2022 Electrotherapy - Part 1

Principles of
Electrotherapy

In order to prepare for the module on principles of electrotherapy,
please read the corresponding chapter in Physical Agent Modalities:
Theory and Application for the Occupational Therapist, by Dr.
Alfred G. Bracciano.

Therapeutic Technologies for
Occupational Therapy: Learning

Objectives
• Identify the relationship between technical

terminology and sensory responses
• Discuss the available parameters of

electrical stimulation devices
• Describe the principles and concepts of

electricity
• Identify the physiological effects of

electrical stimulation

Upon completion of this module, the participant will be able to:
• identify the relationship between technical terminology and sensory
responses to electrical stimulation,
• discuss the available parameters of electrical stimulation devices,
• describe the principles and concepts of electricity,
• identify the physiological effects of electrical stimulation on the body.

Overview of Electrotherapy

• Electrotherapy has been used for
centuries dating back to the early
Romans.

• Luigi Galvani
• Snake charmers and charlatans
• Kratzenstein, Deluc, Seiler

The use of electric current to stimulate muscle contraction has a long and colorful
history dating back hundreds of centuries.
In 48 AD, Scribonius Largus, a Roman physician used torpedo fish, a unique fish
with electricity generating organs, to treat chronic headache and gout.
In the late 1700’s Luigi Galvani noted that a frog’s legs would jump, when
stimulated by static electric charges from lightening conducted through his copper
down spouts and railings.
Through the years there have been numerous claims of medical cures attributed to
electricity and its application to the body. Some of the claims made were
propagated by the charlatans and snake oil salesmen of the time. Others have had
a more thorough grounding in science and research.
The medical community viewed the use of electricity as a form of quackery.
Gynecologists, in the late 1800’s used electricity applied through needles as a
method to treat uterine fibroids.
Use and acceptance of electricity as a therapeutic medium has waxed and waned
as the scientific literature attempted to validate its use and application. As
research and science have grounded contemporary applications of electricity in
medicine and therapy, acceptance and use have accelerated.

• Kratzenstein, reported the use of electricity to treat a paralyzed limb.
• Seiler, used electricity to treat scoliosis patients, and
• Deluc pioneered the concept of ion transfer, or iontophoresis.

Pain

• Melzack and Wall’s
Gate Theory of pain

• Technological
advancements

• A tool in the
therapeutic toolbox.

Growth in the use of electrical stimulation accelerated in the mid-1960s as
Melzack and Wall developed their Gate Theory of pain.

Advances in technology also spurred development of smaller, stronger, more
portable units which gave greater therapeutic options for the clinician.

These compact units also allowed patients to use the equipment in their homes.

In order to understand the therapeutic application of electrical stimulation, the
therapist must have a basic knowledge of the terminology and principles of
electrotherapy.

Occupational therapists are often apprehensive about applying electrical current
to a person’s body and it is important that clinicians understand that when used
properly and appropriately, electrotherapeutic agents can be a safe and effective
tool in our therapeutic toolbox.

The evolution of electrotherapeutic devices has also contributed to confusion in
terms of accepted theories and applications, however. The therapeutic application
of electricity can facilitate function in physical disabilities.

Terminology

• Electrical muscle stimulation (EST) for
stimulation of denervated muscle

• Neuromuscular electrical stimulation (NMES)
for stimulation of innervated muscles

• Functional electrical stimulation (FES)
• Electrical stimulation for tissue repair (ESTR);
• Transcutaneous nerve stimulation (TENS).

The American Physical Therapy Association, in an attempt to standardize
terminology, published guidelines and has attempted to standardize the language
used to describe electrotherapy.

Terminology for specific applications is based in part on the therapeutic goals
identified for the patient. Frequently used applications of electrical stimulation
include:

• electrical muscle stimulation (EMS) for stimulation of denervated muscle;
• neuromuscular electrical stimulation (NMES) for stimulation of

innervated muscle;
• functional electrical stimulation (FES);
• electrical stimulation for tissue repair (ESTR); and
• transcutaneous electrical nerve stimulation (TENS).

Common terms used include: NMES, TENS, High Voltage Galvanic, and
Iontophoresis.

Neuromuscular Electrical
Stimulation (NMES):

• Pulsating AC current to
activate muscles

• Stimulation of intact
peripheral nerves.

