Electrical Stimulation

Prepared by: Floriza P. de Leon

Direct Vs Alternating Current

Direct Current Alternating Current

Flow of Electrons Unidirectional Changes periodically

Examples Galvanism and Iontophoresis

Low, medium, and high frequency modalities

Low Vs Medium Vs High Frequency Current

Low Medium High

Frequency 1-2000 Hz 3000-6000 Hz >500,000 Hz

Examples Sinusoidal and faradic currents

Interferential therapy, TENS

SWD, MWD, US

Skin resistance

High Little to none None

Skin Discomfort

Cause discomfort

w/ no discomfort

None

Effect Stimulate nerve

Block pain Thermal

Nerve Stimulation

yes yes No

Definition of Terms Frequency – number of cycles per second (Hz or pulse/sec); actual

frequency of stimulus train where pulses are produced at regular intervals

 Mean frequency value – used for non uniform stimulus trains where pulses are produced at irregular intervals, or for mixed frequency stimulation where more than one frequency is produced during a period of stimulation

 Amplitude – peak to peak amplitude of the cycle and is expressed in mAmp or volts; high voltage stimulators deliver peak outputs of around 150 V and low voltage stimulators of 100 V or less

 Pulse duration – aka pulse width; duration of the output pulse waveforms at 50% of the maximum amplitude (us)

 Charge density – amount of energy applied to the stimulated tissue per pulse; pulse duration x current

 Waveform – shape of a pulse  Galvanic current – continuous unidirectional current  nterrupted Direct Current (IDC) – when galvanic current is interrupted by

periods when no current is flowing

Definition of Terms  Alternating Current – often delivered at high

frequencies that lowers skin impedance and thus delivers more current to the motor nerves

 Interference-modulated current – current produced by the interference pattern produced in the tissues by two slightly different high frequency (4000 Hz) sine waves; known as interferential current

 Burst-Modulated alternating current – aka Russian stimulation; high frequency (2500 Hz) carrier current is interspersed with 10 ms periods when no current is flowing, producing 50 burst per second

 Symmetrical biphasic waveforms – when the shape and amplitude of the pulse is identical in both positive and negative directions

Definition of Terms  Sine wave – an example of symmetrical biphasic

waveforms  Asymmetrical biphasic waveform – shape and amplitude

of the pulse is not identical in positive and negative directions

 Duration of stimulation – time for which stimulation was applied (hours or mins)

 Duty cycle comprised of an “on time” reflecting duration of pulse delivery, and an “off time” – duration of quiescence

 Ramping – gradually increase the charge applied to the tissue and hence increase the intensity of mm contraction attained; achieved by a gradual increase in the amplitude or the pulse width of the pulse train; allows for accommodation of the nervous tissue-to-pulse delivery

The Importance of Stimulation Parameters Waveform

galvanic stimulation is only useful for stimulating denervated muscle whereas IDC, including faradic stimulation is able to stimulate innervated muscle

galvanic and IDC both create thermal and chemical reactions under the electrodes and are often painful and therefore should be used be caution

Amplitude when stimulating a mm at a constant frequency the only way to increase

force produced is to recruit more motor units by increasing the intensity (amplitude of the waveform) of stimulation

Pulse Duration most suitable pulse duration for motor stimulation of triceps was found to be

between 20 and 200 us, the most comfortable being 100 us pulse duration less than 100 us were suitable for sensory stimulation

Notes cutaneous stimulation of healthy mm selectively activates nerve endings and

not the mm fibers directly Slow rising pulses of long duration selectively stimulate denervated muscle,

as opposed to fast rising pulses of short duration that stimulate innervated mm

Basic Electrode System Used for Electrical Stimulation Malleable metal electrode such as triplate or aluminum

with pad of lint, cotton gauze or sponge material at the end Pad/gauze or sponge is wet with water before being applied to

the skin to provide a uniform ion-containing low resistance pathway for the current, the material keeps the water in place

May use ordinary tap water Electrodes kept in place with bandages, straps suction Thickness of pad depends on amount of water needed, this

depends on irregularity of the surface to be treated and degree of chemical reaction desired

If electrodes are unequal in size – smaller electrode is active and most effects will occur here; other electrode is the indifferent or dispersive electrode

May use button electrode for very small motor points

Basic Electrode System Used for Electrical Stimulation Electrodes that conform to the body surface

