African Journal of Biotechnology Vol. 9 (54), pp. 9295-9306, 27 December, 2010
Available online at http://www.academicjournals.org/AJB
ISSN 1684–5315 © 2010 Academic Journals
Review
Novel idea to monitor and measure blood hemoglobin
noninvasively
A. H. Ar-Rawi*, M. Moghavvimi and W. Ibrahim
Faculty of Engineering, University of Malaya, Malaysia.
Accepted 10 December, 2010
Measuring blood hematocrit noninvasively is reviewed in this paper. Although there is an inclination to
measure the hematocrit by determining the bioelectrical impedance of the blood, in vitro experimental
methods still remain practically inapplicable. The blood sample size is determined when blood samples
are examined. Determining the impedance and volume of blood is the biggest challenge in measuring
the hematocrit noninvasively without drawing a blood sample. Calculating the blood impedance in vivo
requires developing an impedance measurement using a multi-frequency method and also calculating
the change in pressure simultaneously during the heart’s pulsatile cycle.
Key words: Blood, hematocrit, measurement.
INTRODUCTION
Currently, a standard method is used for checking the
blood components in order to diagnose patients infected
with any blood viruses, such as human immunodeficiency
virus (HIV) and dengue hemorrhagic fever (DHF), among
others. This method analyzes the blood sample to detect
the blood’s chemical components, obtaining a comprehensive blood picture of the patient. This technique has
many disadvantages, particularly when patients are suspected to be infected with specific viral diseases, such as
DHF, HIV and Hepatitis B virus (HBV), or even the bird
flu virus and other blood transmitted diseases. These
disadvantages require precious personal time for drawing
blood samples and may cause a substantial delay before
data are available, depending on the proximity of the
testing laboratory. Moreover, frequent blood sampling
from the patient may cause further injuries to the subcutaneous tissue, subsequently contributing to delusional
anemia (Abdulrahman, 2003). Frequent blood sampling
can cause inflammation and fever associated with blood
*Corresponding author. E-mail: owner@aoday.com.
Abbreviations: HB, Hemoglobin; BIA, bioelectrical impedance
analysis; RBC, red blood cell; ESR, erythrocyte sedimentation
rate; TBW, total body water; SF-BIA, single frequency BIA; MFBIA, multi-frequency BIA.
flow increase, activation of phagocytes, increase in capillary permeability, complement activation, clotting reaction
walls of the region, regional temperature increase and
activation of specific defenses in the blood (Ibrahim et al.,
2004).
The bioelectrical impedance analysis (BIA) is used to
overcome all these disadvantages. In recent years, BIA
has become an increasingly popular modality in the
assessment of human body composition, that is, bioelectrical tissue conductivity, mass distribution and water
compartments.
This research is conducted to study the possibility of
designing and developing a bioelectrical impedance
apparatus for checking and monitoring blood hematocrit.
Generally, this method has many advantages:
1. Fast results.
2. No blood drawing.
3. Low-cost instrumentation.
4. Ease of applicability in practice.
5. Online monitoring.
THEORY OF BIOELECTRICAL IMPEDANCE
All living things are comprised of cells. Cells are
membrane-bound compartments filled with a concentrated solution of chemicals and salts. Groups of cells
9296
Afr. J. Biotechnol.
Figure 1. Lipid bi-layer structure of the plasma membrane (Fernando, 2007).
perform specialized functions and are linked by an intricate
communication system. The cell membrane maintains an
ion concentration gradient between the intracellular and
extracellular spaces. This gradient creates an electrical
potential difference across the membrane, which is
essential to cell survival. Electrical gradients are necessary to support the movement of oxygen, carbon dioxide
and nutrients. Therefore, the cell membrane has electrically
insulating qualities to maintain an electrical gradient.
Damage to the cell membrane and its functions is as
lethal to the cell as direct damage is to the nucleus itself
(Figure 1).
In a healthy living body, the cell membrane consists of
a layer of non-conductive lipid material sandwiched
between two layers of conductive protein molecules.
