Download Implementation of Bioelectric Impedance Measurement

International Conference on Chemistry, Biomedical and Environment Engineering (ICCBEE'14) Oct 7-8, 2014 Antalya (Turkey)
Implementation of Bioelectric Impedance
Measurement System using Multi-Frequency
Applying Method and Two-Electrode Method
S. W. Baik, Y. J. Kim, J. H. Kim, W. Y. Jang, S. S. Kim, G. C. Park, J. M. Son, and G. R. Jeon

configuration of impedance measuring circuit is complicated
in four-electrode method.
BIA is divided into single-frequency analysis and
multi-frequency analysis depending on the frequency to be
applied [5]. Single-frequency analysis is the method of
measuring the BI while applying single-frequency to the living
tissues and the biological material. Multi-frequency analysis is
the method of measuring the impedance at each frequency by
applying the chirp waveform in combination with multiple
frequencies from low-frequency (LF) to high-frequency (HF).
In addition, the method of measuring BI at each frequency has
been also applied by selectively applying frequency in range of
LF, middle-frequency and HF. Single-frequency analysis
method has the advantage that the impedance can be measured
in a short period of time when characteristics of the living
tissue and biological samples are analyzed in a particular
frequency bandwidth, but has the disadvantage that BI cannot
be analyzed in various frequency bandwidth [6]. On the other
hand, multi-frequency analysis method has the merit that
characteristics of the living tissue and biological samples can
be analyzed in various frequency bandwidth but the demerit
that the measurement time is long in comparison with the
single-frequency method and the measurement circuit is
complicated [7].
Studies on the BIA have been carried out by many
researchers to analyze the composition of the living tissue and
the biological material [8-14]. Deurenberg et al [8]
investigated the applicability of the BI method for determining
changes in the body composition. The resistance of the human
body to the conduction of an alternating electrical current is
related to the volume of fluid within the body [9]. Bioelectrical
impedance analysis (BIA) is based on this principle and is
currently utilized to determine the extracellular water (ECW)
and total body water (TBW) content in normal humans [10].
Scheltinga et al [11] measured electrical resistance across the
whole body and its various segments before and after the
intravenous administration of
of saline. They also
determined the effect of blood donation on body resistance.
They reported that bioelectrical impedance analysis is a
sensitive method which detected minimal alterations in body
fluid volume. Miyatani et al [12, 13] investigated the validity
of BI and ultrasonographic methods for predicting the muscle
volume of upper arm. BI and series cross-sectional images of
the forearm, upper arm, lower leg, and thigh on the right side
were determined in 22 healthy young adult men using a
specially designed BI acquisition system and magnetic
Abstract— In order to measure the segmental impedance of the
body, bioelectrical impedance measurement system (BIMS) was
implemented in this study using multi-frequency applying method
and two-electrode method. It was composed of constant current
source unit, automatic gain control unit, and multi-frequency
generation unit. Three experiments were executed using implemented
BIMS and commercial impedance analyzer First, bioelectrical
impedance (BI) was measured by applying multi-frequencies - 5, 10,
50, 100, 150, 200, 300, 400, and 500 KHz – to each circuit after
composing 4 RC circuits connecting resistance and capacitor in serial
and parallel in order to evaluate the performance of BIMS. BI values
as a function of frequency for 4 RC circuits were compared to those
obtained by using CIA. Second, after measuring BI at each frequency
by applying multi-frequency to the left or right region of forearm and
popliteal of the body, BI values were compared to those acquired by
CIA. Third, when the distance between two electrodes was changed
to 1, 3, 5, 7, 9, 11, 13, and 15 cm, BI measured at each frequency from
10 to 500 KHz was also compared to that from CIA.
Keywords—Bioelectrical Impedance, Impedance analyzer,
Multi-frequency impedance meter, extracellular fluid, intracellular
fluid.
