A stethoscope is a medical instrument used for auscultation, the process of listening to the internal sounds of the body. This acoustic device allows healthcare professionals to detect and evaluate sounds generated by the heart, lungs, and intestines. Its design captures faint internal vibrations and amplifies them for diagnostic assessment.
The Chestpiece
The component placed directly onto a patient’s body is called the chestpiece. This is the primary sound-gathering element, engineered to convert physical vibrations into acoustic waves. The chestpiece is typically designed to house two distinct listening surfaces that enable the user to listen to a full spectrum of internal body sounds. It connects to the rest of the device via a stem, which often acts as a valve to direct sound from one surface into the tubing.
The Diaphragm and Bell
The two surfaces on the chestpiece—the diaphragm and the bell—are specialized for filtering different sound frequencies. The diaphragm is the larger, flat side, covered by a taut, thin membrane designed to detect high-frequency sounds. When pressed firmly against the skin, the diaphragm selectively filters out low-frequency noise, making it ideal for listening to clear lung sounds, normal heart sounds, and typical bowel movements. Its stiff membrane vibrates primarily in response to the rapid pressure fluctuations characteristic of higher-pitched noises.
Conversely, the bell is the smaller, cup-shaped side, engineered to pick up low-frequency sounds. The bell works by resting lightly on the patient’s skin, allowing the skin itself to act as the vibrating membrane. This technique is useful for detecting subtle, lower-pitched sounds, such as certain heart murmurs or vascular sounds known as bruits. Due to its required light application, the bell effectively captures these deeper sounds that the diaphragm might otherwise filter out.
How Sound is Transmitted
Once the chestpiece captures the sound vibrations, they are transmitted to the listener’s ears. The sound waves travel through the hollow, flexible tubing, typically constructed from medical-grade polyvinyl chloride (PVC). This material minimizes external noise interference and ensures sound fidelity via multiple reflection off the interior walls. The tubing splits into two channels connecting to the metal eartubes, directing sound into the soft earpieces, which form an acoustic seal within the ear canal to block ambient noise and deliver the collected internal sounds clearly.