Which of the following is a cause of apnea?

Apnea, the temporary cessation of breathing, can be caused by several factors, but severe brain trauma is a significant one. This is because the brain houses crucial centers that control respiratory rhythm, including the medulla and pons. When severe damage occurs, it can disrupt these centers, leading to impaired respiratory function and potentially causing episodes of apnea.

In contrast, smoking primarily affects lung function and airways over time, which may lead to chronic respiratory conditions but does not directly cause apnea. High altitude can lead to hypoxia and is associated with altitude sickness rather than immediate cessation of breathing. Frequent exercise enhances respiratory efficiency and can improve lung function, making it unlikely to cause apnea unless there are underlying health issues.