What does a "continuous positive airway pressure" (CPAP) machine do?

A continuous positive airway pressure (CPAP) machine is specifically designed to provide a constant flow of air that maintains open airways during sleep. This is particularly important for individuals with conditions such as obstructive sleep apnea, where the airway can collapse or become blocked, leading to breathing interruptions. By keeping the airways open, a CPAP machine helps prevent these blockages, allowing for uninterrupted breathing and promoting better sleep quality.

While the other options touch on aspects related to respiratory health, they do not accurately describe the primary function of a CPAP machine. For instance, it does not focus on reducing lung pressure or increasing blood oxygen content, nor is it primarily intended for medication delivery during sleep. The main goal is the maintenance of airway patency through continuous air pressure, which is precisely why the provided answer is the most accurate.