Made of carbon-impregnated silicon rubber May be used with sponge pads or coupled to skin with thin layer of

conducting gel Kept in place with strap or adhesive tape Carbon rubber and similar electrodes convenient for long term use

and repeated self-application by px Water pad conduction methods, whether metal or carbon rubber

electrodes, more appropriate for larger treatment areas with higher currents

Carbon rubber less efficient in passing current compared to the metal electrodes which have a lower impedance

Carbon rubber however, has lower impedance compared to available polymer electrodes

Note: if electrode is coupled to skin by a wet pad, current density is determined by the area of the pad, however, if it is applied in direct contact with the skin area is determined by the electrode

Basic Electrode System Used for Electrical Stimulation Water Bath

Used for hand, forearm, foot and leg which is placed between the electrodes

Provide a large area for the indifferent electrode and for applying muscle stimulating currents

Current density depends on location of electrodes  

Factors That Affect Current Flow Quantity of current flow and path to be followed depends on

impedance of the pathway Impedance includes: ohmic resistance; capacitive

resistance/reactance; inductive resistance (negligible in tissues) Ohmic resistance:

Determined by thickness and nature of skin under the electrodes primarily and

Inter-electrode distance secondarily High ohmic resistance: epidermis (highest), bone and fat Low ohmic resistance: watery tissue such as blood, mm and nerve

For slowly changing current and direct current, skin resistance is high so most electrical energy is released in the skin and subcutaneous tissues thus, cutaneous nerves are stimulated

Short pulse (phase) lengths penetrate skin more easily To stimulate deeply placed low-threshold nerves (motor nerves) – use shorter

pulse of about 1/20th of a millisecond (0.45/5 ms) because of skin capacitance To stimulate high threshold unmyelinated pain fibers (C fibers) in skin – use

longer pulses of a few milliseconds

Technique to Reduce Electrical Resistance at Skin Surface Wash surface to be treated to remove some of

the keratin and sebum and leave skin wet Warm skin which will increase rate of particle

and ionic movement Scrape surface of sandpaper surface – if small

currents will be used

Possible Areas of Abnormal Resistance Low resistance – cuts, abrasions (may be

protected with a thin layer of petroleum jelly and covered with cotton wool)

High resistance – warts, scars, grease/emollients

Arrangement of Electrodes Increasing the size of the electrodes will decrease current density Adding one or more parallel electrode will also decrease current

density For carbon-rubber electrodes may have slightly higher current

thru region where wire enters electrodes Use small electrode to give high localized current density applied

over motor point or acupuncture point; dispersive electrode placed close to it – the further away the dispersive electrode is placed the more current is needed and less effective localization will occur

For same sized electrodes current density under each will be similar thus sensory stimulation will occur in both areas – if electrodes placed close together effect will be localized to the region between electrodes and at adjacent edges; if electrodes are placed at either end of the long axis of the belly of a mm then the mm will be stimulated

Important Safety Precaution Turn the power switch on before connecting

patient to the circuit to prevent a spike in the output

Current density for any electrode/skin contact area should not exceed 2 mA ms/cm2

Unipolar Vs Bipolar Motor Point Stimulation

Unipolar Motor Point Stimulation

Bipolar Motor PointStimulation

Electrodes Used One small active electrode and one large dispersive electrode

Equal sized electrodes

Site of Stimulation Motor point for stronger response

Effect depends on placement

Description Same amount of current passes thru each electrode

Smaller sized electrode will have higher current density, thus effects here is stronger (active electrode)

Current density equal in both electrodes

Convenient for stimulating mm groups or very large mm

Equally small electrodes used for stimulating denervated mm

Ways in Which Electrical Current Can Cause Tissue Damage Direct or uniphasic currents cause

electrochemical damage called chemical burns

Currents with varying rates that stimulate mm or nerve may cause damage if an excessively strong or prolonged mm contraction is elicited; this is particularly dangerous if the heart mm is involved as this may stop circulation

Currents of sufficient intensity may cause heating leading to heat burns

Comparison of Electrical Excitability of Nerve and Muscle

Nerve Muscle

Resting Membrane Potential

-70 mV -90 mv

Accommodation Rate

higher Lower

Pulse Duration Used for Stimulation

Shorter pulse duration

Longer pulse duration

Intensity Need for Stimulation

Higher intensities (since pulse duration is short)