• Stimulation of the nerve
causes a motor response

• Used to decrease muscle
spasm, for muscle
strengthening, and for its
effect on muscle pumping
which can reduce edema.

Neuromuscular electrical stimulation or NMES is the use of electrical stimulation
to activate muscles through the stimulation of intact peripheral nerves.

Stimulation of the nerve produces a motor response with subsequent movement of
the muscle and/or extremity.

Functional electrical stimulation or FES is a form of NMES and is the use of the
electrical current to cause a muscular contraction or movement which is a
substitute for an orthotic device or to assist in a functional activity such as grasp or
release.

NMES is often used to decrease muscle spasm, to increase muscle strength and for
its muscle pumping action which can reduce edema in an extremity.

Transcutaneous Electrical
Stimulation (TENS):

• TENS is a term used
to describe the wide
variety of stimulators
which are used for
pain control.

• TENS uses surface
electrodes with the
goal of sensory
analgesia rather than
a motor response.

Transcutaneous electrical stimulation or TENS, is a generic term that is used to
describe a class of stimulators which can be used for pain control.

The term TENS encompasses all forms of electrical stimulation, but clinically,
the term is used to describe pain control.

As with most other clinically applied electrotherapuetic modalities, TENS uses
surface electrodes to deliver the stimulation across the skin.

The therapeutic goal of TENS is to achieve sensory analgesia rather than a
motor response.

High Voltage Galvanic
Stimulation (HVGS)

• Electrical Stimulation for
Tissue Repair (ESTR):

• interrupted monophasic
wave form which is
greater than 100 volts.

• Treatment of

– chronic or acute edema and
pain

– facilitate wound healing
– decrease muscle spasm
– delay atrophy
– increase blood flow.

High voltage galvanic stimulation is also known as electrical stimulation for
tissue repair or ESTR.

High voltage galvanic stimulation refers to a class of stimulator that uses an
interrupted monophasic wave form which is most often greater than 100 volts.

There are a variety of uses for electrical stimulation for tissue repair including
• the treatment of chronic and acute edema, chronic and acute pain,
• to facilitate wound healing,
• decrease muscle spasm,
• delay muscle atrophy and
• to increase blood flow.

Iontophoresis:

• Iontophoresis: use of
low-voltage direct
current to ionize
topically applied
medication into the
tissue.

• Used in the treatment
of inflammatory
conditions or scar
formation and
management.

Iontophoresis is the transcutaneous delivery of ions into the body using a low
voltage direct galvanic current.

Iontophoresis has been used as an effective alternative to either oral or
parenteral (injected) methods of drug delivery.

Clinically, iontophoresis is most often used by occupational therapists to treat
inflammatory conditions such as tendinitis, and for modifying scar formation.

There are a variety of medications and chemical compounds which can be used
clinically for iontophoresis.

Principles of Electricity:

• Electric current is the movement of ions
or electrons, which are charged particles,
from one point to another in order to
equalize the charge.

• Current occurs when there is an
imbalance in the number of electrons in
two distinct locations and is measured in
amperes (amp).

Electricity is a form of energy which exhibits magnetic, chemical, mechanical,
and thermal effects.

Electric current occurs when there is an imbalance in the number of electrons in
two locations.

• Electrical current is the flow or movement of ions or electrons, which are
charged particles, from one point to another in order to equalize the
charge.

• Electrical current most often take the path of least resistance and flows
from an area of high electron concentration, the cathode, to an area which
has less concentration, the anode or “positive pole”.

There are three primary forms of electrical current which are used in clinical
application: direct current or DC, alternating current, or AC, and pulsatile or
pulsed current, PC.

Principles of Electricity:

• Amperes indicate the rate of electron flow
• Voltage is the potential or electromotive

force that drives the current and is
measured in volts, (V).

In the body, a closed circuit is created between the patient and electrical stimulator
by attaching leads of opposite polarity to the body.

In electrical stimulation, the electrons flow from the generator, through the
patient’s body, and back to the generator completing the circuit.

A complete circuit must be established for current flow to occur.

An uninterrupted circuit is known as a closed circuit in which a complete loop is
formed allowing the current to move to and from the source.

In the body, current flow is movement from the anode to the cathode.

