Source: Jaideep S. Talwalkar, MD, Internal Medicine and Pediatrics, Yale School of Medicine, New Haven, CT

Through auscultation, the clinician is able "to eavesdrop on the workings of the body" to gain important diagnostic information.¹ Historically, the term "auscultation" was synonymous with "immediate auscultation," in which the examiner's ear was placed directly against the patient's skin. Although this was standard practice for centuries, the method proved inadequate in nineteenth-century France, due to social norms and suboptimal diagnostic yield. This led René Laënnec to invent the first stethoscope in 1816 (Figure 1), a tool that has since become inseparable from auscultation in modern clinical practice, and patients hold it as a symbol of honor and trustworthiness among those who carry them.²

Figure 1. A representative illustration of the first stethoscope invented by René Laënnec.

The stethoscope has undergone many technologic advances since Laënnec's initial hollow wooden tube. Practically speaking, the provider must understand the difference between the two sides of the modern stethoscope's chest piece: the diaphragm and the bell (Figure 2).

Figure 2. Parts of a modern stethoscope.

When applied firmly against the patient's skin, the diaphragm transmits high frequency sounds. Sounds from within the patient vibrate the membrane of the diaphragm. These vibrations result in the propagation of sound through the column of air inside the stethoscope and into the examiner's ears. Conversely, when applied lightly, the bell transmits low frequency sounds. The bell acts as a cup that directly transmits sounds from within the patient through the tubing of the stethoscope. Pressing more firmly with the bell can stretch the underlying skin, essentially turning it into a diaphragm. Auscultation is used in a wide variety of clinical settings. It most commonly plays a role in the examination of the chest, heart, abdomen, and vasculature.