The stethoscope is a foundational tool used for auscultation, the act of listening to internal body sounds. While commonly associated with the heart, it also evaluates lung, bowel, and vascular sounds. This guide focuses specifically on the technique required to listen to the heart, offering a basic overview of the process. This information is intended solely for educational purposes and should not be considered a substitute for professional medical training or diagnosis.
Understanding the Stethoscope Components
The modern stethoscope is an acoustic device engineered to amplify internal sounds, transmitting them from the patient to the listener’s ears. The earpieces are a crucial element and must be worn correctly, angled forward to align with the natural slope of the ear canals to create an acoustic seal and enhance sound transmission. The tubing connects the earpieces to the chestpiece, which is placed on the body.
The chestpiece typically features two sides: the diaphragm and the bell, each designed for different sound frequencies. The diaphragm is the larger, flat side, covered by a thin membrane that captures and transmits higher-frequency sounds, such as the main heart sounds, S1 and S2. The bell is the smaller, cup-shaped side and is best suited for detecting lower-frequency sounds, which can include abnormal heart sounds or murmurs. For effective listening, the tubing must be intact, and the earpieces should fit snugly to block out external noise.
Preparing the Patient and Environment
Accurate heart auscultation depends heavily on minimizing external interference and correctly positioning the person being examined. The examination must be conducted in a quiet environment, which may involve turning off background noise. The person should generally be sitting upright or lying down, as these are standard positions for a cardiac examination.
For the best quality of sound transmission, the stethoscope chestpiece must be placed directly onto bare skin. Listening through clothing, even thin fabric, introduces artifacts from the material rubbing against the instrument, obscuring subtle heart sounds. Asking the patient to breathe quietly and avoid speaking further reduces ambient noise and improves sound clarity. Having the person lean forward or turn slightly to their left side can bring the heart closer to the chest wall, making faint sounds easier to hear.
Mapping the Heart Auscultation Points
Listening to the heart is performed systematically over four primary areas on the chest. These locations correspond to where sounds from the four heart valves are best transmitted to the surface.
The four primary auscultation points are:
- Aortic area: Second intercostal space, just to the right of the sternum.
- Pulmonic area: Second intercostal space, on the left side of the sternum.
- Tricuspid area: Fourth or fifth intercostal space, along the left lower sternal border.
- Mitral area (apex): Fifth intercostal space, along the midclavicular line. The midclavicular line is an imaginary line running down the middle of the collarbone.
When using the diaphragm for higher-pitched sounds, apply firm pressure to the chestpiece to create a seal. Conversely, when using the bell for lower-pitched sounds, use only light pressure. Pressing too firmly stretches the skin and filters out the low-pitched sounds.
Distinguishing Basic Heart Sounds
Once the stethoscope is properly placed, the listener focuses on identifying the two fundamental, normal heart sounds, often described as a “lub-dub” rhythm. The first sound, S1 or “lub,” is produced by the closure of the mitral and tricuspid valves at the beginning of ventricular contraction (systole) and is heard most clearly over the Mitral and Tricuspid areas. The second sound, S2 or “dub,” immediately follows S1 and is caused by the closure of the aortic and pulmonic valves at the beginning of ventricular relaxation (diastole). S2 is best heard over the Aortic and Pulmonic areas at the base of the heart. By noting the regularity of the “lub-dub” sequence, one determines the heart rate rhythm; pauses or irregularities suggest an altered rhythm.