physiological and therapeutic uses of low frequency(f/g) currents
DESCRIPTION
education purposeTRANSCRIPT
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FARADIC AND GALVANIC
CURRENTSA.THANGAMANI RAMALINGAM
PT, MSc (PSY), MIAP
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HISTORY OF ES 420B.C-hippocrates-in torpaedo fish 46A.D-scribonius
largus-gout/headache 1700-luigi galvani & alessantro volta 1745-leyden jar for ES 1831-michael faraday 1850s-duchene-motor points(father
of ES) 1909-rheo/chron-louis 1916-SD curve-Adrian FES-1961-liberson 1962-HVPC-robert becker
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Types of electrical stimulatorsConstant current stimulator
Constant voltage stimulator
Less areamore currentburn
Less arealess currentsafety
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BLOCK DIAGRAM TO ILLUSTRATE ELECTRICAL PULSE GENERATORS.
Transformers Rectifiers Filters Regulators are used for pulse generation in circuits
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PHYSIOLOGICAL EFFECTS OF ELECTRICAL STIMULATION Cellular level Tissue level Segmental level Systemic level
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EFFECTS AT CELLULAR LEVEL Excitation of nerve cells Changes in cell membrane permeability Protein synthesis Stimulation of fibrobloast, osteoblast Modification of microcirculation
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EFFECTS AT TISSUE LEVEL Skeletal muscle contraction Smooth muscle contraction Tissue regeneration
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EFFECTS AT SEGMENTAL LEVEL Modification of joint mobility Muscle pumping action to change
circulation and lymphatic activity Alteration of the microvascular system
not associated with muscle pumping Increased movement of charged
proteins into the lymphatic channels
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EFFECTS AT SEGMENTAL LEVEL Transcutaneous electrical stimulation
cannot directly stimulate lymph smooth muscle, or the autonomic nervous system without also stimulating a motor nerve
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SYSTEMATIC EFFECTS Analgesic effects as endongenous pain
suppressors are released and act at different levels to control pain
Analgesic effects from the stimulation of certain neurotransmitters to control neural activity in the presence of pain stimuli
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Electro chemical effect2cl2 +H20 4HCl+O2 - under anode-
coagulation/sclerosis2Na +2H202NaoH +H2 -under cathode –
sclerolytic/haemorrhage Electro thermal effect- H α I2 R t Electro physiological effect –
RMPAPconduction
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THERAPEUTIC USES FOR ELECTRICAL STIMULATION Control acute & chronic pain Reduce edema Reduce & or inhibit muscle spasm Reduce joint contractures Minimize atrophy Facilitate tissue healing Facilitate muscle reeducation Facilitate fracture healing Strengthen muscle
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FARADIC VS GALVANIC
AC/DC Short duration
pulse <1sec or micro
sec
DC Long duration pulse >1sec elicits a muscle
contraction from de -nervated muscle, but the phase duration is so long that C fibers are also stimulated
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UNEVEN AC/ FARADIC Two phases PD: 1 ms No polarity
needed Surged Mild prickling
sensation
Freq:50 HzPD: 1 ms
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GALVANIC Faradic is high
frequency current(50-100Hz), where as galvanic is low frequency
single phase PD: >1 ms polarity needed
galvanic give stabing type of sensation
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TECHNIQUES OF APPLICATION/PRINCIPLES
OF APPLICATION
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TYPES OF ELECTRODES Metal electrode Rubber/silicon Water bath Adhesive Needle Probe electrode Pad electrode
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ELECTRODE PLACEMENT
Unipolar method Bipolar method
Stabile Labile
Nerve conduction method
Group stimulation method
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CURRENT DENSITY
Current Density- - Refers To The Volume Of Current In The Tissues
Highest At Surface And Diminishes In Deeper Tissue
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ALTERING CURRENT DENSITY
Change The Spacing Of ElectrodesMoving Further Apart Increases Current
Density In Deeper TissuesCurrent density for any electrode/skin contact
area should not exceed 2 mA rms/cm’
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SKIN RESISTENCE LOWERING washing the
surface to remove some of the keratin and sebum and leaving the skin wet.
