What physical finding may indicate "impaired gas exchange" in an elderly female patient?

The correct answer is clubbing of the fingers, which can be indicative of chronic hypoxia or impaired gas exchange in the body. In the case of chronic respiratory conditions, clubbing often develops as a result of long-term low oxygen levels in the blood. This physiological change occurs due to the proliferation of soft tissue at the nail bed, commonly seen in conditions like chronic obstructive pulmonary disease (COPD) or interstitial lung disease.

Other findings related to impaired gas exchange, such as nasal flaring and the use of accessory muscles, typically reflect acute respiratory distress rather than long-standing issues. Nasal flaring is often an instinctual reaction to shortness of breath, while the use of accessory muscles indicates that a patient is struggling to breathe but does not directly indicate chronic hypoxia. A cough can be a symptom of various conditions, including infections or lung diseases, but by itself does not specifically indicate impaired gas exchange. Therefore, clubbing of the fingers is a more specific indicator of prolonged problems with oxygenation, particularly in an elderly patient.