Ultrasound
Ultrasound, unlike other electrical modalities, is different in that
the longitudinal waveform associated with sound is not electromagnetic
in nature. Such wave represents the compression and rarefaction of a
vibrating medium. Electromagnetic waves can be transmitted across a
vacuum but sound waves need a medium for transmission. Ultrasound
has been found useful in reduction of muscular and tendinous spasm.
Water can be utilized as an excellent conduction medium to permit
exposure of some regions difficult to reach with standard techniques.
Physics:
The frequency of the therapeutic ultrasound (1 Mc) is reached by
the transformation of household current of 60 cycles, 110 volt alternating
current to 500 volts or more by electromagnetic components in the
ultrasound apparatus. Then, the higher voltage is applied to oscillators,
which limit the household frequency to the desired level of 1 Mc.
 Piezoelectricity:
Piezoelectricity is a natural phenomenon found in certain mineral
crystals such as quartz but may be synthesized for commercial purposes.
The higher frequency emitted from the apparatus is imposed on a crystal
with piezoelectric qualities, which transforms the mechanical energy into
electrical energy and vice-versa. So, this piezoelectric head should be
kept away from compression or deformation, otherwise the electrical
charge within this head will be reduced. The human bone exhibits
piezoelectric characteristics.
1
 Transformation of electrical energy into sound:
The high-frequency current of 1 Mc alternating current is imposed
on the piezoelectric crystal, transforming its energy into vibration, at the
same frequency of 1 Mc. As this crystal is held in contact with the
metallic or plastic faceplate of the apparatus, it causes vibration of the
housing at the same frequency of 1 Mc. Thus, the electrical energy of the
original current is transformed into vibratory sound waves (ultrasound). It
is termed so, as it is beyond the normal range of audible sound waves
(25:15000 counts / second).
 Conduction of the wave energy:
Substances such as water, oils and gels are good conductors for the
wave energy, in contrast to air. Thus, air should be replaced by a more
effective medium to conduct the wave energy to the adjoining surfaces,
including the human skin.
 Penetration and absorption:
Researches have proven that ultrasound can penetrate as deep as 4
to 6 cm into the tissues, which varies in their absorbability. It is found
that tissues with high fluid content, such as blood and muscles, can
absorb sound waves better than those, which are less hydrated. Although
seemingly not hydrated, nerve tissue is an excellent conductor of
ultrasound waves.
Physiological effects:
1. Chemical reactions:
Ultrasound can stimulate tissue through its power to enhance
chemical reactions, similar to shaking a test tube in the lab. It ensures
circulation of necessary elements and radicals for combination.
2
2. Biological responses:
Ultrasound can increase the permeability of membranes, which
enhances transfer of fluids and nutrients to the tissues. This quality is
utilized in the process of phonophoresis, in which molecules are pushed
through the skin by the ultrasound waves.
3. Mechanical responses:
The high-frequency vibration of ultrasound deforms the molecular
structures of loosely bonded substances. Thus, ultrasound is useful
therapeutically in:
- Reducing muscle and tendon spasm.
- Increasing range of motion due to adherent structures.
- Breaking up calcified depositions.
- Mobilizing adhesions and scar tissues.
This is termed the "sclerotic effect" of ultrasound. It apparently
increases the extensibility of shortened structures. The deformation
mechanism of ultrasonic should be monitored carefully, otherwise if used
for maximum power or duration; it may collapse the molecules, causing
destruction of substances (cavitation). The presence of unwanted
collagenous materials makes this semi-destructive force useful.
4. Thermal effect:
There is a fact that rapid oscillations of molecules, produced by
ultrasound, causes a build up of heat, which refers to the ultrasonic
diathermy. However, the mechanical effect of ultrasound is believed to be
the prime factor in clinical success, as the highly-selective absorption
behavior limits the efficacy of ultrasound as a therapeutic heating agent.
3
Most of the heat produced by ultrasound is found at an interface
where two different tissues about, with a common space intervening. The
most common sites for heat buildup are the periosteal zones between the
hard surface of bones and the glistening under-surface of the periosteum.
When the sound wave front enters the tissues and approaches this
boundary, the change of media from moist tissue to periosteum, to air
found in the periosteal zone; and then to bone leads to refraction of the
ultrasound wave, multiplied considerably due to various tissues. When
the longitudinal wave front is refracted into the periosteal-bone interface
layer, the angle of incidence is exaggerated enough to cause reflection
from the osseous surface back to the underside of the periosteum and
back to the bone again, etc…...
If the longitudinal waveform of ultrasound is transformed into
transverse waveform of the same frequency of 1 Mc, it produces
considerable heat. As the space between the bone and periosteum has no
or little opportunity for the heat buildup to dissipate, an extremely
dangerous lesion in the form of periosteal burn can result. The
transformation of the longitudinal wave into transverse waveform is
called "shearing effect", with systemic manifestations (pain and fever),
that should be avoided.