Current flow continues as long as there is a difference in electron distribution
between the two poles, the anode or positive pole and the cathode, the negatively
charged pole.

This potential difference between the two poles is referred to as “voltage” and is
measured in “volts”. This potential difference produces an electromotive force
which drives the current flow.

The term “amperes” indicates the rate or “strength” of the electron flow. The
electrical current flow is related to the voltage of the current and the resistance that
it encounters.

Principles of Electricity:

Amperes indicate the rate of electron flow
•Voltage is the potential or electromotive
force that drives the current and is measured
in volts, (V).

Principles of Electricity:

• Opposition or resistance to current flow is
measured in ohms.

• Ohm’s law states that voltage (V) is
proportional to both current (I) and resistance
(R), such that V = I x R.

• The rate at which electrical current flows is the
“ampere” (amp)

Any substance which allows the movement of charged particles through it is
considered electrically conductive.

The human body is considered to be electrically conductive since it allows the
passage of charged particles through a variety of tissues and fluids.

Opposition to the flow of charged particles is known as resistance, and is
measured in ohms.

• Resistance is affected by the nature and structure of the material.
• Resistance increases as the cross-sectional area of a conductor decreases

and the length of the area increases.

Amperage describes the rate at which the electrical charge flows. The symbol for
current flow is “I”. Most of the frequently used electrical therapeutic agents have
current flow which is measured in milliamperes (mA), 1/1,000 of an ampere, or
microamperes (µA), 1/1,000,000 of an ampere.

Electron Flow/Water Flow Analogy

• ELECTRON FLOW • WATER FLOW

– Volt – Pump

– Amperes – Gallons

– Ohm (properties of – Resistance (length
conductor) and distance of
hose)

Electron flow can be compared to the flow of water through a hose.

The pump provides the electromotive force or voltage, forcing the water through
the hose.

The amount of water being forced through the hose is measured in gallons,
electrical flow is measured in amperes.

The resistance to the water flowing through the hose is based in part on the
diameter of the hose and the length of the hose.

• If the hose has a large diameter, the water will flow easily through it.
• As the diameter of the hose gets smaller and the length of the hose gets

longer, there is greater resistance to the water flow.

Extrapolating to electrical current, the resistance to the electrical current is
measured in Ohm’s, which indicates the properties of the conductor, in clinical
cases, the human body or specific tissue.

Electrotherapeutic Currents

• For clinical application, there are three specific
forms of electrical current used:
– direct current (DC)
– alternating current (AC)
– and pulsatile (pulsed) current

Electrical currents which are most frequently used therapeutically are direct (DC),
alternating (AC), and pulsatile (PC).

• Direct currents and alternating currents differ depending on the course of
flow.

• Pulsed currents are electrical current which has been modified in order to
produce a specific biophysical effect.

• Alternating or direct current describe the uninterrupted flow of electrons
between the two poles.

• Pulsed current indicates that the electron flow has been modified to be
periodically interrupted and may flow in either one direction,
unidirectional or bidirectional. The primary characteristic of pulsed
currents is that there are periods of no current flow.

Direct Current:

• DC current is unidirectional with the electrons
moving continuously in one direction with the
electrodes maintaining their polarity.

• DC flow is characterized by the square wave,
and can cause chemical reactions in the body
and facilitate the ionization of medication
through the skin.

Direct current has also been known as galvanic current and describes an
uninterrupted flow of charged particles in one direction, unidirectional.

The basic pattern of direct current flow is the square wave, characterized by the
current flowing continuously until the circuit is disconnected.

• Direct current is used in electrotherapy for iontophoresis, wound healing,
and stimulation of denervated muscle.

Use of direct current can cause chemical reactions in the body.
• Tissues with acidic reactions occur at the anode due to oxidation of the
anions, while alkaline reactions can occur at the cathode.

Direct current does not consist of singular phases or cycles. Direct current is
delivered continuously in one direction until it is turned off. Direct current has a
much greater accumulation of ions under the electrodes.

This effect can be either beneficial or detrimental and occurs with direct current
rather than with monphasic pulsed current or unbalanced biphasic pulsed current.

Alternating Current:

• AC current is characterized by period
changes in the direction of the
current flow.