Biologically, the cell membrane functions as a permeable
barrier separating the intracellular (cytoplasm) and extracellular components. The lipid membrane is transversed
by proteins, which are soluble in water, creating pores
through which water, ions and other chemicals can enter
and exit the cell. Controlling the flow of these materials is
essential to life. The cell membrane protects the interior
of the cell, while allowing passage of some materials to
which it is permeable. The cell membrane is composed
mostly of a double layer of phospholipids arranged tail to
tail along the width of the cell membrane. This structure is
called the lipid bilayer and it acts as an electrical insulator
(dielectric) in a similar manner as in fats and oils. The
heads of the phospholipids are polar (carry a charge),
whereas the tails are non-polar. The heads interact with
water, whereas the tails are repulsed by water aligning
them tail to tail with the heads facing the outside and
inside of the cell.
Impedance is a complex quantity that has both a
resistive and reactive component. It has a magnitude and
a phase angle. Specifically, it is the vector sum of resistance and reactance, where reactance is the Y coordinate
and resistance is the X coordinate. The square root of the
squared sums of X and Y is the impedance. The phase
angle is the angle (degrees) between the resistance
coordinate and impedance magnitude (line). For example,
if there was zero resistance and any value of reactance,
then the phase angle would be 90 degrees. In contrast, if
the reactance was zero and the resistance had any finite
value, then the phase angle would be zero degrees. Phase
angle is a simple method of expressing the effective ratio
of resistance and reactance from 0 to 90° and describing
electrically, how voltage and current lead or lag each
other in any circuit of resistors and capacitors. Impedance and phase angle only exist with alternating current
(Aroom et al., 2009) (Figures 2 and 3).
Hence:
(1)
where
is the capacitive reactance Ohm,
is the
capacitance value in Farad, and is the radian frequency
=
(2)
where f is the frequency and
= 3.142
Referring to Equations 1 and 2, the reactance is inversely
proportional to frequency. Based on the aforementioned
studies, the cell with currents below 50 KHz works as a
resistor only. In very high frequencies, the capacitor acts
as a short circuit that allows the equivalent circuit of the
cell to become similar to the two resistors in parallel
(Mager et al., 2008; Aroom et al., 2009) (Figure 4).
The bioelectrical properties of an organism depend on
its geometry and specific resistivity. The latter varies as a
function of the composition of the tissue and the
frequency of the test signal. Hoffer et al. (1969) proposed
that the complex geometries of the human body could be
treated as a single conductor of uniform cylindrical geometry. Assuming that the test signal frequency is constant,
then the impedance (Z) is a function of the cross
sectional area (A) and length (L) of the conductor (Figure
5a)
Z=
where
L/A
(3)
is the specific resistivity.
Ar-Rawi et al.
9297
Figure 2. How an electrical capacitor is formed from the outer boundary of a cell and its
dielectric nature. The outer boundary of the cell is a plasma membrane of phospholipids
molecules that become a dielectric to form an electrical capacitor when a radio
frequency is introduced to the cells environment.
Figure 3. Equivalent electrical circuit of a cell. The circuit in (b) is the equivalent of the model in (a) after
performing some circuit simplifications and considering the large value of Rm. The circuit in (c) is the equivalent
circuit of the cell, neglecting the effect of Rm. Note the Cm (Fernando, 2007).
Multiplying the right side of Equation 3 by L/L and setting
AL equal to the volume (V) of the conductor, yields the
following:
Z=
L2/V
(4)
Rearranging Equation 4 gives:
V=
L2/Z
(5)
Thus, the volume of the conductor can be related to two
9298
Afr. J. Biotechnol.
Low frequency
Mid. frequency
High frequency
Figure 4. Current paths in a suspension of cells at various frequencies (Fernando, 2007).
the cell. At 300 MHz, there is virtually no difference between
the resistivity of normal saline and lean tissue. Thus, at
higher frequencies, the volume derived from Equation 5
is related to the total body water. However, the impedance depends on electrolyte concentration; hence, the
comparison should be against normal saline rather than
water. The dependence on electrolyte concentration could
be a problem, except that the concentrations of electrolytes in body fluids are relatively constant in healthy
subjects. Moreover, the choice of frequency is less critical
than is usually required (Jaffrin et al., 2008; Schoeller et
al., 1989).