Indications:
- Spasm in neuromuscular conditions.
- Spasm in musculo-skeletal conditions.
- Scar tissue problems.
- Ganglia.
- Engorgement pain during post-partum nursing.
4
Contraindications and precautions:
- Certain organs: CNS, eyes, ears, testes, ovaries and pregnant uterus.
- Growing epiphyses.
- Bony prominences.
- Impaired blood supply.
- Active bacterial infection.
Treatment procedures:
1. Transmission media:
a) Through contact cream or oil:
Commercial transmission gels are effective for sound wave
transmission to the patient. Mineral oil, cream, liquid paraffin or contact
cream can be used effectively as a successful medium. A sufficient
amount of gel is applied to the target area.
b) Through water bath:
This method is used for body parts which are small or irregular for
direct applications. It can be used also for hypersensitive areas, where
contact with the treatment head would cause discomfort. The treatment
head is immersed in water and moved at a distance of 1.5 to 3 cm from
the treated area. If bubbles collect, treatment should be interrupted until
these bubbles are wiped from the skin and the treatment head.
c) On the surface of water:
This method may be used where there are some contraindications
to immerse the target part in the water. The water should be boiled before
use to repel the dissolved air and air bubbles. The treatment head is
placed in water and a reflector directs the ultrasonic to the surface. The
part should be supported so that the skin is just in contact with the water.
5
d) Water bags:
In this method, a rubber bag containing boiled water is placed in
contact with the skin and the ultrasonic waves are applied through such
water bag. The treatment head is moved over the other surface of the bag.
2. Setting up the parameters:
- Pre-warm the head in your band palm or warm water.
- After tuning on the ultrasound unit, a time should be allowed for the
unit to be warmed up.
- The treatment duration should be set up. It usually ranges from 1 to 8
minutes, depending on the condition treated, the anatomic target site and
the technique used. For most cases, from 2 to 3 minutes is effective, when
administered manually on the surface, while underwater administration
requires from 5 to 8 minutes.
3. Application of the head:
- Increase the power slowly, when the head is on the target area, as
recommended before.
- The head should be moved slowly and perpendicularly over the target
area, in a combination of small circular and long stroking motions.
- Special care should be used over bony prominences to avoid periosteal
irritation.
4. Frequency of treatment:
Treatment with ultrasound may be applied daily if indicated;
otherwise it is applied two or three times per week. Prolonged treatment
without noted progress requires a change in treatment regimen.
6
Power voltage:
The recommended dosage of ultrasound for clinical purpose ranges
from 0.5 to 1 W / cm2 of the transducer’s head. As most instruments have
a crystal area ranging between 5 and 10 cm2, the total voltage then will be
2.5 to 10 W for most applications.
Modes:
Ultrasound can be applied in an intermittent or pulsed mode,
usually in the order of 60 pulses per second. Using such mode, with
minimizing the time of application, reduces the heat buildup in the target
tissues.
7
Ultrasound in conjunction with other modalities
If additional modalities are to be administered during the
same treatment session, consideration should be given to the
condition of the patient’s skin. When using oils or gels, sounding
should be preceded with electrical stimulation or iontophoresis to
assure optimal electrical transmission.
Ultrasound and electrical stimulation:
If electrical stimulation (EMS) is to be combined with ultrasound,
the transducer becomes one of the two electrodes in the circuit. The
secondary electrode is placed on the patient, usually homo-lateral, neither
too distant nor too close and not on an antagonistic muscle. If the upper
extremity is to be treated, the electrode is placed on the brachial area or
dorsal (thoracic) spine; while if the lower extremity is the target, the
electrode is then placed on the lumbar spine.
The transducer then serves as the stimulating electrode and
ultrasound is administered simultaneously. Various forms of stimulating
currents are available for this purpose (alternating, direct, continuous,
surged and pulsed).
Dosages are problematic since ultrasound may require only a few
minutes for sufficient treatment, whereas electrical stimulation may
require 15 to 30 minutes for treatment time. A competent therapist will
be able to adjust and design a proper dosage combination. Some
manufacturers offer units pre-designed for combined operations, whereas
others make the circuitry possible through special jacks, connectors and
controls. To date, few if any references describe the advantages or
disadvantages of the combined techniques. The choice now is clearly the
therapist’s.
8
Ultrasound and Iontophoresis:
There have been reports of administration of iontophoresis in
combination with the use of ultrasound / electrical stimulation equipment.
Theoretically, this has not been demonstrated to be possible, since only a
continuous direct current will serve for ionic transfer and time-in-place is
a necessary factor with iontophoresis. Till now, there is no available
combined unit that offers a continuous direct current. Moreover, the
movement of the ultrasound head associated with ultrasound techniques
precludes the time-in-place requirement. With this technique however,
there may be phonophoretic rather than iontophoretic effects.
9