In patients with airway foreign body or open pneumothorax, the pressure on both sides of the chest cavity is not equalized, and the mediastinum undergoes a side-to-side oscillation during respiration, which is called mediastinal oscillation.
When a foreign body enters the airway, the airway is partially obstructed, the air entering the lung on the obstructed side decreases during inspiration, causing the mediastinum to shift toward the obstructed side, and during expiration there is no significant obstruction to the process of gas expulsion from the lungs, and the mediastinum returns to an intermediate position, resulting in slight mediastinal sway.
Open pneumothorax creates a direct communication between the pleural cavity and the outside atmosphere, and the pressure in the pleural cavity on the injured side is equal to the atmospheric pressure, while the pleural cavity on the healthy side remains negative and lower than that on the injured side, causing the mediastinum to oscillate during respiration.
Patients with mediastinal swing often have symptoms such as chest pain, dyspnea, and asphyxia, and need to go to the hospital as soon as these symptoms appear.