Warming the skin
If the adhesion of the electrode to the skin surface alters, or the pressure of sponge or pad decreases, this can lead to a higher resistance
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PHYSIOLOGICAL EFFECTS Sensory nerves:
Marked prickling sensation longer duration
Motor nerves: Tetanizes, with a sequence of contraction followed by relaxation
NO chemical effects
Swelling: Absorption of exudate
Circulation: Superficial vasodilation via axon reflex (capillary vasodilation) hyperaemia
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THERAPEUTIC EFFECTS Give as a group activity Facilitate muscle contraction Re-educate muscle action Train new muscle action Exercise for paralyzed muscles Hypertrophy Increase strength Improve circulation Prevent and loosen adhesions
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ELECTROTHERAPEUTIC WINDOWS • Amplitude window
• Frequency window
• Acute window
• chronic window
• Energy based window
• Time based window
• Interval based
window
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THE ARNDT-SCHULZ RULE OR LAW
For every substance, small doses stimulate, moderate doses inhibit, large doses kill.
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VOLUNTARY CONTRACTION VS ELECTRICAL STIMULATION
Recruitment order small->large Fibre type slow->fast twitch Central fatigue Fatigue resistant motor
units first More force-more fatigue
Opp
Opp
Peripheral fatigue Opp
high/low-no difference
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Muscle Re-Education Muscular inhibition after surgery
or injury is primary indication Patient feels the muscle
contract, sees the muscle contract, and can attempt to duplicate this muscular response
Current intensity must be adequate for muscle contraction but comfortable
Pulse duration must be set as close as possible to the duration needed for chronaxie of the tissue to be stimulated
Pulses per second should be high enough to give a tetanic contraction (20 to 40 pps)
Interrupted or surged current must be used
High-voltage pulsed or medium-frequency alternating current may be most effective
On time should be 1 to 2 seconds
Off time should be 4 to 10 seconds
Total treatment time should be about 15 minutes, repeated several times daily
Next, patient should alternate voluntary muscle contractions with current-induced contractions
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Muscle Pump Contractions Used to duplicate the
regular muscle contractions that help stimulate circulation by pumping fluid and blood through venous and lymphatic channels back to the heart
Can help in reestablishing proper circulatory pattern while keeping injured part protected
Current intensity must be high enough to provide a strong, comfortable muscle contraction
Pulse duration should be set as close as possible to the duration needed for chronaxie of the motor nerve to be stimulated if not preset
Pulses per second should be at beginning of tetany range (20 pps).
Interrupted or surged current must be used
On time should be 5 to 10 seconds. Off time should be 5 to 10 seconds. The part to be treated should be
elevated Total treatment time should be 20 to
30 minutesrepeated two to five times daily
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Retardation of Atrophy Electrical stimulation reproduces
physical and chemical events associated with normal voluntary muscle contraction and helps to maintain normal muscle function
Current intensity should be as high as can be tolerated
Contraction should be capable of moving the limb through the antigravity range or of achieving 25% or more of the normal maximum voluntary isometric contraction (MVIC) torque for the muscle
Patient can be instructed to work with electrically induced contraction, but voluntary effort is not necessary
Total treatment time should be 15 to 20 minutes, or enough time to allow a minimum of 10 contractions
Treatment can be repeated two times daily
duration should be set as close as possible to the duration needed for chronaxie of the motor nerve to be stimulated
Pulses per second should be in the tetany range (20 to 85 pps)
Interrupted or surge type current should be used
Medium-frequency alternating current stimulator is the machine of choice
On time should be between 6 and 15 seconds
Off time should be at least one minute preferably two minutes.
Muscle should be given some resistance, either gravity or external resistance provided by the addition of weights or by fixing the joint so that the contraction becomes isometric
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Muscle Strengthening Current intensity should make
muscle develop 60% of torque developed in a maximum voluntary isometric contraction (MVIC)
Pulse duration should be set as close as possible to the duration needed for chronaxie of the motor nerve to be stimulated
Muscle is given an isometric contraction torque equal to or greater than 25% of the MVIC torque
Patient instructed to work with the electrically induced contraction, but voluntary effort is not necessary
Total treatment should mimick normal active resistive training protocols of 3 sets of 10 contractions
Pulses per second should be in the tetany range (20 –85 pps)
Surged or interrupted current with a gradual ramp to peak intensity most effective
On time should be 10-15 seconds
Off time should be 50 seconds to 2 minutes
Medium-frequency alternating current stimulator is machine of choice
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Increasing Range of Motion Electrically stimulating a muscle
contraction pulls joint through limited range
Continued contraction of muscle group over extended time appears to make contracted joint and muscle tissue modify and lengthen
