Stethoscopes—now look hear

Ultrasound stethoscopy will revolutionise the art of bedside diagnosis. Manique Wijesinghe describes the invention and development of the stethoscope and the importance of this new technology

The invention of the stethoscope by the French physician René Laennec in 1816 marked a revolution in the art of physical examination and bedside diagnosis.^w1 The stethoscope is the main instrument used for non-invasive investigation of almost any presenting complaint by today's physicians, and was the first technological aid in clinical medicine.^w2 Most commonly used to identify abnormalities of the heart and lung sounds, stethoscopes are also used to listen for bowel sounds. Research suggesting that muscle sounds characteristic of Parkinson's disease, where the normal mode of muscle discharge (Piper band sounds, frequency 40-50 Hz) is replaced by a pulsatile muscular activity of 10 Hz, can be identified by stethoscopy is rarely of clinical importance.^w3

The birth of the stethoscope

These were prophetic words indeed. Before Laennec's invention, physicians used the technique of “immediate auscultation” to listen to the chest—that is, direct application of the ear on to the patient's chest.^w1 This practice had obvious limitations, being in Laennec's opinion “as uncomfortable for the doctor as it was for the patient, disgust in itself making it impracticable.^w1

The stethoscope was invented when “a young woman labouring under general symptoms of a diseased heart” consulted Laennec.^w1 As immediate auscultation was unsuitable as a method of examining this patient “on account of the great degree of fatness,” Laennec, a keen musician, improvised.^w1 Recalling a simple principle of acoustics—that sound is better conveyed through solid objects—the young physician rolled a quire (24 sheets) of paper into a cylinder and applied one end to the woman's chest and the other to his ear.^{w1 w4} Lo and behold, the heart sounds were transmitted with much greater clarity and distinction than ever before. And the rest, as they say, is history.

The evolution of the stethoscope

Laennec's contribution to cardiac auscultation did not end with his invention, which he called simply Le Cylindre.^w1 Auscultating almost 3000 patients between 1817 and 1819, he carefully correlated observations before death with findings at postmortem examination,^w1 publishing his Traite de L'auscultation Mediate (On Mediate Auscultation) in 1819. From him we get the terms we use to describe auscultatory findings today, such as bruit, rhonchi, rales, crepitations and pectoriloquy.^w1 Despite the importance of Laennec's findings, the conclusions drawn from them were often erroneous. For example, he asserted that ventricular contraction preceded that of the atria, and was responsible for the second heart sound.^w1

Others, such as James Hope and C J B Williams, experimentally related auscultatory findings with the underlying disease process, providing rational explanations for the presence and abnormalities of heart sounds.^w1

The design of the stethoscope has changed gradually over the past two centuries, with the first important improvement being made by Pierre Adolphe Piorry in 1828.^w4 The Piorry stethoscope, the inspiration behind Sir Oliver Wendell Holmes's humorous poem “The Stethoscope Song,” was trumpet shaped and had a thinner stem than the original instrument.^{w4 w5} Although the idea for a binaural stethoscope (with earpieces for both ears—the first stethoscopes were monaural) had existed before this, the production of the first recognised binaural stethoscope is attributed to Dr George Camman, working in New York in the early 1850s.^{w4 w6}

The stethoscope today

One million professional stethoscopes are sold around the world each year.^w7 A number of different models are available, including electronic stethoscopes, which can amplify sound while filtering external noise.^w8 These can also record sounds for playback and analysis later.^{w7 w8} The most commonly used stethoscopes consist of two earpieces, polyvinyl chloride tubing, and a chest piece with a tunable diaphragm for picking up high frequency sounds and a bell for low frequency sounds. Specialist cardiology stethoscopes, some of which have sophisticated features such as simultaneous heart rate measurement (displayed on a screen on the chest piece), and paediatric and infant stethoscopes are widely used by clinicians. Disposable stethoscopes are also manufactured, which may reduce the risk of transmission of infections.

Heart and lung teleauscultation is a technique in which an electronic stethoscope transmits heart and lung sounds to a remote internet enabled computer. This has been recognised as a reliable method for assessing patients with cardiac abnormalities, especially in rural areas and in developing countries, where access to medical practitioners may be limited.^w9 Paediatric cardiologists, for example, can interpret heart murmurs they receive as email attachments from remote clinics.^w2

The future of stethoscopy

Advanced medical imaging technologies such as magnetic resonance imaging, computed tomography, and ultrasound scanning are widely available. With interobserver variation in the evaluation of auscultatory findings being a considerable disadvantage, the importance of the stethoscope as a diagnostic tool has somewhat diminished, given the availability of these imaging modalities.^{w1 w2 w10}

However, the advent of ultrasound stethoscopy is revolutionising the art of bedside diagnosis. The ultrasound stethoscope is a handheld personal device, expected to come into widespread use over the coming decades. This will enable physicians to make a rapid assessment of the patient and identify structural abnormalities well before they became audible via a stethoscope. These systems incorporate phased array transducers, providing two-dimensional, dynamic grey scale images, with colour Doppler flow imaging.^w2 They can be either battery or mains powered.

A number of different models of echo stethoscopes are already available.^w2 Enabling direct, instant visualisation of the heart and other organs, the word stethoscope (Greek stethos=chest, skopein=to see) is more appropriate for these systems than for traditional ‘stethoscopes.^w2

The ultrasound stethoscope can be extremely useful in a critical care environment—for example, in identifying right ventricular abnormalities in acute myocardial infarction and the presence of pulmonary emboli.^w2 It can be helpful in guiding procedures such as emergency pericardioscentesis and central line placement. It can also be used to assess left ventricular function and valvular function, and in screening for left ventricular hypertrophy in patients with hypertension and for diseases such as hypertrophic cardiomyopathy.^w2 Echo stethoscopes can be useful not only in cardiology, but also in paediatrics, abdominal examinations, and even for intraoperative monitoring.^w10

As the use of these light, handheld devices becomes more widespread, it is essential that users get adequate training in echocardiographic interpretation.^w2 The level of training required depends on the purpose for which the investigation is done.^w2 Ultrasound stethoscopes are reportedly being used by American doctors stationed in Iraq.^w2

Ultrasound stethoscopes are set to have a crucial role in bedside diagnosis and screening. By ensuring that medical students receive basic echocardiographic training—currently lacking—they will be well equipped to make full use of this technology, thus optimising their effectiveness as future clinicians.

Manique Wijesinghe, third year medical student, University of Southampton
Email: manique.w@gmail.com


studentBMJ 2006;14:265-308 July ISSN 0966-6494