MEDIUM FREQUENCY CURRENTS Interferential current

Historical Background  Intro. By dr. Nemec in Vienna in the early 1950’s  He wanted to overcome the problems of discomfort caused by low-frequency currents, while maintaining their claimed therapeutic effect  It disappeared until late 1960s and 1970s when work on pain mechanism by Melzak/wall showed that pain could be decreased by stimulating primary afferent neurons

DEFINITION  Transcutaneous application of two alternating medium frequency electrical currents used to produce low frequency therapeutic effects.

Interferential current

Why need of IF current  Faradic and sinusoidal(low frequency currents) —very high skin impedance  Medium frequency currents---- reduce skin impedance  Z=1/2ƒ π C

PRINCIPLE  The principle of IFT is to pass two Medium Frequency Alternating Currents which are slightly out of phase, through the tissues, where the currents intersect to produce a low frequency effect.  The superimposition of one alternating current on the other is called interference

Principles Of Wave Interference:  Combined Effects & Constructive interference:  Constructive interference:  when two sinusoidal waves that are exactly in phase or one, two or three wavelengths out of phase, the waves supplement each other in constructive interference

Destructive interference  when the two waves are different by 1/2 a wavelength (of any multiple) the result is cancellation of both waves

Continuous interference  Two waves slightly out of phase collide and form a single wave with progressively increasing and decreasing amplitude

Working  One of the alternating currents has a fixed frequency of 4,000 Hz  frequency of the other alternating current can be set between 4,000 and 4,250 Hz or less than 4000 (varying frequency).

Working  The frequency of the new medium-frequency alternating current can be calculated as follows:  Example:  f1 = 4,000Hz f2 = 4,150 Hz  f 1 - f2 = 4, ,150 = 150 Hz (AMF or treatment frequency, beat freq)  The AMF has a value of: AMF = Δ f = f1 – f2

Amplitude modulated frequency

 In interferential therapy the AMF (treatment frequency) corresponds to frequencies which are used in low-frequency electrotherapy.  The frequency with which the amplitude varies is referred to as the amplitude modulation frequency (AMF).

Current pathway pattern

Sweep Principle :  Rhythmical progression through full range of beat frequency  automatically vary the effective stimulation frequency using either pre-set or user set sweep ranges.  Such sweep prevents accommodation of nerves.

Sweep patterns

 If rhythmical range of Hz required, vary the freq of second circuit btw Hz over a period of 5-10 second.

Application Methods of applications are:  Static interference  Dynamic interference  Bipolar interference

Static Interference  It lies 45°angles to the perpendicular lines from each  This area of static interference gives an appearance of ‘clover leaf ’.  Here the area in which IFT is set up remains stationary

Dynamic Interference  The dynamic area of interference is also called as vector sweep, vector scan, rotating vector, etc.  It is obtained by varying the current intensity from 50 to 100%.  This is moving the area of interference current in a to and fro manner through 45°.

Bipolar Interference  IFT is generated inside the equipment and is delivered to the patient through 2 electrodes.  Here pre-modulated IFT are applied through 2 surface electrodes  Useful for smaller areas.

Physiological Effects This depends upon: 1) Magnitude of current 2) Type of mode used i.e. Rhythmic or constant 3) The frequency range used 4) Accuracy of electrode positioning

Physiological Effects Main clinical applications are : 1. Pain relief 2. Muscle stimulation 3. Increased local blood flow 4. Reduction of edema

Pain relief  Local pumping effect  Effect of autonomic nerves  vasodilation  100 Hz or Hz rhythmic  large diameter fiber  pain gait  stimulation of the descending pain suppression system at frequencies of Hz  or by blocking ‘c’ fiber transmission AT > 50 Hz

Muscle Stimulation  For patients who can not generate useful voluntary contraction, IFT may be beneficial.  1-100Hz commonly used  Partial & complete tetany…??  When employing IFT it is possible to continue to stimulate the muscle beyond its point of fatigue. Some machines employ a ‘surged’ mode to overcome this.  Most effective motor nerve stimulation range is between 10-25Hz

Effects of blood flow  Effects of blood flow is believed to be due to: 1) Effects of suction electrodes on tissue 2) Effects of muscle stimulation on circulation. 3) Deep tissue penetration stimulates parasympathetic nerve fibers for increased blood flow. Experimentation demonstrated vascular changes at 10-25Hz.

EDEMA  The use of suction electrodes may also be beneficial.  Local muscle contraction combined with its local vascular changes encourages the reabsorbtion of tissue fluid  1-10Hz rhytmic

Indications  Pain  Swelling  Motor stimulation  Stress incontinence

CONTRAINDICATIONS 1. Cardiac pacemaker 2. Advanced cardiac disease 3. Hypertension 4. Thrombosis 5. Hemorrhage 6. Pregnancy 7. Neoplasm 8. Tb 9. Fever 10. Infections 11. The eyes 12. Skin disorders 13. Epiphyseal region in children

PRECAUTIONS  Position suction electrode below the level of damage or discomfort.  Over anterior chest wall  Epileptic patients  Patients with febrile conditions  IFT apparatus must be at least 6 meters away from SWD machine

Placement of electrodes Position of electrodes on shoulders Position of electrodes on elbows

Position of electrodes on neck and lower back

Position of electrodes on knee

Types of Electrodes  Vacuum  Plate

Plate Electrodes  Attached to the patient by means of straps to assure a good contact and greater tolerance of treatment  Smaller electrodes are used for a localized effect, but this effect is more superficial  larger plates electrodes give more comfortable treatment and deeper effect  Made of conducting rubber which are comfortable and long lasting

Vacuum Electrodes  not indicated for treatment of the hairy areas because can’t get an airtight seal  excellent for treating flat smooth areas for example back or a plump knee  wet sponges are placed in the cups and moisten the edges of the cups for better adherence,  suction should not be constant because it can be uncomfortable and causes bruising  made from a vacuum unit plug into a rubber suction cup connected to a machine capable of producing a vacuum

Any question? The end