What is CPAP primarily used to treat?

CPAP, which stands for Continuous Positive Airway Pressure, is primarily used to treat sleep apnea. Sleep apnea is a condition characterized by repeated interruptions in breathing during sleep, often due to the collapse of the airway. CPAP machines work by delivering a steady stream of air through a mask that keeps the airways open, allowing individuals to breathe more easily while they sleep. This treatment helps to alleviate the symptoms of sleep apnea, enhancing overall sleep quality and reducing associated health risks.

In the context of the other conditions listed, heart failure, asthma attacks, and lung cancer do not primarily rely on CPAP therapy for treatment. Heart failure can involve a variety of medications and lifestyle changes, while asthma attacks are typically managed with bronchodilators and anti-inflammatory medications. Lung cancer treatments can include surgery, chemotherapy, and radiation therapy, none of which directly involve CPAP. Thus, CPAP's specific application to sleep apnea makes it the correct choice for this question.