Which statement describes how CPAP improves oxygenation and ventilation in certain respiratory conditions?

• A. It prevents alveolar collapse by pushing air into the lungs during inhalation.
• B. It pushes thick, infected pulmonary secretions into isolated areas of the lung.
• C. It forces the alveoli open and pushes oxygen across the alveolar membrane.
• D. It decreases intrathoracic pressure, which allows more room for lung expansion.

Answer: (C)

CPAP works by delivering a steady positive pressure to the airways, which keeps the alveoli open throughout the breathing cycle. By preventing alveolar collapse, more surface area participates in gas exchange, so oxygen diffuses more effectively across the alveolar membrane into the blood. That combination—keeping alveoli open and enhancing oxygen transfer—is how CPAP improves oxygenation and overall ventilation in conditions where alveoli tend to collapse or fill with fluid. The other ideas aren’t how CPAP operates: it isn’t about pushing secretions into parts of the lung, it provides continuous pressure rather than pressure only during inhalation, and it raises intrathoracic pressure rather than decreasing it.