Principles of Electrical
Currents
HuP 272
Electricity is an element of PT
modalities most frightening and least
understood.
Understanding the basis principles will later
aid you in establishing treatment protocols.
General Therapeutic Uses of
Electricity
 Controlling acute and chronic pain
 Edema reduction
 Muscle spasm reduction
 Reducing joint contractures
 Minimizing disuse/ atrophy
 Facilitating tissue healing
 Strengthening muscle
 Facilitating fracture healing
Contraindications of Electrotherapy
 Cardiac disability
 Pacemakers
 Pregnancy
 Menstruation (over abdomen, lumbar or
pelvic region)
 Cancerous lesions
 Site of infection
 Exposed metal implants
 Nerve Sensitivity
Terms of electricity
 Electrical current: the flow of energy between
two points
Needs
 A driving force (voltage)
 some material which will conduct the electricity
 Amper: unit of measurement, the amount of
current (amp)
 Conductors: Materials and tissues which allow
free flow of energy
Fundamentals of Electricity
Electricity is the force created by an
imbalance in the number of electrons at
two points
Negative pole an area of high electron
concentration (Cathode)
Positive pole and area of low electron
concentration (Anode)
Charge
An imbalance in energy. The charge of a
solution has significance when attempting
to “drive” medicinal drugs topically via
inotophoresis and in attempting to
artificially fires a denervated muscle
Charge: Factors to understand
Coulomb’s Law: Like charges repel,
unlike charges attract
Like charges repel
allow the drug to be “driven”
Reduce edema/blood
Charge: Factors
Membranes rest at a “resting potential”
which is an electrical balance of charges.
This balance must be disrupted to achieve
muscle firing
Muscle depolarization is difficult to achieve with
physical therapy modalities
Nerve depolarization occurs very easily with PT
modalities
Terms of electricity
Insulators: materials and tissues which
deter the passage of energy
Semiconductors: both insulators and
conductors. These materials will conduct
better in one direction than the other
Rate: How fast the energy travels. This
depends on two factors: the voltage (the
driving force) and the resistance.
Terms of electricity
Voltage: electromotive force or potential
difference between the two poles
Voltage: an electromotive force, a driving
force. Two modality classification are:
Hi Volt: greater than 100-150 V
Lo Volt: less than 100-150 V
Terms of electricity
Resistance: the opposition to flow of
current. Factors affecting resistance:
Material composition
Length (greater length yields greater
resistance)
Temperature (increased temperature, increase
resistance)
Clinical application of Electricity:
minimizing the resistance
 Reduce the skin-electrode resistance
Minimize air-electrode interface
Keep electrode clean of oils, etc.
Clean the skill on oils, etc.
 Use the shortest pathway for energy flow
 Use the largest electrode that will selectively
stimulate the target tissues
 If resistance increases, more voltage will be
needed to get the same current flow
Clinical application of Electricity:
Temperature
Relationship
An increase in temperature increases
resistance to current flow
Applicability
Preheating the tx area may increase the
comfort of the tx but also increases resistance
and need for higher output intensities
Clinical Application of Electricity:
Length of Circuit
Relationship:
Greater the cross-sectional area of a path the
less resistance to current flow
Application:
Nerves having a larger diameter are
depolarized before nerves having smaller
diameters
Clinical Application of Electricity:
Material of Circuit
 Not all of the body’s
tissues conduct
electrical current the
same
 Excitable Tissues
Nerves
Muscle fibers
blood cells
cell membranes
 Non-excitable tissues
Bone
Cartilage
Tendons
Ligaments
 Current prefers to
travel along excitable
tissues
Stimulation Parameter:
Amplitude: the intensity of the current,
the magnitude of the charge. The
amplitude is associated with the depth
of penetration.
The deeper the penetration the more muscle
fiber recruitment possible
remember the all or none response and the
Arndt-Schultz Principle
Simulation Parameter
Pulse duration: the length of time the
electrical flow is “on” also known as the
pulse width. It is the time of 1 cycle to
take place (will be both phases in a
biphasic current)
phase duration important factor in
determining which tissue stimulated: if too
short there will be no action potential
Stimulation Parameter:
Pulse rise time: the time to peak
intensity of the pulse (ramp)
rapid rising pulses cause nerve
depolarization
Slow rise: the nerve accommodates to
stimulus and a action potential is not elicited
Good for muscle reeducation with assisted
contraction - ramping (shock of current is
reduced)
Stimulation Parameters
 Pulse Frequency: (PPS=Hertz) How many
pulses occur in a unit of time
Do not assume the lower the frequency the longer the
pulse duration
Low Frequency: 1K Hz and below (MENS .1-1K Hz),
muscle stim units)
Medium frequency: 1K ot 100K Hz (Interferential,
Russian stim LVGS)
High Frequency: above 100K Hz (TENS, HVGS,
diathermies)
Stimulation Parameter:
Current types: alternating or Direct
Current (AC or DC)
AC indicates that the energy travels in a
positive and negative direction. The wave
form which occurs will be replicated on both
sides of the isoelectric line
DC indicated that the energy travels only in
the positive or on in the negative direction
DC
AC
Stimulation Parameter:
Waveforms; the path of the energy. May
be smooth (sine) spiked, square,,
continuous etc.
