Adventitious lung sounds are “extra” or abnormal noises heard when a healthcare professional listens to a person’s chest with a stethoscope, a process known as auscultation. These sounds are not part of the expected, quiet rush of air moving in and out of the lungs. They signal that something is disrupting the smooth flow of air, which can be the first indication of a respiratory problem or illness.
Distinguishing Adventitious Sounds from Normal Breathing
Normal breath sounds are called vesicular sounds, establishing the baseline for a healthy respiratory system. Vesicular sounds are soft, low-pitched, and heard predominantly during inhalation, with a quieter, shorter expiration. These sounds occur because air moves smoothly through the smaller airways and air sacs.
The fundamental difference is that normal sounds reflect laminar airflow, where air moves quietly and parallel to the airway walls, while adventitious sounds indicate turbulent airflow. Turbulent air movement is caused by an obstruction, narrowing, or the presence of fluid or secretions within the airways or surrounding lung structures. Detecting these abnormal sounds suggests that the mechanics of gas exchange or air passage are being compromised. The characteristics of the noise, such as its pitch, duration, and timing, help pinpoint the location and nature of the underlying issue.
Major Classifications of Abnormal Lung Sounds
Adventitious sounds are categorized by their acoustic characteristics, which fall into two main groups: continuous and noncontinuous sounds. Crackles (previously known as rales) are brief, noncontinuous popping sounds, often resembling the noise of hook-and-loop fasteners being pulled apart. Fine crackles are higher-pitched and shorter, caused by the sudden opening of small, deflated airways during inspiration. Coarse crackles are lower-pitched and louder, attributed to air bubbling through thick secretions in larger airways.
Wheezes are continuous, musical, high-pitched sounds typically heard during exhalation. They are generated when air is forced through severely narrowed lower airways. Rhonchi are also continuous, low-pitched sounds, often described as sounding like snoring or a gurgling rumble. Rhonchi are created when air passes over thick secretions in the larger bronchial tubes, causing the airway walls to vibrate.
Stridor is a harsh, high-pitched, continuous sound heard predominantly during inspiration. Unlike wheezes, stridor originates from a significant obstruction or narrowing in the upper airway, such as the larynx or trachea. A pleural friction rub is a non-musical, creaking or grating sound, likened to walking on fresh snow or rubbing two pieces of leather together. This sound is generated when the inflamed layers of the pleura (the membranes lining the lungs and chest cavity) rub directly against one another.
The Medical Significance of Different Lung Sounds
Crackles indicate fluid accumulation within the small air sacs or the collapse and re-opening of peripheral airways. Fine, late-inspiratory crackles are associated with conditions like pulmonary edema (from congestive heart failure) or interstitial lung diseases (like pulmonary fibrosis). Coarse crackles, which may clear with a strong cough, are linked to conditions producing excessive secretions, such as pneumonia or chronic bronchitis.
Wheezes characterize lower airway diseases that cause bronchoconstriction. The high-pitched whistling is a hallmark of conditions such as asthma, chronic obstructive pulmonary disease (COPD), or acute bronchitis, where the bronchial tubes are narrowed. Rhonchi signify the presence of thick, tenacious mucus in the larger airways. This sound is common in illnesses like chronic bronchitis or cystic fibrosis, where the body struggles to clear secretions.
Stridor represents a serious medical situation because it suggests a life-threatening obstruction of the main windpipe or throat. This sound can be heard in cases of viral croup, epiglottitis, or foreign object aspiration. The pleural friction rub points to inflammation of the pleural lining (pleurisy), which can be caused by infections like bacterial pneumonia, pulmonary embolism, or autoimmune disorders. The identification of any adventitious lung sound should prompt a professional medical evaluation to determine the underlying cause, especially if accompanied by shortness of breath or respiratory distress.