Transcript Pulse duration

What are low frequency currents?
Currents with frequency ranges from 50 to 100 Hz
Primary use is to stimulate nerves & muscles
Various currents in this category are used for
physiotherapeutic treatments
Commonly used are
Direct current
Faradic current
Faradic current: Short duration
Less than 10 msec
Stimulate denervated muscles
Repetition more (50-100 Hz)
Direct current: Long duration
More than 10 msec
Stimulate innervated muscles
Repetition rate shorter (30Hz)
Faradic Type Currents
•Short duration interrupted direct current with a pulse
duration of 0.02 to 1 ms and frequency of 50 – 70 Hz.
•The current is normally surged, ranging from 4 – 30
surges per minute with varying rest period.
•Faradic type and original faradic currents are muscle
stimulating currents acting directly on nerve fibres.
(used to stimulate the muscle with intact nerve supply)
Physiological effects
1. Stimulation of sensory nerves:
minimal; feels prickling sensation; causes vasodilatation of superficial
blood vessels > reddening under the active electrode.
2. Stimulation of motor nerves:
stimulation causes muscle contraction; surged to allow the muscle
relaxation > surge gradually increase and decrease > contraction similar
to voluntary contraction; changes taking place within the muscle is
similar to voluntary contraction =>↑ metabolism,
↑ O and food stuff up take, ↑ output of waste products => ↑ blood
supply to the muscle; muscle contraction and relaxation causes pumping
effect on veins and lymphatic vessels => ↑ venous and lymphatic return
3. No stimulation of denervated muscles
4. Ionic movement in intracellular and extracellular tissue fluids:
faradic alter the permeability of the cell membrane hence reduce the
swelling by accelerating the movement of tissue fluid. It also causes
arteriolar dilatation which removes all metabolites and waste products.
Indications
Facilitation of muscle contraction when inhibited by pain:
pain inhibits the transmission of impulses to the motor units at anterior horn cells and
stimulation ↓ inhibition & ↑ transmission of voluntary impulses and induce
relaxation to antagonists.
Re-education of muscle action:
restore the sense of movement if unable to contract a muscle voluntarily. Active
contraction should be attempted with stimulation
Training a new muscle action:
need after tendon transplant or other reconstruction of muscles which required to
perform different action; Active contraction should be attempted with stimulation
with concentrating on the movement
Neuropraxia of a motor nerve:
nerve is stimulated below the site of the lesion to contract the muscles.
Venous and lymphatic drainage:
pumping action of alternate contraction & relaxation of muscles & joint movements ↑
venous and lymphatic return
Reduce formation and loosening of adhesions:
adhesion formation by the effusion is prevented by the movements; stimulation contract
muscles if active exercise is impossible.
Contraindications
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Skin lesions
Infection
Inflammation
Thrombosis
Marked loss of skin sensation
Active TB or cancer
Cardiac pace makers
Unreliable patients
Superficial metals
A
Preparation of the apparatus
Operator should test the apparatus by attaching leads &
electrodes to the terminals holding the two electrodes in a
moistened hand
Current turned up until a mild prickling sensation is
experienced 7 a muscle contraction is produced
If the surging is automatic the duration & frequency of the
surge should also be tested
to
Preparation of the apparatus
The active electrode may be a disc electrode or a
small lint pad with a flat plate electrode
This is preferable for large muscle like
quadriceps & glutei
A flat plate electrode & lint pad are used for an
indifferent electrode to complete the circuit
Pad should contain at least eight layers of lint so
that they are thick enough to make good contact
with the tissue
They should be folded evenly with no creases &
soaked in warm 1% saline
Tap water can be used but in addition of salt
reduces the wetting solution
Electrodes should be 1cm smaller & to reduce
the danger of coming contacted with the skin
Corners of the electrode should be rounded
Because points may become bent & dig into the
pad
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Long duration I.D.C.
• Unidirectional currents with long durations, interrupted at
regular intervals are given directly to muscles aiming to
reduce, prevent or reverse the course of muscle atrophy. It
has the ability to regrowth and repair the nerve.
• Pulse duration: Specific pulse duration varying from 100 –
2000 ms. 1 -100 ms are taken as either long or short duration
pulses.
• Pause duration: It should be at least 2-3 times as long as that
of the pulse duration.
• Frequency: Generally from 5 – 10 Hz, depending on the pulse
duration.
• As muscle tissue is less excitable than the nerves greater
electric charge is needed.
Production of interrupted direct current
This is produced by modification in the form of interruption in direct
current where current is made to flow & seized at regular intervals
This production of IDC involves
1. Source of IDC
2. Transistor
3. Potential divider
4. Timer circuit
Which is needed to provide therapeutic D.C is a steady unidirectional
voltage
A means of regulating the voltage applied to the tissue via terminals
marked positive & negative & means of measuring current flow
The mains voltage is rectified & reduced & a potential divider is placed in
parallel with the patient
Moving the control can alter this divider
With potential divider at zero no voltage is applied so that no current will
flow
The milliameter in series with the patient will indicate zero current flow
Effects of electrical stimulation on
denervated muscles
Reduction of denervation atrophy:
early stimulation retard the denervation atrophy due to the contractions of muscles.
It normalise the rate of glycogen synthesis and enhance the role of carbohydrate
oxidation. It assists to protect the bone density and systemic functioning if the large
muscles are paralysed.
Utilisation of substances:
electrically produced contractions and relaxations of muscles use the substrates
that come to the area due to increased blood supply.
Increase venous and lymphatic return:
pumping effect increase the venous and lymphatic circulation. Otherwise
accumulation of tissue fluid in fascial planes and in and around muscles can cause
contractures in muscles and soft tissues.
Working hypertrophy:
in a partial damage of a nerve, some of the muscles supplied by the nerve escape
damage and get disuse atrophy but stimulation will produce working hypertrophy
of these muscles.
Selection of treatment for denervated muscles
Time:
Stimulation should start in early stage because maximal atrophy occurs in
the first 3 months.
Pulse duration:
Neuropraxia – 100 ms rectangular pulses
Axonotmesis – 100 -600 ms triangular or trapezoidal pulses
Axonotmesis and neurotmesis – 100 – 2000 ms triangular or saw tooth
pulses
Regeneration – do not use faradic type currents with maximal
contractions. Continue using long duration pulses.
Type of contraction and frequency of treatment:
20 -30 isometric contractions at least twice a day or 90 -200 contractions
daily.
Important to have a rest phase between contractions (1 -2 min.).
If 90 -200 contractions are used, there should be 1 -2 min. interval between
groups of 30 contractions.
Long time treatment should be given for about 1 -2 years until the patient get
voluntary contractions.
Contraindications
1. Gross oedema
2. Pain
3. Scar tissues and contractures
4. Skin lesions
5. Lack of pain sensation
6. Active TB or cancer
7. Over cardiac pacemakers
8. Thrombosis and thrombophlebiltis
9. Unreliable patients
10. Superficial metal
11. Infections
12. Transthoracic or neck currents
Dangers
Muscle damage: excessive stimulation can
damage the denervated muscle
Shocks
Burns
Method of application
– Monopolar technique (for small
muscles):
• Active electrode (cathode)
on the muscle belly slightly
distally. Inactive electrode
(anode) is kept away from
the muscle on the opposite
side of the part.
– Bipolar technique (for large
muscles):
• two electrodes on the either
end of the muscle belly,
cathode is generally placed
at the distal end.
Thank You..