Method to direct current
Peaked - sharper
Sign - smoother
Stimulation Parameter:
Duty cycles: on-off time. May also be
called inter-pulse interval which is the
time between pulses. The more rest of
“off” time, the less muscle fatigue will
occur
1:1 Raito fatigues muscle rapidly
1:5 ratio less fatigue
1:7 no fatigue (passive muscle exercise)
Stimulation Parameter:
Average current (also called Root Mean
Square)
the “average” intensity
Factors effective the average current:
• pulse amplitude
• pulse duration
• waveform (DC has more net charge over time thus
causing a thermal effect. AC has a zero net charge
(ZNC). The DC may have long term adverse
physiological effects)
Stimulation Parameter:
Current Density
The amount of charge per unit area. This is
usually relative to the size of the electrode.
Density will be greater with a small electrode,
but also the small electrode offers more
resistance.
Capacitance:
The ability of tissue (or other material) to
store electricity. For a given current
intensity and pulse duration
The higher the capacitance the longer before a
response. Body tissues have different
capacitance. From least to most:
Nerve (will fire first, if healthy)
Muscle fiber
Muscle tissue
Capacitance:
Increase intensity (with decrease pulse
duration) is needed to stimulate tissues
with a higher capacitance.
Muscle membrane has 10x the
capacitance of nerve
Factors effecting the clinical
application of electricity
Factors effecting the clinical application of
electricity Rise Time: the time to peak
intensity
The onset of stimulation must be rapid
enough that tissue accommodation is
prevented
The lower the capacitance the less the
charge can be stored
If a stimulus is applied too slowly, it is
dispersed
Factors effecting the clinical
application of electricity
 An increase in the diameter of a nerve
decreased it’s capacitance and it will
respond more quickly. Thus, large nerves
will respond more quickly than small
nerves.
Denervated muscles will require a long rise
time to allow accommodation of sensory
nerves. Best source for denervated muscle
stimulation is continuous current DC
Factors effecting the clinical
application of electricity:
Ramp: A group of waveforms may be
ramped (surge function) which is an
increase of intensity over time.
The rise time is of the specific waveform and is
intrinsic to the machine.
Law of DuBois Reymond:
 The amplitude of the individual stimulus must
be high enough so that depolarization of the
membrane will occur.
 The rate of change of voltage must be
sufficiently rapid so that accommodation does
not occur
 The duration of the individual stimulus must
be long enough so that the time course of the
latent period (capacitance), action potential,
and recovery can take place
Muscle Contractions & Frequency
 Are described according to the pulse width
1 pps = twitch
10 pps = summation
25-30 pps = tetanus (most fibers will reach tetany by 50
pps)
 Frequency selection:
100Hz - pain relief
50-60 Hz = muscle contraction
1-50 Hz = increased circulation
The higher the frequency (Hz) the more quickly the
muscle will fatigue
Frequency selection:
100Hz - pain relief
50-60 Hz = muscle contraction
1-50 Hz = increased circulation
The higher the frequency (Hz) the more
quickly the muscle will fatigue
Electrodes used in clinical application
of current:
Electrodes used in clinical application of current:At least
two electrodes are required to complete the circuit
The body becomes the conductor
Monophasic application requires one negative electrode
and one positive electrode
The strongest stimulation is where the current exists the
body
Electrodes placed close together will give a superficial
stimulation and be of high density
Electrodes used in clinical application
of current:
Electrodes spaced far apart will penetrate more deeply
with less current density
Generally the larger the electrode the less density. If a
large “dispersive” pad is creating muscle contractions
there may be areas of high current concentration and
other areas relatively inactive, thus functionally reducing
the total size of the electrode
A multitude of placement techniques may be used to
create the clinical and physiological effects you desire
General E-Stim Parameters
Pain
Edema
Muscle Re-ed.
Tissue Healing
Hz: 100+
Tens, HVGS, IFC
Hz: 100-150
HVGS, IFC
Hz: 50-60
Type: depends on purpose
Hz: 100+ or 1(? inc. circ)
IFC, Ionto, Mens (?)
