A healthcare professional uses a stethoscope for auscultation to detect normal and abnormal breath sounds. Sounds heard in addition to expected air movement are known as adventitious sounds, indicating disruption within the respiratory system. These added noises include wheezes, rhonchi, and crackles, which are characterized as brief, discontinuous clicking or rattling sounds. Crackles, sometimes called “rales,” are divided into fine and coarse categories based on their acoustic properties. This difference in sound is highly significant, pointing to distinct underlying physical mechanisms and locations within the lung. This article focuses specifically on the character and origin of coarse crackles.
Describing the Auditory Experience
Coarse crackles are distinctive and generally easier to hear than their finer counterparts because they are louder and have a lower pitch. They are often described as having a wet, bubbly quality, like the sound of a liquid being boiled vigorously or air passing through thick fluid, and tend to last longer than the higher-pitched sounds of fine crackles. For the general public, the sound is sometimes compared to blowing through a straw into water or the noise of gently tearing open a strip of a hook-and-loop fastener. They are often heard during both the inspiratory and expiratory phases of the breathing cycle, though they may be more prominent during inhalation. This timing differs from fine crackles, which are typically faint, high-pitched, and often restricted to the very end of inhalation.
The Physiological Cause of the Sound
The production of coarse crackles is directly linked to the presence of thick, viscous secretions or excessive fluid within the larger conducting airways of the lungs, specifically the bronchi and trachea. When air moves in and out of the lungs, it must pass through these fluid-filled passages and bubbles through the secretions, causing the distinctive low-pitched, gurgling sound. The larger diameter of the affected airways contributes to the deeper, coarser, and louder nature of the sound. The sound occurs as the air momentarily displaces the fluid or mucus, creating a rapid series of popping noises. Unlike fine crackles, which are caused by the sudden opening of collapsed smaller airways and alveoli, coarse crackles originate in the more central, large-caliber bronchial tubes.
Common Conditions Associated with Coarse Crackles
The presence of coarse crackles indicates a condition that causes a significant buildup of fluid or thick mucus in the larger bronchi. One common condition is severe or chronic bronchitis, where long-term inflammation leads to excessive mucus production and a narrowing of the bronchial tubes, and Chronic Obstructive Pulmonary Disease (COPD) can also frequently produce these sounds. Pneumonia, especially in cases where the infection has caused a large amount of thick, purulent secretions, is another frequent cause of coarse crackles. They may also be heard in cases of pulmonary edema, which is fluid accumulation in the lungs often due to heart failure, though fine crackles are more typical in this condition. A key diagnostic feature is that coarse crackles may change in volume or even disappear temporarily after a patient coughs, as this action can successfully move the secretions out of the larger airways.