A 72-year-old, otherwise healthy patient is admitted to the postanesthesia care unit after open reduction and internal fixation of the hip performed with general anesthesia. An age-related change in which of the following is MOST likely to explain this patient's increased risk for postoperative hypoxia?

Aging causes progressive changes that reduce the functional reserve of organs in the body (Table). Important changes in the respiratory system involve a loss of alveolar surface area, loss of elastic recoil, and a decrease in chest wall compliance. As the elastin and collagen of the supporting structure of lung parenchyma undergo changes, dilation of alveolar ducts and alveoli accompany the reduction of total alveolar surface area. These changes, along with altered surfactant production, cause early collapse of smaller airways, increasing closing volume.

The ventilatory response to hypoxia and hypercarbia is diminished...

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