PPS: 70-100
Polarity: purpose & comfort
PPS: 120
Polarity: negative
PPS: 1-20
Polarity: purpose & comfort
PPS: vary but typically tens like
Polarity: purpose & comfort
Time: 20-60 min
Time: 20 min
Time: Fatigue (1-15 min)
Time: 20 min
Other:
Electrode Spacing
Burst Option, Voltage/Acc.
Accupoint (1-5pps)
Other:
Electrode Spacing
Voltage/Acc.
With muscle cxn or pain reduction
Other:
Electrode Spacing, surge
Burst Option, Voltage/Acc.
Accupoint (1-5pps)
Other:
Electrode Spacing
Voltage/Acc.
Accupoint
E-Stim for Pain Control: typical
Settings
Neuromuscular Stimulation
High Volt Pulsed Stim
Gate Control Theory
High-Volt Pulsed Stim
Opiate Release
High-Volt Pulsed Stim
Brief-Intense (Probe)
High-Volt Pulsed Stim
Intensity: Stong & comfortable
Intensity: Sensory
Intensity: Motor level
Intensity: Noxious
Type title here
Pulse Rate: <15
35-50 for tonic contraction
Pulse Rate: 60-100 pps
Pulse Rate 2-4 pps
Pulse Rate: 120pps
Polarity: + or -
Phase Duration < 100 usec
Phase Duration: 150-250 usec
Phase Duration: 300-1000 usec
Alternating Rate: Alternating
Mode: continuous
Mode: Continuous
Mode: 15-60 sec at each site
Electrode Placement
Biopolar: Distal & Proximal to muscle
Monopolar: Over motor points
Electrode Placement
Directly over motor points
Electrode Placement
Directly over motor points
Electrode Placement
Grid Tech: distal & proximal to site
High Volt Pulsed Stimulation
CURRENT CONCEPTS
EVIDENCE BASED
ES increased 20% verses control (no
activity) demonstrating that ES “can alter
the blood flow in muscle being stimulated”
Currier et all 1996
Currier et al 1988: Similar study but 15%
Bettany et al 1990: Edema formation in
frogs decreased with HVPC 10 minutes
after the trauma
CURRENT CONCEPTS
EVIDENCE BASED
 Walker et al 1988: HVS at a pulse rate of 30 Hz
and intensities to evoke 10% - 20% MVC did not
increase blood flow to the popliteal artery. The
exercise group demonstrated 30% increase
 Von Schroeder et al 1991: Femoral venous flow
shown to increase greatest with passive SLR
elevation, then CPM, active ankle dorsiflexion,
manual calf compression and passive
dorsiflexion
HVPS
 The application of monophasic current with a
known polarity
typically a twin-peaked waveform
duration of 5 - 260 msec
 Wide variety of uses:
muscle reeducation (requires 150V)
nerve stimulation (requires 150V)
edema reduction
pain control
Clinical Application:
 Physiological response
can be excitatory and
non-excitatory
 Excitatory
 Peripheral nerve
stimulation for pain
modulation (sensory,
motor and pain fibers)
 Promote circulation:
inhibits sympathetic
nervous system
activity, muscle
pumping and
endogenous
vasodilatation
 Non-Excitatory
(cellular level)
 Protein synthesis
 Mobilization of blood
proteins
 Bacteriocyte affects
(by increased CT
micro-circulation
there is a
reabsorption of the
interstitial fluids)
General Background
Early in history HVS was called EGS, then
HVGS, then HVPS
Current qualifications to be considered
HVS
Must have twin peak monophasic current
Must have 100 or 150 volts (up to 500 V)
HVPS
 Precautions
Stimulation may cause
unwanted tension on
muscle fibers
Muscle fatigue if
insufficient duty cycle
Improper electrodes
can burn or irritate
Intense stim may result
in muscle spasm or
soreness
 Contraindications
 Cardiac disability
 Pacemakers
 Pregnancy
 Menstruation
 Cancerous lesion
 Infection
 Metal implants
 Nerve sensitivity
 Indications
 past slide
Treatment Duration
General - 15-30 minutes repeated as
often as needed
Pain reduction - sensory 30 minutes with
30 minute rest between tx
Current Parameters
greater than 100-150 V
usually provides up to 500 V
high peak, low average current
strength duration curve = short pulse