As discussed, body impedance can be represented as
various resistors and capacitors connected in series and
parallel as shown in Figure 6 (Schoeller et al., 1989). The
International Society for Electrical Bio-Impedance registers
the resistivity of various body tissues as follows (Sutton et
al., 1999):
Figure 1. Conductor showing (a) its cross sectional area and
length, (b) different resistivities arranged in parallel (Schoeller et al.,
1989).
readily measured parameters of length and impedance.
This volume can be interpreted with respect to body composition if the body is viewed as several components with
differing resistivities arranged in parallel (Figure 5b).
Using this model, the volume estimated from length and
impedance is approximated by that of the component
with the lowest resistivity. The resistivity of the adipose
tissue is considerably greater than that of the muscle and
the difference is proportional to the water content of these
tissues (that is, about 75% of weight for muscle and 5 to
20% for adipose). Based on this difference, fat, which is
anhydrous, has a very high resistivity and the volume
derived from Equation 5 is related to fat-free mass or,
more specifically, some compartment of water in a fatfree mass. This fat-free compartment depends on the
frequency of the test signal. At frequencies between 100
and 100 MHz, cell membranes have low electrical permittivity; thus, the impedance reflects the extra cellular fluid.
At higher frequencies, the resistance of the cell membrane begins to short out because of the capacitance of
1. Blood: 150 .cm
2. Urine: 30 .cm
3. Muscle: 300 to 1600
4. Lung: 1275 .cm
5. Fat: 2500 .cm
.cm
Based on the aforementioned resistivities, fat tissues have
high impedance, whereas urine tissues have the lowest.
The frequency also affects impedance as shown in the
aforelisted equations. Thus, each tissue type conducts in
the frequency range depending on the tissue geometry
itself (Hills et al., 1998).
BIOELECTRICAL IMPEDANCE TECHNIQUES
The bioelectrical impedance technique is defined as the
measurement of biocell electrical impedance by applying
fixed current and measuring the voltage and phase shifts,
allowing the bioimpedance to be calculated.
There are two main methods for measuring bioimpedance: The two-electrode method and the four-electrode
method. Each method has its own advantages and
disadvantages. However, the second method is more
widely used as thus explained.
Ar-Rawi et al.
9299
Both resistance and reactance can be calculated based
on the aforementioned equations. The two-electrode
technique has several limitations (that is, bioimpedance
and bioelectricity basics). The results from this technique
are often irreproducible due to the excessive interference
by electrochemical reactions at the subcutaneous needle
electrode surface, causing additional electrode polarization
anomalies. In addition, the small diameter of the electrode
needles results in a much greater current density near
the electrodes than in the rest of the body. Therefore, the
integrity of the tissue near the electrodes and the electrode size can affect the measurement of impedance
between electrodes and confuse the desired data
(Grimnes et al., 2000). To surmount these limitations, the
four-electrode method is used.
Four-electrode technique
Figure 6. The human body as a circuit of resistors and capacitors,
connected in series and parallel.
Two-electrode technique
This technique is simple. It applies the current source
through the cells and measures the voltage and phase
angles, allowing the impedance to be calculated as follows
(Figure 7):
Q = Tan −1
Xc
R
The four-electrode system is preferred when the distal
volume segment of the current part is the zone of interest
and when the effect of the zones proximal to the currentcarrying electrodes has to be eliminated. Four-electrode
systems correspond to a ‘2-port four-terminal network’
equivalent. Transfer functions may be set up to describe
the signal path from the current-carrying to the signalrecording electrodes. This is the case in impedance
plethysmography or impedance imaging. They are also
the best systems for measuring excised tissue samples in
vitro. An in vitro version is shown in Figure 8.
