The stethoscope is one of the most recognizable instruments in healthcare, used to listen to the internal sounds of the body, a practice known as auscultation. This process allows clinicians to gather information about the heart, lungs, and gastrointestinal system. The entire instrument works by transmitting vibrations from a patient’s body to the ears of the user. The specific terminology for the part placed against the skin is often unclear.
The Chestpiece: Anatomy of the Sound Receptor
The component placed directly onto the patient’s body to capture internal sounds is formally called the chestpiece. This part is typically made from a durable metal like stainless steel or brass, which helps ensure optimal sound transmission. The chestpiece itself is usually dual-sided, featuring two different surfaces for sound collection. It connects to the rest of the instrument via the stem, which attaches the chestpiece to the flexible tubing.
The chestpiece must be placed directly on the skin to create an effective acoustic seal and minimize external noise interference. One side presents a large, flat surface called the diaphragm, while the opposite side is a smaller, concave cup known as the bell. In many modern stethoscopes, a non-chill ring made of plastic or rubber encircles both surfaces to prevent patient discomfort upon contact.
Differential Listening: Diaphragm Versus Bell
The two surfaces of the chestpiece are engineered to detect different frequencies of sound within the body. The diaphragm is the larger, flat side covered by a thin, tensioned membrane designed to pick up higher-frequency sounds. When placed on the patient, the flat membrane vibrates in response to the body sounds, filtering out lower frequencies. This surface is typically used for listening to lung sounds, normal heart sounds, and most bowel sounds.
Conversely, the bell is the smaller, hollow, cup-shaped side that functions best for detecting low-frequency sounds. The bell works by creating a seal with the patient’s skin, which then acts as the vibrating membrane itself. The clinician must apply very light pressure when using the bell. Pressing too firmly stretches the skin, which converts the bell’s function to that of the diaphragm. Low-frequency sounds, such as specific heart murmurs or vascular bruits, are best heard using this light-touch technique.
The Acoustic Pathway: Tubing and Headset
Once the chestpiece captures the vibrations, the sound travels through the acoustic pathway, beginning with the flexible tubing. This tubing is typically made from a thick, durable material like polyvinyl chloride (PVC) and is designed to transmit sound with minimal distortion or loss. Many contemporary models utilize double-lumen tubing, which provides two separate sound channels from the chestpiece to the headset, improving acoustic clarity. The tubing length is standardized to balance sound quality with clinical maneuverability.
The sound waves ultimately reach the headset, the upper assembly of the stethoscope that the clinician wears. The headset consists of metal ear tubes, which are angled to align with the natural curve of the ear canal for an optimal fit. Attached to the ear tubes are soft-sealing eartips, usually made of silicone or rubber, which create a comfortable and acoustically tight seal in the ear canal. This seal blocks out ambient noise and directs the faint internal body sounds captured by the chestpiece directly to the listener’s ears.