Lower intensities (since pulse duration is longer)

Laws Relevant to Neuromuscular Stimulation Law of Dubois-Reymond

Governs the nerve and mm response to external stimuli

States that the variation in current density rather than the absolute density acts as a stimulus to the nerve or mm

Intensity of the stimulus and resulting mm contraction are directly proportional to the magnitude and change in current strength

Intensity is proportional to rate of fluctuation In order to stimulate the excitable membrane

Amplitude must be high enough Rate of change of voltage must be sufficiently rapid Duration of stimulus application must be long enough

Laws Relevant to Neuromuscular Stimulation Erb’s Law

Normal polar formula of response is CCC>ACC>AOC>COC A continuous direct current can only produce contraction if the circuit is

opened (make) or closed (break); closing the circuit causes an increase in irritability at the cathode and a decrease irritability in the anode

If a direct current is applied, the surface of the membrane nearer the cathode becomes negative in relation to the opposite surface, while the surface of the membrane nearer the anode becomes more positive. The resting potential increases at the membrane nearer the anode while a decrease in potential differences occurs at the cathode. If the potential difference falls below, this increases the permeability to sodium ions and an impulse is not initiated

With the cathode as the stimulating electrode, less current is needed to produce a response than when the anode is used. In other words, the cathode closing contraction (CCC) is greater than the anode closing contraction (ACC) is greater than the anode opening contraction (AOC) is greater than the cathode opening contraction (COC)

A reversal of polarity occurs when an injured nerve have undergone degeneration. A greater amount of current is needed to produce a response and ACC>CCC>COC>AOC. This polar inversion has never been satisfactorily explained

 Stimulation of Innervated Vs Denervated Muscle

Innervated Denervated

Type of Contraction 1/sec- single brisk contraction20/sec – partial tetany60/sec- full tetany

Sluggish

Rate of Change of Current

Sudden increase in intensity

Gradual rise in intensity

Strength of Contraction Depends on number of motor units activated

Depends on number of mm fibers activated

Intensity higher Lower

Pulse duration Less 10 ms-short pulse duration

More than 10 ms – longer pulse duration

Pole used Either terminal Anode

Chronaxie < 1 ms > 50 ms

Ideal current Faradic or faradic type currents

IDC

Comparison Between Anode and Cathode

Anode Cathode

Charge Positive (+) Negative (-)

Ions attracted Anions

Polar Effects Acid reactiono Release of Cl ionso Repels metals and

alkaloids Anelectrotonus

(decrease in nerve irritability)

Alkaline Reactiono Release H ionso Repels acids and

radicals Catelectrotonus

(increase in nerve irritability)

Physiological effects Galvanic hyperemia Drying or hardening

effect (unequal electrode size –active)

sedative

galvanic hyperemia softening (active

electrode is of unequal size)

stimulative

Type of mm contraction Slow, sluggish twitch Brisk twitch

Intensity low Higher

Duration 15-30 mins 10-20 mins

Frequency of treatment Alternate days, may be daily

Alternate days

Summary of Contraindications to Electrical Stimulation strong muscle contraction that might cause joint or

mm damage; detachment of thrombus, spread of infection and hemorrhage

stimulation of autonomic nerves which may alter the cardiac rhythm or other autonomic effects

the current might be localized (concentrating its effect) over open wounds or skin lesions such as eczema

neoplasm and tuberculous infection – electrical stimulation may provoke undesirable metabolic effects

if current is not evenly biphasic skin damage and irritation may occur especially if the treatment site is anesthetic

Therapeutic Direct Current

Therapeutic Direct Current Direct cuurent refers to a current that passes

for more than one second continuously in the direction (unidirectional current)

Also called constant current or galvanism or galvanic current

Available units medium frequency D.C. type current with pulse duration of 125 us and intervals of 5 us giving a duty cycle of 96%

Transmission Current is transmitted to the site of stimulation through a

metal electrode (conductor) that has a wet pad at the end The effect is a chemical change at the electrode-tissue

junction (changes of electrolysis) Nature of the change depends on the available electrolytes

at this junction In general, acids form at the positive electrode (anode), while

bases form at the negative electrode (cathode) Follows Ohm’s Law: current in any circuit is directly

proportional to the voltage and inversely to the resistance; thus, the intensity to be used also depends on the resistance encountered