The measured segment is determined by the position of
the two recording electrodes, R and R ′ , or more exactly by
the position of their electrolyte/salt bridge connections to
the measuring cell. The two stippled equipotential lines
indicate that this current is recorded with a current-reading
operational amplifier. The recording electrodes are connected each to one buffer amplifier. No current flows in
the electrode leads; thus, the electrodes cannot be
polarized externally (but internal currents may polarize
them). Electrolyte/salt bridge connections are used to
increase the electrode metal area, increase electrode
admittance and reduce noise. Large electrodes inserted
directly into the measuring cell disturb the ionic current
flow pattern, causing polarization to occur on the metal
surface. The electrode metal should not be in direct
contact with the electrolyte, but must be recessed instead
(Figure 9) (Grimnes et al., 2000).
The electrolyte is contained in a tube with isolating
walls. When part of this wall is substituted by electrode
metal, the current prefers the high conductivity path of the
metal. The current lines deviate from the path parallel to
the tube walls, causing the current to enter one part of
the area and leave the other. Thus, the electrodes are
polarized, but not by a current in the external leads. The
polarization may not be uniform over the electrode
surface area, and polarization occurs according to the
local current direction and polarization admittance. When
9300
Afr. J. Biotechnol.
Figure 7. Two–electrode system.
Figure 8. Four-electrode system. Tubular in vitro version (Grimnes, 2000).
the metal is recessed, the current also deviates into the
electrolyte of the bridge path, but does not pass through
any metal surface. Thus, polarization does not occur.
Figure 10 shows a four-electrode in vivo skin surface
version. The two recording electrodes ensure that only
the current path segment between these electrodes contributes to the result. The stippled equipotential lines
indicate the segment being measured. However, not all
tissue volumes contribute equally. Sensitivity is proportional to the local current density in the measured volume
Ar-Rawi et al.
Figure 9. The non-recessed electrode on the left implies
polarization from the current entering and leaving the metal
(Grimnes et al., 2000).
9301
Figure 11. Cole-Cole plot.
Xc =
1
2πFC
(7)
Based on the aforementioned equations, if the frequency
has a very large value, then Xc will be near zero:
(8)
. If the frequency F is
and will be called Z infinity
zero, Xc will then act as an open circuit:
(9)
Figure 10. Four-electrode system, in vivo version. Equipotential
lines are shown in the tissue. The position of R -R’ determines the
tissue segment measured and the size of the proximal zones
measured by M and M'.(Grimnes et al., 2000).
segment. Sensitivity is zero in the two segments proximal
to the current-carrying electrodes as long as the potential
difference is taken from the R -R' electrodes. Measuring
all three voltages, M-R, R-R', and R'-M', simultaneously,
as well as the admittance/impedance of the two constrictional zones and one distal volume is also possible
(Grimnes et al., 2000).
BIOELECTRICAL IMPEDANCE METHODS
When alternating current (AC) is used, various methods
can be applied to measure the BIA depending on the
frequency. The variance in tissue membrane makes the
capacitance of the membrane differ in each tissue type.
Referring to the tissue equivalent circuit in Figure 3,
(6)
and
Between zero and infinity, the impedance, Z varies
depending on the Xc variation with frequency, and both
the imaginary and real parts are frequency dependent as
shown in the Cole-Cole plot in Figure 11. Figure 11 shows
that the very high and very low frequencies of the impedance become pure resistance. It is due to this reason
(that is, the impedance changing with frequency) that
various methods are used.
Single frequency measurements (SF-BIA)
Single frequency BIA (SF-BIA) is used to simplify the
calculations. This method is used particularly in measuring body composition applications. A single frequency
from 10 KHz to less than 10 MHz is used depending on
the tissue to be diagnosed. For example, blood tissue
does not conduct at low frequencies and requires the use
of high frequencies to check. Lean tissues can be verified
at frequencies less than 100 KHz. Simplicity is the main
advantage of this method, but it is not accurate and has
many limitations. For accurate readings and diagnostics,
the Multi-frequency BIA (MF-BIA) is preferred.
Multi-frequency measurements
As with SF-BIA, MF-BIA uses empirical linear regression
9302
Afr. J. Biotechnol.
models, but includes impedances at multiple frequencies.