duration required higher intensity for a
response
high peak intensities (watts) allow a
deeper penetration with less superficial
stimulation
Current Parameters
 Pulse Rate:
 ranges from 1-120 pps
 varies according to the
desire clinical
application Current
 Pulse Charge
 related to an excess or
deficiency of negatively
charged particles
 associated with the
beneficial or harmful
responses (thermal,
chemical, physical)
 Modulations
 intrapulse spacing
 duty cycle: reciprocal
mode usually 1:1 ratio
 ramped or surged
cycles
 Clinical Considerations:
 always reset intensity
after use (safety)
 electrode arrangements
may be mono or bipolar
 units usually have a
hand held probe for
local (point) stimulation
 most units have an
intensity balance control
Application Techniques
Monopolar: 2 unequal sized electrodes. Smaller is
generally over the treatment site and the large
serves as a dispersive pad, usually located proximal
to the treatment area
Bipolar: two electrodes of equal size, both are over
or near the treatment site
Water immersion - used for irregularly shaped areas
Probes: one hand-held active lead
 advantages: can locate and treat small triggers
 disadvantages: one on one treatment requires full
attention of the trainer
Electrodes
Material
carbon impregnated silicone electrodes are
recommended but will develop hot spots with
repeated use
you want conductive durable and flexible
material
tin with overlying sponge has a decreased
conformity and reduced conductivity
Electrodes
Size
based on size of target area
current density is important. The smaller the
electrode size the greater the density
Neuromuscular Stimulation
Roles:
re-educate a muscle how to contract after
immobilization (does not produce strength
augmentation but retards atrophy)
Parameter
Setting
Intensity
Strong, comfortable
Pulse
frequency
Polarity
Muscle cxn <15pps
Tonic cxn 35-50 pps
+ or -
Alternation
Yes
Pain Control
Roles:
Control acute or chronic pain both sensory (gate control 100-150 pps)) and motor level (opiate release - through
voltage)
Parameter
Intensity
Setting for Gate Control
Method
Sensory
Pulse
frequency
Phase
Duration
Mode
60-100 pps
Continuous
Placement
Directly over pain site
< 100sec
Pain Control - Opiate Release Setting
Parameter
Intensity
Phase
Duration
Pulse
frequency
Mode
Setting Opiate
Release
Motor Level 150V
150-250 msec
2-4pps
Continuous
Placement Directly over pain site
Evidence Based
Clinical Studies on HVPC and pain
modulation is misleading – pain
associated with muscle spasm is
decreased secondary to muscle
fatigue/exhaustion (Belanger, 2003)
Studies on muscle strengthening have
indicated no effect (Alon 1985, Mohr et al,
1985; Wong 1986)
Control and Reduction of Edema
Roles:
Sensory level used to limit acute edema
Motor-level stimulation used to reduce subacute or
chronic inflammation
Parameter
Setting Sensory Level Control
Intensity
Sensory
Pulse
frequency
Polarity
120 pps
Pulse
Duration
Mode
Maximum allowed by generator
-
Continuous
Motor-Level Edema Reduction
Cell Metabolism: increased and may increase blood flow
Wound Healing: May increase collagnase levels and
inhibit bacteria in infected wounds (for this effect 20 min
- polarity followed by 40 min + polarity recommended)
Parameter
Setting
Intensity
Strong, comfortable
Pulse
frequency
Polarity
Low 2-4 pps
Alternation
Yes
+ or -
Russian Current
Continuous sine-wave modulation of
2,5000 pps and burst-modulated for fixed
periods of 10 msec resulting in a
frequency of 50 bursts per second.
Thought to depolarize both sensory and
motor concomitantly (knots 1977). Thus
simulating muscle training.
No North American has been able to duplicate
Knots’ claims
T.E.N.S.
