How a Stethoscope Works

A stethoscope is a medical device for listening to sounds inside the body. The initial stethoscope was invented in the early 19th century by French physician René Laennec, but was actually trying to achieve a rather different end: doctor-patient distance. The stethoscope can be placed against the patient's chest to listen to her breath or heartbeat, or against the lower abdomen to listen to the intestines. On one end of the stethoscope is a diaphragm, a vibrating membrane designed to pick up sound. The diaphragm is connected to a hollow, air-filled tube. That tube splits in two and leads to earpieces, which the doctor wears.

When the heart beats or the lung fills with air, it produces small sound vibrations through the body. These vibrations are picked up and amplified by the diaphragm. The sound passes into the tube, which transfers it into the doctor's earpieces. There are also electrical stethoscopes, which use a kind of microphone to pick up and amplify the sound.

To understand how a stethoscope conveys, say, the "lub-lub" of a heart beat from a heart to a doctor's ears, we'll start with the core components of the tool.

 

Chestpiece: This is the part that contacts the patient, capturing sound. The chestpiece is constructed of metal and is typically double-sided to work for differently sized patients and different areas of the body. The chestpiece has deep cups that capture sounds from the target area and may be ringed with a "chill ring" to keep the patient from being uncomfortable when touched by the cold metal chestpiece. There are two sides of the chestpiece. On one side is the diaphragm, a flat, metal disc that in turn contains a flat, plastic disc. The diaphragm is the larger component of the chestpiece. On the other side is the bell, a hollow, bell-shaped piece of metal with a tiny hole on top. The bell is better at picking up low-pitch sounds, such as heart murmurs (the aforementioned "whoosh"); the diaphragm excels in the higher-pitch range, which includes normal breath sounds and heartbeats ("lub-lub").

 

Acoustic Tubes and Ear Tubes: A Y-shaped configuration of rubber tubesruns from the chestpiece to the headset. The sounds picked up by the chestpiece initially travel through a single tube, eventually splitting into two channels as they near the headset so the listener can hear it in both ears. Stethoscope tubing typically ranges from about 18 to 27 inches (45 to 68 centimeters) long. The acoustic tube connects the ear tubes to the chestpiece and is a flexible tube made of a rubberized material. The acoustic tubing can be filled with different materials to best transmit sound from the patient to the health-care provider. The ear tubes attach the earpieces to the main body of the stethoscope. They are typically constructed of metal and consist of hollow tubes that are ideally suited to transmitting low-frequency sound.

 

Earpieces/ Headset: The earpieces are fitted into the ears and are typically rubberized for comfort and to isolate from external sounds. They are designed to transmit sounds directly into the ears. The rubber tubing ends at a set of metal tubes that carry the sound to the eartips in the listener's ears. The eartips are made of soft rubber, not only for comfort but also to create a seal that helps block out environmental noise.