2.

DIATHERMY:

When heat is applied to the particular area of the body, the temperature of the tissue
increases. Due to the dilation of blood vessels, the flow of blood increases at that area.
Various methods are used to raise the tissue temperature. One of them is called as external
method or conductive heating. The main disadvantage of this methods is it increases the
skin temperature but the heat does not penetrate very deeply into the body. The devices
used for the purpose of external heating are hot compressors, infra red lamp, etc. the
externally used heat sources like hot towels, heat lamps and heating pads often produce
inconvenience and discomfort to the patients. This results in the burning of skin before the
penetration of adequate heat to the deeper tissues. Hence to overcome such demerits,
diathermy technique is adopted. In this method the patient’s body becomes a part of
electrical circuit, hence heat is produced within the body instead of transferring through the
skin. Diathermy is te treatment process by which cutting, coagulation of tissues are obtained.

Advantage of Diathermy:

 The treatment can be controlled easily

 Use of appropriate electrodes permits the heat to be localized only in the region to be
treated.
 Amount of heat that is to be delivered can be adjusted accurately
 Inter lying tissue, muscles, bones, internal organs, etc., can be provided with heat by
using high frequency energy.

Types of Diathermy

 Short wave Diathermy

 Microwave Diathermy
 Ultrasonic diathermy
 Surgical Diathermy

2.1 Short wave diathermy

It involves high frequency of 27.12 MHz and wavelength of 11m. Since high
frequency current are used, the motor and sensory nerves are not stimulated and there is no
muscle contraction. This method has no discomfort to the patient. The basic operation of
shortwave diathermy unit can be explained with the help of block diagram as shown in fig.4.1
 Fig 4.1 Basic block diagram of Short wave diathermy.

The output of RF oscillator is given to the patient electrodes. The RF energy heats the tisues
and help in heating of injured tissues. The power delivered by the unit is about 500W. the
intensity of the current used can be regulated and adjusted. The electrodes are not directly
in contact with the skin. Usually layers of towels are interposed between the metal and
surface of the body.

CIRCUIT DESCRIPTION:
The short wave diathermy machine consist of two main circuits: an oscillating circuit,
which produces a high frequency current and a patient circuit, which is connected to the
oscillating circuit and through which the electrical energy is transferred to the patient.
Earlier models of diathermy machines employed single-ended or push-pull power
oscillator operation from unfiltered of partially filtered power supplies. They usually made use
of a valve circuit, a typical example of which is shown below in fig 4.2. Transformer T1, the
primary of which can be energized from the main supply, is a step-up transformer. The
transformer for providing EHT for the anode of the triode valve. A second winding can
provide heating current for the cathode of the triode valve, the tank cuiruit is formed by the
coil AB in parallel with the condenser C1.

Fig 4.2 simplified circuit diagram of a short-wave diathermy unit

 The positive feedback is generated by coil CD. There is another coil EF an a variable
condenser C2 Which form the patient’s resonator circuit due to its coupling with eh oscillator
coil AB.
The anode supply of such a circuit is around 4000V. The conduction in the triode takes place
during the positive half-cycle and the high frequency is generated only during theis
period.The variable condenser C2 is adjusted to achieve a amaximum reading on the meter.
The maximum power delivered by these machines are 500w.
There are several ways to control the current intensity to the patients as follows,
(i) Controlling the anode voltage, (ii) controlling the filament heating current,
(iii) adjusting the grid bias by change of grid leak, (iv) adjusting the position of the resonator
coil with respect to theoscillator coil.

There are two methods of short wave Diathermy. They are

 Capacitive method
 Inductive method

Capacitive method

Here, the patient electrode pads form a capacitor plates and the body tissue between
the pads act as a dielectric. Thus the whole arrangement forms a capacitor. When the RF
current is applied to the electrodes, the capacitor produces heat in the interlaying tissues.
This technique is called as capacitive method. The setup for the inductive diathermy as
shown below the fig.4.3

Fig 4.3 Capacitive diathermy

Inductive method
 In this method a flexible cable is coiled around the arm or knee or any other portion
of the body which is to be treated. This is used where the plate electrodes are inconvenient
to use. When the electrostatic field set up is given between the ends of the cable, deep
heating of the tissue occurs. The superficial tissues are heated by the eddy currents that are
produced due to the magnetic field around the cable. This technique is also called as
Inductothermy.The setup for the inductive diathermy as shown below the fig.4.4

Fig 4.4 Inductive Diathermy

Advantages:

 Healing rate of tissue is increased

 Depth of penetration of RF waves can be easily adjusted
 There is no danger of burns or irritation and the patient has no discomfort.