General Concepts:
 An Approach to pain control
Trancutaneous Electrical Nerve Stimulation:
Any stimulation in which a current is applied across
the skin to stimulate nerves
1965 Gate Control Theory created a great popularity
of TENS
TENS has 50-80% efficacy rate
TENS stimulates afferent sensory fibers to elicit
production of neurohumneral substances such as
endorphins, enkephalins and serotonin (i.e. gate
theory)
TENS
 Indications
Control Chronic Pain
Management postsurgical pain
Reduction of posttraumatic & acute pain
 Precautions
 Can mask underlying pain
 Burns or skin irritation
 prolonged use may result
in muscle
spasm/soreness
 caffeine intake may
reduce effectiveness
 Narcotics decrease
effectiveness
Research is variable regarding the benefits of TENS
Therapy (see Table 2-2; Belanger, 2001)
TENS may be:
high voltage
interferential
acuscope
low voltage AC stimulator
classical portable TENS unit
Biophysical Effects
 Primary use is to control pain through Gate
Control Theory
(between 0-100% can be placebo effect (Thorsteinsson
et al., 1978, Wall,1994)
 Opiate pain relief through stimulation of
naloxone (antagonist to endogenous opiates)
 May produce muscle contractions
 Various methods
High TENS (Activate A-delta fibers)
Low TENS (release of -endorphins from pituitary)
Brief-Intense TENS (noxious stimulation to active C
fibers)
Techniques of TENS application:
 Conventional or High Frequency
 Short Duration , high frequency and low to comfortable current
amplitude
 Only modulation that uses the Gate Control Theory (opiate all others)
 Acupuncture or Low Frequency
 Long pulse duration, Low frequency and low to comfortable current
amplitude
 Brief Intense
 Long pulse duration, high frequency, comfortable to tolerable amplitude
 Burst Mode
 Burst not individual pulses, modulated current amplitude
 Modulated
 Random electronic modulation of pulse duration, frequency and current
amplitude
Protocol for Various Methods of
TENS
Parameter
High TENS
Low TENS
Intensity
Sensory
Motor
Brief-Intense
TENS
Noxious
Pulse Fq
60-100 pps
2-4 pps
Variable
Pulse
Duration
Mode
60-100 sec 150-250 sec
Modulated
Tx Duration
As needed
Modulated
Burst
30 min
Onset of
Relief
< 10 min
20-40 min
300-1000sec
Modluated
<15 min
15-30 min
Conventional Tens/High Frequency
TENS
Paresthesia is created without motor
response
A Beta filers are stimulated to SG
enkephlin interneuron (pure gate theory)
Creates the fastest relief of all techniques
Applied 30 minutes to 24 hours
relief is short lives (45 sec 1/2 life)
May stop the pain-spasms cycle
Application of High TENS
Pulse rate: high 75-100 Hz (generally
80), constant
Pulse width: narrow, less than 300
mSec generally 60 microSec
Intensity: comfortable to tolerance
Set up:
2 to 4 electrodes, often will be placed on
post-op. Readjust parameters after
response has been established. Turn on
the intensity to a strong stimulation.
Increase the pulse width and ask if the
stimulation is getting wider (if
deeper=good, if stronger...use shorter
width)
Low Frequency/Acupuncture-like
TENS:
Level III pain relief, A delta fibers get Beta
endorphins
Longer lasting pain relief but slower to
start
Application
pulse rate low 1-5ppx (below 10)
Pulse width: 200-300 microSec
Intensity: strong you want rhythmical
contractions within the patient’s tolerance
Burst Mode TENS
Carrier frequency is at a certain rate with a built in
duty cycle
Similar to low frequency TENS
Carrier frequency of 70-100 Hz packaged in bursts
of about 7 bursts per second
Pulses within burst can vary
Burst frequency is 1-5 bursts per second
Strong contraction at lower frequencies
Combines efficacy of low rate TENS with the comfort
of conventional TENS
Burst Mode TENS - Application
Pulse width: high 100-200 microSec
Pulse rate: 70-100 pps modulated to 1-5
burst/sec
Intensity: strong but comfortable
treatment length: 20-60 minutes
Brief, Intense TENS: hyperstimulation analgesia
Stimulates C fibers for level II pain control (PAG etc.)
Similar to high frequency TENS
Highest rate (100 Hz), 200 mSec pulse width intensity to
a very strong but tolerable level
Treatment time is only 15 minutes, if no relief then treat
again after 2-3 minutes
Mono or biphasic current give a “bee sting” sensation
Utilize motor, trigger or acupuncture points.
Brief Intense TENS - Application
Pulse width: as high as possible
Pulse rate: depends on the type of
stimulator
Intensity: as high as tolerated
Duration: 15 minutes with conventional
TENS unit. Locus stimulator is advocated
for this treatment type, treatment time is
30 seconds per point.
Locus point stimulator
Locus (point) stimulators treatment occurs
once per day generally 8 points per
session
Auricular points are often utilized
Treat distal to proximal
Allow three treatment trails before efficacy
is determined
Use first then try other modalities
Modulated Stimulation:
Keeps tissues reactive so no
accommodation occurs
Simultaneous modulation of amplitude and
pulse width
As amplitude is decreased, pulse width is
automatically increased to deliver more
consistent energy per pulse
Rate can also be modulated
Electrode Placement:
May be over the painful sites,
dermatomes, myotomes, trigger points,
acupuncture points or spinal nerve roots.
May be crossed or uncrossed (horizontal
or vertical
Contraindications:
Demand pacemakers
over carotid sinuses
Pregnancy
Cerebral vascular disorders (stroke
patients)
Over the chest if patient has any cardiac
condition
Interferential Current - IFC
Interferential Current
 History: In 1950 Nemec used interference of electrical
currents to achieve therapeutic benefits. Further
research and refinements have led to the current IFC
available today
 Two AC are generated on separate channels (one channel
produces a constant high frequency sine wave (40005000Hz) and the other a variable sine wave
 The channels combine/interface to produce a frequency of 1100 Hz (medium frequency)
 Evidence Based: Although IFC has been used for 40
years, only a few clinical studies have been published
regarding use (DeDomenico, 1981,1987; Savage,
1984; Nikolova, 1987).