• The current is uninterrupted and bi-
directional without any true positive
or negative pole.

Alternating current describes the continuous flow of charged particles in
alternating directions.
Current flow remains uninterrupted, but is bidirectional. Unlike direct current,
alternating current possesses no true positive or negative pole.
Charged particles change directions and the electrical fields alternate and
change polarity.

• Household electricity uses alternating current.
• Alternating current may be used for stimulating innervated muscle.
The basic pattern of an alternating current is the sine wave. Because the
electrodes are changing their polarity with the shift in the direction of the
current, there are minimal chemical effects to the tissue.

Alternating Current:

• Household electricity uses alternating current.
There are minimal chemical effects to the
tissue.

• Hertz (Hz) is the number of times that the
current reverses direction in one second
(cycles per second).

Hertz (Hz) is the term used to measure the number of times that the current
reverses direction in one second (cycles per second).
A current of 1 megahertz (MHz) would change the direction of the current one
million times per second.

Pulsatile Current:

• Pulsed current is the term used when
modification to the current occurs, when the
electron flow is periodically interrupted.

• These interrupted currents can flow in one
direction (monophasic) or two directions, bi-
directional (biphasic).

Pulsed or pulsatile current is the most common type of current used in
electrotherapeutic devices. It is not used, however for iontophoresis.
Pulsed current is used to describe modifications to the current, where the electron
flow is periodically interrupted.
Pulsed current can flow in a unidirectional (monophasic) or bi-directional
(biphasic) movement.
The current is interrupted for extremely short periods of time, measured in
milliseconds or microseconds.
This can be visualized as a strobe light, the output flashing so quickly as to be
almost imperceptible.

Pulsatile Current:

• In pulsed current, the current is interrupted for
very short periods of milliseconds or
microseconds.

• Most stimulators can be classified under one of
three wave forms: monophasic, biphasic, or
polyphasic.

The geometric or visual representation of an electrical current flow is known as the
waveform.
The geometric shape of the wave describes the amplitude and the pulse duration of
each stimulus.
The basic properties of the electrical current flow are the amplitude (or intensity),
and the duration (or length) of the current.
There are three classifications of wave form: monophasic, biphasic, and
polyphasic.

Monophasic:

• Monophasic wave forms have a single
phase to each pulse, with the current flow
being unidirectional, and either of negative
or positive polarity.

• A monophasic pulse has a pulse duration
averaging 40 to 60 milliseconds

Unidirectional and bidirectional current flow is represented graphically with the
current being either on one side only of the zero-current baseline or by alternating
above and below.
Current represented above the baseline is positively charged while the current
below the baseline is negatively charged. The direction of the current flow is
related to the phase of the electrical current for a finite period of time.
Monophasic pulses have only one phase to a single pulse, and the current flow is
unidirectional.

Pulse, phase, and waveform are synonymous terms used to describe monophasic
currents.

Types of current:

• 1) Direct.
• 2) Alternating.
• 3) Pulsatile.
• 4) Classifiers of

interrupted direct
current, one phase
of AC or one phase
of a pulse.

Biphasic:

• Biphasic currents

have two opposing
phases within a
single pulse
• Biphasic pulses may
be symmetrical or
asymmetrical with a
phase duration
between 25 and
250 milliseconds.

Biphasic currents have two opposing phases, each occurring on opposite sides of
the baseline. The lead phase of the pulse is represented above or below the
baseline and the final phase occurs in the opposite direction.

Biphasic pulses may be symmetrical or asymmetrical.
• If the waveform is symmetrical, the phase has the same shape for both
directions of current flow.
• Biphasic asymmetrical current has phases with different shapes for the
different directions of the flow.

A pulse is considered symmetrical because both phases are equal in their
magnitude and duration, each phase has an equal, but opposite, electrical balance.

• Symmetrical biphasic waveforms are more comfortable for the patient
because they deliver lower charges per phase.

Polyphasic:

• These waveforms consist of a burst of
three or more phases

– series of pulses delivered as a single charge.

• Inferential current or “Russian” current
• No known physiologic advantages to this

type of waveform.

Some manufacturers will describe their electrotherapy equipment as being
polyphasic. This current is also known as inferential current, or “Russian”
current.
There have been many claims as to the uniqueness of this type of current, though
there are no known physiologic advantages to this type of waveform.
These waveforms consist of a burst of three or more phases, they are a series of
pulses delivered as a single charge.

