Which of the following is a common sign of an exacerbation of obstructive sleep apnea?

Hypoxemia is a common sign of an exacerbation of obstructive sleep apnea (OSA). OSA is characterized by the intermittent obstruction of the airway during sleep, which leads to repeated apneas or hypopneas. As a result, affected individuals often experience significant drops in oxygen saturation levels due to the obstructed airflow, causing hypoxemia. This lack of adequate oxygen can lead to various symptoms and complications, including daytime sleepiness, cognitive impairment, and cardiovascular issues.

The other options, while they may indicate other health issues or symptoms, are not typically associated with a worsening of obstructive sleep apnea in the same direct manner as hypoxemia. Persistent cough, for example, could suggest respiratory infections or allergies rather than a direct result of airway obstruction that characterizes OSA. Rapid weight gain can be a risk factor for the development of OSA, rather than a sign of exacerbation. Increased heart rate may be a response to different conditions but does not specifically indicate the exacerbation of OSA like hypoxemia does. Hence, the presence of hypoxemia is a clear and direct indicator of worsening obstructive sleep apnea.