In pneumothorax, intrapleural pressure equalizes with what?

• A. Negative pressure
• B. Atmospheric pressure
• C. Positive pressure
• D. Intrathoracic pressure

Answer: (B)

In a pneumothorax, the intrapleural pressure equalizes with atmospheric pressure. Normally, the intrapleural pressure is negative, which helps to keep the lungs inflated and facilitates the mechanics of breathing. This negative pressure is critical for normal lung expansion during inhalation.

When a pneumothorax occurs, air enters the pleural space, disrupting the negative pressure gradient. This influx of air causes the intrapleural pressure to rise and become equal to atmospheric pressure. As a result, the lung on the affected side can collapse because the necessary pressure difference to keep it inflated is lost. Thus, in the case of pneumothorax, the equilibrium with atmospheric pressure directly impacts lung function, leading to compromised ventilation and gas exchange.