Effects of IFC treatment:
 Primary Physiological Effect: Capacity of IFC
to depolarize Sensory and motor nerve fibers
 Main Therapeutic Effects
Sensory nerve fibers - Pain reduction - receive a
lower amplitude stimulation than the area of tissue
affected by the vector, thus IFC is said to be more
comfortable than equal amplitudes delivered by
conventional means
Blood flow/edema management
Muscle fatigue - muscle spasm - is reduced when
using IFC versus HVS due to the asynchronous
firing of the motor units being stimulated
Positive effects of IFC include:
reduction of pain and muscle discomfort
following joint or muscle trauma
these effects can be obtained with the of
IFC and without associated muscle fatigue
which may predispose the athlete to
further injury.
Evidence Based Research
 Low frequency
 This has been claimed as the key to IFC (Savage, 1984,
Nikolova, 1987)
 Palmer, 1999: IFC unlikely to produce physiological and
therapeutic effects different from those achieved by
TENS
 Alon, 1999 states that IFC simply provides a more expensive,
different, least effective and somewhat redundant approach to
achieving the same effects as other electrical stimulation
parameters/waveforms
 Pain sensation: Although the physiological changes are
not different with IFC, Pain perception is decreased with
IFC (Palmer, 1999)
Evidence Based Literature:
 IFC does not lower skin impedance (Alon, 1999;
Gerleman et al, 1999)
 Any pulsed biphasic current, regardless of waveform, having a medium
frequency are capable of a deeper stimulating effect (Alon, 1999;
Hayes, 2000; Kloth, 1991;) Snyder-Mackler, et al 1989)
 Increased Circulation is an anecdotal claim and has not
been recreated in studies (Bersglien et al, 1988;
Indergand et al.k 1995; Johnson, 1999; Nusswbaum et
al., 1990: Olson et al., 1999)
 Analgesic Effect: Similar not superior to other
stimulations (TENS) (DeDomenico, 1982, 1987;
Nikolova, 1987; Savage, 1984)
 Stephenson et al., 1995: Superior to a control group with ice/pain
 Cramp et al., 2000: Failed to demonstrate any effective pain relief with
IFC
Principles of wave interference Combined Effects
Constructive, Destructive, & Continuous
Constructive interference: when two
sinusoidal waves that are exactly in phase
or one, two, three or more wavelengths
our of phase, the waves supplement each
other in constructive interference
+
=
Principles of wave interference Combined Effects
Destructive interference: when the two
waves are different by 1/2 a wavelength
(of any multiple) the result is cancellation
of both waves
+
=
Principles of wave interference Combined Effects
Continuous Interference
Two waves slightly out of phase collide and
form a single wave with progressively
increasing and decreasing amplitude
+
=
Amplitude-Modulated Beats:
Rate at which the resultant waveform
(from continuous interference) changes
When sine waves from two similar sources
have different frequencies are out of
phase and blend (heterodyne) to produce
the interference beating effect
IFC
 Duration of tx 15-20
minutes
Burst mode typically
applied 3x a week in 30
minute bouts
 Precautions
same as all electrical
currents
 Contraindications
Pain of central origin
Pain of unknown origin
 Indications
Acute pain
Chronic pain
Muscle spasm
IFC Techniques of treatment:
 Almost exclusively IFC is delivered using the
four-pad or quad-polar technique.
 Various electrode positioning techniques are
employed:
Electrodes (Nemectrody: vacuum electrodes):
 four independent pads allow specific placement of
pads to achieve desired effect an understanding of the
current interference is essential
 four electrodes in one applicator allows IFC treatment
to very small surface areas. The field vector is predetermined by the equipment
Quad-polar Technique
Pads placed at 45º angles from center of
tx area
Can reduce inaccuracy of appropriate
tissues by selecting rotation or scan
Channel B
Channel B
Channel A
Channel A
SCAN
Bipolar Electrode Placement
The mix of two channels occurs in
generator instead of tissues
Biopolar does not penetrate tissues as
deeply, but is more accurate
When effects are targeted for one muscle
or muscle group only one channel is used
Two-circuit IFC:
At other points along the time axes the wave
amplitude will be zero because the positive
phase from one circuit cancels the negative
phase from the second circuit (destructive
interference)
The rhythmical rise and fall of the amplitude
results in a beat frequency and is equal to
the number of times each second that the
current amplitude increases to its maximum
value and then decreases to its minimum
value
Special Modulations of IFC:
Constant beat frequencies (model): the
difference between the frequencies of the two
circuits is constant and the result is a constant
beat frequency. That is, if the difference in
frequency between the two circuits is 40 pps,
the beat frequency will be constant at 40 bps.