MF-BIA uses different frequencies (that is, 0, 1, 5, 50,
100, 200 and 500 kHz) to evaluate FFM, TBW, ICW, and
ECW. At frequencies below 5 kHz and above 200 kHz, poor
reproducibility has been noted, especially for the reactance at low frequencies. MF-BIA is more accurate and
less biased than SF-BIA for the prediction of ECW,
whereas SF-BIA, compared with MF-BIA, is more accurate and less biased for TBW in critically ill subjects.
Moreover, some researchers have noted that MF-BIA,
compared with bioelectrical spectroscopy (BIS), results in
better prediction of TBW and equal prediction for ECW in
surgical patients. They determined that MF-BIA is unable
to detect changes in the distribution or movement of fluid
between the extracellular and intracellular spaces in
elderly patients (Ursula and Ingvar, 2004)
BIOELECTRICAL IMPEDANCE APPLICATIONS
In 1940, clinically induced changes in hydration status
were first correlated with total body changes in resistance
and capacitive reactance. In the same year, some researchers also pioneered studies on bioelectrical impedance
changes to dynamic changes in pulsatile blood flow to
organs, arterial pulse waveforms and respiration. The
applications of impedance plethysmography or the measurement of electrical impedance changes in limbs, organs
and other body sites to detect dynamic blood. Volume
changes have been validated extensively by many investigators.
The relationship between TBW and electrical impedance
was first reported by Thomasett (1962) and further
delineated by Hoffer et al. (1969). For over a decade,
there were no subsequent attempts to determine the
usefulness of impedance in the analysis of human body
composition. Nyboer et al. (1983) applied the electrical
volume resistivity principles of impedance plethysmography to the study of body composition using static total
body impedance measurements. From 1983 onwards,
BIA has been used for many applications in medical diagnosis.
Blood measurements
Various studies have used BIA methods to measure blood
characteristics. These methods guide us in making noninvasive diagnostics through the body. Blood consists
mainly of plasma and erythrocyte cells. Blood, as with
any body tissue, has the same equivalent electric circuit
as shown in Figure 3, where Ro denotes the plasma, Ri
denotes the interior water of the erythrocyte and Ci is the
membrane capacitance of the erythrocyte.
Fricke (1925) measured the impedance of several
blood samples in the frequency range between 800 Hz
and 4.5 MHz in vitro. Fricke found that blood below 100
KHz behaves as a resistor because the red cell does not
conduct at low frequencies. The study by Fricke was
followed by similar studies by Cole (1968), Frewer (1972),
Jenin and Schwan (1980) and Ludt and Herrmann
(1973). The properties of blood can be measured, but the
measuring technique is complicated. Zhao (1996) found a
novel approach to measure the blood properties (that is,
Ro, Ri, Ci) using only three frequencies (that is, 0.1, 0.8,
and 1.2 MHz). All these studies have significant results,
but they are still experimental (that is, in vitro only). As
the blood volume is known, the plasma and red blood cell
(RBC) resistivity can be calculated depending on the
general equation ρ = ZV , where Z is the impedance, V
L2
is the blood volume, L is the length of the tested
segment, and ρ is the resistivity.
Recently, Adler and Dai (2006) and Charles (2006)
measured the blood non-invasively using the blood
pulsatile. This method is used to measure the impedance
of blood in the systole and diastole cycles. The difference
between the two impedances is the blood impedance;
however, some difficulties in the measurement of blood
resistivity are still encountered. Only the impedance can
be measured; thus, the problem is with the blood volume.
Yamakoshi and Tanaka (1994) proposed a novel method
to obtain blood volume. However, their results were still
not accurate because the measured frequency was 50
KHz, and the resistivity was attributed to the plasma only.
Blood impedance measurements using pulsatile
state
Nyboer et al. (1950), Weltman and Ukkestad (1972),
Yamakoshi and Tanaka (1994), Adler and Dai (2006) and
Charles (2006) measured blood impedance using blood
pulse non-invasively. The basis of this method depends
on the difference between the tested segment impedance
in the diastole and systole cycles. The impedance of a
segment in body consists of three impedances in parallel
as shown in Figure 12, and includes the following:
1. Body tissue impedance ( Z T ), which includes all the
tissues inside the tested segment excluding blood tissue
(that is, bon, lean, fat…, etc.)
