2. Basic physics of electrotherapy
▪ All matter is composed of atoms that contain
positively and negatively charged particles called
ions.
▪ These charged particles possess electrical energy
and thus have the ability to move about. They tend
to move from an area of higher concentration
toward an area of lower concentration.
▪ An electrical force is capable of propelling these
particles from higher to lower energy levels, thus
establishing electrical potentials.
3. Basic physics of electrotherapy
▪ Electrons are particles of matter possessing a
negative charge and very small mass. The net
movement of electrons is referred to as an
electrical current.
▪ The movement or flow of these electrons will
always go from a higher potential to a lower
potential. An electrical force is oriented only
in the direction of the applied force.
4. Basic physics of electrotherapy
▪ The unit of measurement of the electrical
current flows is the ampere (A).
▪ Amperes indicate the rate of electron flow.
▪ In therapeutic modalities, current flow is
generally described in milliamperes (mA) or in
microamperes (µA).
5. Basic physics of electrotherapy
▪ Materials that offer little opposition to current
flow are good conductors.
▪ Metals (copper, gold, silver, aluminum) are
good conductors of electricity, as are electrolyte
solutions, because both are composed of large
numbers of free electrons.
▪ Materials that resist current flow are called
insulators which contain relatively fewer free
electrons and thus offer greater resistance to
electron flow such as; Air, wood, and glass.
7. Parameters of electrical currents
Waveforms
The graphic representation of the shape, direction, amplitude,
duration, and pulse frequency of the electrical current.
▪ Sinusoidal wave; alternating current with equal energy level under
the positive and negative phase.
▪ Rectangular or square wave; Current with rapid rise, maintained
constant for the duration of stimulus and sharp drop off.
▪ Triangular wave; gradual increase and decrease of the current
intensity through prolonged duration.
▪ Spiked wave; suddenly rise up of current intensity and gradually
drop off.
9. Parameters of electrical currents
Pulse: an individual complete waveform.
Phase: portion of the pulse that rises in one direction either above
or below the baseline.
Direct current: unidirectional-monophasic current. It has only a
single pulse and phase which are the same.
Alternating current: bidirectional-biphasic current, It has two
separate phases during each individual cycle.
11. Parameters of electrical currents
Biphasic symmetrical waveform has the same shape and size for each
phase in both directions.,
Biphasic asymmetrical waveform has different shapes for each phase.
Balanced, the net charge in each direction is equal.
Unbalanced, there is a greater net charge in one phase than in the
other.
13. Parameters of electrical currents
Pulse amplitude
The amplitude of each pulse reflects the intensity of the current,
represented the tip or highest point of each phase.
Peak amplitude is determined by measuring the maximal distance to
which the wave rises above or below the baseline.
Amplitude is measured in amperes, milliamps (mA) or microamps
(µA).
14. Parameters of electrical currents
Rate of rise and decay of pulse
▪ The rate of rise in amplitude, or the rise time, refers to how
quickly the pulse reaches its maximum amplitude in each
phase.
▪ Decay time refers to the time in which a pulse goes from
peak amplitude to (0) V.
▪ The rate of rise is important physiologically because of the
accommodation phenomenon, in which a fiber that has been
subjected to a constant level of depolarization will become
unexcitable at that same intensity or amplitude.
▪ The faster the rate of rise, the greater the current's ability to
excite nervous tissue.
15. Parameters of electrical currents
▪ Pulse duration (Pulse width) is the length of time current is flowing in one
cycle.
▪ Phase duration is the length of time for a single phase to complete its rout.
▪ Pulse duration and phase duration expressed in second (sec), millisecond (ms),
or microsecond (µ sec).
▪ The current flow is off for a period of time (interpulse interval).
▪ A single pulse or phase may be interrupted by an intrapulse interval.
▪ The combined time of the pulse duration and the interpulse interval is referred to
as the pulse period.
Pulse duration
19. Parameters of electrical currents
Pulse frequency
▪ Pulse frequency indicates the number of pulses or cycles per
second.
▪ It is expressed as pulse per second (pps) or as pulse frequency in
hertz (Hz).
▪ An inverse relationship exists between the pulse frequency (pulse
rate) and an electrical current and the resistance offered by the
tissues.
▪ A current with lower pulse frequency i.e. 10 pps would meet
resistance than a current with pulse frequency 1000 pps and would
require an increased intensity to overcome the resistance.