Special Modulations of IFC:
Variable beat mode: the frequency between the
two circuits varies within preselected ranges.
The time taken to vary the beat frequency
through any programmed range is usually fixed
by the device at about 15 sec. IFC machines
often allow the clinician to choose from a variety
of beat frequency programs.
Pain Control
Similar to TENS - beat frequency 100Hz
• Low beat frequencies when combined with motor
level intensities (2-10Hz) initiate the release of
opiates
• 30 Hz frequencies affects the widest range of
receptors
Parameter
Range
Intensity
Sensory
Electrode Config
Quadpolar
Beat Fq
High – Gate Control
Low – Opiate release
Long Duration
Sweep Fq
Neuromuscular Stimulation
Beat frequency of approximately 15 HZ
is used to reduce edema
General Parameters
Parameter
Range
Intensity
1-100mA
Carrier Fq
2500-5000Hz
Beat Fq
0-299 Hz
Sweep Fq
10-500sec
IFC Technique of treatment:
Electrode placement:
 The resultant vector should be visualized in placing
the electrodes for a treatment . The target tissue
should be identified and the vector positioned to hit
that area. Typically at 45º angles is most effective.
 Segregation of the pin tips is essential in the proper
electrode positioning for IFC. The electrodes may be
of the same size or two different sizes (causing a shift
in the intersecting vector). Treatment through a joint
has also been advocated without adequate research
to establish efficacy of the treatment technique.
Bone Stimulating Current:
Bone Stimulating Current:Bone Stimulating
Current:IFC has been used (Laabs et al)
studied the healing of a surgically induced
fracture in the forelegs of sheep. Their study
indicated an acceleration of healing in the
sheep treated with IFC as compared to the
control group
Bone Stimulating Current:
 This study validated an earlier study by Gittler
and Kleditzsch which showed similar results in
callus formation in rabbits. Several other
studies have shown an increase in the healing
rate of fractures but the exact mechanism by
which the healing occurs is not understood.
Bone Stimulating Current:
 Some speculation is that an increased blood
flow to the injured area is produced which
allowed natural healing processes to occur
more rapidly.
In one study (mandible fractures ) the IFC
caused very mild muscle contraction of the jaw
and this muscle activity was thought to have
been a potential accelerator of the healing.
MENS or LIDC
(low-intensity direct current)
MENS
No universally accepted definition or
protocol & has yet to be substantiated
This form of modality is at the sub-sensory
or very low sensory level
current less than 1000A (approx 1/1000 amp
of TENS)
Theorized that this is the current of injury
(Becker et al 1967, Becker & Seldon, 1987)
Biophysical Effects
Theory:
Currents below 500A increases the level of
ATP (high Amp decreases ATP levels)
Increase in ATP encourages amino acid
transport and increased protein synthesis
MENS reestablishes the body’s natural
electrical balance allowing metabolic energy for
healing without shocking the system (other
types of e-stim)
Studies conducted indicate no difference
from control group for wound healing
MENS
 Duration
 30 min to 2 hours up to 4x a
day
 Research suggests high degree
of variability on tx protocols
 Precautions
 Dehydrated patients
 on Scar tissue (too much
impedance)
 Contraindications
 Pain of unknown origin
 Osteomyelitis
 Inconclusive Data:
 DOMS as an indication
(Allen et al 1999, Weber et
al 1994)
 Indications
 Acute & Chronic Pain
 Acute & Chronic
Inflammation
 Edema reduction
 sprains & Strains
 Contusion
 TMJ dysfunction
 Neuropathies
 Superficial wound healing
 Carpal Tunnel Syndrome
Electrode Placement
 Electrodes should be placed in a like that
transects the target tissues
Remember that electrical current travels in path of least
resistance, thus it is not always a straight line.
TARGET
Either the + or – electrode can be placed on the injured
tissue (Research is inconclusive: Lampe 1998,
Sussmen et al 1999)
 Suggest alternating + and - electrode
Application Techniques
Standard electrical stimulation pads
generator may have bells & Whistles since
MENS is sub-sensory
Probe
Bone Stimulating Current:
 MENS
 Has been advocated in the healing of bone, using implanted
electrodes and delivering a DC current with the negative pole at
the fracture site. Further use of MENS has allowed increased
rate of fracture healing using surface electrodes in a noninvasive technique. Theories on the physiology behind the
healing focus on the electrical charge present in the normal
tissue as compared to the electrical charge found with the
injured tissue. MENS is said to allow an induction of an
electrical charge to return to he tissues to a better “healing”
environment
 Research on bone stimulating current is inconclusive.