Resistance here is from the epidermis – the larger the cross-sectional area the lesser the resistance

 

Others Chemical burns are more likely to occur at

the cathode The extent of the chemical change

depends on the Current intensity per unit area or current density Duration of time that the current is flowing

Iontophoresis

Iontophoresis Movement of ions across a biological

membrane by means of an electric current (direct current is used)

A drug in ionic form is applied at the end of the electrode which will move to either the cathode or anode depending on whether it is an acid or base; the drug can therefore be introduced into the tissue

The amount of drug introduced depends on the current density and duration of treatment – thus, dosage is expressed in terms of total current in mA multiplied by time in minutes

Current density is limited by the skin tolerance

Prescription Current density = 0.1-0.5 mA/cm2, others

recommend 0.1-0.3 mA/cm2

Duration = 10-30 mins Recommended concentration of the ions in

the solution used is 1-2%  

Physiological Effects/Therapeutic Use Direct current

Sensory changes Mild tingling or pricking sensation which may merge into a mild irritation or itching

sensation Localized erythema (will prolonged stimulation), more marked in cathode

Capillary hyperemia (not arteriolar dilatation) Electrotonus – depolarization at cathode and hyperpolarization at

anode Relief of pain Acceleration of heating Tissue destruction – at higher current densities

Iontophoresis Local anesthesia Relief of idiopathic hyperhidrosis (this is probably the most common

purpose for doing iontophoresis at present) Application of drugs such as antibiotics and anti-inflammatory drugs;

use of vinca alkaloids has been used in iontophoresis to relieve neurogenic pain

Contraindications for Ion Transfer Anesthetic skin in area to be treated Recent scars in treatment site Metal embedded close to skin of treatment

site Acute injury if active bleeding is still present Patients with cardiac pacemaker  

Transcutaneous Nerve Stimulation

Definition of Terms Carry-over: refers to the period after removal of TENS

where the px remains pain-free – TENS units with a short carry-over by mechanism of action may clinically increase the length of the pain-free period after TENS treatment by breaking into the pain-muscle spasm cycle or reduce muscle guarding

Adaptation: a physiologic phenomenon which clinically presents as a patient who no longer experiences the same amount of relief with the same “dosage” of the TENS thus, the amplitude or pulse width has to be increased to get the same effect

Parameter ranges: refers to the stimulus strength used expressed as the pulse width, pulse rate and amplitude

Electrode Placement of TENS Four approaches to be considered

Usual practice is to apply the electrodes close where the pain is felt

Within dermatome, sclerotome, or myotome where pain is felt, placed to pass current through the long axis of the dermatome

Over trigger or acupuncture points, located by their lower resistance compared with surrounding skin (due to active sweat glands and/or local vasodilation)

Over peripheral nerve, placed in the line of the nerve where it is superficial, this method is primarily used in the treatment of neurogenic pain such as post-herpetic neuralgia

Ultimately technique used is which ever is most effective

 

Prescription Most often given as short pulses of about 0.05

ms at 50-100 Hz – referred to as Conventional TENS – is a high frequency, low intensity stimulation

Intensity turned up gradually until prickling or tingling sensation is felt; intensity should not cause pain nor stimulate a muscle contraction

Recommended duration and timing: 30-60 min; session o.d. or b.i.d to continuous TENS for minimum of eight hours up to 24 hours

TENS: Hyperstimulation

Description A form of neuromodulation that uses noxious input to control pain A painful stimulus is used to inhibits pain Parameter ranges: pulse width = 250 us to 10 ms

Pulse rate = 1-4 pps Amplitude = to point where px can tolerate the noxious stimulus

To further increase the current density a small diameter point-probe active electrode is used, since the surface area of the electrode is small compared to the unit output, the current density is high

Hyperstimulation analgesia may also be produced by other techniques such as dry needling, acupuncture, intense cold or heat, mechanical pressure or chemical irritation of the skin – thus, technique use may be Non invasive (surface) stimulation or Invasive stimulation

These TENS units have Stimulation mode combined with

These TENS units have Stimulation mode combined with Skin resistance or “point locating” modes

