Positive-pressure ventilation differs from negative-pressure ventilation in that positive-pressure ventilation:

• A. Draws air into the lungs by chest expansion
• B. Reduces airway pressure
• C. Forces air into the lungs
• D. Allows passive expiration only

Answer: (C)

Positive-pressure ventilation forces air into the lungs by pushing it in, raising airway pressure above atmospheric. This is how breaths are delivered with devices like a bag–valve mask or a mechanical ventilator. In contrast, negative-pressure ventilation works by surrounding the chest with lower pressure, so the chest expands and air is drawn into the lungs. So the defining difference is pushing air into the lungs rather than letting chest expansion pull air in. Expiration is typically passive, and positive-pressure ventilation may allow assisted or passive expiration, but the key distinction is the act of forcing air in.