OBJECTIVE
Without reference, identify at least four out of
six principles pertaining to the application of
ultrasonic therapy.

Ultrasonic therapy- is the therapeutic application
of a form of acoustic vibration at frequencies too
high to be heard by the human ear. The sound
waves spread through the tissues, where they are
absorbed and converted into hear. This type of
heating is by conversion. Conversion is just thatheat transferred when energy penetrates into deep
layers of the body tissue where it is converted into
heat. The following features of ultrasound are to
be considered:
 Acoustic vibrations below 20,000 Hz are called
sound
 Acoustic vibrations above 20,000 Hz are called
ultrasound. This frequency is inaudible.
 The physics of ultrasound is the same as audible
sound, except for the differences in frequency.
 For therapeutic purposes, the ultrasound
frequencies range from 0.8 to 1 megahertz (MHz)
 There
are three circuits generally found in
all therapeutic ultrasound devices:
 Power supply circuit- transforms the alternating
wall current into a high voltage DC, and a lowvoltage AC for the oscillating circuit. The power
supply circuit is constructed so the 220V, 50Hz
AC line current does not noticeably modify the
steady output of the power supply circuit.
 Oscillating circuit- Produces an AC having a high
frequency of about 0.8 to 1 MHz. The frequency of
the oscillating circuit equals the mechanical
frequency of the crystal in the transducer. It is
possible to adjust the frequency of this AC by
tuning unless the manufacturer installed a device
for controlling the oscillating frequency. The
oscillating circuit is also referred to as the
generator.
 Transducer circuit- is where the high-frequency AC
produced by the oscillating circuit is supplied to a
crystal. This crystal converts the electrical current
into mechanical (acoustic) vibrations. This
conversion happens by a reversal of the
piezoelectric effect. The transducer circuit is also
known as the transducer, applicator, or sound head,
and is attached to the machine by a coaxial cable.
This coaxial cable transmits the high-frequency AC
from the generator to the crystal housed within the
sound head (transducer circuit)

Clinical application
 There are two types of techniques for
administering therapeutic ultrasound to the
patient.
• Direct contact, a viscous fluid is used as a coupling
agent between the applicator and skin. Mineral oil
or an aqueous gel are the most frequently used
coupling agents. The direct contact method is used
to apply ultrasonic energy to areas of the body that
are relatively smooth and have few bony
prominences.

Indirect method utilizes H2O as the coupling
agent between the applicator and skin. The
applicator is held ½ to 1 inch away from the
skin with the transducer and body part
submerged in H2O. This is the ideal way for
applying ultrasonic energy to irregular
surfaces and bony prominences.
 During ultrasonic therapy treatment, clinically we cannot
measure the parameters that determine the biologic
response to ultrasound: temperature obtained in the
tissues, duration of the temperature elevation, and rate
of temperature rise within the tissues. We can however,
measure the amount of energy (intensity) expressed in
terms of watts per centimeter squared (W/CM2), which
refers to the average intensity of the field. On most
ultrasound machines, this information is obtained from
the meter on the panel. The intensities of ultrasound
for therapeutic purposes range from 0.5 to 4 W/CM2.
For most applications, the duration varies from 3 to 10
minutes for each field in the area of application.
 Ultrasound is an effective deep-heating
agent. It is possible to produce higher
temperatures in bone than either the fatty
or muscular tissues even when the bone is
covered by more than 6 centimeter (CM) of
soft tissue. Unlike the other thermal
treatments, ultrasound can be used safely
in the presence of metal implants. The
metal implants have a very high thermal
conductivity so the heat is removed from
the area more rapidly than it is absorbed.
 Ultrasound is applied to heat joints
covered with a thick layer of soft tissue,
such as the hip-joint. Other modalities,
even shortwave diathermy, cannot heat
these deeper structures to a therapeutic
level producing results comparable to
ultrasound.
 Ultrasound selectively heats denser
structures permitting an increase in their
extensibility. For this reason, it is very
effective when applied to a joint with
limited mobility. Three denser structures
that this can be applied to are: joint
capsules, ligaments, and tendons.
 Ultrasound may also be used as a heating
agent over nerves. The heating effect may
reduce the irritability of the nerve, and
relieve the pain and spasm effects of the
nerve root irritation.
 Physiological
effects
 Most of the physiological effects that are
of potential therapeutic value are a result
of the increase in tissue temperature
resulting from the absorption of ultrasonic
energy. The following table list the local
and systemic effects that occur:

Some precautions you must be aware of when
working around ultrasound equipment are:
 Do not apply ultrasound to the eyes, areas with
decreased blood flow, malignancies, a pregnant
uterus, or to a patient with predisposition to
hemorrhagic disease.
 Apply ultrasound with caution to areas of sensory
impairment.
 Observe the patient during treatment for signs of
possible tissue damage due to heat.

