A 2-year-old boy is brought to the emergency department by his mother who reports he was playing with his older brother's toy collection when he suddenly began coughing and developed respiratory distress. On arrival, he is anxious and diaphoretic. Vital signs: respiratory rate 34/min, heart rate 118/min, blood pressure 95/58 mmHg, temperature 37.2°C. Pulse oximetry shows oxygen saturation of 87% on room air. Physical examination reveals nasal flaring, intercostal retractions, and unilaterally diminished breath sounds on the right with no adventitious sounds. The left lung has normal breath sounds. After placement of a non-rebreather mask with 100% oxygen, repeat pulse oximetry shows only minimal improvement to 89% oxygen saturation. Chest X-ray shows opacification of the right lower lobe with normal left lung fields. Which of the following pathophysiologic mechanisms best explains the patient's hypoxemia and poor response to supplemental oxygen?

1. A)Ventilation-perfusion mismatch with areas of low V/Q ratio
2. B)Alveolar hypoventilation secondary to decreased respiratory muscle strength
3. C)Diffusion impairment across the alveolar-capillary membrane
4. D)Anatomic right-to-left shunt with perfused but unventilated lung unitsGABARITO
5. E)Increased alveolar dead space from pulmonary vascular obstruction