Use of a pressure-sensitive radiotelemetering capsule to study the canine gastric interdigestive complex

An inexpensive pressure-sensitive radiotelemetering capsule, transmitting at 100 MHz, was used to study gastric interdigestive complexes. The oscillator was frequency modulated; pressure changes on a rubber diaphragm caused displacements of a ferromagnetic core altering the frequency of oscillation by modifying the inductance in the circuit. The system was linear for applied pressures up to 40 mm of Hg; for 40 mm Hg the frequency decreased by 22 kHz. Three fasted dogs were used; an encapsulated radio pill picked up the presence fluctuations associated with gastric contractions and transmitted these signals as radio waves. An FM receiver intercepted, amplified, and relayed the signals to a chart recorder, which produced a permanent record. During the first part of each 24-hour recording period, cyclical interdigestive patterns consisting of a series of high-amplitude contractions followed by long-lasting quiescence were recorded. Regular outbursts showed mean durations ranging from 11.6 to 17.6 minutes, mean periods from 27 to 51 minutes, and mean amplitudes from 9.9 to 11.1 mm Hg. Noncyclical, irregular recordings were obtained during the last part of each recording period. These results are similar to ones obtained using force transducers.