Iontophoresis
Iontophoresis:
 Categorized as continuous direct electric current
 The transfer of ions across the skin
(transdermal)by use of continuous direct current
Iontophoresis is based on the principle that an
electrically charged electrode will repel a similarly
charged ion (first reported by LeDuc in 1903).
 This is pore dependant (Banga et al 1998)
Delivers a low-volt High-amp DC current
Local blood flow is increased for 1 hour post tx
Iontophoresis
 Duration of Tx:
 Based on intensity
desired usually every
other day for 3 weeks
 Indications
 Acute or Chronic Inflam
 Arthritis
 Myositis
 Myofacial Pain
Syndromes
 Invasive method for
delivering drugs
 Contraindications
 Hypersensitivity to
electrical currents
 Contraindications to
meds.
 Pain of unknown origin
 Precautions
 Prescription
 Dosage
 Do not reuse electrode
 Burns if intensity to
great
Iontophoresis
Effects of treatment depends on the ion(s) delivered
 musculoskeletal inflammatory conditions (tendonitis,
bursitis) have been successfully treated:
 Using desamethosone sodium phosphate (decadron)
and Xylocaine
 Reduction of edema has been achieved by driving
hyaluronidase
 Transitory (5min) local anesthesia has been produced
by delivering lidocaine to the tissues. The anesthesia
was better than that achieved by topical application
but less effective than infiltration of the area with
lidocaine.
Medication Dosage
Medication dose delivered during tx is
measured in mA based on relationship of
amperage, tx duration
Current Amp (mA) x Tx Duration - mA/min
Iontophoresors are dose-oriented - where
user indicated desired tx does and
generator calculated duration and intensity
Indications – evidence based
Condition
Ions
Benefit Reference
Yes
Kahn, 1982, Reidle et all
2000, Montorsi et all
2000, Rothfield et al
1967
Inflamm. Disorders Dex
Musc.
Yes
Bertolucci, 1982,
Delacerda, 1982Harris,
1982, Pellecchia et al
1994,
TMJ
Dex & dex/lido
Yes
Braun 1987; Reid et al
1994;Schiffman et al
1996
TMJ
Epicondylitis
Hydrocort/US
Dex
No
No
Kahn, 1980
Epicondylitis
Carpal tunnel
Edema
Na+ Salcycil.
Dex
Hualuronidase
Yes
Yes
Yes
Demiratas et al 1998
Plantar Faciitis
Dex/lido.
Panus et al 1996
Banta, 1994
Magistro 1964, Boone
1969
Iontophoresis: Evidence Based
Condition
Ions
Benefit Reference
Scar Tissue
Iodine
Yes
Tennenbaum, 1980
Tendon Adhesion
Iodine
Yes
Langley 1984
Subdeltoid Bursa
Magnesium
Yes
Weinstein et al 1958
Plantar warts
Heel Pain
Salicylate
Acetate
Yes
Yes
Gordon et al 1969
Myositis Oss.
Acetate
Yes
Weider, 1992
Myopathy
Postsurgical hip
pain
Calcium
Salicylate
?
Yes
Kahn, 1975
Japour et al, 1999
Garzione, 1978
Biophysical Effects
Dependant on Medication
See following chart
Sample Medications
Meds
Pathology
Dose
Polarity
Acetic Acid
Myositis
80mA/min
+
Dexamethasone Inflammation 41mA/min
& Lidocain & Pain control & 40 mA
-
Lidocain &
Epinphrine
Pain Control
30mA/min
+
Lidocain &
Epinphrine
Pain Control 20 mA/min
+
Dexamethasone Inflammation 41mA/min
-
Electrode Placement
Delivery Electrode (drug electrode)
placed over target tissue
Active electrode (dispersive electrode)
place 4-6 inches from drug electrode
Side Effects: Tissue “burning”
An alkaline reaction occurs under the
cathode (negative electrode) which is much
more caustic to the skin than the acidic
reaction occurring at the anode. The
cathode may be increased in size to attempt
to decrease this caustic reaction
Side Effects: Tissue “burning”
Continuous unidirectional current (as needed for
iontophoresis) tends to cause tissue irritation
because skin will not tolerate current density greater
than 1mA/sq.cm. Thin tissue areas, areas of skin
abrasion and areas of scarring are certain areas to
avoid. This potential for burn is exacerbated by the
fact that there is an anesthetic effect of DC under the
electrode. Thus tissue irritation may develop without
the patient’s realization
Don’t need to drive every day 1-2x a week