Waveforms

• Term waveform indicates a graphic
representation of the:

– shape
– direction
– amplitude
– duration
– pulse frequency

• of the electrical current produced by the device

There are a number of parameters used to deliver and modify the electric current.

The geometric representation of the electrical pulse or stimulus is referred to as
the waveform.

The waveform is the shape or visual representation of the current or voltage over
a finite period of time.

Waveforms have been described as sinusoidal, rectangular, and twin-spiked.

Waveform Shape

• Electrical currents may take on a:

– sinusoidal
– rectangular
– square
– spiked waveform configuration

• Alternating, direct and pulsed currents
may take on any of the waveform shapes

Waveforms

Waveforms

• Wave forms are classified as being :

– unidirectional or bi-directional
(monophasic or biphasic)

– and further divided into continuous DC
– or pulsed which is interrupted DC or AC.

Duration:

• In monophasic current, phase and pulse
duration are synonymous
– refer to the length of time between the
beginning and end of one phase of the
pulse.

• In biphasic currents, the pulse duration is
equal to the total of the two phase durations,
including the intrapulse interval.

Pulse duration is also known as width. Pulse duration is the length of time one
pulse lasts.
In biphasic pulsed current, the pulse consist of two phases.
The length of time that each phase lasts is called the phase duration.
There may be an interruption in current flow between these two phases of the
pulse which is known as the interphase interval.

Duration:

• As phase duration increases, comfort levels
decrease.

• Shorter pulse and duration result in better
conductivity of the current with less impedance
(Currier, 1993)

Phase duration is an important factor in determining which type of tissue will be
stimulated and the level of comfort of the stimulation to the patient.

• As phase duration increases, comfort levels decrease. There is a direct
effect on the degree of chemical changes which occur in the tissue
combined with the phase duration.

• As the phase duration increases, there is a concurrent increase in chemical
effects.

Shorter pulse and short phase durations result in better conductivity of the current
into the tissue with decreased impedance.

Parameters:

• Wide variety of stimulators to choose
from

• Poorly supported claims by both
manufacturers and clinicians.

• Anectodal evidence
• Research has been equivocal

Clinicians have a wide variety of stimulators to choose from with a variety of
poorly supported claims and anecdotal evidence offered by both manufacturers
and clinicians.

Research has been somewhat equivocal and the clinician must remain current
with the research and claims, critically evaluating the claims as well as the
outcomes of electrotherapeutic interventions.

Parameters:

• Commercial current flowing from wall
outlets produces an electromotive force of
either 115 or 220 V.

• Electrotherapeutic devices modify
voltages.

Electrical current can be modified or adjusted to achieve therapeutic effects.
• In a home or office in the United States, commercial current flowing from
wall outlets produces an electromotive force of either 115 or 220 V.

Electrotherapeutic devices modify voltages to achieve specific biophysiological
effects.

Parameters:

• low or high-voltage.
• Low-voltage units are those which function

between one to one hundred volts.
• High-voltage units have an output of up to

500 volts.

Some manufacturers classify stimulators according to their output.
Stimulators can be classified as low or high-voltage.

• Low-voltage units are those which function between one to one hundred
volts.

• High-voltage units have an output of up to 500 volts.

Pulse Amplitude

• Amplitude of each pulse reflects the
intensity of the current, the maximum
amplitude being the highest point of each
phase

• Higher the amplitude, the greater the peak
voltage or intensity

Amplitude is also known as intensity. Amplitude/intensity is the magnitude of the
electrical current and is measured in Amperes, milliAmperes, microAmperes, or
the magnitude of the voltage measured in volts, millivolts, or microvolts.

There are a variety of different amplitude measures. The one used most often in
clinical practice is the peak amplitude.

• Peak amplitude describes the maximum amplitude per phase, and total or
average current.

Total current is affected by the peak amplitude, pulse frequency, and pulse
duration. On some electrotherapy equipment, amplitude is often labeled
intensity.

Resistance

• Depth of electrical current penetration is
related to the peak amplitude.

• Higher voltage applied, the larger the current
that will be passed through the tissue.

