Sleep apnea

 A 71-year-old Caucasian man is brought to the emergency department by his wife. The wife mentions that this is the second time she notices important breathing pauses while her husband sleeps. The patient's medical history is relevant for a recent hospitalization due to decompensated heart failure and an ischemic stroke 2 years ago. He currently takes low-dose aspirin, metoprolol, and furosemide. Upon further interrogation, the patient reports "lacking air" and extreme daytime tiredness. On physical examination, the patient looks pale. Auscultatory findings reveal a progressively faster breathing followed by breathing apneas. His temperature is 36.7°C (98.2°F), pulse is 91/min, respirations are 18/min, blood pressure is 130/61 mm Hg. Laboratory findings reveal a high carbon dioxide saturation of blood after awakening. Which of the following best explains this patient's findings?