Interaction of Electric and Magnetic Fields With a Human Body

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Title: Interaction of Electric and Magnetic Fields With a Human Body

1
Interaction of Electric and Magnetic Fields With
a Human Body

2
Electricity

- results from elmg. forces between protons and
charged electrons
- in a wire it depends on a movement of free
elec-trons
in solutions it depends on a flow of a negatively
charged -Anions, which are repealed by a
negati-vely charged Cathode, and attracted by a
positi-vely charged Anode.
- However, the direction of electric current was
ge-nerally aknowledged from the Anode to
Catho-de

3
Electric Units

4
Types of Electric Currents

Direct Current (DC) half wave shaped current.
Sources are batteries and rectifiers.
Alternating Current (AC) sinusoidally shaped,
220V, 50Hz ( in Slovakia) USA 120V, 60Hz

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(No Transcript)
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Human Body and Electricity

Body is a non-uniform space conductor where an
electric current flows according to electric
tissue conductivity.Body tissues have diffe-rent
resistances (impedances), and therefore different
conductances.
The highest el. resistance (Impedance) have the
fat and bone tissues (R 40-50 O/m)
The lowest el. resistance (Impedance) have a
blood, liquor, lymphatic fluid (R 0.8 O/m)
El. resistance for dry skin is high (R1000 O/m)
El. resist. for moistured skin is low (R50 O/m)

7
Impedance, Resistance and Reactance
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Biological Effects of Electric Currents on Human
Body

Both DC and AC Currents have 3 main effects
Stimulatory, Electrolytic, Thermal.
I. Stimulatory is typical for AC current
with
f 50-100 Hz, but also for DC current
Max. harmless AC current is 5 mA, and for
DC current is 25 mA
Stimulatory effects of DC current (a) and
AC (b) are used in
Chronaximetry (e.g. chronaxia for sceletal
mus-cle is 1.0 msec, but for nerve is 0.1 ms.
Thus, an excitability of nerve tissue is
10-times higher than that one for muscle tissue)
Therapy with stimulatory (diadynamic) currents

9
Stimulatory Currents in Medicine

1.Rectangular DC Currents mostly used for
stimu-lation of muscles and nerves in
rehabilitation
2.Faradic (Triangle) Currents used for
stimulation of sceletal muscles ( muscle twitch,
summation, superposition, tetanus)
3. Sinusoidally shaped AC current
4.Sinusoidally modulated AC currents- relieve a
pain

10
Methods of Electric Stimulation with AC Currents
(see also Therapeutic Methods)

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Methods of Electric Stimulation with DC Current

Pacemaking
It is a useful method of treatment sick sinus
syndrome (i.e. the sinoatrial (SA) node is not
working properly, and as a result bradycardia and
collapse may appear in patient.
Point A pacemaker device (battery operated
generator of DC current) is sewed under the skin
around a clavi-cula, or abdomen. Under X-ray
method the wires with hook electrodes are
introduced through caval veins into the heart
right atrium, or into both the right atrium and
the right ventricle ON DEMAND pacemaker- it works
(stimulates the heart) only when SA node is
silent.

12
Heart
Pacemaker
13
II. Electrolytic Effect

Is a typical feature for DC current, when
passing the salt solution
E.g. NaCl when dissolved in water brea-kes to
Na Cl - ions
When DC electric current passes such solution,
then Na cations run towards the Cathode.
Similarly Cl anions run towar-ds the ANODE

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Methods that use Electrolytic Effect of DC
Current (see also Therapeutic methods)

IONOPHORESIS is a method of an introducing of
drugs dissolved in water to the eye, knee,
joints, skin ..
Point The method based on the fact that ions
with the same charges are repelled. Contrary, the
ions with the opposite charges are attracted.
E.g. Drugs as anesthetics when dissolved in
water create Cations . Thus, when Anodal
Current is app-lied, then drugs are electrically
pushed to the body. Or drugs as antibiotics,
aspirine or iodine salts create Anions-. When
Cathodal - Current passes the solution then
dissolved drugs are pushed to the body.

15
III. Thermal Effect

This effect is typical for AC current, mainly at
frequencies above 100 kHz.
As a result- a heat is produced in tissues - this
property of High Frequency AC Currents is used in
thermotherapeutical method named- Diathermy.
Types short wave (27 MHz)
ultra short
wave (434 MHz)
microwave
(2400 MHz)

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Magnetic Fields

Permanent (stable) magnets as Earth (it results
of rotation of hot magma within the Earth core)
Non-stable artificial magnetic fields arise in
a vicinity of wire (within a coil) under
electricity
Magnetic fields with low frequency - increase the
excitability of brain, decrease the blood flow in
vessels with a high diameter - aorta (this in
turn, may decrease the blood pressure)
Magnetic fields with high frequency- have mainly
thermal effects (used in Diathermy)
Both types of fields are used in the Nuclear
Magnetic Resonance Scanning (NMRS)

17
Electromagnetic Field
18
Patient Protection Against Electric Shock Basic
Rules

At a time of Recording (e.g. ENG, EKG..) or at a
time of Defibrilation remember do not ground a
patient.
For diagnostic and treatment goals doctors must
use only devices approved for their use in
Medicine, being equipped with sepa-ratory
transformes. Hence, in the time of an accident
i.e. a short circuit- the transformer is able
to disconnect the primary el. circuit , 220V,
from the secondary (patient) circuit.

The harmful effect of electricity on a living
body depends on Intensity of el. current, on the
impedance and the insulation of the body against
the ground.
Electric shock is caused only by Electric
Cu-rent, which is determined both by a Volta-ge
and body Resistance.