Shortwave Diathermy
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DIATHERMY What is DIATHERMY? • The use of non-ionizing electromagnetic energy from the radio-frequency spectrum as therapeutic agent Types of Diathermy Long wave - longest wavelength 300 – 30 m - most penetrating - no longer utilized due to high potential of causing burns and interference with radio transmissions Shortwave Microwave SHORTWAVE DIATHERMY Superficial and Method of Heat deep heating Transfer modality - Conversion Frequency Manner of Delivery - 27.12 MHz - continuous Wavelength - pulsed - 11 m Continuous vs Pulsed SWD PULSED SWD Pulse Repetition Rate (PRR) - 15 to 800 Hz Pulse Duration (PD) - 25 to 400 microseconds Peak Pulse Power (PPP) - 100 to 1000 watts Duration - 20 minutes (5-15 acute; 10-20 chronic) Calculating Mean Power in PSWD 1. Cycle Duration = 1000 / PRR 2. % cycle SWD delivered = (PD x 100) / Cycle Duration 3. Mean Power delivered = PPP x % cycle SWD SHORTWAVE DIATHERMY UNIT HEAT PRODUCTION • Dependent on: SPECIFIC ABSORPTION RATE Tissue conductivity charged molecules dipolar molecules non-polar molecules Electrical field magnitude Charged Molecules Ions and certain proteins Molecules are accelerated along + - lines of electric force + - + - Most efficient way of + - heat production Dipolar Molecules Water and some proteins Positive pole of the molecule aligns itself to the negative pole of the electric field (vice versa) Moderately efficient heat production Non-Polar Molecules • Fat cells • Electron cloud is distorted but negligible heat is produced • Least efficient heat production Clinical Implication ! • Blood, having high ionic content, is a good conductor vascular tissues as well • Metal and sweat are good conductors if metal implants and sweat are present within the electric field, may cause burn SHORTWAVE DIATHERMY Condenser Induction Field Field CONDENSER FIELD • Patient’s tissues are used as DIELECTRIC between the conducting electrodes • Oscillation and rotation of the molecules of the tissues produces heat • Either flexible metal plates (malleable) or rigid metal discs can be used as electrodes • Can be applied in 3 ways: contraplanar, coplanar, or longitudinal Ways of Application Contraplanar - aka Transverse positioning - plates are on either side of the limb Ways of Application Coplanar - plates parallel with the longitudinal section of the body part; same side Ways of Application Longitudinal - plates are placed at each end of the limb In what way should SWD be applied? • No conclusive evidence as to the technique of application that will produce the most effect on the heated tissue (Kitchen and Bazin, 1996) GUIDELINES ! Electrodes should be: Equal in size Slightly larger than the area treated Equidistant and at right angles to the skin surface INDUCTION FIELD • Patient is in the electromagnetic field or the electric circuit produce strong magnetic field induce electrical currents within the body (EDDY currents) • Utilizes either an insulated cable or an inductive coil applicator Arrangement of Inductive Coil Monode: coil arranged in one plane Hinged Diplode: permits electrode to be positioned at various angles around the three sides of the body part, or in one plane Which is more effective: condenser or induction field? Some studies argue that inductive diathermy produces greater increase in temperature of deeper tissues compared to condenser/capacitive technique Any deep effects following capacitive technique requires considerable increase in superficial tissue temperature THERAPEUTIC EFFECTS (continuous and pulsed) Increase blood flow Assist in resolution of inflammation Increase extensibility of deep collagen tissue Decrease joint stiffness Relieve deep muscle pain and spasm INDICATIONS Soft tissue healing - conflicting evidence as regards effectiveness of SWD - controlled animal studies revealed insignificant results as well as trials involving human subjects (Kitchen and Bazin, 1996); to date, no studies in the treatment setting was conducted INDICATIONS • Recent ankle injuries - inconclusive results following three double-blind protocols (Kitchen and Bazin) INDICATIONS A. Nerve Regeneration Pain Syndromes - studies were done on cats - Pulsed SWD may and rats provide better - PSWD induced regeneration of axons, pain relief in some acceleration and recovery of musculoskeletal nerve conduction conditions (neck B. Osteoarthritis and back) than - no established effect SWD C. Post-operative - insignificant (abdominal MICROWAVE DIATHERMY Superficial and deep heating Frequency: 300 MHz to 300 GHz Wavelength: 1m to 1mm Therapeutic Parameters: A. 122.5 mm – 2456 MHz B. 327 mm – 915 MHz C. 690 mm – 433.9 MHz Dosage: acute 5 to 15 minutes chronic 10 to 20 minutes MICROWAVE DIATHERMY APPARATUS How is microwave produced? Direct current (DC) is