The syndrome characterized by prolonged episodes of severe hypoxemia and associated PaCO2 elevation that worsens during sleep is:

The syndrome characterized by prolonged episodes of severe hypoxemia and associated PaCO2 elevation that worsens during sleep is:

• A. Gastroesophageal reflux
• B. Pulmonary hypertension
• C. Obesity hypoventilation
• D. Upper airway resistance

Answer: (C)

Obesity hypoventilation syndrome. This condition occurs when the excess body mass leads to inadequate ventilation, causing chronic hypercapnia (elevated PaCO2) and hypoxemia that are often present at night and worsen during sleep. The added weight makes the chest wall stiffer and reduces lung volumes, so even during wakefulness ventilation can be insufficient; sleep then further depresses ventilatory drive, exaggerating CO2 retention and desaturation. That combination—prolonged severe hypoxemia with a rising PaCO2 that gets worse during sleep—is the hallmark of this syndrome. Gastroesophageal reflux can cause reflux-related symptoms and is more common in obesity, but it does not produce persistent CO2 retention or nocturnal hypercapnia. Pulmonary hypertension can develop as a consequence of chronic hypoxemia but is not the syndrome characterized by nocturnal CO2 retention itself. Upper airway resistance syndrome involves increased airway resistance and sleep fragmentation without the sustained hypercapnia that defines obesity hypoventilation.

Obesity hypoventilation syndrome. This condition occurs when the excess body mass leads to inadequate ventilation, causing chronic hypercapnia (elevated PaCO2) and hypoxemia that are often present at night and worsen during sleep. The added weight makes the chest wall stiffer and reduces lung volumes, so even during wakefulness ventilation can be insufficient; sleep then further depresses ventilatory drive, exaggerating CO2 retention and desaturation. That combination—prolonged severe hypoxemia with a rising PaCO2 that gets worse during sleep—is the hallmark of this syndrome.

Gastroesophageal reflux can cause reflux-related symptoms and is more common in obesity, but it does not produce persistent CO2 retention or nocturnal hypercapnia. Pulmonary hypertension can develop as a consequence of chronic hypoxemia but is not the syndrome characterized by nocturnal CO2 retention itself. Upper airway resistance syndrome involves increased airway resistance and sleep fragmentation without the sustained hypercapnia that defines obesity hypoventilation.