2. Artery blood impedance ( Z AB ) during the systole cycle
in the tested segment
3. Impedance of blood increment during the diastole
cycle ( Z IB ) (Figure 12):
1
Z total
=
1
1
1
+
+
Z t Z AB Z IB
(10)
Taking Y=1/Z, where Y is the admittance of the material,
Ar-Rawi et al.
9303
changes, such as in NaCl, dextrose, urea and albumin,
among others. All the aforementioned results are
significant, but they are still experimental and in vitro (that
is, invasive). Most of the aforementioned studies also
used a single frequency to obtain the results. A more
accurate result is expected using the multi-frequency test.
Triple frequency approach
Figure 12. Segment impedances.
we obtain:
Ytotal = Yt + Y AB + YIB
(11)
where Yt , YAB , YIB and Ytotal are the admittance of
tissue, artery blood, incremental blood, and the total,
respectively. From Equation 11, we obtain:
YIB = Yb = Ytotal − Yt − Y AB
(12)
where Yb is the blood admittance, and Yb=1 / Zb. We
assume
Y fix = Yt + Y AB
(13)
where Yfix is the total admittances of the non-blood tissue
and artery blood impedances. Rearranging Equation 12,
we obtain
Yb = Ytotal − Y fix
(14)
where Ytotal is the admittance in the diastole cycle, and Yfix
is the admittance in the systole cycle (Papezova, 2003).
Impedance and blood component
Hill et al. (1975), Zhao (1993) and Treo et al. (2005)
conducted various tests and studies on the hematocrit in
blood in vitro and related it to bioelectric impedance.
They found that there is an exponential relation between
the hematocrit and blood resistivity.
Zhao (1996), Kichul and Elaine (1994) and some other
researchers investigated the relation between erythrocyte
sedimentation rate (ESR) and blood resistivity and found
a relation between ESR and blood resistivity. Fuller
(1991) investigated the plasma in blood in vitro using the
bioelectrical impedance method and found that the
resistivity of plasma changes when the plasma component
As discussed in the review, there are two methods in BIA,
that is, single frequency and multi-frequency. The single
frequency is easier to use, but is not accurate especially
with blood investigations. In contrast, multi-frequency is
more accurate, but has a more complicated process of
measurement.
Zhao (1993) used only three frequencies to diagnose
blood, making his method less complicated. He used 100
KHz, 800 KHz, and 1.2 MHz to compute the three electrical components of blood, Ri, Ro and Cm (that is, plasma
resistance, RBC intracellular water resistance and RBC
membrane capacitance).
Hence, the relation between blood components and
resistivity, not with impedance, and the relation between
impedance and resistivity depend on the volume. However, the important question is how to determine a
method to calculate the volume of blood pulse.
Yamakoshi approach
Yamakoshi and Tanaka (1994) designed an apparatus to
calculate hematocrit using a novel approach to measure
the blood volume (Figure 13).
He used a comparative electrolyte solution with known
resistivity that surrounds the limb (tested segment). He
conducted impedance measurements, which appear as
two systems working in parallel: One system to measure
the impedance of electrolyte solution and the other to
measure limb impedance. Increasing limb volume during
the blood pulse travel decreases the solution volume and
the impedance of the solution changes (Figure14).
The Yamakoshi and Tanaka (1994) approach is used
as the basis of our apparatus, whereas the triple frequency
method is used for collecting various information needed
for our study.
CONCLUSION
Many previous studies on the electrical impedance of
blood were carried out at only one frequency below 100
KHz. However, because blood cells do not conduct at low
frequencies, the measured resistivity relates only to the
properties of the plasma and the volume concentration of
blood cells. The method was used to measure hematocrit,
cardiac output and ESR, among others. It was extended
to monitor fluid volume and measure other body tissues.
9304
Afr. J. Biotechnol.
Figure 13. Yamakoshi approach in the measurement of blood volume.
Figure 14. Changes in the impedance of the electrolyte solution.
However, such a single-frequency method could not fully
utilize the possibilities of the impedance technique for
clinical applications. In particular, the determination of the
capacitive component of the impedance may yield information on the membranes of RBC, which is difficult to
measure with other techniques (Zhao, 1996).
