Apparatus and method for analyzing body composition based on bioelectrical impedance analysis

An apparatus for analyzing body composition based on bioelectrical impedance analysis, and a method therefor are disclosed. The method for analyzing body composition includes the step of providing eight electrodes for being contacted to a right palm, a right thumb, a left palm, a left thumb, a right front sole, a right rear sole, a left front sole and a left rear sole. Then a switch is selected by a command of a micro-processor so as to form a current path. Then a current is made to flow through said selected electrodes and through a human body to an impedance measuring instrument. Then a switch is selected by a command of said micro-processor so as to form voltage electrodes. Then impedances for respective body portions are measured by means of the impedance measuring instrument. Then impedances of two body portions are decided based on the current and voltage of the impedance measuring instrument. Then the body composition is analyzed based on the measured impedance.

FIELD OF THE INVENTION 
The present invention relates to an apparatus for analyzing body 
composition based on bioelectrical impedance analysis, and a method 
therefor. Particularly, the present invention relates to an apparatus for 
measuring the impedance of the body segments by contacting the hands and 
the feet to novel metal electrodes, and a method for quantitatively 
analyzing body composition such as body fluid, body fat, and the like. 
BACKGROUND OF THE INVENTION 
A human body is composed of water, protein, bone and fat, in addition to 
small amounts of special components. The total of these elements 
constitutes the body weight. Quantitatively measuring the respective 
elements is called body composition analysis. The proportion occupied by 
the fat is called fatness and is used in diagnosing various adult 
diseases. In the medical terms, of the body composition, fat free mass 
(FFM) is the main component for supporting the human body. Patients 
suffering from malnutrition related, for example to cancer are subject to 
a periodic FFM measurement to determine a remission state or monitor 
progress of the disease. In the case where a fatty man performs athletic 
exercises to reduce the body weight, it frequently happens that the body 
weight shows almost no variation within a relatively short period of 
several months. In this case, if the body composition is measured, it will 
be found that the amount of muscle has increased, although the amount of 
fat has decreased. In this way, the effect of the athletic exercise can be 
measured in a rational manner. Further, based on the analysis of the body 
composition, the growth of children and the nutritional status of elderly 
men can be diagnosed. Particularly, for various patients, the segmental 
water distribution can be measured to determine patient's hydration 
status. 
There are various conventional methods for measuring the body composition. 
One of them is hydrodensitometry, and this method is carried out in the 
following manner. That is, the human body is immersed into water, and in 
this state, the body weight is measured. Then based on the density of the 
human body, the amount of fat is calculated. This method is based on the 
principle that fat is lighter than FFM. This measuring method shows a high 
accuracy, and therefore, it is used as a standard method. However, it has 
the disadvantage that it is a troublesome task to carry out it, and thus 
cannot be applied to an elderly man or to a patient. 
Another conventional method is to measure the thickness of the 
sub-cutaneous fat layer by using a caliper or near infrared rays. This 
method has the disadvantage that the accuracy is low. 
Further, there are photographic methods such as nuclear magnetic resonance 
(NMR), and dual energy X-ray absorptionmetry (DEXA), and a dilution 
methods such as heavy water (D20) and bromide solution. However, these 
methods are expensive to carry out, and therefore, they cannot be applied 
to general patients in an economical manner. 
As another method for measuring the body composition, there is 
bioelectrical impedance analysis (BIA). This method has the advantages 
that it is safe compared with the other conventional methods, the 
measuring cost is very low, and the measuring is done in a fast manner. 
This method is carried out In the following manner. That is, a weak 
alternating electric current is passed across the human body to measure 
the electrical resistance or conductance of the body, as well as measuring 
the height and weight. Based on these measured values, the amount of the 
body fluid, the fluid balance inside and outside the cell, and the amount 
of the body fat are calculated. 
In U.S. patent application Ser. No. 07/979,791, the analysis method based 
on the bioelectrical impedance is carried out in the following manner. 
That is, in a state with a patient lying, contact electrodes are attached 
on the skin of the body. The electrodes are surface electrodes which are 
similar to the electrodes for the electro-cardiogram. 
In the conventional method, four electrodes which are similar to the 
electrodes for the electro-cardiographic test are attached on the wrist, 
back of hand, ankle and back of foot, thereby electrically connecting the 
human body to an impedance measuring instrument. Then an electric current 
is let to flow, and thus, the resistance between the wrist and the ankle 
is measured. 
In this method, in a state with a human body lying, the electrodes are 
attached to the skin of the human body, and then, the impedance of the 
human body is measured. Then based on the measured values, the results 
such as percent body fat and the like are obtained by using a computer. 
