Osh state University lecture on biophysics

1. Electrical Currents and Electromagnetic
Fields Effects on Biological Objects

2. Plan of the lecture
R
e
2
R
e
C
h
r 
iп
1. Electrical properties of biological
tissues
2. Direct current effect on biological
tissues
3. Pulse current effect on biological
tissues
4. Alternating current effect on
biological tissues
5. Alternating electromagnetic field
effect on biological tissues
6. Direct electric and magnetic fields
effect on biological tissues
th





 
 1
Chr
Re
ithr


3. A great number of diagnostic and
therapeutic methods of modern medicine
are based on effects
developing in human body tissues
under the influence of external electrical currents
and electromagnetic fields.

4. Electrical currents and fields effect
on biological objects depends on:
1) Properties of External electrical current
or fields
2) Own Electrical activity of biological tissue

5. 1. Electrical properties of Biological
Tissues
All biological tissue can be divided into
conductors (conduct electric current well)
and dielectrics (conduct electric current
poorly) :
conductors are cerebro-spinal fluid, blood,
lymph,
dielectrics are bone without periosteum,
nervous, fatty tissue, dried-up skin.

6. Electrical specific conductivity (  )
for various biological tissues :
Biologi-
cal
tissue
Cereb
ro-
spinal
fluid
Blood Muscu
lar
tissue
Nervous
tissue
Fatty
tissue
Skin
(dried
-up)
Bone
without
peri-
osteum
Specific
conduc-
tivity ,
Ohm-1m-1
1.8 0.6 0.5 7·10-2 3·10-2 10-5
10-7

7. • The best conductor of electrical current is
cerebrospinal fluid.
• The best dielectric is
bone without periosteum.

8. Two classes of conductors:
first - fine metals (free charge carriers are electrons),
second – electrolytes (free charge carriers are ions).
Biological tissues are second class conductors,
or ionic conductors (it means, current carriers in
biological tissues are ions).

9. Electrical properties of biological tissue
depend on its Impedance (Z).
Impedance (Z) is a Total Resistance,
it has two components:
• Active resistance (R) Resistor Symbol
• Reactive resistance (X):
- capacitive (XC) Capacitor Symbol
- inductive (XL ) Inductor Symbol

11. Biological tissues have only:
• active resistance (R)
• capacitive resistance (XC )
• Inductive resistance XL of biological tissue
is zero XL ≈ 0 !!!

13. • Due to capacity resistance (XC )
electrical properties of the biological tissue
are different for direct and alternating
currents:
Direct Current (DC) doesn’t pass through
structures with the capacity properties,
and Alternating Current (AC) passes
(the bigger frequency of alternating
current, the better it passes).

14. • Human body has capacity properties
(XC ) due to capacitor analogs in the
body :
1) an intact cell
Cell membrane is a dielectric;
cell content and intercellular fluid are conductors.
Membrane is located between two conductors,
like a dielectric layer between two conductors in a capacitor.
2) tissues-dielectrics and tissues-conductors

15. solid line – for
alive tissue,
dotted line – for
dead tissue
• When frequency ω increases, the tissue impedance
modulus decreases (solid line),
but not to zero, up to constant value (dotted line).
Z
• Dependence of tissue impedance Z
on alternating current frequency ω :

16. • Coefficient of dispersion (К)
is calculated for evaluation of tissues functional state,
widely used in transplantology :
hf
lf
Z
Z
K 
Zlf is impedance at low frequencies (102-104 Hz);
Zhf is impedance at high frequencies (106-108 Hz)
• If К=1 , the biological tissue is dead;
• If К>1 , the biological tissue is alive.

17. Electrical equivalent of a biological tissue
is an electrical circuit having impedance
dependence on alternating current frequency the
same as the biological tissue;
• it consists of two resistors (R1 and R2) and one
capacitor (C)
resistor R1 - corresponds to intercellular fluid,
resistor R2 - corresponds to intracellular contents,
capacitor C - corresponds to cell membranes.

18. 2. Electrical currents effects
on biological tissues
Electrical current effect on tissues depends on current type.
Basic types of current :
1. direct current
2. alternating current
3. pulse current

19. 1. Direct current 2. Alternating current

20. 3. Pulse current
Electrical pulses can have different shape –
rectangular, triangular, trapezoid etc.

21. Currents that can change in time are divided into pulse and alternating one.
• Alternating current - changes in time
according to the harmonic low (a sine or
a cosine law).
• Pulse current - depends on time
periodically but not harmonically.
Single electrical pulses are also used in medicine.