Some investigators measured blood impedance over a
large frequency range, from several hundred Hz to several MHz (that is, Cole-Cole plot). The properties of blood
cells and plasma could be obtained, but the measuring
procedure was complicated (Zhao, 1996).
Blood, as a vital body fluid, has been extensively studied
using the electrical impedance technique. As determined
late in the last century, the conductance of blood decreases
as the erythrocyte concentration increases. Successive
studies reveal that the RBC membrane is a very poor
conductor, whereas the interior fluid is an electrolyte with
a resistivity of 200 cm. Later, Philipson measured the
Ar-Rawi et al.
9305
Figure 15. Sending of data from a PC through a serial port.
I+
I-
Current source
Multi frequency
V+
V-
Voltage
Sensor
High
speed
ADC
DSP processing
or computer
Pressure
Sensor
Figure 16. Complete block diagram of the proposed device.
impedance amplitude of packed blood cells over a
frequency range of 500 Hz to 3 MHz and found that the
internal resistively of RBCs was about 3.5 times that of
plasma (Ibrahim et al., 2004).
Extensive studies on blood impedance, both theoretically and experimentally, were carried out by Fricke and
Morse (1925). They determined the capacity of the RBC
2
membrane to be 0.81 µF/cm and measured the impedance of RBC suspensions over the frequency range of
800 Hz-4.5 MHz. They represented these results by an
equivalent circuit as shown in Figure 1.
Although these studies provide us with significant
results, the results are still not applicable. They are only
experimental and require laboratory devices to measure.
For further research, the work aims at developing and
designing a non-invasive bio-impedance multi-frequency
instrument for checking and monitoring blood hematocrit.
This system is expected to be non-invasive, compactable, low cost, locally made and applicable to real applications.
The instrument will be designed using three components:
1. For a non-invasive method using BIA measurements,
we will use bio-impedance sensors (probes) and reshape
the sensors to fit the upper arm portion. The brachial artery
makes the impedance change in this part noticeably.
2. Using a sphygmomanometer cuff to measure the change
in the blood pressure will allow us to know when the
blood volume changes.
3. High speed analog to digital technique (ADC) will be
used to convert the measured data from analog to digital
form. The converted data will be sent to the microcontroller
embedded unit for calculation and for evaluating the
impedance and Xc. Finally, the data will be sent to the
PC through a serial port (RS232) (third component)
(Figure 15).
4. The PC software will read the data from the microcontroller unit through a serial port and saves it to a
database for later analysis and creation of reports.
The complete suggested block diagram of the complete
system is shown in Figure16.
REFERENCES
Abdulrahman FN (2003). "Physiological and chemical changes in blood
picture of jaundice." J. Iraqi Med. 3: 346-355.
Aroom KR, Harting MT, et al, (2009). "Bioimpedance Analysis: A Guide
to Simple Design and Implementation." J. Surg. Res. 153(1): 23-30.
Charles Davis L (2006). Noninvasve method of determining arterial wall
tension and arterial segmentation by pulse transit time and pulse
wave velocity. U. S. P. A. P. (10). USA. 2006/0247538 Al.
9306
Afr. J. Biotechnol.
Cole KS (1968). "Membranes, ions and impulses." (University of
California Press.
Adler A, Dai T (2006). "Blood Impedance Characterization from
Pulsatile Measurements." IEEE CCECE/CCGEI.
Fernando SM (2007). Electrical Bioimpedance Cerebral Monitoring:
Fundamental Steps towards Clinical Application. Department of
Signals and Systems. Göteborg, Chalmers University of Technology.
PhD: p. 137.
Frewer RA (1972). "The effect of frequency changes on the electrical
conductance of moving-and stationary blood." Med. Bid. Eng. Comp.
10: 734-41.
Fricke H (1925). "The electric capacity of suspensions with special
reference to blood.” J. Gen. Physlol. 9: 137-152.
Fricke H, Morse S (1925). "The electric resistance and capacity of blood
for frequencies between 800 and 4.5 million cycles." J. Gen. Physiol.
9: 153-167.
