760 Handbook of Biomedical Instrumentation
HAPTER
29
Physiotherapy and Electrotherapy
Equipment
29.1 HIGH FREQUENCY HEAT THERAPY
Physical stimulus commonly employed in the practice of physiotherapy is in the form of heat,
either by simple heat radiation or by the application of high frequency energy obtained from
special generators. The use of high frequency energy in thermotherapy has the advantage of
considerable penetration as compared with ‘simple’ heat application. Thus, with high frequency
energy, deeper lying tissues, e.g. muscles, bones, internal organs, etc. can be provided heat.
High frequency heat therapy is based on the fact that the dipole molecules of the body are
normally placed randomly. Under the influence of an electric field, they rotate according to the
polarity of their charge in the direction of the field lines (Fig. 29.1). The positively charged end of
the dipole then orients itself to the minus pole and the negatively charged end to the plus pole.
Since the polarity of the electric field alternates, a micro-heating effect results from the continuous
re-alignment of the molecules.
High frequency energy for heating is obtained by various ways. It may be from the short-wave
therapy unit making use of either the condenser field or the inductor field method. Microwaves
and ultrasonic waves are also used for heating purposes in special cases.
29.2 SHORT-WAVE DIATHERMY
The term ‘diathermy’ means ‘through heating’ or producing deep heating directly in the tissues of
the body. Externally applied sources of heat like hot towels, infrared lamps and electric heating
pads often produce discomfort and skin burns long before adequate heat has penetrated to the
deeper tissues. But with the diathermy technique, the subject’s body becomes a part of the electrical
circuit and the heat is produced within the body and not transferred through the skin (Yang and
Wang, 1979).
, Physiotherapy and Electrotherapy Equipment 761
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(a) (b)
Fig. 29.1 Principle of high frequency heat therapy units
(a) The dipole molecules of the body are at first ordered completely
randomly
(b) Under the influence of an electric field, they rotate according to the
polarity of their charge in the direction of the field lines
Another advantage of diathermy is that the treatment can be controlled precisely. Careful
placement of the electrodes permits localization of the heat to the region that has to be treated. The
amount of heat can be closely adjusted by means of circuit parameters. The heating of the tissues
is carried out by high frequency alternating current which generally has a frequency of 27.12 MHz
and a wavelength of 11 m. Currents of such high frequencies do not stimulate motor or sensory
nerves, nor do they produce any muscle contraction. Thus, when such a current is passed through
the body, no discomfort is caused to the subject. The current being alternating, it is possible to pass
through the tissues currents of a much greater intensity to produce direct heating in the tissues
similar to any other electrical conductor.
The method consists in applying the output of a radio frequency (RF) oscillator to a pair of
electrodes which are positioned on the body over the region to be treated. The RF energy heats the
tissues and promotes healing of injured tissues and inflammations.
Circuit Description: The short wave diathermy machine consists 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 oscillators
operating from unfiltered or partially filtered power supplies. They usually made use of a valve
circuit, a typical example of which is shown in Fig. 29.2. Transformer Tl, the primary of which can
be energized from the mains supply, is a step-up transformer for providing EHT for the anode of
HAPTER
29
Physiotherapy and Electrotherapy
Equipment
29.1 HIGH FREQUENCY HEAT THERAPY
Physical stimulus commonly employed in the practice of physiotherapy is in the form of heat,
either by simple heat radiation or by the application of high frequency energy obtained from
special generators. The use of high frequency energy in thermotherapy has the advantage of
considerable penetration as compared with ‘simple’ heat application. Thus, with high frequency
energy, deeper lying tissues, e.g. muscles, bones, internal organs, etc. can be provided heat.
High frequency heat therapy is based on the fact that the dipole molecules of the body are
normally placed randomly. Under the influence of an electric field, they rotate according to the
polarity of their charge in the direction of the field lines (Fig. 29.1). The positively charged end of
the dipole then orients itself to the minus pole and the negatively charged end to the plus pole.
Since the polarity of the electric field alternates, a micro-heating effect results from the continuous
re-alignment of the molecules.
High frequency energy for heating is obtained by various ways. It may be from the short-wave
therapy unit making use of either the condenser field or the inductor field method. Microwaves
and ultrasonic waves are also used for heating purposes in special cases.
29.2 SHORT-WAVE DIATHERMY
The term ‘diathermy’ means ‘through heating’ or producing deep heating directly in the tissues of
the body. Externally applied sources of heat like hot towels, infrared lamps and electric heating
pads often produce discomfort and skin burns long before adequate heat has penetrated to the
deeper tissues. But with the diathermy technique, the subject’s body becomes a part of the electrical
circuit and the heat is produced within the body and not transferred through the skin (Yang and
Wang, 1979).
, Physiotherapy and Electrotherapy Equipment 761
–
– – – – – – – +
–
–
–
– – – – – – – +
–
–
–
– –
– – – – – – +
–
–
–
–
–
–
–
–
– – – – – +
– – –
–
–
– – – – – +
– – –
–
– –
–
– – – – – +
–
–
–
– –
– – – – – +
–
–
–
–
–
–
–
– – – – – – +
(a) (b)
Fig. 29.1 Principle of high frequency heat therapy units
(a) The dipole molecules of the body are at first ordered completely
randomly
(b) Under the influence of an electric field, they rotate according to the
polarity of their charge in the direction of the field lines
Another advantage of diathermy is that the treatment can be controlled precisely. Careful
placement of the electrodes permits localization of the heat to the region that has to be treated. The
amount of heat can be closely adjusted by means of circuit parameters. The heating of the tissues
is carried out by high frequency alternating current which generally has a frequency of 27.12 MHz
and a wavelength of 11 m. Currents of such high frequencies do not stimulate motor or sensory
nerves, nor do they produce any muscle contraction. Thus, when such a current is passed through
the body, no discomfort is caused to the subject. The current being alternating, it is possible to pass
through the tissues currents of a much greater intensity to produce direct heating in the tissues
similar to any other electrical conductor.
The method consists in applying the output of a radio frequency (RF) oscillator to a pair of
electrodes which are positioned on the body over the region to be treated. The RF energy heats the
tissues and promotes healing of injured tissues and inflammations.
Circuit Description: The short wave diathermy machine consists 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 oscillators
operating from unfiltered or partially filtered power supplies. They usually made use of a valve
circuit, a typical example of which is shown in Fig. 29.2. Transformer Tl, the primary of which can
be energized from the mains supply, is a step-up transformer for providing EHT for the anode of
