is
1
stands for the electric current flowing through the stray capacitance Cs
1
of the high-frequency current supplying cable C
1
.
The electric current Is
4
flows through the stray capacitance Cs
4
, which appears between the voltage-measuring cable C
4
and the ground. The electric current I
3
flows in the load. Assuming that the input impedance as seen inward from the voltage measuring terminals N
3
and N
4
of the impedance gauge is infinitively large, and that the impedance of each cable is zero, the electric current I
2
is given by:
I
2
=I
3
+Is
4
.
Thus, the electric current
13
flowing in the load is given by:
I
3
=I
1
−Is
1
−Is
4
The current I
1
flowing from the impedance gauge into the high-frequency current supplying cable C
1
(measured by the current detector) cannot be equal to the current I
3
passing through the impedance Z, thus causing an error in measurement. As a matter of fact, the impedance measured by the impedance gauge is smaller than the impedance of the load Z.
Such an error can be corrected to some extent, but no satisfactory correction can be made; as the cables change in position, their stray capacitances vary. Thus, the measurement will be adversely affected, and the adverse effect is apt to increase with the increase both of the frequency of the electric current and of the cable length.
It takes a significant time for the current signal I
1
to flow from one terminal N
1
to the other terminal N
2
through the out-going high-frequency current supplying cable C
1
, the load Z and the in-coming high-frequency current supplying cable C
2
, allowing this delay time to appear as phase lag, which is proportional to the frequency of the electric current flowing in the load Z, thus contributing to the error in the measurement.
SUMMARY OF THE INVENTION
In view of the above one object of the present invention is to provide an improved apparatus for measuring the bioelectrical impedance of a living body, which apparatus is guaranteed to be free of the adverse effect caused by the stray capacitances and lengths of associated cables, thus permitting the exact measurement of bioelectrical impedance over an expanded range from low to high frequencies.
To attain this object an apparatus for measuring the bioelectrical impedance of a living body in which the impedance of the living body can be determined by making a weak electric current of high-frequency flow between two selected points on the living body and by determining the voltage between said two selected points or between another two points selected in the current passage in which the weak electric current flows_ is improved according to the present invention in that it comprises: a measuring apparatus including a high-frequency current source, a high-frequency current determining section and a voltage determining section; at least one high-frequency current supplying probe connected to said high-frequency current source via a shielded-conductor cable; a pair of high-frequency current supplying electrodes to be applied to said two selected points; two voltage measuring probes connected to said voltage determining section via shielded-conductor cables; and a pair of voltage measuring electrodes to be applied to said two selected points or said another two points, said high-frequency current supplying probe having a high-frequency current detector connected to and positioned in the vicinity of one of said pair of high-frequency current supplying electrodes.
An apparatus for measuring the bioelectrical impedance of a living body in which the impedance of the living body can be determined by making a weak electric current of high-frequency flow between two selected points on the living body and by determining the voltage between said two selected points or between another two points selected in the current passage in which the weak electric current flows, is improved according to the present invention in that it comprises: a measuring apparatus including a high-frequency current source, a high-frequency current determining section and a voltage determining section; at least one high-frequency current supplying probe connected to said high-frequency current source via a shielded-conductor cable; a pair of high-frequency current supplying electrodes to be applied to said two selected points; two voltage measuring probes connected to said voltage determining section via shielded-conductor cables; and a pair of voltage measuring electrodes to be applied to said two selected points or said another two points, each of said voltage measuring probes having a high input-impedance amplifier connected to and positioned in the vicinity of one or the other voltage measuring electrode.
Two high-frequency current supplying probes may be connected to said high-frequency current source via shielded-conductor cables.
One high-frequency current supplying probe may be connected to said high-frequency current source via a shielded cable, said high-frequency current supplying probe having a high-frequency current detector connected to and positioned in the vicinity of one of the high-fr
Deb Anjan K.
Tanita Corporation
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