Lung auscultation is a foundational diagnostic technique used to evaluate the respiratory system by listening to the sounds generated within the body. Performed with a stethoscope, this process allows a clinician to hear the movement of air through the lungs and airways. Interpreting these sounds provides immediate, valuable insight into a patient’s breathing status, making it a routine part of nearly every physical examination.
How the Procedure is Performed
The procedure begins with the patient positioned upright, ideally sitting, to allow for full lung expansion and access to the chest and back. A quiet environment is necessary to clearly hear the subtle sounds of airflow within the chest cavity. The clinician uses the diaphragm of the stethoscope, which is better for detecting the higher-pitched sounds associated with the lungs, and applies it directly to the skin.
The patient is instructed to breathe slowly and deeply through the mouth, which increases the volume and intensity of the breath sounds. The clinician systematically moves the stethoscope across specific auscultation points, following a pattern that allows for a side-to-side comparison. This comparison is important because diminished or absent sounds on one side can signal an underlying issue like a collapsed lung or fluid accumulation. The examination covers the anterior chest, the lateral sides, and the posterior chest, moving from the apex of the lungs downward to ensure all lobes are evaluated.
Understanding Normal Respiratory Sounds
Normal airflow produces two primary types of sounds: vesicular and bronchial, which serve as the healthy baseline for comparison. Vesicular sounds are soft, low-pitched, and are heard predominantly over the vast majority of the lung tissue, known as the periphery. They are generated by air rushing into the small sacs of the alveoli, and the inspiratory phase is noticeably longer than the expiratory phase.
Bronchial sounds are significantly louder, higher-pitched, and have a more hollow quality, normally heard only over the trachea and main bronchi. These sounds are created by turbulent airflow moving through the large, central airways. Unlike vesicular sounds, the inspiratory and expiratory phases are roughly equal in duration, and a slight pause may be heard between them. The presence of bronchial sounds in an area where vesicular sounds should be heard is an abnormal finding, suggesting the lung tissue itself has become consolidated.
Categorizing Abnormal Breath Sounds
Sounds heard beyond the normal repertoire are termed adventitious, and they are classified as either continuous or discontinuous. Wheezes are a continuous, musical sound, usually high-pitched and often heard during exhalation, though they can occur during both phases of breathing. They are generated by air attempting to pass through airways that have been severely narrowed or compressed.
Rhonchi are also continuous, but they present as a lower-pitched, coarse sound, often described as snoring or gurgling in quality. This sound originates from the movement of air over thick secretions or mucus that has accumulated within the larger airways. Unlike other abnormal sounds, rhonchi may clear or change significantly after a patient coughs, as the physical obstruction is temporarily moved.
Crackles, previously called rales, are discontinuous sounds, meaning they are brief, intermittent, and non-musical, often likened to the sound of popping or clicking. These sounds are primarily heard during inhalation and are caused by the sudden opening of small, collapsed airways or alveoli that were stuck shut due to fluid or inflammatory processes. Fine crackles are shorter and higher-pitched, similar to the sound of hair being rubbed between fingers, while coarse crackles are lower-pitched and last slightly longer, sounding more like bubbling.
A Pleural friction rub is a distinct, harsh, grating, or creaking sound that is heard during both inhalation and exhalation. This sound is not generated within the airways themselves but rather by the inflamed layers of the pleura, the membranes lining the lungs and the chest cavity, rubbing against each other. The rub is often localized to a specific area and may be particularly noticeable because the sound is created very close to the chest wall.
Linking Sounds to Common Respiratory Illnesses
The presence and character of adventitious sounds provide clues for the clinician to narrow the diagnostic possibilities. Wheezes are suggestive of conditions characterized by widespread bronchoconstriction and airway obstruction, such as asthma or Chronic Obstructive Pulmonary Disease (COPD). In these illnesses, the narrowing of the bronchial tubes creates the high-pitched whistling sound.
The finding of crackles, particularly fine crackles, often points toward conditions involving fluid in the lung tissue or collapsed alveoli. They are commonly heard in patients with pneumonia, where inflammatory fluid fills the small air sacs, or in congestive heart failure, which causes pulmonary edema. Coarse crackles, which arise from larger airways, may indicate fluid accumulation, such as that seen in early pulmonary congestion or severe bronchitis.
Rhonchi, the low-pitched, snoring-like sounds, are associated with conditions that produce excessive mucus, like acute bronchitis or cystic fibrosis. The mucus partially obstructs the flow of air in the larger bronchi, creating the rumbling noise that often shifts or diminishes with coughing. By combining the type of sound, its location, and the phase of breathing, auscultation allows for the rapid, initial identification of a respiratory problem.