Pulses per second should be at the beginning of the tetany range (20 to 30 pps)
Interrupted or surged current should be used
On time should be between 15 and 20 secs
Off time should be equal to or greater than on time, fatigue is a big consideration
High-voltage pulsed or medium-frequency alternating current stimulators are suggested
Current intensity must be of sufficient intensity and duration to make muscle contract strongly enough to move the body part through antigravity range
Pulse duration should be set as close as possible to the duration needed for chronaxie of the motor nerve to be stimulated
Stimulated muscle group should be antagonistic to joint contracture and patient should be positioned so joint will be moved to the limits of available range
Patient is passive in treatment and does not work with electrical contraction
Total treatment time should be 90 minutes daily broken into 3 x 30-minute treatments
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Reducing EdemaSensory level direct current used
as a driving force to make charged plasma protein ions in interstitial spaces move in the direction of oppositely charged electrode
Distal electrode should be negative
Treatment should begin immediately after injury
Thirty minute treatment showed good control of volume for 4 to 5 hours
High voltage pulsed generators are effective, low voltage generators are not effective
Current intensity should be (30V-50V) or 10% less than needed to produce a visible muscle contraction
Preset short duration interrupted DC currents with high pulse frequencies (120 pps) on high voltage equipment are effective
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Stimulating Denervated Muscle Purpose for electrically stimulating
denervated muscle is to help minimize the extent of atrophy while the nerve is regenerating
Degenerative changes progress until muscle is reinnervated by axons regenerating across site of lesion
If reinnervation does not occur within 2 years fibrous connective tissue replaces contractile elements and recovery of muscle function is not possible
Length of pulse should be as short as possible but long enough to elicit a contraction
Current waveform should have pulse duration = or > than chronaxie of denervated muscle
Amplitude of current along with pulse duration must be sufficient to stimulate a denervated muscle with a prolonged chronaxie while producing a moderately strong contraction of muscle fibers
Muscle fibers experience a decrease in size, diameter and weight of the individual muscle fibers
There is a decrease in amount of tension which can be generated and an increase in the time required for contraction
A current with an asymmetric, biphasic (faradic)waveform pulse duration < 1 ms may be used during the first 2 weeks
After 2 weeks, either an interrupted DC square wave or a progressive DC exponential wave with long pulse duration > 10 ms, or a AC sine wave with frequency < 10 Hz will produce a twitch contraction
Pause between stimuli should be 4 to 5 times longer (about 3-6 seconds) than stimulus duration to minimize fatigue
Either a monopolar or bipolar electrode setup can be used with small diameter active electrode placed over most electrically active point
Stimulation should begin immediately using 3 sets of 5 -20 repetitions 3 x per day
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Basic Model of Electrotherapy
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Denervated muscle stimulationES may disrupt regenerating NMJTrauma of the muscleTime consumingThree stimulation sessions/day three to five sets of 5-20 isometric
contractions5s –rest period/contraction 1m-rest period /set pW >than chronoxie
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Muscle Contractions 1 pps = twitch
10 pps = summation 25-30 pps = tetanus (most fibers will reach
tetany by 50 pps)
50-100 micro sec –sensory stimulation 200-300 micro sec –motor stimulation
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Frequency selection:100Hz - pain relief50-60 Hz = muscle contraction1-50 Hz = increased circulationThe higher the frequency (Hz) the more
quickly the muscle will fatigue1-4 Hz-beta endorphin40-100Hz-enkepalin,serotonin
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Electrocution and dangersElectric and earth shockELCB BF/CF areasGuidelines by Robertson et al(2001)AC is more dangerous than DC(P=V*I)
The strongest stimulation is where the current exits the body
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Unexpected effects of ESOver and above the normal physiological and
psychological limitsSkinEyesGeneral symptomsCardio-respNeurologicalAttitudemusculoskeletal
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Risk ManagementRisk grading-0,(1,2),3Safety& maintenance( quality assurance)InfectionAversionChildren (guidelines)
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ContraindicationOther Low Frequency (e.g. muscule stim, diadynamics etc)
Pregnancy (local) CI** SEE NOTE
Local Circulatory Insufficiency
PRECAUTION
Pregnancy (general) Epilepsy CI NECK
Malignancy LOCAL CI Devitalised Tissues PRECAUTION
Specialised Tissues
EYE,TESTIS
Active Epiphysis LOCAL CI
Active Implants (incl Pacemakers)
CI TESTS
Tissue Bleeding CI Thermal Skin
Test
Metal Implant Sharp/Blunt Skin Tests YES
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Polarity With Continuous DC CurrentImportant Consideration When Using Iontophoresis
Positive PoleAttracts - IonsAcidic ReactionHardening of TissuesDecreased Nerve Irritability
Negative Pole• Attracts + Ions• Alkaline Reaction• Softening of
Tissues• Increased Nerve
Irritability
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Motor points