Extremely of low frequency Magnetic Field on RBCs

To My Father

Presented by / Fatma Abd-Elhamied AhmedSupervisor / Dr. Sally Eldeghaidy

Also they provide information that helps in understanding the interaction between electromagnetic fields and biological systems.

Why we are Interested in Studying the Dielectric Properties of Tissues??

Analysis of dielectric properties of cells as a whole and the cells structure parts (membrane, cytoplasm, etc) provide valuable knowledge about different cell structures, function and metabolic mechanisms.

Outline

A review on the effect of (ELF) magnetic field on the

dielectric properties of RBCs

Polarization mechanisms

Measurements of dielectric properties

Dielectric spectroscopy for soft tissues

The dielectric properties of tissues will be discussed

in details including:

Dielectric Polarisation When an electric field is applied to a dielectric material,

electric charges slightly shift from their average equilibrium positions causing dielectric polarization

A dipole is formed,and the material is

said to be polarized After the electric

field is turned off

Before the application of electric field

Electric field is applied

The polarization (P) is related to the applied electric field (E) by

where ε0 is the electric constant, and χ is the electric susceptibility of the medium.

The x  is related to the relative permittivity by

EP 0

1 r

Dielectric Polarisation Mechanisms in Biological Material

Several mechanisms contribute to the dielectric properties of tissues and other biological materials.

• The main mechanisms giving rise to dielectric polarization is tissue are:

• Dipole polarisation • Interfacial polarisation • Counter-ion polarisation

Depending on the material and frequency range of interest one or another might predominate in its influence.

Dipole Polarisation This mechanism of polarization is particular to polar

molecules, such as water, and many proteins. In the absence of an external electric field, the permanent dipole moments are oriented at random directions

Water molecule

When an externally electric field is applied, on polarmolecules, permanent dipoles (each with dipolemoment M) will reorient and experience a rotationalforce (F), defined by the torque:

)sin( MF

where θ is the angle between the dipole moment and the field.

The relaxation time in dipole polarization can be obtained by considering the diffusion of the molecules in a viscous medium:

where η is the viscosity (Poise), a is the molecule radius, T is the absolute temperature, and k is Boltzmann’s constant . The relaxation time t ranges from picoseconds for small dipolar molecules such as water, to microseconds for large globular proteins in aqueous solution.

kTa34

Interfacial Polarisation This mechanism arises from the heterogeneity of the

material leading to changes in the distribution of electric fields within the material at different frequencies.

This effect is caused mainly due to cell membrane. Characteristics “charging effects”.

At low frequencies, the current flows around the spheres “cells” because of membrane's high impedance.

As the frequency is increased, progressively more current

flows through the cells.

At very high frequencies, the membranes are short-circuited owing to their capacitance, and no longer impede current flow. The permittivity and conductivity will be close to those of the media that are contained by and surround the spheres.

The relaxation time is given by:

)12

1(ia

maC

Where a is the radius of the spheres, Cm is the capacitance of the membrane and σa , σi are the conductivities of the

outer and inner media.

Counter-ion Polarisation The polarisation originates from ionic diffusion effects (displacements of ions)

near cell surfaces and the formation of counter-ion or electric double layers during the presence of electric field.

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Electric fieldElectric fieldNo Electric field No Electric field appliedapplied

The relaxation time can be calculated by:

kTea

2

2

where a is the radius of the sphere, e is the elementary charge, and μ is counter-ion mobility.

How Dielectric Properties can be Measured?

The response of a material to an applied electric field is described by its permittivity (ε) and conductivity (σ)

'''

0

rrr

r

j

Dielectric constant storage

Dielectric loss

1j

LRC meter is usually used to measure the capacitance and resistance for the sample under study at various frequencies.

The permittivity is calculated for each frequency, using

Where d, is the inter-electrode distance, A is the area of electrode measured from the cell used, and ε0 is the permittivity of free space.

ACd

0

'

The loss tangent (tanδ), the dielectric loss (ε’’) and the AC conductivity σ are calculated from the relations

where, f is the frequency applied, and R is the resistance of the specimen.