If for any reason the unit does not appear to be
operating properly, a simple test to check for
normal output from the transducer is:
 Wrap a piece of 1-inch adhesive or masking tape around
the front edge of the transducer to form a cup
 With the transducer head in the inverted and vertical
position, pour approximately ¼” water into the cup formed
by the tape
 Operate the machine in the normal manner,
slowly increasing the intensity control from zero
to maximum output
 As the intensity is advanced, the water forms a
small cone; at full output, it forms a sharp peak
and shows violent agitation

The test can also be performed in a tank of water
of sufficient depth to accommodate the transducer,
with the transducer free in a horizontal position
about ¼” below the surface
 If you discover you have little or no activity shown
by the preceding tests, this indicates improper unit
operation, or possible transducer cable or head
problems

The transducer assembly and cable can be spotchecked rather quickly by removing the whole
assembly and taking am X-ray of it to detect possible
breaks in the cable wiring. Another method,
depending on availability, is to swap out the
transducer and cable assembly with another unit
manufactured by the same company. Emphasis here
in on the word “same;” never attempt to use another
manufacturer’s parts on the unit you are servicing.
Severe damage may occur to the unit or component
parts being trouble shot, resulting in two units being
unserviceable instead of one. Also, there is a
possibility of creating an electrical shock hazard
endangering you, the operator, or the patient.

Physical therapy uses a wide variety of
therapeutic equipment; this lesson discusses
hydrotherapy units. If you look at the word
“hydrotherapy,” it tells you exactly what type
of equipment this is— H2O (water) therapy
specifically, we address the principles and
applications of the whirlpool bath A whirlpool
bath is a vessel in which H20 at a given
temperature is kept in constant agitation and
permits immersion of an extremity.


Principles of operation - The whirlpool bath
combines heat with mechanical action to
stimulate circulation and relax muscles.
There are three major types of whirlpool baths.
◦ The arm bath, which is a small tank mounted on a
pedestal.
◦ The leg bath, which is a larger tank mounted on the
floor.
◦ The body bath, also floor mounted. These are the largest
of the three types. Since the only difference in the three
types is their physical size, we will discuss them in
generic terms.

Whirlpool baths are constructed in three main
components: the tank, turbine ejector, and
the aerator assembly.
◦ The tank is fabricated of heavy-gauge stainless
steel with a satin finish inside and out.
 It contains a quick-acting thermometer to indicate H20
temperature.
 Drainage of the tank is accomplished by a combination
drain and overflow valve.
 The turbine ejector is constructed to move in all
directions.
 It has four main components: turbine housing assembly,
suspension bracket, aerator tube assembly, and electric
motor.
 The turbine ejector bracket is attached to a raising and
lowering rod attached to the outside of the tank.
 The aerator tube assembly contains a butterfly valve to
regulate the volume of air passing through the tube.
 The motor is a vertically mounted, inductive-type unit
protected by a manually reset thermal overload switch. It
contains permanently lubricated, sealed bearings.

The whirlpool bath must have a means to
regulate the H20 temperature delivered to the
patient; this is done by the using a
thermostatic mixing valve.
◦ the mixing assembly is composed of a thermostatic
mixing valve, hot H20 inlet, cold H20 inlet, volume
control valve, and vacuum breaker.
◦ The normal four positions obtained from this valve
are shut or off, cold, warm, and hot.
◦ The normal temperature range for the average arm
and leg whirlpools is approximately 100°F to 110°F.
◦ The approximate range for a body bath is between
90° to 100°F.
◦ These ranges vary depending on the patient’s
disability and sensitivity, and the physical
therapist’s preference.

Clinical application
◦ Whirlpools are used therapeutically to heat large
areas of the body at one time, at a constant
temperature, and attain a uniform coverage.
◦ They also massage body tissues by the moving H20.
◦ Whirlpools are widely accepted and used in cleaning
and debridement of open wounds and severe burns.
◦ Often, a bacterial agent is added to the bath to take
advantage of whirlpool agitation.
◦ The whirlpool is also used to increase body
circulation by alternating the hot and cold H20 of
the bath.
◦ The buoyancy obtained in the whirlpool bath helps
the therapists with exercise routines.
◦ As you can see, anyone having generalized joint
involvement, such as arthritis, is a prime candidate
for the whirlpool bath.
◦ Patients suffering from post-cast stiffness can
benefit, as well as patients with traumatic or
inflammatory conditions, such as sprains, strains,
and contusions.

