Auscultation is the technique of listening to the internal sounds of the body, and it is a foundational method for assessing respiratory health. The sounds generated by air moving through the lungs offer immediate insights into the condition of the airways and surrounding tissues. Listening to breath sounds helps determine if airflow is clear or if blockages, fluid, or inflammation are present. This guide provides an overview of the tools, procedures, and basic interpretations involved in lung auscultation.
Essential Equipment and Setup
The primary instrument for listening to breath sounds is the stethoscope, which amplifies internal acoustic signals. The device features a chest piece with two sides: the diaphragm and the bell. For lung sounds, the diaphragm is typically used because it detects the higher-pitched sounds produced by air movement in the chest.
The bell is better suited for hearing low-pitched sounds, such as certain heart murmurs, and is not utilized for a standard pulmonary assessment. For an accurate assessment, the environment must be quiet to prevent external noise from obscuring subtle internal sounds. The person being examined should be in a comfortable, upright position, ideally sitting, as this allows for full lung expansion and easier access to the back and sides.
All clothing should be removed from the chest and back area, as listening through fabric can introduce artifact noise and muffle genuine lung sounds. Applying the diaphragm firmly against the bare skin ensures direct transmission of the respiratory sounds. Friction from hair or clothing brushing against the tubing can generate sounds that mimic abnormal lung patterns, leading to misinterpretation.
Proper Technique for Listening to the Lungs
A systematic approach is required for effective auscultation to ensure all lung fields are adequately assessed and compared. The person must be instructed to breathe deeper than normal and consistently through their mouth, which increases the volume of the breath sounds. The technique involves a side-to-side comparison, moving the stethoscope from one side of the chest or back to the corresponding location on the opposite side.
Starting on the anterior chest, the stethoscope is placed systematically from the apices (above the clavicles), moving downward toward the base of the lungs. The lateral sides are also assessed along the mid-axillary line to listen to the lower lobes. When listening to the back, the subject should lean forward slightly to move the scapulae out of the way.
Listening points on the back begin above the scapulae and proceed down the back in a ladder-like pattern. It is important to avoid placing the stethoscope directly over bone, such as the scapulae or the spine, as bone does not transmit lung sounds effectively. Comparing symmetrical points helps identify if a sound is present in one area but absent or diminished in another.
Distinguishing Normal Breath Sounds
Normal airflow through healthy lung tissue produces characteristic acoustic patterns that vary depending on stethoscope placement. Vesicular breath sounds are the most common, heard over most peripheral lung fields. These sounds are low-pitched, gentle, and have an inspiratory phase that is distinctly longer than the expiratory phase.
Bronchial sounds are heard over the trachea and the manubrium (top part of the sternum), and are loud, high-pitched, and hollow-sounding. Bronchial sounds feature an expiratory phase that is longer than the inspiratory phase, reflecting the tubular nature of the large airways. These sounds are normal only when heard in their specific central anatomical locations.
A third category is the bronchovesicular sound, which mixes the characteristics of the other two types. These sounds have an intermediate pitch and intensity, with the duration of inspiration and expiration being approximately equal. Bronchovesicular sounds are typically heard near the sternum in the upper anterior chest and posteriorly between the scapulae.
Identifying Common Abnormal Lung Sounds
Abnormal lung sounds, termed adventitious sounds, signal an underlying respiratory condition.
Wheezes
Wheezes are continuous, high-pitched, musical sounds generally heard during exhalation. They are caused by air being forced through narrowed airways due to bronchospasm, mucosal edema, or obstruction. Wheezes are commonly associated with conditions like asthma and chronic obstructive pulmonary disease (COPD).
Crackles (Rales)
Crackles (rales) are short, discontinuous, non-musical sounds described as brief popping or rattling noises. These sounds are often linked to the sudden opening of collapsed small airways or the movement of fluid within the alveoli. Fine crackles may occur with pulmonary edema or heart failure, while coarser crackles can be heard in cases of pneumonia or bronchitis.
Rhonchi
Rhonchi are continuous, low-pitched sounds that have a coarse, snoring, or gurgling quality. They are caused by the passage of air over thick secretions in the larger airways. Unlike crackles, rhonchi are continuous and may clear or change location after a strong cough, indicating mucus movement. They are frequently heard in individuals experiencing a respiratory infection or chronic bronchitis.
Stridor
Stridor is a harsh, high-pitched sound typically heard during inhalation, originating from turbulent airflow in the upper airway (larynx or trachea). This sound suggests a severe narrowing or obstruction of the main windpipe, such as from croup or a foreign object. Stridor is a serious medical sign that demands immediate professional assessment due to the potential for complete airway blockage.