I. INTRODUCTION
Bioelectrical impedance analysis (BIA) is a non-invasive
method of measuring a component of the biological tissues and
biological samples with ease [1-4]. A method of measuring
bioelectrical impedance (BI) is divided into two-electrode
method, three-electrode method, and four-electrode method,
depending on the number of electrodes attached to the human
body. Four-electrode method has been widely used in order to
overcome the interference problems that occur at the interface
between the electrode and the skin. However, two-electrode
method is widely used to measure the impedance since the
Prof. Dr. S. W. Baik, Anesthesiology and Pain Medicine, Pusan National
Univ. Yangsan, South Korea, email id: [email protected]
Prof. Dr. Y. J. Kim, Anesthesiology and Pain Medicine, College of
medicine, Inje Univ., South Korea, email id: [email protected]
Prof. H. J. Kim, Computer simulation, Inje Univ., South Korea, email id:
[email protected]
Mr. W. Y. Jang, Mr. S. S. Kim, Mr. G. C. Park, Mr. J. M. Son, are with
Biomedical Engineering, school of Medicine, Pusan National Univ. Yangsan
South Korea, email id: [email protected], [email protected],
[email protected], [email protected]
Prof. G. R. Jeon, Biomedical Engineering, school of Medicine, Pusan
National Univ. Yangsan, South Korea., email id: [email protected]
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International Conference on Chemistry, Biomedical and Environment Engineering (ICCBEE'14) Oct 7-8, 2014 Antalya (Turkey)
B. Impedance Measurement System
As shown in Fig. 2, BIMS implemented in this study is
composed of main control unit (MCU, ATmega128, Newtc
Co., Korea), multi-frequency generation (MFG) unit,
automatic gain control (AGC) unit, constant current source
(CCS), electrode, preprocessing part, and PC. Fig 2 shows the
configuration for measuring BI. The function of these units in
Fig. 2 is as follows. MCU outputs the control command with
respect to the frequency generated by MFG and controls the
overall function of the implemented BIMS. Frequencies of 10,
50, 100, 150, 200, 300, 400, and 500 KHz are generated in
MFG unit. The output voltage of frequency generated by MFG
is automatically controlled in AGC unit. AC constant current
of
is generated in CCS part, where the current is to be
output to the electrode. The body segmental BI is measured
while the current applied from two electrodes attached to the
body tissue is following into BI measuring region. The body
segmental BI is transferred to PC after preprocessing.
resonance imaging (MRI) method, respectively. Jeon et al [14]
reported implementation of the blood pressure and blood flow
variation rate detection system using impedance method.
On the other hand, Thomasset et al [2] estimated the total
body water in a living body. Chumlea et al [15] performed the
study for analyzing the distribution of intracellular fluid (ICF)
and extracellular fluid (ECF) within tissues in the human body.
Studies were performed to analyze the distribution of ICF and
ECF in the body tissues by Kanai et al [16]. Lorenzo et al [17]
announced that while LF current was being applied to the
human tissue, BI was increased since the LF current flew
outside the cell, not passing through the cell membrane. While
HF current was being applied to the human tissue, BI
decreased since HF current flew in the inner cell. That is, ECF
was determined from BI measured by applying LF current, the
total body water was measured by applying HF current, and
ICF was estimated from subtracting HF impedance value from
LF impedance value [18, 19].
II. RESEARCH METHOD
A. An Equivalent Circuit of Human Body Impedance
Cell constituting the human organ consists of ICF and ECF
that behave as electrical conductors, and cell membranes that
act as electrical condensers and are regarded as imperfect
reactive elements [20]. BI of the human tissue is measured
differently depending on the frequency of the current to be
applied. Current flows outside the cell membrane when LF
current is applied to human tissue, whereas current flows into
the cell through the cell membrane as well as outside the cell
when HF current is applied to human tissue. That is, when the
current with LF less than 10 KHz is applied to the cells, current
only flows in the interstitial fluid i.e., ECF, but when the
current with HF above 100 KHz is applied to the cells, the
current flows in both ECF and ICF. This phenomenon is due to
the fact that ECF performs as an electrical conductor in the LF
bandwidth, ICF performs as an electrical conductor in the HF
bandwidth, and the cell membrane acts a kind of capacitor
filled with condenser dielectric substance [21]. Therefore, the
equivalent circuit in Fig. 1 was proposed to analyze BI of the
human tissue. The circuit in the top-right corner in Fig. 1
represents BI of interface between the electrodes and the gel.
