Lung Sounds (Breath Sounds)

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Lung Sounds:

Normal lung sounds are soft, breezy, low-pitched vesicular breath sounds over peripheral lung fields.

Crackles, or "rales", are intermittent, non-musical, popping or crackling sounds. They occur when airways pop open as air enters and are classified as fine or coarse based on their quality. 
Coarse crackles resemble tearing apart a piece of velcro. 
Fine crackles sound similar to rubbing a lock of hair between your fingers. 
Crackles indicate alveolar or small airway pathology and can signify conditions like pneumonia, pulmonary fibrosis, heart failure with pulmonary edema, and more.

Wheezes are continuous, musical, high-pitched whistling sounds resulting from narrowed or obstructed airways. They can be polyphonic (multiple pitches perceived) or monophonic (single whistling pitch). Wheezes arise from turbulent airflow through constricted bronchi or bronchioles caused by bronchoconstriction, mucus plugs, or extrinsic airway compression. Common wheeze-producing conditions include asthma, COPD, bronchiectasis, and obstructive lung cancers.

Stridor refers to a harsh, continuous, monophonic, crowing or vibrating sound caused by turbulent airflow through a narrowed trachea or larynx. It indicates significant extrathoracic upper airway obstruction often due to masses, inflammation, trauma, or foreign bodies. Stridor represents a more worrisome, emergent breathing issue requiring prompt intervention.

Rhonchi are low-pitched, continuous, snoring, snorkeling, gurgling, or rumbling breath sounds caused by air moving through bronchi containing secretions or mucus. Unlike wheezes, rhonchi are often clear with coughing or suctioning. They commonly occur with bronchitis, COPD exacerbations, pneumonia, or any condition producing excessive airway secretions.  

Pleural friction rub is a grating, scratching, or creaking sound resembling walking on a creaky wooden floor, caused by inflamed pleural surfaces rubbing against each other during inspiration and expiration. It indicates pleurisy or pleural inflammation and can occur in conditions such as pneumonia, pulmonary embolism, rheumatoid arthritis, and mesothelioma.