A symbol of medicine, a triumph of simplicity

I rolled a quire of paper into a sort of cylinder and applied one end of it to the region of the heart and the other to my ear, and was surprised and pleased to find that I could thereby perceive the action of the heart in a manner much more clear and distinct than I had ever been able to do by the immediate application of the ear..."

RENE-THEOPHILE-HYACINTHE LAENNEC (1781-1826)

Despite the trend toward the use of hi-tech diagnostic equipment, the simple stethoscope remains the tool most closely identified with medical care. Even those doctors in specialties other an internal medicine who do not routinely examine patients’ hearts and lungs tend to keep a stethoscope close at hand. More than just a helpful device, it has become a fully-fledged symbol of medicine.

The 18th-century doctor attempting to diagnose diseases of the heart and lungs had to rely almost completely on the patient’s verbal inscription of symptoms – the ‘history’. Although the then novel practice of anatomical dissection was leading to revelations about the physical basis of many diseases, doctors had few means of gathering objective data that might point to a specific condition such as a leaky heart valve) before the patient reached the autopsy table.

In trying to hear the sounds coming from the thoracic organs, the doctor would press an ear directly against the patient’s chest – a manoeuvre known as "direct auscultation," from the Latin auscultare, to listen carefully. Apart from being unrewarding from a diagnostic standpoint, this technique was considered undignified and sometimes imprudent. Since it required close physical contact between doctor and patient, it inevitably increased the incidence of contagious diseases spreading. Such transmission may have contributed to the death of one proponent of this approach, the French doctor Robert Bayle, who died of tuberculosis.

Laënnec solved the problem by recalling an acoustic phenomenon he had experimented with as a child in Brittany. By scratching one end of a wooden plank, he could send coded messages to his friends at the other end. When he applied this principle to the problem at hand, Laënnec literally transformed the practice of medicine. Tightly rolling up the pages of his notebook, he placed one end of the makeshift cylinder on his patient’s chest and put the other to his ear: the heart sounds could be heard more distinctly.

Laënnec later replaced the rolled-up paper tube with a slim wooden one resembling a child’s horn. With this simple instrument he was able to hear and describe the sounds associated with diseases that were the scourges of his time. Continuing to study patients from hospital ward to autopsy table, the dedicated doctor tried to match the sounds he had heard in the clinic to the physical signs of disease found after death. For example, the large cavities noted in lungs ravaged by tuberculosis produced one type of sound, while the solidified lung tissues of pneumonia yielded another. The names he applied to these distinctive sounds – rales, bruits, and egophony – are still used.

The stethoscope did not remain a stiff unwieldy tube for long. To make it more compact, Laënnec divided the cylinder into sections that could be carried more easily in an inside pocket. Other European doctors later developed flexible versions, and in 1855 an American doctor named George Cammann devisee a binaural stethoscope that had two ivory-tipped earpieces connected to an ebony chest plate by cloth-covered, spiral-wire tubes. This version, which cost about £2, allowed doctors to listen to a patient's chest with both ears.

Since then, the stethoscope has changed only modestly. Today it is a precision-engineered instrument (often costing £80 or more), with two plastic earpieces attached by rubber tubes to a chest piece with interchangeable ‘heads’: a flat diaphragm, used to hear distinct, high-frequency sounds such as the clicks characteristic of mitral valve prolapse, and a domelike bell, which allows the listener to detect soft, low-frequency noises such as the rumbling murmur of blood flowing through a narrowed mitral valve. To hear these various heart sounds, doctors will often use the diaphragm to listen to several areas of the chest and then apply the bell to the same areas.

Beyond providing insights into heart and lung diseases, Laënnec’s invention encouraged doctors to pursue objective data investigating these and other conditions, instead of relying solely on a patient’s often misleading account of his or her complaints. Doctors not only attended more carefully to sounds emitted by the chest, but – in the interest of correlating their findings on physical examination with what they had learned at autopsy – they also began what has been referred to as "laying on of hands": probing more deeply, palpating the abdomen and other areas of the body, and using the sense of touch to detect abnormalities such as tumours.

Laënnec’s discovery reflected the impact of the French Revolution on the field of medicine. As the Old Regime was driven out, new ideas could be explored that emphasized observation rather than reason alone. These philosophical shifts helped make Paris the centre of medical science in the early 1800s. Whether Laënnec started a revolution or simply rode on the wave of change, the trend toward collecting information by more objective means and correlating physical findings with laboratory data continues today with the widespread use of x-rays, echocardiography, and other diagnostic tests. With his invention, medicine moved closer to becoming a science.