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It has been an aim of the clinical physiologist to be
able to measure continuously such physiological
variables as pressure, temperature, and hydrogen ion
concentration under conditions of minimal disturbance
to the subject or his environment.
The development of miniature electronic components,
such as the transistor, has made it possible
to construct transducers and amplifiers within such
a small space that studies can be undertaken in
hitherto inaccessible parts of the human body. A
radio transmitter with a total volume of approximately
2 cc. which can transmit information from
the inside of the body was described in 1957 (Mackay
and Jacobson, 1957). These devices have been
further developed and they have been used mainly
to investigate the gastrointestinal tract. Telemetering
capsules ('radio pills') capable of recording pressure,
temperature, and pH have been produced and a
review of these devices is given elsewhere (Mackay,
1959, 1961; Jacobson, 1960; Wolff, 1961). They
transmit a frequency modulated signal in the
frequency range 300 Kc/s to 10 Mc/s. The pressure
pill modifications described in this paper enable the
construction of a simple, reliable and inexpensive
device.
CONCLUSIONS
The pills described above have been shown capable of
recording pressure changes over the period of the
battery life (80 hours).
The drifts in the recorder base line are small but these
could be reduced considerably by improving the receiver.
These improvements would seem to be essential if the
radio pill is to be used as a diagnostic technique in
gastroenterology.
The information collected over a period of three days
is considerable, and some method of electrical recording
such as magnetic tape is necessary in order that electronic
analysis can be made. Collecting information from pills
sutured in known parts of the intestine will aid this
analysis.
From our experience it is clear that economic considerations
alone demand that the device be recoverable.
Most clinical research projects require a large number of
experiments and, furthermore, it is difficult to envisage
adequate testing of a sealed device without loss of a
large proportion of the useful life.