22. 1. Direct current (DC)
Under the influence of DC the positive and negative
ions in a tissue move in the opposite sides:
positive ions (cations) move to the cathode (-) and
accumulate under it;
negative ions (anions) move to the anode (+).
• The main mechanism of direct current
effect on biological tissues is change of usual
ion concentrations in different parts of tissues.

23. Medical methods based on application of
Direct Current :
1. Galvanization
2. Medical electrophoresis

24. 1. Galvanization :
Voltage is U=60-80 V; current density is j ≤ 1 A·m-2
• Device for galvanization is an alternative current
rectifier.
• Electrodes used to get current to a patient are
made of sheet lead or foil.
• Hydrophilic layers wet with water or physiological
solution are placed between a patient’s skin and the
electrodes.

25. Response reactions of the human organism on
DC:
1. Stimulation of blood circulation, lymph
circulation, metabolism
2. Irritation of the tissues under cathode (“-”
electrode) and
decrease of the tissues sensitivity under anode
(“+” electrode) - the effect of local analgesia
(pain relief).

26. 2. Medical electrophoresis
is a therapeutic method of introducing of
medical substances through the skin or
mucous membranes under the influence of
DC.
• Medical electrophoresis is performed
similar to galvanization but one of
hydrophilic layers is wet not with water but
with a special medicine solution.

27. • Introducing of medical substances by means of
electrophoresis is possible if a medicine, dissolving in
water, forms ions.
• Anions are introduced to patient from under cathode,
• cations are introduced to patient from under anode.
Medical substance
Electrodes

28. 2. Pulse Current
The basic mechanism of pulse currents
effect on biological objects is the irritation
of excitable tissues.
Excitable tissues:
• muscular
• nervous
• glandular

29. • Front is a pulse section that corresponds to
voltage or current growth as well as their
diminution (back front or cut).
• Amplitude is modulus of voltage or current
maximum value (Umax or Imax correspondingly).
• Pulse duration is a
time interval
during which
voltage (or
current) exceeds
0,1·Umax (or 0,1·Imax
for current).
i

i
 2
f

1
f


30. Front steepness (S) is determined as follows
f
max
U
0,8
s



where is a duration of growth (or diminution)
of pulse front when voltage ranges between
0,1·Umax and 0,9·Umax .
Pulse current is characterized by a period of
pulse repetition (T) and pulse repetition
frequency , at that .
f

)
( T
1



31. Irritation action is a result of generation of an action
potential in tissue cells.
Irritation action depends on
• pulse amplitude
• pulse steepness
• pulse frequency
• pulse duration
1) The tissue irritation is possible if pulse amplitude
exceeds certain minimum value.
Minimum current value when response reaction
(irritation) starts is called threshold current (Ithr).

32. 2) The more pulse front steepness is,
the more current irritation action.
• Du Bois-Reymond law describes this
phenomenon:
an electric current irritation action is directly
proportional to the rate of current increasing (or
decreasing) that is proportional to a derivative of current with respect to time.

33. 3) As pulse duration increases its irritation action on
excitable tissues increases, i.e. threshold current
decreases.
• The method of electrodiagnostics is based
on this conclusion - a method of examining of tissue
excitability properties by means of determination of
dependence of a threshold current upon pulse
duration (τ) when single rectangular pulses irritate
tissue.
• Hoorweg-Weiss-Lapicque equation :
where a and b are constants.
b
a
ithr 



34. • From the diagram the more pulse duration, the less the
threshold current depends on  and tends to a certain limiting
value that is called a rheobase (Re) in electrophysiology.
• Rheobase is equal to a limit to which threshold current tends
when pulse duration tends to infinity
Other words,
rheobase is
determined as the
value of threshold
current when it
does not depend
upon pulse
duration.
R
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2
R
e
C
h
r 
iп
ithr thr
i
lim
Re





35. • Chronaxie (Chr) is one more feature that describes
tissue exciting properties as well as rheobase.
Chronaxie is the pulse duration at which threshold
current is equal to doubled rheobase.
• Values of parameters a and b in Hoorweg-Weiss-
Lapicque equation are determined by rheobase and
chronaxie values. Hence, Hoorweq-Weiss-Lapicque
equation can be presented like





 
 1
Chr
Re
ithr

• Rheobase and chronaxie certain values are
characteristic for the exciting tissues state. At different
pathological states these parameters change.

