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MS322 User's Guide
Part 4
Adverse Effects - Shortwave Diathermy Interference
It is extremely important for the physiotherapist to have a clear understanding
of the potential danger involved in the use of a low volt ac stimulator device in
close proximity to an active shortwave diathermy unit.
A medical shortwave diathermy unit is a very powerful transmitter of radio
energy, the larger ones having an output of 500 watts. Any low volt ac stimulator
device with external leads, in close proximity to a shortwave unit, is likely to be
affected by interference. This interference may be in the form of sparking between
electrodes or between the leads and the device casing. The leads connecting the
low volt ac stimulator device to the patient can act as an aerial and collect the
radio frequency energy from the shortwave unit. This could interfere with the
operation of the low volt ac stimulator unit or affect internal functions of the
device. Or, it could result in the patient experiencing some unusual "surges" of
current. There is no significant electrical radiation from a low volt ac stimulator
device.
The increasing electronic sophistication of physiotherapeutic equipment is likely
to mean that this problem is going to become more obvious. The minimum safe
operating distance is difficult to determine since local factors must be considered.
At least two or three meters is needed between the nearest parts of either
instrument, including the cables and electrodes. The low volt ac stimulator device
does not need to be plugged into a power supply to be affected by interference
from a shortwave unit. Some very old types of shortwave generators seem to
produce more interference than others which compounds the problem even
further. With some shortwave units, the distance between devices of at least
three meters may still be inadequate.
In practice, shortwave diathermy units and low volt ac stimulator units should
be placed and operated as far away from each other as possible. It may be
necessary to screen off all shortwave units from other equipment or to have fully
screened rooms in which shortwave diathermy equipment can be operated
without risk of interfering with other sensitive equipment. This is often difficult
in a small practice where space is at a premium. In such cases, the units may
have to be operated at different times, not simultaneously. In all cases, it would
be very dangerous to give shortwave diathermy and low volt ac stimulator
treatment to a patient simultaneously.
Any patient who reports a sudden, unexplainable "surge" in output may be
experiencing the effects of shortwave interference.
Summary of Contents for MS322
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Page 12: ...4 MS322 User s Guide Part 1...
Page 16: ...8 MS322 User s Guide Part 2...
Page 20: ...12 MS322 User s Guide Part 3...