Understanding Lung Crackles

By Rosalie McDonough, MD, MSc - Posted in Clinical Education
Summary: Crackles are adventitious lung sounds characterized by brief, discontinuous, popping, or bubbling noises heard primarily during inspiration. They are often classified as “fine” or “coarse,” crackles are associated with conditions such as pulmonary edema, pneumonia, heart failure, bronchiectasis, and interstitial lung disease, all contributing to respiratory distress and discomfort. Accurate recognition and understanding of the underlying pathophysiology are essential for diagnosing and managing the conditions that cause crackles.
Pathophysiology of crackles

Crackles arise from the sudden opening/closing of small airways or alveoli during inspiration/expiration, which causes air displacement and creates the characteristic "popping" or "bubbling" sounds.1,2 This abnormal sound production is typically due to fluid accumulation, inflammation, or structural changes in the lung tissues.3

Associated symptoms
Patients with crackles often (but not always) present with4,5:
  • Shortness of breath: A common symptom of impaired gas exchange, often worsened by exertion or lying flat.
  • Chest tightness: Discomfort or a sensation of constriction in the chest.
  • Cough: Protective reflex that expels irritants from the airway, involving a sudden, forceful release of air from the lungs.
Underlying causes
Crackles can result from a variety of underlying conditions, including6-9:
  • Pulmonary edema: Fluid accumulation in the lungs, often due to heart failure.
  • Pneumonia: Infection leading to inflammation and fluid in the alveoli.
  • Bronchiectasis: Permanent dilation of the bronchi with mucus accumulation.
  • Interstitial lung disease: Group of disorders causing scarring and stiffness of lung tissue.
  • Heart failure: Reduced cardiac function leading to fluid backup in the lungs.
    Diagnostic tests
    To diagnose the cause of crackles, several tests can be utilized1,2:
    • Clinical history: Detailed questioning regarding symptom onset, severity, and associated factors.
    • Pulmonary auscultation: Identification of the sound's characteristics (e.g., fine vs. coarse) and its location in the lung fields.
    • Pulmonary function tests: Assess lung volume, capacity, flow rates, and gas exchange.
    • Chest X-rays: Imaging to visualize lung structures and identify abnormalities.
    • High-resolution CT: Provides detailed images of lung parenchyma, which is helpful in diagnosing interstitial lung diseases.
    Spotlight auscultation

      Coarse crackles: Discontinuous, low-pitched “bubbling” or “rattling” sounds, typically heard towards the center of the chest during inspiration. They are sometimes described as being similar to the sound of “rocks in a tumbler” or blowing a straw underwater.

        Sound recorded by Eko digital stethoscope technology:

         

        Fine crackles: Brief, discontinuous, high-pitched “crackling” sounds, best heard at the lung bases during inspiration. They are sometimes described as being similar to the sound of a crackling fire or rubbing a hair between fingers.

          Sound recorded by Eko digital stethoscope technology:

           

          Tips for auscultation
          • Optimal positioning: Patients should be seated or in a semi-recumbent position.
          • Sound intensity: Can vary from faint to loud, depending on severity.
          • Radiation: Crackles often radiate bilaterally, particularly in dependent lung regions.
          • Progression: With increased severity, crackles become more widespread and persistent throughout inspiration and expiration.
            Treatment options

            Management depends on the underlying cause10-12:

            • Diuretics: Reduce fluid overload in conditions like heart failure.
            • Antibiotics: Treat bacterial infections such as pneumonia.
            • Bronchodilators: Relax bronchial muscles in conditions like COPD.
            • Corticosteroids: Reduce lung inflammation in interstitial lung diseases.
            • Oxygen therapy: Alleviates hypoxemia in severe respiratory distress.
            • Self-care: Includes smoking cessation, hydration, and respiratory exercises.
            References

            1. Vyshedskiy A et al. (2009). Mechanism of inspiratory and expiratory crackles. Chest. 135(1):156-164. https://doi.org/10.1378/chest.07-1562

            2. Ii S and Wada S. (2017). Direct numerical simulation of expiratory crackles: Relationship between airway closure dynamics and acoustic fluctuations. J Biomech. 4(50):234-239. https://doi.org/10.1016/j.jbiomech.2016.11.033

            3. Piirilä P and Sovijärvi AR. (1995). Crackles: recording, analysis and clinical significance. Eur Respir J. 8(12):2139-48. https://doi.org/10.1183/09031936.95.08122139

            4. Hirons B et al. (2023). Cough in chronic lung disease: a state of the art review. J Thorac Dis. 15(10):5823-5843. https://doi.org/10.21037/jtd-22-1776

            5. Raman D. (2015). Dyspnea. Cleveland Clinic. Accessed Nov 7, 2024 from: https://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/pulmonary/dyspnea/

            6. Epler GR, Carrington CB, Gaensler EA. (1978). Crackles (rales) in the interstitial pulmonary diseases. Chest. 73(3):333-9. https://doi.org/10.1378/chest.73.3.333

            7.  Hogg JC. (2004). Pathophysiology of airflow limitation in chronic obstructive pulmonary disease. Lancet. 364(9435):709-21. https://doi.org/10.1016/s0140-6736(04)16900-6

            8. Vyshedskiy A et al. (2005). Transmission of crackles in patients with interstitial pulmonary fibrosis, congestive heart failure, and pneumonia. Chest. 128(3):1468-74. https://doi.org/10.1378/chest.128.3.1468

            9. Piirilä P (1992). Changes in crackle characteristics during the clinical course of pneumonia. Chest. 102(1):176-83. https://doi.org/10.1378/chest.102.1.176

            10. Aoun M and Klastersky J. (1991). Drug treatment of pneumonia in the hospital. What are the choices? Drugs. 42(6):962-73. https://doi.org/10.2165/00003495-199142060-00005

            11. Martinez-Sole J et al. (2023). Overview of the Treatment of Congestion in Heart Failure. Curr Pharm Des. 29(20):1592-1601. https://doi.org/10.2174/1381612829666230714153404

            12. Owens RL et al. (2023). Supplemental oxygen and noninvasive ventilation. Eur Respir Rev. 32(167):220159. https://doi.org/10.1183/16000617.0159-2022

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            About the Author

            Rosalie McDonough, MD, MSc
            Rosalie McDonough, MD, MSc - Clinician Scientist

            Rosalie McDonough, MD, MSc, is a clinician scientist with a diverse background in medical research and clinical practice. She earned her Master of Science degree from McGill University in Montreal, Canada, later completing her medical degree at the University Medical Center Hamburg-Eppendorf in Hamburg, Germany. Dr. McDonough’s career has spanned various fields within medicine, focusing on clinical research and health technology. Her interests have encompassed cardiopulmonary disease, lung cancer, molecular cardiology, occupational medicine, and acute ischemic stroke imaging. She is currently the Senior Manager of Medical Affairs at Eko Health.