The Radio Pill Tech

Gut, 1962, 3, 181

Methods and techniques

Telemetering from within the body using a pressure-sensitive radio pill
B. W. WATSON, B. ROSS, AND A. W. KAY From the Regional Medical Physics Department and the University Department of Surgery, Royal Infirmary, Sheffield
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.
7 The frequency on which the pill transmits should be variable so that two or more pills can be used synchronously in one subject. 8 The characteristics of the diaphragm should not be affected by the body fluids encountered by the capsule. 9 The design should be flexible so that parameters other than pressure can be measured without necessitating major basic modifications of the capsule. The pills described so far have fallen short of these ideal requirements in one or more respects. All circuits use the variation in

References: return of typical type 3 pressure waves is observed on the permanent record. The duration of small bowel paralysis after various operations, including resection of the vagus nerves to the stomach, has been determined and is soon to be reported. Changes in gastric motility are recorded by suturing a capsule to the gastric mucosa. The results of these studies have an important bearing on the postoperative management of patients undergoing gastrointestinal surgery. In some patients, recordings have been made simultaneously from the stomach and small intestine. This has been rendered feasible by the flexibility of the design of our telemetering device. In clinical experiments on the urinary bladder, the stability of our pill has permitted measurement of absolute pressures during postural changes, and recordings of intravesical pressure during normal micturition. 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. Connell, A. M., and Rowlands, E. N. (1960). Wireless telemetering from the digestive tract. Gut, 1, 266-272. Jacobson, B. (1960). Development and use of endoradiosonde techniques. Progressive Report, Karolinska Institutet, Department of Medical Electronics. -, and Lindberg, B. (1960). F.M. receiving system for endoradiosonde techniques. IR.E. Transactions on Medical Electronics, October 1960, pp. 334-339. Mackay, R. S. (1959). Radio telemetering from within the human body. IR.E. Transactions on Medical Electronics, June 1959, pp. 100-105. (1961). Radio telemetering from within the body. Science, 134, 1196-1202. and Jacobson, B. (1957). Endoradiosonde. Nature (Lond.), 179, 1239-1240. Rowlands, E. N., and Wolff, H. S. (1960). The radio pill. Telemetering from the digestive tract. British Communications and Electronics, 7, 598-601. Wolff, H. S. (1961). 'The Radio Pill '. New Scientist, 12, 419-421.