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Classic Projects: medical stethoscope

There can be no single image that immediately conjures up the medical profession with more powerful effect than that of a stethoscope around the neck of a doctor. Invented in 1816, the instrument has been with us for almost two centuries, its purpose - listening to sounds inside the body - never changing.

Today there are electronic models, and mechanics have developed them as a tool for listening to the sounds made by engines, but the principle remains the same: to achieve a diagnosis by listening to the patient's inner workings. Although we associate the stethoscope with heart and lung diagnosis, they play a role in monitoring pregnancy and bowel health.

It was French scientist René Laennec's brilliant idea to roll up a sheet of paper into a tube in the hope of amplifying the acoustic signal. As with virtually every doctor before him, he had been using a technique called auscultation that involved placing the ear directly on the patient's chest, often combined with a percussion technique that in turn would help to reveal a diagnosis. The problem for Laennec was that his female patient was overweight and in order to listen to her heart and lungs he needed to boost the audio. The paper tube evolved into a wooden tube and although it was virtually indistinguishable from the ear trumpet, which can be traced back to the 17th century, the doctor called his invention the stethoscope, derived from the Greek word for chest and the Latin word for instrument.

Within half a century the monaural instrument had become a staple of the doctor's diagnostic armory, allowing them to hear a patient's lungs and heart with more clarity than ever, and in so doing paved the way forward for modern medicine.

In the mid-19th century design changes were brought in to include British doctor Golding Bird's flexible tube. By the Great Exhibition of 1851 the instrument had become binaural with developments by Irish physician Arthur Leared. The following year New York-based doctor George Cammann adapted the design for mass production, and in a display of medical altruism refused to patent the design on the grounds that he wished it to be available to everyone. The Cammann stethoscope, with its ivory earpieces and silk-wound tubes, was to remain the boilerplate design for decades.

The development of the chest piece, which amplified sound by employing a stiff diaphragm, took a leap forward in the 1940s when a design emerged where one side was specifically for cardiovascular auscultation and the other for respiratory diagnosis. Further refinements in materials, weight and comfort over the decades mean that by increments, the classic doctor's stethoscope that we think of today emerged: cheap, portable, practical and indispensable.

It was only a matter of time before the acoustic stethoscope became electronic. As with the evolution of electric guitars, the idea was basically to put a pick-up at the source of the audio (ie the chest piece) and convert these into an electronic signal. The advantages of such a system vary from being able to send the signal to a recorder or laptop, to more advanced telemedicine. But even electronically amplified stethoscopes will soon become a thing of the past as handheld ultrasound devices invade the market. Industry analysts GIA say they are gaining an upper hand over conventional stethoscopes, mainly due to "enhanced digital sound transmission capabilities of electronic stethoscopes in applications such as telemedicine and teaching".

Date: 1816
Inventor: René Laennec
Basic unit cost: £30-70
Next month: The Brennan torpedo

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