Ehc means a half cell potential, Cd and Rd mean capacitor and
resistor, respectively. Rs means the impedance of skin. The
central figure on the right illustrates capacitor and resister
representing the BI components in the sweet and the duct of
epidermis. Ru in the lower right represents the resistance in the
skin and subcutaneous layer.
Fig. 2. The configuration of the impedance measurement system
C. Multi-Frequency Generation Unit
A sine waves having multi-frequency should be applied to
human tissue to measure the human segmental BI. It is
possible to measure ICF, total body water, and ECF when
multi-frequency is applied to the human body. Accordingly,
eight kinds of multi-frequencies i.e., 10, 50, 100, 150, 200, 300,
400, and 500 KHz were generated using the frequency
generating device (XR-2206, EXAR Co., USA).
The process of generating multi frequencies in frequency
generating device is as follows. Control command is output
from MCU to digital to analogue converter (DAC, DAC0800,
Texas Int. Co., USA). Control command has different
digitalized values according to multi-frequency. These
digitalized values are converted to analogue values in DAC.
These analogue values are output to frequency generating
device (FGD). Input analogue values are transferred to VCO
included in FGD. Eight kinds of frequencies are generated
according to input voltage values in VCO.
Eight kinds of multi-frequencies generated from FGD were
sequentially applied to the measurement sites of the human
body. Fig. 3 shows the designed circuit of MFG unit.
Fig. 1. The Equivalent circuit of electrode and the skin proposed for
measuring BI.
Fig. 3. A circuit designed for multi-frequency generation unit.
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International Conference on Chemistry, Biomedical and Environment Engineering (ICCBEE'14) Oct 7-8, 2014 Antalya (Turkey)
D.Automatic Gain Control Unit
The output signal of MFG is automatically controlled in the
automatic gain control (AGC) unit, which adjusts the
amplification rate of the output signal of MFG. When AGC
circuit is not used, experimental errors occur in measured
impedance since the output voltage fluctuates. The designed
circuit of AGC is shown in Fig. 4. It was designed to maintain
a constant output voltage according to the selected
multi-frequency. Since the output in Fig. 4 is current, it is
converted to voltage by voltage follower circuit.
form of graphs and tables, and then stored in PC using USB
communication protocol.
(a)
(b)
Fig. 6. PC program and monitoring screen implemented for BI
measurement: (a) PC program using LabVIEW and (b) monitoring
screen.
III. RESULTS
Multi frequency BIMS was implemented for measuring BI
of the body segments in this study. Two-electrode method was
applied to the embodied BIMS. Ag/AgCl electrode
(Monitoring electrode, 3M Co., USA) commercialized for
ECG measurement was used for electrode. Eight different
frequencies generated from MFG unit were sequentially
applied to the electrode attached to body surface through AGC
and CCG. At this time, a current of 500uA was set to be
supplied to the body surface at each frequency.
In order to evaluate the performance of multi frequency
BIMS, experiments were carried out 10 times using BIMS and
CIA after configuring four kinds of circuits connected in series
and (or) in parallel with resistor and capacitor as shown in Fig.
7. In particular, Fig 7(d) shows the equivalent circuit for
biological tissues; Rout the resistance of ECF, Rin the resistance
of ICF, and Cin the capacitance of cell membrane, which were
reported by Cornish et al [22].
Fig. 4. A circuit designed for automatic gain control.
E. Constant Current Source
In order to measure the body composition such as ECF, the
cell membrane, ICF, total body water, and body fat of the
living tissue, AC constant current with a frequency from LF to
HF should be applied to the body. In this study, AC constant
current of 500uA was applied to the human body to measure
the segmental BI of human body. The circuit as shown in Fig.
5 was designed to generate AC constant current.
Fig. 5. A circuit designed for constant current source.
(
)
(1)
(2)
Fig. 7. RC circuits suggested for impedance measurement: (a) resistor
R, (b) R and C connected in parallel, (c) R and R and C connected in
parallel and then connected in series with R, (d) R and C connected in
series and then connected in parallel with R
From Millman’s theorem, the output voltage
is
obtained from amplifying the input voltage
according to
Eq. 1. When output voltage
is applied to the load resistor
, constant current flows according to Ohm’s law .
