A 36-year-old woman comes to the physician because of a 4-day history of fever, malaise, chills, and a cough productive of moderate amounts of yellow-colored sputum. An x-ray of the chest shows an infiltrate at the right middle lobe. Her temperature is 38.8°C (101.8°F), pulse is 92/min, respirations are 20/min, and blood pressure is 128/74 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 91%. The patient is treated with appropriate antibiotics. Two days later, the patient feels well overall and her pulse oximetry is improved to 97% on room air. Examination reveals unchanged crackles and egophony from her previous visit. Which of the following processes best explains this patient's improved oxygenation?

Question

A 36-year-old woman comes to the physician because of a 4-day history of fever, malaise, chills, and a cough productive of moderate amounts of yellow-colored sputum. An x-ray of the chest shows an infiltrate at the right middle lobe. Her temperature is 38.8°C (101.8°F), pulse is 92/min, respirations are 20/min, and blood pressure is 128/74 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 91%. The patient is treated with appropriate antibiotics.  Two days later, the patient feels well overall and her pulse oximetry is improved to 97% on room air.  Examination reveals unchanged crackles and egophony from her previous visit.  Which of the following processes best explains this patient's improved oxygenation?

Quizplus · Accepted Answer

Eductional Objective: Hypoxic pulmonary vasoconstriction (HPV) limits perfusion to nonventilated alveoli, shunting blood toward better-ventilated ones, preserving ventilation-perfusion matching to maintain oxygenation.  HPV can be impaired by inflammatory vasodilation (eg, pneumonia or sepsis), and restoration of HPV optimizes oxygenation despite minimal improvement in ventilation of consolidated alveoli.

A 36-Year-Old Woman Comes to the Physician Because of a 4-Day