Compressive atelectasis

Definition and physical conditions of occurrence

Compression atelectasis occurs when external pressure is exerted on the lung tissue, forcing the alveoli to collapse. A fundamental feature of this specific type of atelectasis is that, despite the lack of air in the respiratory divisions, the ventilating bronchus remains patent.

Normally, healthy lung tissue is a heterogeneous porous medium that effectively dampens coarse sound vibrations originating from the central airways (glottis and trachea). However, in compression atelectasis, two crucial physical conditions form that radically alter the acoustics of the chest:

1. Consolidation of lung tissue — the displacement of air turns a section of the lung into a homogeneous dense mass that becomes an ideal conductor for sound waves.
2. Preservation of the air column — the open lumen of the bronchus directly connects the compressed area of the lung with the source of the rough sound.

Auscultatory pattern in lung collapse

To understand the essence of pathological changes, it is necessary to recall the physiology of respiratory sounds. Normally, vesicular breath sounds are heard over the lungs — a soft, rustling noise produced by the rapid expansion of the elastic walls of numerous alveoli. Graphically, it is characterized by a long inspiratory phase and a very short (or inaudible) expiratory phase. The presence of this sound confirms that the lung segment is "breathing".

In compression atelectasis, the alveoli are compressed and cannot expand. Consequently, vesicular breath sounds completely disappear over the affected area. Instead, pathological bronchial breath sounds are conducted through the consolidated tissue.

This is a loud, harsh sound devoid of softness. As the classic of auscultation R. Laënnec wrote: "air passes into an empty and wide space". Unlike vesicular breathing, the graphical inspiratory phase here is shorter and harsher, while expiration is prolonged, loud, and predominates over inspiration. The appearance of such a sound outside the projection of the trachea always indicates pathological consolidation of the lung tissue.

Mechanism of development in spontaneous pneumothorax

A classic example of severe compression atelectasis is spontaneous pneumothorax. This pathology often occurs as a complication of a prolonged course of bronchial asthma against the background of episodes of persistent, paroxysmal coughing.

The pathogenesis of the process unfolds in several stages:

• Severe coughing leads to acute overdistension of the alveoli, resulting in barotrauma.
• Rupture of the visceral pleura occurs.
• Air from the lung rushes into the pleural cavity.
• A check-valve mechanism is formed: with each new breath, the volume of free air in the pleural cavity steadily increases.
• The rising pressure in the pleura begins to compress the lung from the outside, rapidly causing its compression atelectasis.

Clinical manifestations and hemodynamic disorders

The symptoms of compression atelectasis in pneumothorax develop acutely. At the moment of visceral pleural rupture, the patient experiences sharp, severe pain. Due to the exclusion of the compressed part of the lung from gas exchange, dyspnea rapidly increases.

In addition, the air accumulating in the pleural cavity exerts pressure not only on the lung tissue but also shifts the mediastinal organs. This leads to severe hemodynamic disorders, primarily a sharp drop in blood pressure. The situation may be aggravated by the development of pneumomediastinum (air breakthrough into the mediastinum). In this case, acute pain syndrome can clinically mimic myocardial infarction, requiring immediate differential diagnosis.

Class and exam questions

What else to study on this topic

• Mechanisms of generation of main respiratory sounds (vesicular and physiological bronchial breathing).
• Differences between compression atelectasis and obstructive atelectasis (the role of the closed bronchus).
• Spontaneous pneumothorax and pneumomediastinum as complications of barotrauma.
• Acute complications of a severe asthma attack (status asthmaticus): development of the "silent chest" syndrome.
• Chronic cor pulmonale (cor pulmonale): mechanisms of formation during pulmonary tissue remodeling.
• Special variants of bronchial breathing: conditions for the formation of amphoric breathing in cavitary lesions.

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