The stethoscope is a medical instrument used to listen to the internal sounds of the body (auscultation). This tool functions by amplifying subtle acoustic vibrations from within a patient, allowing a healthcare provider to assess the circulatory, respiratory, and gastrointestinal systems. Learning the proper use of this device begins with a detailed understanding of its physical design and how to achieve an optimal fit for accurate sound transmission.
Understanding the Components and Fit
A modern acoustic stethoscope is composed of several parts that transmit sound from the patient’s body to the user’s ears. The main components are the headset, the tubing, and the chest piece. The headset includes the metal binaurals and the earpieces, which are designed for acoustic isolation and comfort.
The earpieces must be inserted into the ear canals pointing forward, aligning with the natural direction of the auditory canal. This forward angle, often around 15 degrees, ensures a tight acoustic seal that minimizes external noise interference. Users may need to adjust the tension of the binaurals by gently squeezing or pulling them apart to achieve a comfortable yet snug fit.
The chest piece, which contacts the patient, is typically dual-sided, featuring a diaphragm and a bell. The diaphragm is the larger, flat side covered by a thin membrane that vibrates to pick up high-frequency sounds, such as normal heartbeats and breath sounds. The bell is the smaller, concave side used to detect low-frequency sounds, including certain heart murmurs and vascular bruits.
On a dual-head stethoscope, only one side of the chest piece is acoustically active at a time. The user selects the desired side by rotating the stem connecting the chest piece to the tubing until a distinct click is heard. This indexing process ensures the sound path is open from the chosen surface to the earpieces.
Listening Technique and Environment
Effective auscultation requires controlling the listening environment and mastering the application of the chest piece. The surrounding area should be quiet to prevent extraneous sounds from obscuring the subtle internal body noises. Furthermore, the chest piece should be placed directly against the patient’s bare skin, as clothing can create friction noise and significantly dampen the transmission of internal sounds.
When utilizing the diaphragm for high-frequency sounds, the user must apply firm pressure to the patient’s skin. This firm contact tenses the membrane, which effectively filters out lower frequencies and accentuates the higher-pitched acoustic signals. This technique is used for most routine assessments, including listening to lung sounds and the primary S1 and S2 heart sounds.
To hear the low-frequency sounds using a traditional bell, the technique shifts to applying only light contact. The bell functions as an air-filled chamber, and resting it gently on the skin allows the skin itself to act as the vibrating membrane. Pressing too firmly with the bell will stretch the skin, turning it into an artificial diaphragm that dampens the low-frequency sounds one is attempting to hear.
Some modern stethoscopes feature a tunable diaphragm, which streamlines the listening process by eliminating the need to flip the chest piece. With this design, light pressure activates the diaphragm to pick up low frequencies, mimicking the bell’s function. Increasing the pressure on the same side then engages the diaphragm to capture high frequencies, offering versatility through a simple variation in hand contact.
Basic Areas for Auscultation
The stethoscope is systematically employed across three primary regions of the body: the chest for cardiac and pulmonary assessment, and the abdomen. Cardiac auscultation involves listening over specific anatomical landmarks where the sounds of the heart valves are best heard. The expected sounds are the distinct “lub-dub” rhythm, which represents the closure of the heart valves (S1 and S2).
Cardiac Auscultation Points
These primary areas include:
- The Aortic area: Second intercostal space at the right sternal border.
- The Pulmonic area: Second intercostal space at the left sternal border.
- The Tricuspid area: Fourth and fifth intercostal spaces near the left sternal border.
- The Mitral area: Located at the heart’s apex, typically around the fifth intercostal space at the midclavicular line.
Pulmonary auscultation requires a methodical approach, beginning at the lung apices above the clavicles and working downward, comparing corresponding sites on the left and right sides. The chest piece is moved across the anterior, lateral, and posterior fields of the thorax, with the patient taking deep breaths through the mouth. The normal finding is vesicular breathing, a soft, low-pitched sound heard primarily during inspiration.
For abdominal assessment, the stethoscope is placed lightly on the four quadrants of the abdomen to listen for bowel sounds. These sounds are high-pitched gurgling and clicking noises produced by the movement of gas and fluid through the intestines. The absence or excessive presence of these sounds can provide information regarding gastrointestinal motility.