Therefore, this method can be carried out only by employing a particularly 
trained person. Therefore, it cannot be used by the general public in 
saunas, athletic rooms and the like. 
Further, in this method, the impedances of the body segments such as arm, 
trunk and leg cannot be separately measured, and therefore, the difference 
between individuals in the regional impedance distribution causes a 
measurement error. 
Further, in this conventional method, the measuring person attaches the 
electrodes to the body portions of the person to be measured, and 
therefore, the attachments are not always done to the exact position, 
thereby generating measuring errors. 
Further, if hairs exist on the attachment positions, there is the 
inconvenience that the hairs have to be removed before attaching the 
electrodes. 
Further, this conventional method has the inconvenience that the body 
impedance is measured, and then, a computer is used to calculate the fat 
proportion. That is, the measuring person has to attach the electrodes to 
the relevant positions of the body of the person to be measured, the body 
weight and the body height have to be measured separately, and then, a 
computer has to be used to calculate the fatness. Therefore, it takes much 
time in carrying out the measuring and analyzing. 
In an attempt to overcome the above described disadvantages of the 
conventional techniques, the present inventor developed an apparatus for 
analyzing body composition and a method therefor, and filed a patent 
application under Korean Patent Application No. 94-23440 (filed on Sep. 
15, 1994). 
The present invention is an improvement of the above invention, in which 
the different segments of the body impedance can be measured and analyzed 
in a convenient and precise manner. 
OBJECTS OF THE INVENTION 
Therefore, it is an object of the present invention to provide an apparatus 
for analyzing the body composition by measuring the bioelectrical 
impedance, in which the body composition can be analyzed in a simple and 
convenient manner even without a specially trained person, like when 
measuring body weight on an electronic scale. 
It is another object of the present invention to provide an apparatus for 
measuring the body impedance, in which a person can attach his palms of 
hands and his soles of feet to the electrodes without an assistance of 
other people, thereby quickly and conveniently connecting an impedance 
measuring apparatus to the body. 
It is still another object of the present invention to provide an apparatus 
for precisely measuring the segmental body impedance by attaching the 
palms of hands and the soles of feet to 8 metal plate electrodes. 
It is still another object of the present invention to provide an apparatus 
for analyzing the body composition, in which the body weight can be 
simultaneously measured, and the body height can be inputted in a simple 
manner. 
It is still another object of the present invention to provide an apparatus 
for analyzing the body composition, in which the composition analysis 
results can be known through a display unit immediately, and can be 
printed simultaneously. 
SUMMARY OF THE INVENTION 
In achieving the above objects, the apparatus for analyzing the body 
composition based on the bioelectrical impedance analysis according to the 
present invention includes: 
a plurality of electrodes E1-E8 for contacting with a right palm, a right 
thumb, a left palm, a left thumb, a right front sole, a right rear sole, a 
left front sole, and a left rear sole respectively; 
an impedance measuring instrument 11 for measuring the impedance based on a 
voltage-current ratio after making an alternating current flow between two 
of the electrodes and by reading the voltage difference; 
an electronic switch 10 for being controlled by a micro-processor 14 to 
select electrical connections between the electrodes 1-8 and the impedance 
measuring instrument 
a weight measuring sensor 18 for measuring the body weight of the person to 
be measured; 
a keyboard 15 for inputting the body height, age and sex of the person to 
be measured; 
an A/D converter 13 and amplifiers 12 and 19 for interfacing the impedance 
measuring instrument 11 and the weight sensor 18 to the micro-processor 
14; 
the micro-processor 14 controlling the electronic switch 10 and processing 
the data received from the impedance measuring instrument 11 and the 
keyboard 15; and 
a display unit 16 for displaying the results. 
In the body composition analyzing apparatus of the present invention, the 
results processed by the micro-processor 14 are displayed on the display 
unit 16, and when needed, a printer 17 is added for printing the data. 
In another aspect of the present invention, the method for measuring the 
body impedance according to the present invention includes the steps of; 
contacting a right palm, a right thumb, a left palm, a left thumb, a right 
front sole, a right rear sole, a left front sole and a left rear sole to 
eight electrodes 1-8; 
measuring segmental impedances by means of an impedance measuring 
instrument 11 by selecting an electronic switch 10 which is controlled by 
a micro-processor 14; 
measuring body weight by means of a weight measuring sensor 18; 
inputting body height, age and sex through a keyboard 15; and 
measuring an amount of body fluid (TBW), an amount of fat free mass (FFM), 
a percent body fat (%BF) and a distribution of body fluid (ECW/ICW), by 
means of the micro-processor 14. 