shunted to the cathode in the magnetron valve Release of electrons from the cathode to the multi-cavity anode valve Electrons oscillate at predetermined frequency High frequency alternating current is transmitted along a coaxial cable Coaxial cable transmits energy to a director Fate of Microwave Absorbed - energy is taken up by the material Transmitted - pass through the material without being absorbed Refracted - direction of propagation is altered Reflected - turned back from the surface THERAPEUTIC EFFECTS • Increased blood flow or circulation to the area • Increased tissue temperature • Increased metabolism • Facilitate relaxation • Increased pain threshold • Decreased blood viscosity INDICATIONS • Soft tissue injury • Mobilization • Pain relief CONTRAINDICATIONS • Pacemakers • Malignant CA • Metal implants • Active TB • Impaired • Fever sensation • Thrombosis • Pregnancy • X-ray exposure • Hemorrhage • Uncooperative • Ischemic Tissue patient • Testicles and eyes • Areas of poor circulation PRECAUTIONS • Operator should observe caution when handling the machine: same contraindications apply Production of Microwave: - Produced by high frequency current and have same frequency as the currents which produce them - Not produced by Oscillators/ Vacuum tube valves / Solid state devices Magnetron: - Consists of cylindrical cathode surrounded by an anode structure with cavities opening into the cathode Anode space by means of slot. • O/P energy is derived from the resonator system by means of a coupling loop forced into one of the cavities. • The energy picked up on the coupling loop is carried out of the magnetron on the central conductor of a co-axial o/p tube throgh a glass seal to the director • Director has radiating element of antenna • Electrical current transformed to antenna & emits EM radiation. Then a reflector which direct energy to the patient. Components of Microwave Diathermy • Main supply voltage • Interference Suppression filter( Bypass the high frequency pick up generated by Magnetron) • Fan motor connected with power supply ( Used to cool magnetron) Delay Circuit • Magnetron has to warmup for 3 to 4 minutes before power may be delivered from it • Delay ckt – connects the anode supply to the magnetron after this time elapse • Lamp lights up after 5 minutes – For indicates that apparatus is ready to use Magnetron Circuit • Filament heating voltage is obtained directly from the secondary winding of the transformer • Cathode circuit contains suppression filters • Anode supply may be DC or AC. • DC voltage from full wave rectifier followed by voltage doubler circuit • A high wattage variable resistance in series controls current applied to the anode circuit • AC voltage is applied to the anode of the through series connected thyrotron sothat AC voltages of both tubes are equal in phase. • The amount of the current through the magnetron /output power can be varied by shifting the phase of the control grid voltage with respect to the phase of the anode voltage • Phase shift can be achieved – By using capacitor resistor network. Safety circuit • Fuse(500 mA) in the anode supply circuit • Large self inductance coils in primary supply– For considerable interference • Due to small dimensions – cores become saturated- to avoid that coils are split up in such a way that no magnetization • Duration of irradiation – 10 to 25 minutes. • Skin should be dry as these waves are absorbed by water. Electrotherapy i-t curve • First stimulated with long impulses ( first 1s pulse duration then 0-05ms) • For each impulse duration the current intensity is adjusted until the stimulation threshold has been exceeded. • So the current intensity has to be achieved to keep threshold value • Impulse Duration(1000-300-100-10-3-1-0.05ms) Chronaxie Period: Minimum duration of impulse that will produce a response with a current of double of the rheobase Rheobase: Minimum intensity of current that will produce a response if the stimulus is of finite duration Galvanic current • Steady flow of direct current • Movement of ions and their collection at the skin areas lying beneath the electrodes • Bright red coloration due to increased blood flow • For atonic Paralysis, for treatment of disturbance in blood flow, iontophoresis • Current intensity – 0.3 to 0.5 ma/sq.cm • Duration : 10-20 minutes Faradic current • Sequence of pulses with defined shape & current intensity • Pulse duration – 1minute triangular waves with interval 20 minutes • Acts upon muscle tissue and upon the motor nerves to produce muscle contractions • No ion transfer & No chemical effect • Treatment of muscle weakness after immobilization and disuse atrophy & functional paralysis treatment Surging current • Peak current increases & decreases rhythmically & the rate of increase and decrease of peak amplitude