PSWT employs the same operating frequency as traditional SWD
ie. 27.12MHz

The output from the machine is pulsed such that the ‘on’ time is considerably shorter than
the ‘off’ time,
thus the mean power delivered to the patient is relatively low
even though the peak power
(i.e. during the on pulses) can be quite high (typically around 150 – 200 Watts peak power
with modern machines,
though some still go up to 1000W).

the duration (time) of each ‘ON’ phase
The pulse durations are very short – measured in microseconds (millionths
of a second)

Can usually select from a range of preset options (depends on machine)

• e.g. Megapulse
  100 / 200 / 400 / 600 / 800 pps
• e.g. Curapulse 403
  26 / 35 / 46 / 62 / 82 / 110 / 150 / 200 / 300 / 400 pps

is a variable parameter on many but not all machines

It is sometimes fixed (most usually on the machines that deliver both pulsed and continuous shortwave energy, and most commonly ‘fixed’ at 400 microsec)

The term pulse duration is preferable to pulse width (commonly used)
as it is a time based measurement rather than a size.

The number of cycles completed during each pulse (or ‘on’ phase) remains quite high.

Pulse Duration ---- No of cycles completed per pulse
65 microsec 1,763 cycles
100 microsec 2,712 cycles
400 microsec 10,848 cycles

The output of the monode applicator can be thought of as a
form of pulsed inductothermy.

There is an element of tissue heating
which occurs during the
`on' pulse,
but this is dissipated
during the prolonged ‘off' phase
& therefore, it is possible to give treatment with no NET increase in tissue temperature
(loosely termed a nonthermal’ treatment).

Non thermal treatment the mean power applied

Normal cell membranes exhibit a
potential difference due to the
relative concentration differences of various ions on either side of the membrane.

Of these ions,
sodium (Na+),
potassium (K+),
calcium (Ca++),
chloride (Cl-),
& bicarbonate (HCO3-)
are probably the most important.

Cell membrane potentials
vary according to the cell type,
but a typical membrane potential is
-70mV, internally negative.

It is actively maintained by a series of
pumps & gated channels, & cellular energy (ATP) must therefore be utilized to maintain the
potential.

A cell involved in the inflammatory process demonstrates a
reduced cell membrane potential
& consequently, the cell function is disturbed.

The altered potential affects ion transport across the membrane, &
the resulting ionic imbalance alters cellular osmotic pressures.

The application of PSWT to cells affected in this way is claimed to

• restore the cell membrane potential to their ‘normal’ values & also
• restores normal membrane transport
• & ionic balance

More acute the presentation the lower the delivered mean power
(i.e. 3 Watts is max for this group)

Using

• narrower (shorter duration) pulses and a
• higher the repetition rate may be beneficial.

As the condition becomes less acute, use wider (longer duration) pulses

Mean power of more than 5 Watts
is usually required in order to
achieve a reasonable tissue response.
[Be careful with the thermal component as research has shown that at mean powers of about 12 Watts or more, most people
can feel some heating effect.
If you want to avoid heating, you
MUST keep the mean power lower than this.
To be safe, better
to keep the mean power below 5 Watts
at the present time].

Pulses of longer duration are probably of benefit if there is a choice

Pacemakers
(some but not all pacemakers can be adversely
influenced by shortwave and pulsed shortwave fields. The current recommendation is that a 3m separation should be maintained between a patient with a pacemaker and an operating shortwave (continuous or pulsed) machine

Pregnancy
(given the potential adverse effect on the foetus, it is suggested that a patient who is pregnant should not be treated with pulsed shortwave at all.

Current tissue bleeding
(it is fine to apply PSWT soon after an injury so
long as in the clinical judgement of the therapist, tissue bleeding has stopped)

Malignancy
(PSWT, like US and Laser has the capacity to increase the rate of division of malignant tissue and therefore it is best avoided. A history of malignancy is not the contraindication (often confused). It is the delivery of the energy to tissue which is malignant, or is considered that it might be thus.)

Active tuberculosis
(no absolute evidence on this, but widely held to be a contraindication)

Avoid treatment of the
abdomen and pelvis during menstruation
(precaution rather than a contraindication)

Severe circulatory compromise
or deficit including ischaemic tissue,
thrombosis and associated conditions

Deep X Ray therapy or other ionizing radiations (in the last 6 months)
in the region to be treated (historical and assumed rather than actually evidenced)

Patients who are unable to comprehend the therapists instructions or
who are unable to cooperate

It is considered safe to deliver a low dose (less than 5 Watts mean power)
when there is metal in the tissues

In the interest of physiotherapist safety,
it is recommended
that once the machine has been switched on,
the physiotherapist and all other personnel
should keep at least 1 metre from the
operating machine, leads and electrodes.

Pregnant physiotherapists
or others with concerns may want
to ask a colleague
to turn the SWD / PSWD machine on.
Almost all modern machines will turn off automatically

It is recommended that other electrotherapy devices,
especially electrical stimulation apparatus, are kept at least 2 metres from the PSWT machine

The output of some machines (e.g. interferential therapy devices) can be affected by close proximity to an operating SWD / PSWT machine