The results of the analysis can be displayed on a display unit 12 or can be 
printed through a printer 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is a schematic view showing a person measuring the body composition 
by standing on the body composition analyzing apparatus according to the 
present invention. 
The apparatus of the present invention includes: a right palm electrode E1 
for being surrounded by a right hand and the fingers excluding the right 
thumb; a right thumb electrode E2 for contacting with only a right thumb; 
a left palm electrode E3 for being surrounded by a left palm and the left 
fingers excluding the left thumb; a left thumb electrode E4 for contacting 
only with a left thumb, a right front electrode E5 for contacting only 
with a right front sole; a right rear sole electrode E6 for contacting 
only with a right rear sole; a left front sole electrode E7 for contacting 
only with a left front sole; and a left rear sole electrode E8 for 
contacting only with a left rear sole. 
Thus, the body composition analyzing apparatus according to the present 
invention includes eight electrodes for contacting with eight extremity 
portions of the human body. A person to be measured stands on the 
apparatus in an upright posture, and in this state, the hands and feet are 
contacted to the electrodes. Therefore, the impedance measurement can be 
carried out in a convenient manner. 
The apparatus of the present invention is provided with eight electrodes to 
contact with eight portions of the human body as described above, and the 
impedance model of the human body is as shown in FIG. 2. 
FIG. 2 schematically illustrates impedance models to be measured by the 
apparatus according to the present invention. 
It will be indicated as follows. That is, the resistance from the right 
wrist to the joint of the right shoulder is indicated by R1, the 
resistance from the left wrist to the joint of the left shoulder is 
indicated by R2, the resistance from the right ankle to the joint of the 
right hip joint is indicated by R3, the resistance from the left ankle to 
the joint of the left hip joint is indicated by R4, the resistance of the 
trunk is indicated by RS, the resistance from the palm to the wrist is 
indicated by Ra, the resistance from the thumb to the wrist is indicated 
by Rb, the resistance from the front sole to the ankle is indicated by Rc, 
and the resistance from the rear sole to the ankle is indicated by Rd. 
FIG. 3 illustrates the circuit of the body composition analyzing apparatus 
according to the present invention. 
The apparatus of the present invention is provided with a weight measuring 
sensor 18 so as to make it possible to measure the body weight of a 
person. The information on the body weight thus measured is inputted into 
the micro-processor 14, and then, the body height, age and sex are entered 
through the keyboard 15, so that the micro-processor 14 can compute the 
amount of the body fluid (TBW), fat free mass (FFM), and the percent body 
fat (% BF). 
The apparatus for analyzing the body composition based on the bioelectrical 
impedance method according to the present invention includes: 
a plurality of electrodes E1-E8 for contacting with a right palm, a right 
thumb, a left palm, a left thumb, a right front sole, a right rear sole, a 
left front sole, and a left rear sole respectively; 
an impedance measuring instrument 11 for measuring the impedance based on a 
voltage-current ratio by injecting an alternating current flow between two 
electrodes and by reading the voltage difference between two electrodes; 
an electronic switch 10 for being controlled by a micro-processor to select 
electrical connections between the electrodes E1-E8 and the impedance 
measuring instrument 11; 
a weight measuring sensor 18 for measuring the body weight of the person to 
be measured: 
a keyboard 15 for inputting the body height, age and sex of the person to 
be measured; 
an A/D converter 13 and amplifiers 12 and 19 for interfacing the impedance 
measuring instrument 11 and the weight sensor 18 to the micro-processor 
14; 
the micro-processor 14 for controlling the electronic switch 10 and for 
processing the data received from the impedance measuring instrument 11 
and the keyboard 15; and 
a display unit 16 for displaying the processed results. 
In the body composition analyzing apparatus of the present invention, the 
results processed by the micro-processor 14 are displayed on the display 
unit 16, and when needed, a printer 17 is added for printing the data. 
FIGS. 4A to 4H illustrate electric circuits representing the regional 
impedances of a human body to be measured according to the present 
invention. 
Referring to FIGS. 3 and 4, the resistances of the different body portions 
R1, R2, R3, R4, R5 will be described in detail as to how they are 
measured. 
As shown in FIG. 4A, the electronic switch 10 is connected between 
electrodes E2 and E4 by a command of the micro-processor 14, so that an 
electric current would flow between the electrodes E2 and E4. Further, the 
electronic switch 10 is connected between electrodes E1 and E5 by a 
command of the micro-processor 14, so that the voltage between the 
electrodes E1 and E5 can be measured. Thus the resistance R1 can be 
obtained from the above mentioned current and voltage. 