36. Medical methods based on use of
Pulse Current :
1. Pacing
2. Defibrillation
3. Electrogymnastics
4. Electrosleeping

37. 1. Pacing
• In normal state pulses causing heart systoles are produced by
a sine node (nodus sinuatrialis) called a rhythm driver.
• If sine node does not execute its function, external rhythm
driver (or heart pacemaker) is used.
• Heart pacemaker is carried or implanted cardiological
electrical stimulator. Heart pacemaker generates electrical
pulses with repetition frequency of 1-1.2 Hz and pulse duration
of 0.8 –3 ms.

38. • 2. Defibrillation
Defibrillator is used during cardiac arrest or heart ventricle
fibrillation, i.e. when separate muscle fibers are contracted
irregularly as a result of their irritation by each other.
Defibrillator produces single high voltage electrical pulses
(discharges) that cause great contractions of heart muscle and
restoration of regular heart rhythm.
Voltage equal to 8 kV is commonly used. In case of unsuccessful
attempt to start the heart a greater voltage is used for the
following attempts.

39. 3. Electrogymnastics
(electrical exercises for muscles)
support muscle tonus, improve circulation of the blood
and metabolism in weak muscles or in muscles with
bad innervations, support their ability for contraction.
• Pulse current with pulses of a triangle shape with pulse duration of 1-1.5 ms and repetition
frequency of 100 Hz as well as pulses of an exponential shape with pulse duration of 3-60 ms
and repetition frequency of 8-80 Hz are used for electrical exercises.

40. 4. Electrosleeping
(electrical sleep)
• is a method of inhibition of central nervous system by
a pulse current of a rectangular shape with
pulse duration of 0.1-1 ms and repetition frequency of
5-150 Hz.

41. 3. Alternating Current (AC)
AC effect on tissues can be different and
depends on its frequency :
• at low frequencies AC causes irritation of
excitable tissues (similar to pulse current);
• at high frequencies AC causes thermal effect
(tissue heating).

42. Dependence of threshold current (ithr) upon
frequency () is defined by Nernst law:
• in frequency range from 100 to 300 Hz
threshold current is proportional to square root from current frequency

2
k
ithr

• in frequency range from 50 to 300 kHz
threshold current is proportional to current frequency
where k1 and k2 are certain constants.
In case of alternating current threshold current is also called perception current.

1
k
ithr


43. Medical methods based on use of
Alternating Current :
1. Rheography
2. Diathermy (diathermocoagulation,
diathermotomy)
3. Local D’Arsonvalisation

44. 1. Rheography
(or impedance-plethysmography,
or rheoplethysmo-graphy)
is diagnostic method based on registration of
changing of tissue impedance Z that takes
place due to change in tissue filling with the
blood (that was caused by heart functioning)
At frequency 30 Hz current does not irritate
excitable tissues (currents strength is less then
threshold current).

45. • When cerebrum is examined with the help of rheography we get a
rheoencephalogram,
• when heart is examined with the help of rheography, we get a
rheocardiogram.
• Arterial vessels of lungs, liver and extremities can be examined with
the help rheography. In stomatology vessels of paradont, mouth
mucous membrane, salivary glands etc. can be examined with the
help of rheography.

46. • Rheodentography - a method similar to
rheography, is used in stomatology : tooth
pulp is examined.
• An alternating current of 0.5-1 MHz frequencies is
used.

47. 
 2
j
q
2. Diathermy
• is based on heating effect when alternating current
flows through tissues.
• There are therapeutic diathermy and surgical
diathermy (electrical surgery), which, in its turn, is
divided into diathermotomy and
diathermocoagulation.
• When diathermy is used a specific heat power (an amount of heat evolved
per 1 second in 1 m3 of tissue) of current flowing through the tissue is
defined by the formula :
where q is specific heat power ; j is current density;
ρ is resistivity of tissue through which current flows.

48. • In electrical surgery - the current of 10 MHz
frequency is used. Two electrodes are applied for it: one electrode have a great
area of contact with patient’s body and the other electrode is sharp.
• During diathermocoagulation (j = 6…10 mА/mm2)
there is possibility to ‘seal’ blood vessels due to the
effect of coagulation.
• During diathermotomy (j ≈ 40 mА/mm2) a sharp
electrode acts as an electrical knife, which cuts tissue
by burning it.
Diathermotomy is good for a surgeon, as this method is practically bloodless because the
vessels are cut and sealed simultaneously.

49. • So, at local D’Arsonvalisation the alternating current of
100-400 kHz frequency acts at a patient, but the
current is applied to him like pulses with repetition
frequency of 50 Hz. In this case the voltage is 10 kV.
• Local D’Arsonvalisation.
When certain methods
used currents are applied,
the current affecting the
patient is an alternating
and a pulse at the same
time.