Fig. 8 illustrates the comparison of experimental results at
each frequency from 10 KHz to 500 KHz, using BIMS and
CIA. Fig. 8(a) shows the impedance which was observed to be
constant regardless of the frequency for the circuit in Fig. 7(a).
Error rate between the impedance values measured by BIMS
and CIA was 0.04%. Fig. 8(b) indicates the impedance as a
function of frequency for the circuit in Fig. 7(b), which
decreased gradually with increasing frequency. BI values
measured by BIMS were in good agreement with those
obtained by CIA. Error rates of BI measured using BIMS and
CIA were as follows: 1.39% for 10 KHz, 0.72% for 50 KHz,
F. PC Program for Measuring Bioelectric Impedance
PC program was developed using LabVIEW (LabVIEW
2010, National Instruments Co., USA) to control the BIMS
and analyze the measured BI data. PC program was configured
to set parameters such as starting frequency, frequency
increment value, the number of increase, and the output
voltage. The measured BI was displayed on the monitor in the
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International Conference on Chemistry, Biomedical and Environment Engineering (ICCBEE'14) Oct 7-8, 2014 Antalya (Turkey)
to be higher than that at the left. In addition, BI exhibited the
different aspect from BI obtained from Fig. 8(d). In reality, the
cell membrane is an imperfect capacitor because of ionic
movement through the cell membrane, and the time constant is
not the same.
A comparison of BI measured at the left and right side of
forearms and popliteal regions by BIMS and CIA indicated
that the error rates at eight frequencies were as follows. As
shown in Fig. 9(a), the error rates occurred in BI measurement
at the left forearm: 0.59% for 10 KHz, 1.59% for 50 KHz,
4.12% for 100 KHz, 3.68% for 150 KHz, 4.7% for 200 KHz,
4.04% for 300 KHz, 4.52% for 400 KHz, and 1.72% for 500
KHz. The error rates occurred in BI measurement at the right
forearm: 0.54% for 10 KHz, 2.1% for 50 KHz, 2.47% for 100
KHz, 3.43% for 150 KHz, 4.32% for 200 KHz, 3.85% for 300
KHz, 4.63% for 400 KHz, and 2.56% for 500 KHz. As shown
in Fig. 9(b), the error rates occurred in BI measurement at the
left popliteal region: 0.63% for 10 KHz, 1.63% for 50 KHz,
3.1% for 100 KHz, 3.09% for 150 KHz, 4.07% for 200 KHz,
3.19% for 300 KHz, 3.52% for 400 KHz, and 1.19 %for 500
KHz. The error rates occurred in BI measurement at the right
popliteal region: 0.44% for 10 KHz, 1.9% for 50 KHz, 2.16%
for 100 KHz, 2.81% for 150 KHz, 3.4% for 200 KHz, 3.13%
for 300 KHz, 3.52% for 400 KHz, and 1.55% for 500 KHz.
2.78% for 100 KHz, 7.52% for 150 KHz, 2.88% for 200 KHz,
2.77% for 300 KHz, 4.55% for 400 KHz, and 0.87% for 500
KHz. Fig. 8(c) shows BI as a function of frequency for the
circuit in Fig. 7(c). It was observed that BI decreased abruptly
at LF between 10 KHz and 50 KHz, decreased gradually at
frequency between 50 KHz and100 KHz, and decreased very
slowly above 100 KHz. A comparison of BI measured by
BIMS and CIA indicated that the error rates were as follows:
1.57% for 10 KHz, 2.71% for 50 KHz, 3.84% for 100 KHz,
2.65% for 150 KHz, 1.18% for 200 KHz, 1.09% for 300 KHz,
0.89% for 400 KHz, and 1.09% for 500 KHz. In addition, Fig.