As shown in FIG. 4B, the electronic switch 10 is connected between 
electrodes E1 and E3 by a command of the micro-processor 14, so that a 
current would flow between the electrodes E1 and E3. Further, the 
electronic switch 10 is connected between electrodes E2 and E6 by a 
command of the micro-processor 14, so that the voltage between the 
electrodes E2 and E6 can be measured. Then the value of the resistance R1 
can be obtained from the current and voltage. 
As shown in FIG. 4C, the electronic switch 10 is connected between 
electrodes E2 and E4 by a command of the micro-processor 14, so that a 
current would flow between the electrodes E2 and E4. Further, the 
electronic switch 10 is connected between electrodes E1 and E8 by a 
command of the micro-processor 14, so that the voltage between the 
electrodes E1 and E8 can be measured. Then the value of the resistance R1 
can be obtained from the current and voltage. 
As shown in FIG. 4D, the electronic switch 10 is connected between the 
electrodes E2 and E4 by a command of the micro-processor 14, so that a 
current would flow between the electrodes E2 and E4. Further, the 
electronic switch 10 is connected between electrodes E3 and E7 by a 
command of the micro-processor 14, so that the voltage between the 
electrodes E3 and E7 can be measured. Then the value of the resistance R2 
can be obtained from the current and the voltage. 
As shown in FIG. 4E, the electronic switch 10 is connected between 
electrodes E4 and E8 by a command of the micro-processor 14, so that a 
current would flow between the electrodes E4 and E8. Further, the 
electronic switch 10 is connected between electrodes E1 and E5 by a 
command of the micro-processor 14, so that the voltage between the 
electrodes E1 and E5 can be measured. Then the value of the resistance R5 
can be obtained from the current and the voltage. 
As shown in FIG. 4F, the electronic switch 10 is connected between 
electrodes E6 and E8 by a command of the micro-processor 14, so that a 
current would flow between the electrodes E6 and E8. Further, the 
electronic switch 10 is connected between electrodes E1 and E5 by a 
command of the micro-processor 14, so that the voltage between the 
electrodes E1 and E5 can be measured. Then the value of the resistance R3 
can be obtained from the current and the voltage. 
As shown in FIG. 4G, the electronic switch 10 is connected between 
electrodes E6 and E8 by a command of the micro-processor 14, so that a 
current would flow between the electrodes E6 and E8. Further, the 
electronic switch 10 is connected between electrodes E3 and E7 by a 
command of the micro-processor 14, so that the voltage between the 
electrodes E3 and E7 can be measured. Then the value of the resistance R4 
can be obtained from the current and the voltage. 
As shown in FIG. 4H, the electronic switch 10 is connected between 
electrodes E2 and E4 by a command of the micro-processor 14, so that a 
current would flow between the electrodes E2 and E4. Further, the 
electronic switch 10 is connected between electrodes E3 and E7 by a 
command of the micro-processor 14, so that the voltage between the 
electrodes E3 and E7 can be measured. Then the value of the resistance of 
the whole human body can be obtained from the current and the voltage. 
FIGS. 4A to 4H illustrate only exemplary cases for measuring the impedances 
by making a current flow between two electrodes among the electrodes E1 to 
E8 and by measuring the voltage between other two electrodes. Besides 
these examples, there can be other examples of measuring the impedances of 
the body segments. 
In the present invention, the impedance measuring instrument 11 is 
connected to the eight electrodes E1-E8. The eight electrodes E1-E8 serve 
as current electrodes. The eight electrodes E1-E8 serve as current 
electrodes and voltage electronic switch 10 by a command of the 
micro-processor 14, in such a manner that they should serve different 
functions. For example, if the electrode E1 is a current electrode, then 
the electrode E2 is a voltage electrode, while if the electrode E2 is a 
current electrode, the electrode E1 is a voltage electrode. The electrodes 
E3 and E4 are also used in such a manner that they should serve different 
functions, and the electrodes E5 and E6 are also used in the same manner, 
while the electrodes E7 and E8 are also used in the same manner. 
That is, each of the electrodes E1-E8 serves as a current electrode or a 
voltage electrode. As shown in FIG. 3, if the electrodes E1, E3, E5 and E7 
are used as current electrodes, then the electrodes E2, E4, E6 and E8 are 
used as voltage electrodes. On the other hand, if the electrodes E2, E4, 
E6 and E8 are used as current electrodes, then the electrodes E1, E3, E5 
and E7 are used as voltage electrodes. 
