Step 1 Question of the Week: Respiratory Physiology

This week’s edition of the Step 1 Question of the Week is about respiratory physiology. See if you can answer the question and then watch the video to learn the correct answer as well as the rationales for each option.


Respiratory Physiology

A 44-year-old man comes to his primary care physician because of fatigue and shortness of breath with exertion that have worsened gradually during the past year. He was diagnosed with obstructive sleep apnea last year. He does not smoke. He is 182.88 cm tall (6 ft) and weighs 150.59 kg (332 lb), and his body mass index is 45 kg/m2. There are no abnormalities on cardiorespiratory examination.

Arterial blood gas shows:
PaO2:  65 mm Hg
PaCO2:  57 mm Hg
pH:  7.35
Serum HCO3–:  30 mEq/L

X-ray of the chest is normal.

Which of the following is the most likely complication of this patient’s condition?

Decreased diffusion capacity for carbon monoxide
B. Destruction of alveoli
C. Intrapulmonary shunting
D. Jugular venous distention
E. Left atrial dilation
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