' tan''2

1tan

fRC

0''2 f

The Dependence of Permittivity and conductivity on frequency.The general trend for the permittivity to decrease as

frequency increases, while the conductivity increases with increasing the frequency.

The Dielectric spectroscopy for Soft Tissues

Schawn defined three frequency regions for the dielectric properties of biological materials from the observed main dispersions of the conductivity and the permittivity.

Conductivity increases with increasing the frequency, while the permittivity decreases over a wide range

Major dispersions in biological Matter

Example for Dielectric properties of Different Tissue Types.

The Effect of ELF Magnetic Field on RBCs

Changes in RBC’s biophysical properties will affect its capability for carrying and transporting oxygen (O2), and therefore on its metabolic functions.

The failure in metabolic function of the RBCs is directly reflected in highly active critical organs, such as heart muscles, brain and bone marrow.

Why did we choose RBC?

Therefore, RBCs were chosen as a good example for the changes that may occur as a result of exposure to ELF magnetic field

The Structure and Function of RBCs

They are biconcave shape with a flattened centre, giving an increase in surface area

Their main function is carrying and transporting O2 to all body

parts

They consists of 4 polypeptide subunits, each contain a heme

group

Each haemoglobin molecule is able to carry up four oxygen

molecule at it's maximum capacity

Review on the Effect of ELF Magnetic Field on RBCs

The effect of prolonged exposure of animals to 50 Hz magnetic field with intensity of 0.2 mT on the RBC’s haemoglobin molecular structure was investigated for 4 groups (6 rats each) for 15, 30, and 45 days. The 4th group was used as control. The field was turned on continuously for the groups under exposure.

The dielectric measurements permittivity (ε) and conductivity (σ) were made in the frequency range from 0.1 to 10 MHz.

Ali et al, Bioelectromagnetics 24:535-545 (2003)

ResultsControl

15 days exposure

30 days exposure 45 days exposure

These results indicate that the prolonged exposure of the animals to 50 Hz magnetic field of intensity 0.2 mT caused structural changes in their Hb molecules, which may affect their properties and hence the RBC’s physiological functions

In another study, the exposure to 50 Hz MFs of intensity 3 mT, showed similar results to the previously shown. However, in this study the exposure time was shorter, 8 hours/day for two, three and four successive weeks.

The dielectric measurements, εr and σ were calculated in a frequency range of 12 Hz – 0.1 MHz.

The relative permittivity and conductivity of Hb showed an increase in response to the exposure of the magnetic field.

SHALABY, and SHAWK. ROMANIAN J. BIOPHYS., Vol. 16, No. 3, P. 169–180, (2006).

Similar results were confirmed in more recent studies.

In these studies [1,2] , the effect of 50 Hz MF was investigated at intensities: 1.8 mT (frequency range 20 Hz to 0.1 MHz) for a duration

of 8 hours/day for 1, 2, 3, and 4 weeks [1] . And at 0.3 mT (frequency range 50 Hz to 0.2 MHz). The

animals were continuously exposed to magnetic field for 21 days another group for 45 days[2] .

[1] Rageb and Sallam. Egypt.J.Biophs.Engng., 8:15-24, (2007) [2] Baieth and Morsy. Egypt.J.Biophs.Engng., 8:1-13, (2007),

Conclusions Analysis of dielectric properties of cells as a whole and the cells

structure parts provide valuable information about different cell structures, function and metabolic mechanisms.

• It helps in understanding the interaction between electromagnetic fields and biological systems.

• Recent studies showed that the exposure of 50 Hz magnetic field with intensities 0.2, 0.3, 1.8 and 3 mT caused structural changes in Hb molecules, which may affect their properties and hence the RBC’s physiological functions. This also consequently damage other organs such as liver and other critical organ.

Acknowledgment I would like to thank all staff members, and colleagues

for all their help and support during the last four years.

In particular, I would like to thank

Prof. Mostafa Kamel, head of the departments. Prof, Yehia Abbas, Prof. Magdy Elshry, and Prof. Wahib Attia.Dr. Sally Eldeghaidy