In the impedance measuring method of the present invention, the variations 
is the values of the resistances Ra, Rb, Rc and Rd do not affect the 
measured values of the impedances of the different body portions. That is, 
when a person to be measured steps on the electrodes E5-E8 with the both 
feet, and holds electrodes E1-E4 with the both hands, even if the contact 
positions between the electrodes and the body are slightly shifted, it 
does not affect the measured resistance values R1-R5. 
In measuring the impedances of the different body segments, the electrical 
connections between the electrodes E1-E8 and the impedance measuring 
instrument 11 have to be changed many times based on the segmental 
measurement described above. In order to automatize this, there is the 
electronic switch 10 which is opened/closed by the micro-processor 14. 
Meanwhile,the body weight is measured by a weight measuring sensor 18 which 
is placed under the foot electrodes E5-E8 of the body composition 
analyzing apparatus of the present invention. The measured body weight is 
transferred through the amplifier 19 and the A/D converter 17 to the 
micro-processor 14. The resistance values R1-R5 which are measured by the 
impedance measuring instrument 11 also are transferred through the 
amplifier 12 and the A/D converter 17 to the micro-processor 14. 
Then body height, age and sex are inputted through the keyboard 15, and 
these data are transferred through an interface to the micro-processor 14. 
Based on the impedances, the body height, weight, age and sex which are 
stored in the micro-processor 14, the body composition such as the amount 
of the body fluid (TBW), the fat free mass (FFM), the body fat 
proportion(% BF), and the body fluid distribution ratio inside and outside 
the cells are analyzed. The analyzed results are displayed on the display 
unit 16, and printed by the printer 17. 
Examples for computing the body composition from the measured impedances 
are as follows. It is assumed that the left and right arms and legs and 
the trunk are five cylindrical conductors which have uniform cross 
sectional areas and which are similar in length. Based on this assumption, 
impedances R1-R5 are measured. The parallel connection value Rarm for both 
arms is defined as follows. 
EQU Rarm=(R1.times.R4)/(R3+R4) (I) 
The parallel connection value Rleg for the both legs is defined as follows. 
EQU Rleg=(R3.times.R4)/(R3+R4) (II) 
The resistance value for the trunk Rtrunk is defined to be R5. 
The amount of water contained in a body segment is proportional to Ht.sup.2 
/R, where R indicates the impedance value for the relevant body segment, 
and Ht indicates the body height of the measuring person. 
The total body water (TBW) is the sum of the segmental water, and is 
defined as follows. 
EQU TBW=C.sub.1.Ht.sup.2 /Rarm+C.sub.2.Ht.sup.2 /Rleg+C.sub.3.Ht.sup.2 
/Rtrunk+C.sub.4 (III) 
In formula III above, C.sub.1, C.sub.2, C.sub.3, and C.sub.4 are the best 
suitable constants, and can be obtained from TBW which is obtained by a 
heavy water dilution method (D.sub.2 O dilution). 
Formula III is stored in the micro-processor 14,and therefore, TBW can be 
obtained from the calculated Rarm, Rleg, Rtrunk and Ht. 
In addition to these variables, sex and age can be used as additional 
valuables. 
EQU TBW=C.sub.1.Ht.sup.2 /Rarm+C.sub.2.Ht.sup.2 /Rleg+C.sub.3.Ht.sup.2 
/Rtrunk+C.sub.4.Sex+C.sub.5.Age+C.sub.6 (IV) 
In the above formula, Sex, 0 is inputted for female, and 1 is inputted for 
male, while Age is the age of the person to be measured. 
Body fat contains relatively small amount of water, and therefore, this 
water content is disregarded. The fat free mass (FFM) contains about 73% 
of water, and therefore, (FFM) is defined as follows. 
EQU FFM=TBW/0.73 (V) 
The amount of body fat (FAT) is defined to be the weight (Wt) minus FFM, 
and is defined by formula VI, thus percent body fat (%BF) is defined by 
formula VII. 
EQU FAT=Wt-FFM (VI) 
EQU % BF=(Wt-FFM).times.100/Wt (VII) 
According to the present invention as described above,even without 
assistance of a specially trained person, the measuring person can stand 
with the two legs on the electrodes, and can grasp the electrode rods with 
two hands, so that the right palm, the right thumb, the left palm, the 
left thumb, the right front sole, the right rear sole, the left front sole 
and the left rear sole would be contacted with 8 different electrodes. 
Thus the impedances of the different body portions are automatically 
measured by the eight electrodes, and the body composition is analyzed in 
a precise and simple manner. 
It should be apparent to those skilled in the art that various changes and 
modifications can be added to the present invention without departing from 
the scope of the present invention which is limited only by the appended 
claims.