• Intermittent, predominantly inspiratory breath sounds caused by sudden opening of small airways.
• Short, explosive, non-musical sounds seen in parenchymal lung diseases such as pneumonia, IPF, and pulmonary edema.
• On sound analysis, appear as rapidly dampened, repetitive waveform deflections.

Classified as fine or coarse crackles.

• Fine crackles → Mid-to-late inspiratory, best heard in dependent lung regions, not transmitted to the mouth.
• Coarse crackles → Early inspiratory, may extend into expiration, with a “popping” quality.

Reference

1. Smith A. Lung sounds: Types and their causes and treatment options. Medicalnewstoday.com. https://www.medicalnewstoday.com/articles/lung-sounds. Accessed July 11, 2022.
2. Zimmerman B, Williams D. Lung sounds. InStatPearls 2021 Aug 30. StatPearls Publishing. Available from https://www.ncbi.nlm.nih.gov/books/NBK537253/. Accessed July 11, 2022.
3. Kim Y, Hyon Y, Jung SS, et al. Respiratory sound classification for crackles, wheezes, and rhonchi in the clinical field using deep learning. Scientific reports. 2021 Aug 25;11(1):1-1.
4. Bohadana A, Izbicki G, Kraman SS. Fundamentals of lung auscultation. New England Journal of Medicine. 2014 Feb 20;370(8):744-51.