The point where the noxious input is to be made is identified by putting the unit on the “point locating” mode first, the point is identified through the meter reading or an audible signal, once this is located the unit is now stretched The point where the noxious input is to be made is identified by putting the unit on the “point locating” mode first, the point is identified through the meter reading or an audible signal, once this is located the unit is now stretched to the stimulation mode for the noxious input which is transmitted through an electric current

 

Purpose and Effect Relief pain through the brainstem which will in

turn inhibit pain at the spinal level Noxious stimuli excite small pain fiber – this

activates the brainstem reticular formation – info from reticular formation excites the midbrain periaqueductal gray area which has a high concentration of opiod peptides – descending antinociceptive pathway is activated – pain signals at spinal cord is inhibited

Advantages Fast-onset analgesia Areas that are difficult to reach by large electrodes

such as the face, scalp, ear and bony prominence can easily be treated with the small, active point electrode

  Disadvantage: unpleasant noxious stimulation

may not be tolerated by px Indications: acute or chronic pain Contraindications: same as conventional TENS  

Interferential Stimulation

Interferential Stimulation Produced by passing two medium frequency alternating currents which

are slightly out phase through the tissues; where two currents intersect a new current is set up

As mentioned earlier this is done to allow nerve stimulation because of the amplitude modulation (a single medium frequency current will not effectively stimulate nerves the way a low frequency current can

Secondly, being a medium frequency current it passes through the skin unlike low frequency currents that encounter skin resistance

Is therefore, a method of producing low frequency alternating currents selectively at any tissue depth without the problem of skin resistance

Principle: two medium frequency alternating currents which are slightly out of phase are applied simultaneously through the tissues. A new current is set up where the two currents intersect (interferential current). In the area where the two currents are heterodyned, the intensity of the combined currents will increase and decrease rhythmically. This is the interference effect. The combined current has a BEAT FREQUENCY which is the difference between the two medium frequencies

Interferential Stimulation When two peaks of amplitude which are of the same direction

coincide, the resultant amplitude is at a maximum; when they are in the opposite direction they cancel each other

The beat frequency is also called the AMPLITUDE MODULATED FREQUENCY (AMF). It is a modulated alternating current with a surge speed which is varied at will. The intensity of the beat current is the sum of the two currents

The beat frequency may be constant or rhythmic/variable. Rhythmic means that the frequency swings continuously changing from a lower to a higher value

The interferential current generators will have two circuits of different frequencies: One circuit has a fixed frequency of 4000 Hz (this will provide a pulse duration

of 125 us which is appropriate for sensory and motor nerve stimulator) Second circuit has varied frequency of 4001 to 4100 Hz (the higher

frequencies will encounter less skin impedance and are therefore more comfortable) Resultant beat frequency ranges from 1-100 beats per second

The second circuit may be set at a fixed or a variably changing frequency

Physiologic Effects Depress action of the sensory nervous system Stimulates large diameter sensory nerve

fibers Stimulates motor nerves Increases vasodilatation Alter the cell membrane permeability  

Purpose/Effects At 50 beats/sec and low amplitude – relief of

pain by stimulating large afferent neurons and interfering with ascending (lemniscal) transmission of pain impulses

At 0-5 beats/sec and an intensity sufficient to cause a mm contraction – relief of pain by stimulating endogenous opiod production or interfering with ascending (extralemniscal) transmission of pain impulses

At 0-10 beats/se – stimulates innervated mm At 30-50 beats/sec – tetanic contraction of

innervated mm; but not effective for mm strengthening

 

Indications: Relief of pain Stimulate mm contraction in an innervated

mm to increase blood flow, cause relaxation and relieve urinary stress incontinence

  Contraindications and Precautions: same

as unipolar technique  

High Voltage Pulsed Galvanic Stimulation

High Voltage Pulsed Galvanic Stimulation Has an electromotive force of up to 500 volts (low

voltage units do not exceed 150 volts) Bypass the impedance of skin allowing use of lower

current amplitudes   Description Waveform (pulse) consists of paired, unidirectional

impulses that rise rapidly and decay exponentially Phase duration at base of each member of a pair of

50-100 us Phase duration not sufficient to stimulate denervated

mm and to perform iontophoresis

Purpose/Effects relief of pain reduced mm guarding promote tissue healing improve blood flow and decrease edema

through intermittent mm contraction delay disuses atrophy and mm re education

through mm stimulation   Contraindications and Precautions:

same as for other modes of ES