In addition to the widespread use of continuously radiated ultrasonic
energy, many doctors have proclaimed the advantage of pulsed ultrasonic
energy. Several investigators in the United States and Europe
have obtained results which seem to corroborate these claims. The
diagrams below graphically describe the difference between continuous
and pulsed ultrasonic energy.
The use of pulsed ultrasound does not change the peak ampirude of
the ultrasound intensity in comparison with continuous ultrasound. The
average value decreases when pulsed ultrasound is used.
Therefore, the heat generated during treatment with continuous
sound is practically eliminated in pulsed sound but the mechanical
action remains at essentially the same level. Thus those
conditions in which pain is not decreased by application of heat or
those in which periosteal or other pain may develop as a
result of the application of ultrasound, may be benefitted by the
mechanical action of pulsed ultrasound.
Pulsed ultrasound has been in widespread use for several years
and, in the minds of those who have employed it, there is an
advantage to the use of pulsed ultrasound in selected
cases. In general, pulsed ultrasound is preferred over
continuous ultrasound in those cases in which heat is
contraindicated or in conditions where it is believed that the
beneficial effects are produced by the mechanical action of
ultrasound. In treating areas in which underlying bone is covered
by a relatively thin layer of soft tissue, it may be desirable to
use the pulsed ultrasound in order to avoid periosteal
Its use seems to be preferred in application to nerve root areas.
It is not expected that pulsed ultrasound will replace continuous
ultrasound but that its use will produce better results in
many cases. Most users recommend the use of the same power
output as is used for continuous ultrasound with the belief that the
mechanical action remains at approximately the same level.
However, some feel that the power may be raised to some extent in
order to increase the mechanical action while keeping the thermal
action at a low level.
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