20. Parameters of electrical currents
Pulse frequency
When stimulating muscle
contraction, the pulse
frequency plays an
important role??
21. Parameters of electrical currents
Pulse frequency
Stimulators are classified as :
▪ Low frequency generators range from one Hz to
several hundred pulses per second.
▪ Medium frequency generators have frequencies of
2500 to 10,000 Hz.
▪ High frequency generators have frequency of more
than 10,000 Hz.
22. Parameters of electrical currents
Duty cycle
▪ The duty cycle is the ratio of the amount of time the current is
flowing (ON) to the amount of time without current (OFF) and
expressed as a percentage or ratio.
▪ Duly cycles play a role in neuromuscular stimulation by preventing
muscle fatigue. Muscular stimulation is started with a 25% duty
cycle and is progressively increased as the condition improves.
On time
Duty Cycle = ـــــــــــــــــــــــــــــــــــــــ X 100%
(On time + Off time)
▪ For example, if the on time equals 10 seconds and the off time
equals 30 seconds, the duty cycle such a pattern of stimulation
would be 25%. A very different pattern of stimulation with an on
time of 5 seconds and an off time of 15 seconds yields the same
25% duty cycle.
23. Parameters of electrical currents
Current modulation
▪ The physiologic responses to electric current depend on
modulation.
▪ Modulation is alteration in the amplitude, duration, or
frequency of the current during a series of pulses or
cycles.
24. Parameters of electrical currents
Burst modulation
▪ With pulsatile currents, sets of pulses are combined. These
combined pulses are called bursts, packets, envelopes, or pulse
trains.
▪ The interruptions between individual bursts are called
interburst intervals.
▪ The time interval over which the series of pulses or cycles is
delivered is called the burst duration.
▪ The number of bursts delivered per unit of time is called the
burst frequency.
25. Parameters of electrical currents
Ramping modulation
▪ Also called surging modulation, current amplitude will
increase or ramp-up gradually to maximum then decrease
or ramp-down to zero.
▪ Ramp-up time is ⅓ of the on time.
▪ Ramping modulation is used clinically to elicit muscle
contraction and is generally considered to be a very
comfortable type of current since it allows for a gradual
increase in the intensity of a muscle contraction.
27. Parameters of electrical currents
Beat modulation
▪ Beat modulation will be produced when two
interfering alternating currents with different
frequencies are delivered through separate channels
within the same generator to produce a beat
frequency equal to the difference between the two
alternating current frequencies.
▪ The two pairs of electrodes are set up in a
crisscrossed or cloverleaf-like pattern so that the
circuits interfere with one another.
29. Physiologic responses to electrical current
▪ Electrical currents are used mainly to produce
either muscle contractions or pain relief through
effects on the motor and sensory nerves.
▪ This function is dependent to a great extent on
selecting the appropriate treatment parameters.
30. Physiologic responses to electrical current
Clinically, therapists use electrical currents for the
following reasons:
▪ To create muscle contraction through nerve or muscle
stimulations.
▪ To help in treating pain.
▪ To stimulate or alter the healing process.
▪ To drive ions beneficial to the healing process into or
through the skin.
31. Physiologic responses to electrical current
The type and extent of physiologic response to
electrical current dependent on:
▪ Type of tissue stimulated.
▪ Nature of the electrical current applied.
32. Physiologic responses to electrical current
As electricity moves through the body's
conductive medium, physiological effects of
electrical stimulation occur through different
levels:
Tissue level
▪ Skeletal muscle contraction.
▪ Tissue regeneration.
33. Physiologic responses to electrical current
Segmental level
▪ Modification of joint mobility.
▪ Muscle pumping action circulation and
lymphatic activity.
▪ Lymphatic contraction more fluid is moved
centrally.
34. Physiologic responses to electrical current
Systematic effects
▪ Release endogenous pain suppressors which act
at different levels to control pain (indirect
effect).
▪ Gate control theory: through stimulation of
certain neurotransmitters to control neural
activity in the presence of pain stimuli (direct
effect).
35. ▪ Pain is conducted either through Aδ (A delta) or C fibers.
▪ The Aδ (A delta) fibers are small myelinated, fast conductive and carry sharp pain.
▪ The C fibers are small unmyelinated, slow conductive and carry chronic dull aching
pain.
36.