2.2 Microwave Diathermy

Microwave diathermy consists in irradiating the tissues of the patient's body with
very short wireless waves having frequency in the microwave region. Microwaves are a
form of electro- magnetic radiation with a frequency range of 300-30,000 MHz and
wavelengths varying from 10 mm to 1 m. In the electromagnetic spectrum, microwaves
lie between short waves and infrared waves. The most commonly used microwave
frequency for therapeutic heating is 2450 MHz corresponding to a wavelength of 12.25
cm. The heating effect is produced by the absorption of the microwaves in the region of
the body under treatment.
Microwave diathermy provides one of the most valuable sources of therapeutic heat
available to the physician. However, in many conditions, though the therapeutic effects
of microwave diathermy are similar to short-wave diathermy, yet in others, better results
are obtained by using microwave.

The technique of application of microwave diathermy is very simple. Unlike the

short-wave diathermy where pads are used to bring in the patient as a part of the circuit,
the microwaves are transmitted from an emitter, and are directed towards the portion of
the body to be treated. Thus, no tuning is necessary for individual treatments. These
waves pass through the intervening air space and are absorbed by the surface of the
body producing the heating effect.

Production of Microwaves: Microwaves are produced by high-frequency currents and

have the same frequency as the currents which produce them. Such currents cannot be
produced with oscillators using ordinary vacuum tube valves or solid-state devices. A
special type of device called 'magnetron' is used for the production of high frequency
currents of high power.The magnetron consists of a cylindrical cathode surrounded by
an anode structure that contains cavities opening into the cathode-anode space by
means of slots. The output energy is derived from the resonator system by means of a
coupling loop which is 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
output tube through a glass seal to a director.
The director consists of a radiating element of antenna and a reflector which directs
the energy for application to the patient. The electrical current is transformed into
electromagnetic radiation on passing through the antenna.The reflector then focuses
this electromagnetic energy and beams it to the tissues where it is subsequently
absorbed, reflected or refracted, according to the electrical properties of the tissue.
Tissues of lower water content (i.e., subcutaneous) are penetrated to a greater depth
but little is absorbed, whereas tissues of high water content (i.e., muscle) absorb more
of the electromagnetic energy but allow little penetration.
The output power of a magnetron depends upon anode voltage, magnetic field
and the magnitude and phase of the load impedance to which the magnetron output
power is delivered. Therefore, the cable used to carry the energy from the magnetron to
the director is always of a definite length for a particular frequency. A part of the energy
fed to the magnetron is also converted into heat in the anode on account of the collision
of the electrons with the anode so that the output energy is considerably less than the
input energy. The efficiency of a magnetron is usually 40 to 60%. The heat produced at
 the anode must be removed which is usually done by using water or air as a means of
cooling.

Schematic Diagram of a Microwave Diathenny Unit: The essential parts of a

microwave diathermy unit are shown in Fig. 29.5. The mains supply voltage is applied
to an interference suppression filter. This filter helps to bypass the high frequency pick-
up generated by the magnetron. A fan motor is directly connected to the mains supply.
The fan is used to cool the magnetron.
The Delay Circuit:It is necessary for the magnetron to warm up for 3 to 4 minutes
before
power may be derived from it. A delay circuit is incorporated in the apparatus which
connects the anode supply to the magnetron only after this time elapses. The arrangement
is such that a lamp lights up after 4 minutes indicating that the apparatus is ready for use.

Fig.4.5 Microwave Diathermy

The Magnetron Circuit:The magnetron filament heating voltage is obtained directly from a
separate secondary winding of the transformer.
The filament cathode circuit contains interference- suppression filters. The anode
supply to the magnetron can be either DC or AC. A DC voltage is obtained by a full wave
rectifier followed by a voltage doubler circuit. A high wattage variable resistance is
connected in series which controls the current applied to the anode of the magnetron. When
using AC, the voltage is applied to the anode of the magnetron through a series connected
thyratron so that the AC voltages of both tubes are equal in phase. By shifting the phase of
the control grid voltage with respect to the phase of the anode voltage, the amount of
current through the magnetron can be determined and thus the output power can be varied.
The phase shift can be achieved by using a capacitor resistor network.