8(d) shows BI as a function of frequency for the circuit shown
in Fig. 7(d). BI values as a function of frequency decreased
from 10 KHz up to 50 KHz and were very similar above 50
KHz. Error rates of BI measured by BIMS and CIA were as
follows: 1.24% for 10 KHz, 0.77% for 50 KHz, 0.59% for 100
KHz, 0.23% for 150 KHz, 0.32% for 200 KHz, 1.38% for 300
KHz, 1.54% for 400 KHz, and 1.94% for 500 KHz.
Fig. 8 The comparison of BI measured by using BIMS and CIA for
four kinds of RC circuits suggested in Fig. 7
In order to evaluate the clinical significance of BIMS, BI
was measured at the left and right side of forearms and
popliteal regions using BIMS, after the selection of the
experimental subjects. The experimental subjects were ten
male adults with a mean age of 27.5 (±2.5 years), average
height of 173 cm (±3.2 cm), and average mass of 75 kg (±4.1
kg). Each experiment was conducted five times for 10 subjects
using BIMS. Each measurement was conducted once again
after taking 10-minute break.
Fig. 9(a) shows the comparison of BI at the left and right
side of forearms measured by using BIMS and CIA. Fig. 9(b)
shows the comparison of BI of the left and right region of
popliteal measured by using BIMS and CIA. Comparative
analysis of the results measured by using BIMS and CIA
indicated that BI exhibited a similar pattern. BI measured at
forearms and popliteal regions was observed to be high at 10
KHz. The decreasing phenomenon of BI could be observed
when HF was applied to the human body. BI was observed to
be lowered since HF alternating current flew in ECF and ICF.
BI values are slightly different in the forearm and popliteal
regions, due to the amount of muscle of forearm and popliteal
region, capacitance and resistance of the cell, the permeability
of the cell membrane, the composition within the cell, size and
shape of the cell, differences in tissue distribution. Fig. 9
shows that BI measured by BIMS was slightly lower than that
by CIA. BI values measured at forearm were lower compared
with those at popliteal region, and BI at the right was observer
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(a)
(b)
Fig. 9. The comparison of BI using BIMS and CIA after applying
eight kinds of frequencies to the left and right region of forearm and
popliteal: (a) BI measured at left and right regions of forearms and (b)
BI measured at left and right regions of popliteal.
Figure 10 shows BI at the right forearm when the distance
between the electrodes was changed to 1, 3, 5, 7, 9, 11, 13, and
15 cm. BI was measured to be about the same value,
at 1
, regardless of the distance between the two
electrodes. However, BI values showed a significant
difference according to the distance between the two
electrodes from 50 to 500 KHz. In addition, BI decreased in
accordance with increasing frequency and decreasing distance
between the electrodes. This corresponds well with the fact
that the resistance is proportional to the resistivity and the
length and inversely proportional to the cross section of the
material as shown in the following equation of resistance,
.
These results are in good agreement with those reported by
Scheltinga et al [11]. They measured the resistance of the
whole body and its segments with two electrodes which apply
alternating current of
at 50 kHz. Initial whole body
resistance was
following an 8-hour overnight
period of bed rest. In contrast, resistance determined by
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International Conference on Chemistry, Biomedical and Environment Engineering (ICCBEE'14) Oct 7-8, 2014 Antalya (Turkey)
proximal electrodes was
and accounted for less
than half of the whole body values. The resistance obtained
from a single arm or a single leg was not significantly different
from that obtained across the body using proximal electrodes
(arm:
, leg:
proximal:
).
The comparison between BI values measured by BIMS and
Scheltinga’s work revealed that BI was strongly dependent on
the frequency and the distance between electrodes, but do not
depend on the location within segment.
BI values measured by BIMS with AC current of
and electrode distance of 7cm at 50 KHz in this study are as
follows:
at left forearm, 751.2 Ω at right forearm,
775.4 Ω at left region of popliteal, and 796.3 Ω at right region
of popliteal. These BI values are different from those reported
by Scheltinga’s study: 221±10 Ω at arm, 240±7 Ω at leg. The
differences of BI values are partly due to the difference of the
applied current- 500μA and 800μA, and due to the cross
section of measuring region.