37. ▪ Electrically stimulating the large sensory fibers when there is
pain in a certain area will force the central nervous system to
make the brain's recognition area aware of the electrical stimuli.
▪ As long as the stimuli are applied, the perception of pain is
diminished.
▪ Electrical stimulation of sensory nerves will evoke the gate
control mechanism and diminish awareness of painful stimuli.
▪ As long as the stimulation is causing firing of the sensory
nerves, the gate to pain should be closed.
▪ If accommodation to the electrical stimulus occurs or if the
stimulus stops, the gate is then open, and pain returns to
perception.
38. ▪ Substantia Gelatinosa (SG) in dorsal horn of spinal
cord acts as a ‘gate’ – only allows one type of
impulses to connect with the SON.
▪ Transmission Cell (T-cell) – distal end of the SON
– transmit stimulus to the brain.
▪ If A-beta neurons are stimulated – SG is activated
which closes the gate to A-delta & C neurons.
▪ If A-delta & C neurons are stimulated – SG is
blocked which closes the gate to A-beta neurons.
39. Brain
Gate (T
cells/ SG)
Pain
Electrical stimuli
▪Gate - located in the dorsal horn of the spinal cord
▪Smaller, slower n. carry pain impulses
▪Larger, faster n. fibers carry other sensations
▪Impulses (electrical) from faster fibers arriving gate 1st inhibit pain
impulses
40.
41. Muscle and nerve responses to electrical
currents
▪ Nerves and muscles are both excitable tissues
which is dependent on the cell membrane's
potential.
▪ Cell membrane potential is produced by unequal
distribution of charged ions on both sides of the
membrane.
▪ The potential difference between the inside and
outside is known as the resting membrane potential
(-70 to -90 mV), because the cell tries to maintain
this electrochemical gradient as its normal
homeostatic environment.
42. Muscle and nerve responses to electrical currents
Active transport pumps
Cell continually moves Na+ from inside cell to outside and
balances this positive charge movement by moving K+ to
the inside.
Produces an electrical gradient with + charges outside and
- charges inside.
43. Muscle and nerve responses to electrical current
Nerve depolarization
▪ To create transmission of an impulse in the nerve
tissue, resting membrane potential must be reduced
below a threshold level.
▪ Changes in the membrane's permeability then may
occur. These changes create an action potential that will
propagate the impulse along the nerve in both
directions from the location of the stimulus.
▪ An action potential created by a stimulus from
chemical, electrical, thermal, or mechanical means
always creates the same result that is membrane
depolarization.
44. Muscle and nerve responses to electrical current
Nerve depolarization
▪ Stimulus must have adequate intensity and last
long enough to equal, or exceed, membrane's
basic threshold for excitation.
▪ Stimulus must alter the membrane so that a
number of ions are pushed across membrane
exceeding ability of the active transport pumps
to maintain the resting potential, thus forcing
membrane to depolarize resulting in an action
potential.
45. Muscle and nerve responses to electrical currents
Depolarization Propagation
Difference in electrical potential between depolarized region
and neighboring inactive regions causes the electrical current
to flow from the depolarized region to the inactive region.
Forms a complete local circuit and makes the wave of
depolarization “self-propagating”.
46. Muscle and nerve responses to electricalcurrent
▪ As nerve impulse reaches
effector, organ or another
nerve cell, impulse is
transferred between the two
at a motor end plate or a
synapse.
▪ At the motor end plate, a
neurotransmitter is released
from nerve.
▪ Neurotransmitter causes
depolarization of the muscle
cell, resulting in a twitch
muscle contraction.
Depolarization Effects
Differs from voluntary muscle
contraction only in rate and
synchrony of muscle fiber
contractions!
47. Factors affecting stimulation of nerves
1.The relative diameter of the nerve:
▪ The amplitude of the current is inversely proportional to the
nerves diameter because the larger cross sectional area
provides less capacitive membrane resistance and less
current is required.
▪ Nerves with larger diameter are stimulated to threshold
before nerves with smaller diameter.
▪ Sensory nerves are stimulated first followed by motor nerves
and then pain fibers.
▪ The small C fibers carrying pain impulses need the greatest
current.
48. Factors affecting stimulation of nerves
2. The duration of the pulse:
▪ Short pulse duration allow the greatest range in stimulation
intensity for excitation of nerves.