Safety Circuits:

There are chances of the magnetron being damaged due to an excessive flow of
current. It is thus protected by inserting a fuse (500 mA) in the anode supply circuit of the
magnetron. The protection of both the patient and the radiator is ensured by the automatic
selection of the control range depending on the type of the radiator used.
The considerable interference produced by the apparatus necessitates the use of
large self- inductance coils in the primary supply. Since the cores are likely to become
saturated in view of the small dimensions, the coils are split up and fitted in such a way that
no magnetization occurs. Excessive dosage can cause skin bums and in all cases, the
sensation experienced by the patient is the primary guide for application. The skin should
be dry as these waves are rapidly absorbed by water. The duration of irradiation generally
ranges from 10 to 25 minutes
Disadvantages:

 Patients with implanted pacemaker should not undergo this treatment.

 There are possibilities of over heating
 Care should be taken while the treatment is made near the eyes.

2.3Ultrasonic Diathermy

It is used for curing the diseases of peripheral nervous system, skeletal muscle
system and skin ulcers. It is adopted when the short wave treatment has failed and it helps
to achieve the localization of heat to the affected part. The heating effect is produced in the
tissues by the absorption of ultrasonic energy.

Fig.4.6 Block diagram of Ultrasonic Diathermy

 The absorption effect is similar to that of a micro massage. It will be better that the
manual massage because the micro massage provides a greater depth of massage without
causing any pain to the patient. The piezo-electric transducer is excited by the high
frequency alternating current produced by the RF oscillator. The ultrasonic output waveform
from the piezo-electric transducer is used for the purpose of treatment.

The ultrasonic waves can be applied in continuous mode or pulse mode. Micro
massage is obtained without ant thermal heating in the pulsed mode. The metal face plate in
the crystal is made to vibrate due to the oscillation of the crystal and the ultrasonic waves
are emitted from this plate.

The frequency range of 800 KHz to 1 MHz is suitable for the ultrasonic method of
treatment. The timer is an electrically operated contact which can be set upto 15 minutes
and get switched off after the preset time. The transducer probe is in direct contact with the
patient and it can be moved up and down or circularly around the treatment area for uniform
distribution of ultrasonic energy.

2.4 SURGICAL DIATHERMY

Apart from the thermal and therapeutical applications, the high frequency currents
are also used for surgical purposes like cutting and coagulation. The frequency of current
used here is 1 to 3 MHz.

Fig.4.7 Surgical Diathermy

CUTTING:

When a high frequency current flows through sharp edge of a wire or the point of a
needle into the tissue, there is a high concentration of current at this point. Thie tissue gets
heated and as a result the cells immediately under the electrode are torn apart by the boiling
of cell fluid. The other electrode called indifferent electrode has large area of contact with the
patient and the RF current passed through it induces only a very little heat at the electrode.
This type of tissue separation is called as electrosurgical cutting.The RF waveform for the
Cutting as shown below in fig.4.8.

Fig.4.8 Cutting RF waveform

COAGULATION:

This process is achieved by the high frequency current flowing through the tissue and
results in heating and coagulation. The process of coagulation is accompanied by a grayish-
white discolorations of the tissue at the edge of electrode. Better coagulation is achieved by
high frequency is used fir cutting and burst wave radio frequency is used for coagulation.

The waveform for the Coagulation as shown below in fig 4.9. The electrode melts
through the tissue and seals capillaries and other vessels. Even if the high frequency
surgery is not used, the method of electro coagulation can be used.

Fig.4.9 Coagulation wave form

Advantages:

 It provides simple and effortless surgery

 This coagulation method prevents the contamination of bacteria
 Simplified method of coagulation saves time
  Bleeding can be arrested immediately by touching the spot with the
coagulation

2.5. Telemetry principles, Bio-telemetry, Frequency Selection

There are many instances in which it is necessary to monitor physiological events

from a distance. The term Biotelemetry is the measurement of biological parameters
over a distance. If the information is transmitted through Wireless mode (Electromagnetic
fields) of transmission and reception, then it is called as Radio telemetry.

2.5.1 Typical Applications of Biotelemetry

 Radio frequency transmission for monitoring astronauts in space.

 Patient monitoring where freedom of movement is desires. Eg; ECG during
exercise
 Patient monitoring in an ambulance and in other locations away from the
hospital.
 Collection of medical data from a home or office.
 Research on unrestrained, anaesthetized animals in their natural habitat
 Use of telephone links for transmission of ECG or other medical data.
 Special internal technique, such as tracking acidity or pressure through the
gastrointestinal tract.
 Isolation of an electrically susceptible patient from power-line-operated ECG
equipment to protect the patient from accident shock.