Physiological effects
◦ Heated H2O in a whirlpool bath produces all the
physiological effects most superficial or local heat
applications produce. The following are effects of
this heated H20:

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







Circulation
General peripheral vasodilation
Lymph circulation and drainage increased
Cardiac output and pulse rate increased
Body temperature increased
Respiration increased
Metabolism increased
Profuse perspiration
Muscle relaxation
Sedation of nerve endings
◦ There are two specific problems that can be
aggravated by whirlpool treatment to patients with
the specific ailments:
 Advanced cardiac conditions — further strain on the
circulatory system could result
 Hyperthyroidism — an already high patient metabolism
may be further increased

Operational inspection
◦ Observe safety at all times when working around
whirlpool equipment. It doesn’t matter what
manufacturer’s brand you are dealing with because
they all have the same general characteristics,
including the use of H2O and electricity—a fatal
combination if appropriate safeguards are not
observed.
◦ Even though a whirlpool bath may seem simple
enough, familiarize yourself with the
manufacturer’s literature before you perform an
operational inspection.
◦ Next, review your work order records to ensure all
basic areas of concern noted in the past are
examined separately.
◦ After you check the unit over and you are sure
everything is in order, it is time for an operational
inspection.
◦ Before you turn the unit on, there is a word of
caution: do not attempt to start the turbine ejector
until the H2O level in the tank is well above the
housing at its lower end.
 This precaution extends the life of the turbine ejector’s
leather bearing, which is lubricated by the H2O; it must
be submerged or it will “freeze up.”
◦ Start the motor by turning the insulated toggle
switch to ON.
◦ Direct the direction of the H20 jet by rotating to the
right or left, or by raising or lowering the turbine
ejector assembly.
 The unit is secured by a friction lock and locking pin.
◦ Proceed to check the turbine ejector in combination
with the aerator, which mechanically agitates the
H20.
 The impeller blades at the bottom of the ejector
should force jet of H20 across the bottom of the tank.
◦ To verify the fan on the motor is functioning
properly, there should be a steady flow of air out
the butterfly valve and into the tank in front of the
jet from the ejector.
◦ If all of these steps prove positive, an operational
inspection of the thermostatic mixing valve is next.
◦ With the thermostatic mixing valve handle set to the
HOT position and the volume control valve open,
the mixing valve should supply hot H20 at a
temperature of approximately 115°F.
◦ Now, turn off the cold H20 supply to test the hot
H20 shutoff.
◦ A properly operating mixer shuts off the hot H20
almost instantly.
◦ Failure to do so could indicate:
 Dirt between the hot seat in the liner and piston,
preventing it from closing; it must be cleaned.
 A stuck piston that cannot move because of scale or
foreign matter in the H20; the unit must be cleaned.
 A malfunctioning thermostat; it must be replaced.
◦ Now that you have checked the hot H20 shutoff,
turn off the hot H2O and check the cold H20 by
opening the cold supply to the mixer.
 This is accomplished by moving the mixing valve
handle to the COLD position.
◦ A full volume of cold H2O should be supplied by
the mixer.
◦ Now, move the handle back to the HOT position as
far as possible.
◦ The flow of cold H20 should decrease to a very
small flow.
◦ Failure to do this indicates:
 A stuck piston; it needs cleaning
 The piston spring has lost strength and needs
replacing.
◦ If you find the mixing valve does need to be
disassembled and cleaned, refer to the service
manual to ensure components are taken off in the
proper sequence or returned properly upon
reassembly.
◦ Check the accuracy of the dial thermometer in the
tank by using a calibrated digital temperature
system or comparable calibrated mercury
thermometer.
◦ The procedure is simple to accomplish:
 Fill the tank at a particular temperature setting
 Immerse your calibrated thermometer next to your
tank thermometer
 Wait 1 or 2 minutes for the thermometer to stabilize
 Compare the reading with the tank thermometer.
◦ If you find more than a 2°F difference, this usually
indicates thermometer replacement is necessary.
◦ Refer to the manufacturer’s service manual for
possible adjustments on some models.