Why does pneumothorax produce Hamman's sign?

Hamman's sign occurs in pneumothorax when air accumulated in the pleural cavity rubs against or collides with the pericardium and pleura during cardiac contraction and relaxation, producing a characteristic crunching or clicking sound near the sternum. This sign is typically more pronounced when lying on the left side or during inspiration. If sudden chest pain and difficulty breathing occur along with Hamman's sign, prompt medical evaluation is recommended.

Under normal conditions, the thoracic cavity maintains a negative pressure with no gas accumulation. In pneumothorax, rupture of lung tissue allows air to enter the pleural space, increasing intrathoracic pressure. The heart, located within the thoracic cavity, experiences impact from the ventricular wall against the air-filled pleural space during systole, while movement of air occurs during diastole. These combined actions generate abnormal friction and vibrations.

These vibrations can be transmitted through the chest wall and detected by a stethoscope, resulting in Hamman's sign. It is commonly seen in tension pneumothorax or small pneumothorax, and more frequently observed in left-sided cases due to the closer anatomical proximity of the left hemithorax to the heart, leading to more evident interaction between cardiac motion and intrathoracic air.

In daily life, avoid activities that may cause lung rupture, such as severe coughing or straining during bowel movements. Individuals with underlying lung diseases should receive regular treatment. When suggestive symptoms appear, remain quiet and rest, minimize physical activity to prevent worsening hypoxia, maintain airway patency, and prepare for timely medical intervention.