Resistance is the property of a substance which opposes or resists the flow
of current. The greater the resistance or “impedance” in an electrical
circuit, the lower the rate of electrical flow.
The depth of electrical current penetration is related to the peak amplitude.
With biological tissue, the higher the voltage applied, the larger the current
that will be passed through the tissue.

Impedance

• Current flow proportional to voltage
• Current flow is inversely related to

resistance.
• Ohm’s Law: I=V/R

– I=current intensity in amperes
– V=potential difference in volts
– R=resistance in Ohms.

Current flow is directly proportional to voltage.
• If there is an increase in voltage combined with constant resistance,
current increases.

Current flow is also inversely related to resistance.
• If current increases but voltage is constant, current decreases.

This is represented by Ohm’s law which describes the relationship between
amperage, voltage, and resistance: I=V/R.

Voltage must be sufficient to overcome the resistance for the current to exist.

Ohm’s Law

• I=V/R or V=IR
• High skin impedance requires higher

voltage
• Ability of material to conduct

current=conductance.

Ohm’s law and resistance to current is an important clinical concept since high
skin impedance requires a higher voltage to allow the current to flow into the
tissue.
The ability of a material to conduct current rather than resist the current is known
as conductance.

• Conductance is considered the inverse of resistance.

Pulse Rate of Rise and Decay Times

• The rate of rise in amplitude (rise time)
refers to how quickly the pulse reaches its
maximum amplitude in each phase

• Rise time is the amount of time needed for
the amplitude to go from zero volts to peak.

• Rate of rise related to the amplitude

Rise time and decay times are associated with their pulse shapes.
The amount of time that is needed for the amplitude (wave form) to go from zero
volts to its peak is known as the rise time.
Nerve depolarization is directly related to the rate of the rise time.
The rate of rise time and nerve depolarization is directly related to the ability of
the amplitude to excite the nervous tissue.

Pulse Rate of Rise and Decay Times

• Decay time refers to the time in which a
pulse goes from peak amplitude to zero
volts.

• Rate of rise is important physiologically
due to the accommodation phenomenon

• in which a fiber that has been subjected to a
constant level of depolarization will become
unexcitable at the same intensity or amplitude

If the rise time is slow, nerve membranes can accommodate or adjust to the
voltage change and an action potential may not be reached.

Rise times occur very quickly and are measures in nanoseconds, which are one
billionth of a second.

The amount of time it takes for the peak amplitude to return back to zero volts
from its peak is known as the decay time.

The accommodation phenomenon occurs when a fiber subjected to a constant
level of depolarization becomes unexcitable at the same intensity or
amplitude.

Pulse Rate of Rise and Decay Times

• Rate of rise and decay times are generally
short durations ranging from:

• nanoseconds (billionths of a second)
• to milliseconds (thousandths of a second)

The patient’s nervous system will accommodate to the electrical stimulation after
about five minutes.
Because of this, the clinician will need to increase slightly the amplitude of the
electrotherapy in order to maintain the desired level of muscle contraction.

Frequency:

• The number of pulses or wave forms, repeated at
regular intervals is known as the pulse or stimulus
frequency.

• The pulse frequency consists of the number of
pulses or cycles per second which are delivered
to the body.

• The rate of successive electrical stimuli are
adjustable and may range from 1 to 120 stimuli
per second (Hz).

• Frequency may also be labeled as the pulse rate.

The rate or “frequency” of the pulses or waveforms is the number of pulses or
cycles which are delivered to the tissue per unit of time.

The frequency is expressed in pulses per second (pps) for pulsed current and in
cycles per second (cps) or hertz (Hz) for alternating current.

• Frequency is often described as being low (up to 1000 pps or Hz),
medium (1,000 to 10,000), or high (greater than 10,000).

• Most equipment used therapeutically uses low frequency.

There is an inverse relationship related to frequency and cycle duration. Because
there is no interruption in the current flow using alternating current, an increase
in the frequency causes a decrease in cycle duration and a decrease in frequency
causes an increase in cycle duration.

Skin impedance also limits current penetration.
• Impedance decreases as the pulse or cycle duration decreases, so that by
increasing the frequency of an alternating current or decreasing the pulse
duration of a pulsed current, you may increase current penetration.

Continue to Principles of Electrotherapy Part 2.