Grimnes S, Martinsen OG (2000). Bioimpedance and bioelectricity
basics, Academic Pres . April 19.
Fuller HD (1991). "The Electrical Impedance of Plasma: A Laboratory
Simulation of the Effect of Changes in Chemistry." Ann. Biomed. Eng.
19: 123-129.
Hill DW, Thompson FD (1975). "The effect of haematocrit on the
o
resistivity of human blood at 37 C and 100 kHz." Medical and
Biological Engineering.
Hills P, Andrew et al., (1998). "Bioelectrical Impedance and Body
Composition Assessment." Malaysian J. Nutr. 4: 107-112.
Hoffer EC, Meador CK, et al., (1969.). "Correlation of whole body
impedance with total body water volume." J. Appl. Physiol. 27: 531.
Ibrahim F, Abas WABW, et al., (2004). "Bioelectrical tissue conductivity
in adult's dengue patients using bioelectrical impedance analysis."
IFMBE, 7: 247-250.
Jaffrin MY, Morel H (2008). "Body fluid volumes measurements by
impedance: A review of bioimpedance spectroscopy (BIS) and
bioimpedance analysis (BIA) methods." Med. Eng. Phys. 30(10):
1257-1269.
Jenin PC, Schwan HP (1980). "Some observations on the dielectric
properties of haemoglobin's suspending medium inside human
erythrocytes." Biaphys. J. 30: 285-94.
Kichul CHA, Elaine Brown F, et al., (1994). "A new bioelectrical
impedance method for measurement of the erythrocyte
sedimentation rate." Physiol. Meas. 15: 499-508.
Ludt H, Herrmann HD (1973). "In vim measurement of tissue
impedance over a wide frequency range." Blophysik, 10: 337-45.
Mager JR, Sibley SD, et al., (2008). "Multifrequency bioelectrical
impedance analysis and bioimpedance spectroscopy for monitoring
fluid and body cell mass changes after gastric bypass surgery." Clin.
Nutr. 27(6): 832-841.
Nyboer J, Kreider MM, et al., (1950). "Electrical Impedance
Plethysmography: A Physical and Physiologic Approach to Peripheral
Vascular Study." Am. Heart Assoc., Inc. 2: 8.821- 11
Nyboer J, Liedtke RJ, et al., (1983). Nontraumatic electrical detection of
total body water and density in man. VIth ICEBI.
Papezova S (2003). "Signal processing of bioimpedance equipment."
Sensors and Actuators B: Chemical, 95(1-3): 328-33.5
Schoeller DA, Kushner RF (1989). "Determination of Body Fluids by the
Impedance Technique. March " IEEE Eng. Med. Biol. Mag. 8(1): 1921.
Sutton R, Ryden L, et al., (1999). The Foundation of Cardiac Pacing,
PT, II: An Illustrating Practical Guide to Rate Variable Pacing.
Armonk, New york, Futura Publishing company Ltd.
Thomasett A (1962). "Bioelectrical properties of tissue impedance."
Lyon Med. 207: 107-118.
Treo EF, Carmelo J, Felice, et al., (2005). "Hematocrit Measurement by
Dielectric Spectroscopy." IEEE Trans. Biomed. Eng.
Ursula G Kylea, Ingvar Bosaeusb, et al., (2004). "Bioelectrical
impedance analysis part I: review of principles and methods." Clin.
Nutr. 23: 1226-1243.
Weltman G, Ukkestad AFD (1972). "A Field-Theory Model of BloodPulse Measurement by Impedance Plethysmography." Ann. Biomed.
Eng. 1: 69-86.
Yamakoshi K, Tanaka S, et al., (1994). "Electrical admittance cuff for
non-invasive and simultaneous measurement of haematocrit, arterial
pressure and elasticity using volume-oscillometric method." Med.
Biol. Eng. Comput. 32: 99-107.
Zhao TX (1993). "Electrical impedance and haematocrit of human blood
with various anticoagulants." Physiol. Meas. 14: 299-307.
Zhao TX (1996). "New applications of electrical impedance of human
blood." J. Med. Eng. Tech 20: 115-120.