(a)
(b)
Fig. 10. BI of the extracellular fluid and the intracellular fluid
according to the frequency and the distance between electrodes: (a)
impedance measurement system (b) commercial impedance analyzer.
Table 1 shows BI of ECF and ICF at the right forearm
according to the distance between the electrodes. BI of ECF
was measured at 10 KHz. BI of ICF was calculated by
subtracting BI values measured at 500 KHz from those
measured at 10 KHz. BI of ICF and ECF increased as the
distance between electrodes increase. Both ICF and BCF
decreased when frequency increased from 10 to 500 KHz, but
increased as the distance between two electrodes increased
from 1 to 15 cm.
TABLE I
BI VALUES OF MEASURED ECF AND ESTIMATED ICF AT RIGHT FOREARM ACCORDING TO THE DISTANCE BETWEEN THE TWO ELECTRODES
Frequency
Dis.
(cm)
1
3
5
7
9
11
13
15
10 KHz
ECF
ICF
(KΩ)
(KΩ)
50 KHz
ECF
ICF
(Ω)
(Ω)
100 KHz
ECF
ICF
(Ω)
(Ω)
150 KHz
ECF
ICF
(Ω)
(Ω)
200 KHz
ECF
ICF
(Ω)
(Ω)
300 KHz
ECF
ICF
(Ω)
(Ω)
400 KHz
ECF
ICF
(Ω)
(Ω)
1.51
1.52
1.53
1.54
1.55
1.55
1.56
1.56
586
676
683
730
738
786
818
858
443
536
553
580
588
610
623
648
393
483
505
525
540
568
588
608
366
440
468
488
513
536
556
573
341
405
430
453
470
486
515
525
316
371
396
413
436
456
476
480
0
0
0
0
0
0
0
0
286
321
323
323
338
348
368
392
143
161
163
165
168
170
173
182
93
115
117
118
120
128
138
142
IV. CONCLUSION
In order to detect the trigger point for patients with chronic
pain and MPS, BIMS of body segments was implemented.
Multi-frequency method of sequentially applying selected
eight frequencies from 10 KHz to 500 KHz was applied in
BIMS with two-electrode method.
The experimental results for evaluating the performance and
verifying the efficiency of BIMS are as follows.
1. BI was measured for the circuit of four kinds of circuits
consisting of passive elements, R and C. BI by BIMS was
observed to be similar compared with that by CIA.
2. BI was measured at each frequency after attaching the
electrode with the separation of 7 cm to the left or the right
of forearm and popliteal regions of the human body.
Experimental results measured by BIMS were compared
with those acquired by CIA. Generally, BI values were
observed to be higher in LF and lower in HF. BI measured
using BIMS and CIA exhibited that the error rates were 1.2 %
at LF and 1.74% at HF, respectively.
3. BI was measured at each frequency according to the
distance between the two electrodes when the distance
between the electrodes was changed from 1 to 15 cm.
Experimental results measured by BIMS were compared
with those acquired using CIA. The average errors of BI
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66
85
88
90
93
96
106
107
41
45
48
50
52
57
65
59
16
16
16
16
16
16
17
14
500 KHz
ECF
ICF
(Ω)
(Ω)
0
0
0
0
0
0
0
0
300
355
380
407
420
440
450
466
measured using BIMS and CIA were 0.775% at LF (10
KHz) and 2.725% at HF (500 KHz), respectively.
4. BI of measured ECF and estimated ICF at the right forearm
was acquired at each frequency according to the distance
between two electrodes. BI of ICF and ECF increased as
the distance between two electrodes increased from 1 to 15
cm, but decreased as frequency increased from 10 to 500
KHz.
From experimental results, BIMS implemented in this study
revealed to ensure the significance of clinical application.
BIMS is expected to be applied to the detection of a trigger
point of patients with chronic pain and MPS.
ACKNOWLEDGMENT
This work was financially supported from the basic research
project (NO. 2013R1A2A2A04015325) by the National
Research Foundation of Korea via the funds of Ministry of
Education, Korea in 2013.
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International Conference on Chemistry, Biomedical and Environment Engineering (ICCBEE'14) Oct 7-8, 2014 Antalya (Turkey)
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