Atelectasis is a common respiratory condition defined by the partial or complete collapse of a lung or a section of a lung (a lobe). This collapse occurs at the level of the alveoli, the microscopic air sacs responsible for gas exchange. When these sacs deflate, the affected lung area loses volume and cannot properly transfer oxygen into the bloodstream. Medical professionals use a stethoscope to listen to the chest, a procedure known as auscultation, to detect changes in airflow that signify this collapse. The sounds heard provide immediate, non-invasive clues about the severity and location of the affected lung tissue.
What Atelectasis Is and Why It Occurs
Atelectasis develops when the alveoli cannot remain open, interfering with normal breathing mechanics. The underlying pathology involves the loss of lung volume, which prevents the efficient exchange of oxygen and carbon dioxide. This condition is categorized by how the alveolar collapse is triggered, falling into two main categories: obstructive and non-obstructive causes.
Obstructive atelectasis, also known as resorptive atelectasis, occurs when an airway leading to a lung segment becomes blocked. Common obstructions include a mucus plug, an inhaled foreign object, or a tumor growing within the airway. Air trapped distal to the obstruction is gradually absorbed into the bloodstream, causing the air sacs to deflate entirely.
Non-obstructive atelectasis results from external forces or internal deficiencies that prevent lung expansion. Compressive atelectasis occurs when a mass or fluid, such as a pleural effusion or a tumor, presses on the lung tissue, squeezing air out of the alveoli. Another form, adhesive atelectasis, involves a deficiency of surfactant, the substance that reduces surface tension and helps keep the alveoli open.
Postoperative atelectasis is the most frequent presentation, commonly occurring after general anesthesia or major surgery. Anesthesia alters the normal breathing pattern and can impair diaphragm function, leading to shallow breaths. This shallow breathing, often compounded by pain, prevents full inflation of the lungs, causing the alveoli at the lung bases to collapse.
The Specific Sounds Heard During Auscultation
The most definitive sign of atelectasis is a reduction or complete absence of normal breath sounds over the affected lung area. Since the alveoli are collapsed and air is not moving effectively, the typical rustling sound of air movement is diminished. A medical professional notes a difference in sound intensity when comparing the affected area to the corresponding healthy lung area.
In cases of severe collapse, breath sounds may be entirely absent, indicating no detectable airflow into that portion of the lung. In milder or resolving atelectasis, however, the sounds may simply be weak or distant. This diminished air entry is a direct consequence of the lack of ventilation in the collapsed segment.
Secondary or adventitious sounds may also be heard, particularly fine, late-inspiratory crackles, often described as sounding like the rubbing of hair near the ear. These sounds are produced as the collapsed air spaces attempt to pop open during the patient’s deep inhalation. The presence of these crackles suggests a partial or resolving collapse as the tissue begins to re-inflate.
When a large lung segment has collapsed but the main airway remains open, transmitted voice sounds can occur. The collapsed, denser lung tissue acts as a better conductor of sound than healthy, air-filled tissue. This results in increased vocal clarity over the affected area, known as bronchophony, or the distinct transmission of whispered words, called whispered pectoriloquy.
Related Patient Symptoms and Confirmatory Diagnosis
Patient symptoms vary significantly depending on the extent of the lung collapse. If only a small portion is involved, the individual may have no noticeable symptoms. When a larger section of the lung is affected, common symptoms include shortness of breath (dyspnea) and a rapid, shallow breathing pattern (tachypnea).
A persistent cough is frequently reported as the body attempts to clear secretions or blockages causing the collapse. In more extensive cases, impaired gas exchange leads to hypoxemia (a lower-than-normal level of oxygen in the blood). This reduction in oxygenation can manifest as a bluish tint to the skin or lips, a sign requiring immediate attention.
While auscultation provides a strong clinical suspicion, the diagnosis of atelectasis is typically confirmed visually through medical imaging. The most common tool is a Chest X-ray (CXR), which reveals characteristic signs of the collapse. On the X-ray image, the affected lung area appears denser or whiter than the surrounding healthy, air-filled tissue.
A Chest X-ray may also show indirect signs of volume loss, such as crowding of the ribs or a shift of the trachea or heart toward the collapsed lung. In complex cases, a Computed Tomography (CT) scan provides a detailed, cross-sectional view of the chest. The CT scan accurately delineates the extent of the collapsed segment and can identify the underlying cause, such as a tumor or large mucus plug.