Crackling sounds in the lungs typically reflect a buildup of fluid. Because the heart and lungs are connected by arteries, crackles are sometimes due to disorders of the heart that lead to a back flow of fluid into the lungs. In other cases, lung disease itself is to blame. Pneumonia and other lung disorders, for example, can cause crackling in the lungs. Lung crackles are breath sounds heard with a stethoscope during a routine physical exam. A detailed medical history, blood tests and imaging studies can help sort out the cause.
Lung infection is a common reason for crackling in the lungs. Viral infections can cause bronchitis, which leads to a persistent cough and shortness of breath. Lung crackles and wheezing may develop because of airway irritation and inflammation. Pneumonia, due to a viral or bacterial infection, can cause crackles as well. As white blood cells congregate in the lungs to help fight off the infection, fluid and other byproducts build up, leading to crackles.
Weakening of the heart muscle due to a heart attack, viral infection, genetic disorder or even some medications can result in heart failure. As the pumping function of the heart worsens, blood backs up into the lungs. Most people diagnosed with heart failure initially feel short of breath because of this accumulation of fluid, known as pulmonary edema. During a physical examination, crackling can be heard in the lungs as fluid tends to shift during a deep breath.
Obstructive Pulmonary Disease
Obstructive lung diseases such as asthma; chronic obstructive pulmonary disease, often called COPD; and cystic fibrosis typically cause wheezing, but they can also cause lung crackles. Obstructive lung conditions interfere with the process of exhalation. As a result, carbon dioxide and other wastes that would normally be exhaled build up in the lungs. This damages lung tissue and can lead to crackles. Over time, the bronchi, the passages that bring air in and out of the lungs, become weakened and dilated, causing a condition called bronchiectasis. Bronchiectasis also contributes to crackling in the lungs as additional fluid accumulates.
Interstitial Lung Disease
Lung disorders that involve the interstitum, or the tissue that surrounds the air sacs in the lungs, are known as interstitial lung diseases. Inflammatory conditions like sarcoidosis, autoimmune disorders like rheumatoid arthritis and exposure to some chemicals, such as asbestos, can cause interstitial lung disease. Some people develop an interstitial lung disorder known as idiopathic pulmonary fibrosis, meaning the cause is unknown. Lung fibrosis, or scarring, due to interstitial lung disease causes crackles because fluid becomes trapped in the affected tissue.