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
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
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
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
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
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
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
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