A 47-year-old man is evaluated for progressively worsening dyspnea on exertion for several months. The patient has frequent awakenings at night due to a choking sensation and feels tired all the time, limiting his physical activity. He does not use tobacco, alcohol, or illicit drugs. Blood pressure is 166/100 mm Hg and pulse is 80/min. BMI is 48 kg/m². Jugular venous pressure is difficult to assess due to neck fat. Heart sounds are distant with no murmurs or gallops. Bilateral breath sounds are normal with no crackles or wheezes. Trace bilateral pitting edema is present. Chest x-ray reveals poor inspiratory effort but clear lung fields. Which of the following additional findings is most likely present in this patient?

Question

Quizplus · Accepted Answer

Obstructive sleep apnea (OSA) can exist alone or in combination with obesity hypoventilation syndrome (OHS). This patient with neck fat, fatigue, and sleep disturbances (consistent with OSA) also has progressive dyspnea on exertion in the setting of morbid obesity (consistent with OHS). Patients with OSA in the absence of OHS experience hypoventilation only at night with transient hypoxia and hypercapnia that resolve while awake. However, in those with OHS, physical restriction of the thoracic cavity caused by excess thoracic tissue continues throughout the day, resulting in chronic hypoxia and hypercapnia. In an effort to maintain a normal pH, the kidneys increase bicarbonate retention and decrease chloride reabsorption (via bicarbonate-chloride exchangers in intercalated cells of the distal nephron) to create a compensatory metabolic alkalosis. In the setting of chronic hypoxia, patients with OHS can develop pulmonary hypertension (due to hypoxic vasoconstriction) with eventual cor pulmonale (right heart failure), which can cause peripheral edema. Systemic hypertension is common with both isolated OSA and comorbid OSA/OHS, possibly due to hypoxic triggering of the sympathetic nervous system and increased levels of circulating catecholamines. (Choice A) Patients with OHS are chronically hypoxic, causing increased erythropoietin secretion and a compensatory erythrocytosis. (Choice C) Patients with OHS have hypoxia and increased (rather than decreased) pCO₂ due to chronic hypoventilation. (Choice D) Antidiuretic hormone (ADH) secretion can be increased in congestive heart failure, which is unlikely given this patient's clear lungs and the lack of vascular congestion. OHS is not classically associated with the syndrome of inappropriate ADH secretion, which can occur due to medications or lung tumors (unlikely given the normal chest x-ray). (Choice E) This patient is roughly euvolemic with a history that does not raise concern for intravascular volume depletion. Educational objective: Patients with combined obesity hypoventilation syndrome and obstructive sleep apnea can develop chronic hypoxia and hypercapnia (with a compensatory metabolic alkalosis), secondary erythrocytosis, pulmonary hypertension, and cor pulmonale. References: Sympathoexcitation and arterial hypertension associated with obstructive sleep apnea and cyclic intermittent hypoxia. (http://www.ncbi.nlm.nih.gov/pubmed/26251511)

A 47-Year-Old Man Is Evaluated for Progressively Worsening Dyspnea on Exertion