How does CPAP improve oxygenation and ventilation in patients with certain respiratory problems?

• A. Decreases intrathoracic pressure, which allows more room for lung expansion
• B. Prevents alveolar collapse by pushing air into the lungs during inhalation
• C. Forces the alveoli open and increases the concentration of oxygen in the alveoli
• D. Pushes thick, infected pulmonary secretions into isolated areas of the lung

Answer: (C)

CPAP works by maintaining a continuous positive pressure in the airways, which keeps alveoli from collapsing at the end of expiration and helps recruit collapsed lung units. By keeping more alveoli open, the surface area for gas exchange increases, so more oxygen can diffuse into the blood. This improves oxygenation, and because the lungs stay more open, the work of breathing is reduced and ventilation becomes more effective as the patient can sustain better, steadier breaths. It’s not about lowering intrathoracic pressure or actively pushing air in during inhalation like a ventilator, and it doesn’t act to move secretions. The idea that CPAP opens the alveoli and raises alveolar oxygen content best captures how it improves both oxygenation and ventilation.