This document provides an overview of basic electrotherapy concepts including: - Ohm's law defines the relationship between current, voltage and resistance. Tissue impedance varies and depends on water content. - Nerves become hyperpolarized under the anode and more excitable under the cathode. An action potential occurs during depolarization and is followed by absolute and relative refractory periods. - Direct current is unidirectional while alternating current changes direction. Pulsed current can be unidirectional or bidirectional. Waveform shape impacts amplitude and duration. Current intensity and tissue response depends on amplitude, frequency, phase duration and waveform.

1. BASIC CONCEPT OF
ELECTROTHERAPY
Aditya Johan .R, M.Fis

2. INTRODUCTI
ON
 Electricity is most often described by its strength (charge),
rate of flow (current), driving force (voltage), and
opposition (resistance/impedance)
 The relationship between current, voltage, and
resistance is defined by ohm’s law

3. CHARACTERI
STIC OF
ELECTROTHE
RAPY

4. CHARACTERI
STIC OF
ELECTROTHE
RAPY
Current flow is directly proportional to voltage, an
increase in voltage when resistance remains constant will
increase current
Current flow is inversely proportional to resistance, an
increase in resistance when voltage is constant will
decrease current
The magnitude of current therefore increases when
voltage increases or resistance decreases
High resistance requires high voltages to produce
necessary current flow in the tissues below

5. CHARACTERI
STIC OF
ELECTROTHE
RAPY
TISSUES
EXCITABLE
Muscle
Nerve Fiber
Blood Cell
Cell Membrane
NON
Bone
Cartilage
Ligaments
Tendons

6. CHARACTERI
STIC OF
ELECTROTHE
RAPY
 The opposition to current flow the body is more
accurately described by the term “impedance” rather than
“resistance”
 Tissue impedance varies throughout the body
 Conductivity depends on the water content of tissue
 High water content decreases impedance and improves
conductance
 Healthy skin contains a thin layer of water containing salt,
yet it offers one of the highest impedances (1000 + V)18 to
current flow because the outer layer of the skin, the
epidermis, contains little fluid
 Minimizing impedance is important for all applications of
electrical stimulation because this allows current intensity
to be reduced and so increase patient comfort

7. CHARACTERI
STIC OF
ELECTROTHE
RAPY
Current will flow under two conditions :
 When there is a source of energy creating a
difference in electrical potential
 When there is a conducting pathway between the
two potentials

8. CHARACTERI
STIC OF
ELECTROTHE
RAPY
Electrotherapy
Generator
Conducting
Pathway
NaCl (Sodium
Chloride)

9. RESTING
MEMBRANE
POTENTIAL
 At rest the nerve is positively charged on the outside
and negatively charged on the inside

10. DEPOLARIZATI
ON &
HYPERPOLARIZ
ATION
 Nerves will become hyperpolarized (less excitable)
under the anode and more excitable under the
cathode

11. ACTION
POTENTIAL

12. ABSOLUTE
REFRACTORY
PERIODE
While nerve is depolarized, no additional action
potential can be generated
During this time the nerve cannot be further excited, no
matter how strong a stimulus is applied
This periode known as the absolute refractory period

13. RELATIVE
REFRACTORY
PERIODE
After depolarization before the nerve returns to its
resting potential, during this period a greater stimulus
than usual is required to produce another action
potential
This period of hyperpolarization is known as relative
refractory period

14. ACTION
POTENTIAL

15. IONIC FLOWS
Positive ions (cations) are repelled from the positive
electrode and migrate toward the negative electrode
(cathode)
The negative ions (anions) migrate toward the
positive electrode (anode)

16. IONIC FLOWS
Sodium ions (Na+), which are positively charged, migrate
toward the negative pole and combine with water,
forming the base sodium hydroxide (NaOh)
This chemical reaction increases the alkalinity of the area
and promotes liquefaction of proteins and the softening
of tissues

17. IONIC FLOWS
Chloride ions (Cl–), which are negatively charged, migrate
to the positive pole and combine with water, forming
hydrochloric acid (HCl)
This chemical reaction increases the acidity of the area,
thus promoting coagulation of proteins and the
hardening of tissues

18. CURRENT
CLASSIFICATI
ON
Direct current (DC)
Alternating current (AC)
Pulsatile/pulsed current

19. DIRECT
CURRENT
(DC)
 Direct current (DC) is a continuous unidirectional flow
 One electrode is always the anode (positive) and one
electrode is always the cathode (negative)
 Because one electrode is always positive and one is always
negative, there is an accumulation of charge
 This accumulation of charge is called chemical or polarity
effect

20. ALTERNATIN
G CURRENT
Alternating current (AC) is an uninterrupted bidirectional
flow of charged particles changing direction at leas once a
second
Each electrode becomes positive for one phase of the cycle
and then negative as the current reverses
Since the electrodes are continuously changing their
polarity, charges do not build up in the tissues / Zero Net
Charge (ZNC)

21. PULSATILE
/INTERUPTED
CURRENT
 Pulsed or pulsatile current can take on the
directionality characteristics ofAC or DC current
 Unidirectional (like DC) or bidirectional (like AC)

22. WAVEFORM
 It is a spatial drawing depicting the shape of the pulse,
reflecting amplitude (strength) and duration (length of
time)
 There are monophasic, biphasic, and polyphasic
waveforms

23. WAVEFORM

24. AMPLITUDE
/INTENSITY
It is the magnitude or intensity of the stimulus and it
is one factor determining strength of stimulation
The amplitude is read on either a milliamp meter or a
volt meter
The amplitude control on stimulator units is labeled
intensity
Peak amplitude is associated with depth of current
penetration

25. DURATION
 Phase duration is the time
period extending from the
beginning to the end of one
phase of a pulse
 Pulse duration is the time
interval between the
beginning and end of all the
phases of the pulse, including
the intrapulse interval
F = Phase Duration
G = Pulse Duration

26. FREQUENCY
The frequency, which often is referred to as pulses per
second (pps) or pulse rate
the number of pulses delivered to the body in 1 second
The body responds to the number of pulses, not the
number of phase
A single monophasic, biphasic, or polyphasic pulse is
counted as one pulse by the body
Whereas peak amplitude defines the intensity of the
muscle response, frequency defines the quality of the
muscle response dictating a twitch or tetanic contraction

27. MODIFICATIO
N OF
CURRENT
Modification of :
A. Peak Amplitude
B. Pulse Frequency
C. Phase duration

28. TOTAL
CURRENT
Total Current Can Be Increased by
A. Increasing Peak Amplitude
B. Increasing Pulse Frequency
C. Increasing Phase Duration

29. LEVEL OF
STIMULATIO
N
Electrical stimulation produces three excitatory responses:
(1)Sensory
(2)Motor
(3)Pain
Four clinical levels of stimulation are possible with electrical
stimulation devices :
(1)subsensory,
(2)Sensory
(3)Motor
(4)noxious or uncomfortable levels of sensation

30. LEVEL OF
STIMULATIO
N