▪ As the pulse duration is increased, less amperage is required to
stimulate nerves.
▪ Pulse duration less than 1 msec. will not be able to stimulate
denervated muscle regardless of the currents amplitude.
▪ Pain fibers are stimulated with longer pulse duration and high
intensity.
49. Factors affecting stimulation of nerves
3. The rate of rise of the pulse:
▪ Rapidly rising pulses cause nerve depolarization and if
the rate of rise is slow, the nerve accommodated to the
stimulus.
▪ Muscle fibers accommodates more slowly than nerve
fibers, so gradual pulse rise may be used.
50. Factors affecting stimulation of nerves
4. The depth of the nerves:
▪ Superficial sensory nerves receive a greater amount of
stimulation than deeply situated motor nerves.
51. Sensation levels
Subsensory level:
▪ Stimulation occurs within the output interval between the point at which
the output intensity rises from zero to the point at which the patient
receive a discrete electrical sensation.
Sensory level:
▪ An intensity that stimulates only sensory nerves.
▪ This level is found by increasing the output to the point at which a slight
muscle twitch is seen and then decreasing the output intensity by
approximately10 %.
Motor Level:
▪ An intensity that produces a visible contraction without causing pain.
Noxious Level:
▪ An intensity that stimulates pain fibers.
53. General contraindications to electrical
stimulation
▪ Unreliable patients (very young and very old).
▪ Lost or impaired sensation.
▪ Patient receiving deep X-ray therapy.
▪ Ischemia and poor circulation.
▪ Neoplasm.
▪ Open infected and/or bleeding wound.
▪ Some dermatological conditions,(dermatitis).
▪ Metal implants.
54. General contraindications to electrical
stimulation
▪ Over the eyes and the reproductive organs.
▪ Over the anterior neck region (carotid sinus) may
result in disruption of normal respiration.
▪ Near pacemakers, as it may interfere with its
function.
▪ Over the abdomen and pelvic region during
pregnancy and menstruation.
▪ Epilepsy.
55. Types of electrodes
▪ Metal Aluminum or foil plates enclosed within wet
sponge.
▪ Carbon-rubber electrodes: It should be enclosed in
wet sponge or use conducting gel.
▪ Pre gelled electrodes.
56. Electrode Placement
▪ On or around the painful area.
▪ Over specific dermatomes or myotomes that
correspond to the painful area.
▪ Close to spinal cord segment that innervates an area
that is painful.
▪ Over sites where peripheral nerves that innervate the
painful area becomes superficial and can be easily
stimulated.
57. Electrode Placement
▪ On or around the painful area.
▪ Over specific dermatomes or myotomes that
correspond to the painful area.
▪ Close to spinal cord segment that innervates an area
that is painful.
▪ Over sites where peripheral nerves that innervate the
painful area becomes superficial and can be easily
stimulated.
58. Electrode Placement
▪ Over superficial vascular structures.
▪ Over trigger or acupuncture point locations.
▪ In a criss-cross pattern surrounding the
treatment area.
▪ If treatment is not working, change electrode
placement.
60. Techniques of electrode application
Monopolar technique
▪ Use of the two electrodes:
(1) active or stimulation electrode placed over the treatment area.
(2) depressive or non treatment electrode used to complete the circuit
and placed at distant location.
▪ The depressive electrode is larger than the active electrode.
▪ The high current density focuses the electrical current under the
smaller active electrode and little or no stimulation should occur
under the depressive electrode.
▪ This technique is usually used with motor, trigger or acupuncture
point stimulation.
61. Techniques of electrode application
Bipolar technique
▪ Use of the two electrodes of equal size.
▪ Both electrodes are placed over the treatment area.
▪ Because current densities under each electrode are equal, an
equal amount of stimulation should occur under each
electrode.
▪ The electrodes should be placed over motor points within the
same muscle or muscle group or may be placed at the origin
and insertion of the same muscle.
62. Techniques of electrode application
Quadripolar technique
▪ Use of two sets of electrodes, each originating from its own channel.
▪ It may be considered the concurrent application of two bipolar
circuits.
▪ This technique could be used in:
➢ Agonist and antagonist placements as in neuromuscular
stimulation.
➢ Crossed pattern placements as in interferential current stimulation.
➢ Coplanar placements for large flat area as the back.
➢ Parallel placements as in certain transcutaneous electrical nerve
stimulation.
