How Stethoscopes Work

Updated April 20, 2020

Amid advancements, stethoscopes maintain a steady pulse in modern medicine

The stethoscope is among the most useful tools in the advancement of medical science, but the physics behind it haven’t changed since it first appeared in the early 1800s.

Since the time of Hippocrates in 400 B.C., a doctor or a nurse could do little else than place his or her ears to the patients’ chests to obtain findings on the heart and lung. By now it was 1816 — and in the interest of propriety (especially among female patients), French physician Rene Théophile-Hyacinthe Laennec had another idea.

The Stethoscopes Origin

Laennec had rolled a stack of paper into a wooden cylinder, with the paper serving as the transmitter of the sounds he sought to hear. Pressing the cylinder to the patient’s chest and his ear to the free end, he supposedly could hear the cardiac activity much more clearly.

In the 1850s, George Camman and Dr. Alfred Learned enhanced the device, substituting rubber for wood and adding another listening port. Their product is thought to be the prototype of stethoscopes used in modern medicine.

The question “how do stethoscopes work” would be addressed in the coming decades as the medical community implemented its improvements. In the early 1960s, Harvard professor David Littmann created a lighter stethoscope, one that transmitted the sounds more clearly yet. In 1999, the first external noise reducing stethoscope was patented. The first stethoscope that works with a smartphone application was unveiled in 2015.

How a Diaphragm Works

Bhahani Balaravi, a Cary, North Carolina cardiac physician, has a concise answer for the query “how does a stethoscope work.” She states in a recent edition of Heart to Heart health awareness magazine that today’s stethoscope (French for “breast hearing”) has a flat, round chest piece on its lower end, covered by a plastic implement called a diaphragm. The diaphragm moves in the presence of sound, which travels up plastic tubing and into metal earpieces, coming to rest in the doctor’s ears.

Balaravi says that a healthy adult’s heart makes two sounds, called a lub (the first part of the beat) and a dub (the second). The lub sound is created by near-simultaneous closure of the mitral and tricuspid valves, located between the atria (upper chambers) and ventricles (lower chambers) of the heart.

“When the blood leaves the heart via the aorta and pulmonary arteries,” Balaravi explains, “the near-simultaneous closure of the aortic and pulmonary valves creates the dub sound. When the valves do not completely close, a raspy or blowing noise can occur. This is a heart murmur, an extra sound produced as a result of turbulent blood flow during heartbeats, which can mean a valve disorder is present.”

Ultrasonic Advancements

Ultrasonic advancements claim their share of effectiveness in detecting cardiac disease, far beyond the scope of the question “how does a stethoscope work”; they permit a nurse or doctor to directly view body processes en route to diagnoses.

This progress has caused at least one physician to remark, “The stethoscope is dead.” Balaravi, however, places more value to the question “how do stethoscopes work,” as she states that auscultation (the audial portion of the complete physical) is a vital complement to visual aids, often capturing the source of a patient’s problem long before the eyes recognize it as a difficulty.

“Today’s stethoscopes,” Balaravi declares, “still play an important role in diagnosing heart, lung and vascular conditions.”

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