Royal Institution Christmas Lectures

Signals From the Interior: Probes, Sondes and Sounds (1975x4)

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If one had to associate a particular instrument with doctors in general, it would certainly be the stethoscope. It enables him with convenience and decorum to listen to the noises inside his patient. Most of the interesting noises occur in the chest and in particular in or close to the heart, though bowel sounds have also received some attention. The interpretation of the sounds takes experience, but this can be supplemented by detecting the sounds electronically and displaying them as a picture, when it also becomes possible to measure the time relationship between them. Man is really a tube about 10 metres long, if one considers the path between mouth and anus in which all our food is digested. It is not easy to explore the inside of this tube except close to the two ends. One way of measuring some of the physical conditions inside it such as pressure, temperature, movement, and even acidity is to swallow a very small radio-transmitter equipped with means to modultate the radio signal in accordance with the conditions it encounters. Such a transmitter can be allowed to pass right through the system, transmitting as it is moved along. Another way of exploring the alimentary canal, which is also applicable to the tubes in the lung, is to use an endoscope. This is an optical system which can allow one to see round corners and also to examine in detail whatever is close to the tip of the device. When great flexibility is required endoscopes can be made out of bundles of special glass fibres, where each fibre carries one image point from the input end of the bundle to the viewing end. It is important therefore that the geometrical arrangement of the ends of the fibres at the two ends is identical in order to avoid scrambling the image, a requirement which makes them difficult and expensive to construct.