50. ALTERNATING ELECTROMAGNETIC
FIELD EFFECT
ON BIOLOGICAL TISSUES
• Electrical currents can be induced in tissues
without electrodes. If tissues (some parts of
human body) are placed into an alternating
electromagnetic field, alternating currents are
induced in them. Heating of tissues with the
help of currents induced by an alternating field
is the base of the following methods, such as
inductothermy, UHF-therapy (UHF – ultra-
high frequencies), and microwave therapy.

51. • In the course of inductothermy an alternating
magnetic field which oscillation frequency is
within the range of 10-15 MHz effect patient’s
tissues.
• A standard instrument for inductothermy produces
magnetic field changing with a frequency of 13.56
MHz. An alternating magnetic field induces eddy
currents in tissues, when those currents flow
tissues are heated and heat is evolved.

52. 2
2
0
B
k
q



• where k is proportionality factor; ω is cyclic frequency of
alternating magnetic field ; B0 is amplitude of magnetic
induction .
• It follows from the formula that tissues having less specific
resistance (i.e. those tissues that are good conductors) are
heated better.
• The tissues are heated effectively up to the depth of 6-
8cm. An increase of temperature in tissues intensify the
circulation of the blood in them, causes different ferments
activation. In the course of inductothermy human body
immune system is being stimulated.
• In the course of inductothermy a specific heat power
is defined by the formula

53. • UHF-therapy. In the course of UHF-therapy an
alternating electric field of UHF-range
(frequencies of 30-300 MHz) effect on a
patient’s tissues.
• A standard instrument for UHF-therapy induces
electromagnetic oscillations of 40.58 MHz
frequency. In this case the wavelength is about
7.5 m.

54. • A specific heat power for tissues-dielectrics
under UHF-therapy is determined by the
formula
• where E is a root-mean-square value of electric-
field intensity ( , where E0 - is the
amplitude of electric-field intensity);
ε is the dielectric permittivity;
ε0 is the electric constant;
δ is the dielectric loss angle.




 tg
E
q o
2
2
E
E 0


55. • Dielectric loss angle is phase difference
between sum current ( ) and its reactive
component.
• Vector diagram: - reactive component current,
- active component current, - sum current,
φ - a phase angle between and U in a circuit
of an alternating current, consisting of resistor R
and capacitor C, δ - dielectric loss angle.

I
C
I
R
I 
I

I

56. • Superhigh frequency therapy (SHF-therapy). If SHF-therapy
is used for heating patient’s tissues, it means that patient’s
tissues are affected by electromagnetic waves with frequency
within the range of 300 MHz – 30 GHz.
• The commonly used devices are those ones that produce
electromagnetic waves from the following standard values of
wavelength: for decimetric waves (DMW) therapy – 65.2 cm
( ), for microwave (MW) therapy – 12.6 cm
( ).
• Decimetric waves and microwave
therapies differ from each other in the
depth of radiation penetration in
tissues. When decimetric therapy is
used, the depth of penetration is 9
cm; when microwave therapy is used,
the depth of penetration is 3-5 cm.
• At SHF-therapy the muscle tissues
and the blood are heated well.
Hz
M
460


Hz
M
2375



57. • Direct electric field influence on tissues causes
dielectric polarization due to molecule
reorientation; in this case they behave as dipoles.
It results in ions shift and change of their concentration
in different sections of tissues. Ions shift lasts until
electric field that they have developed will not
compensate external electric field effect on ions.
• This results in change of functional stat of central
nervous system that is shown in predominance of
inhibitory processes, ascension of neurologic level,
sleep improvement etc.
DIRECT ELECTRIC AND MAGNETIC
FIELDS EFFECT
ON BIOLOGICAL TISSUES

58. • Such methods as electrostatic shower (or
franclinization) and aeroionic therapy are used. At
that a patient is placed in a strong electrostatic field
(voltage up to 50 kV is used) where partial air
ionization occurs. As this takes place, aeroions are
produced as well as air ionization products – ozone
and ozone oxides that irritate skin receptors and
mucous membrane receptors of respiratory tract.

59. • Direct and low frequency magnetic fields biological effect
on human body is not studied enough. The change of tissue
agent diffusion rate, change of rate and direction of biological
reactions, change of water structure and some other effects
happened upon subcellular level are supposed to take place in
magnetic fields.
• There is information on some essential process stimulation as
well as depression in human body under action of magnetic
fields.
• Direct and low frequency alternating magnetic field medical
effect on human body is called magnetic therapy.

60. Questions Take a piece of paper. Write your
name, group number, date
1.What happens when you are exposed to
electromagnetic fields?