A 42-year-old woman with severe pulmonary fibrosis is evaluated by her physician and has the following arterial blood gases: $\mathrm{pH}=7.48, \mathrm{~Pa}_{\mathrm{O}_{2}}=55 \mathrm{~mm} \mathrm{Hg}$, and $\mathrm{Pa}_{\mathrm{CO}_{2}}=32 \mathrm{~mm} \mathrm{Hg}$. Which statement best explains the observed value of $\mathrm{Pa}_{\mathrm{CO}_{2}}$ ?

Question

Quizplus · Accepted Answer

[VIII B; Table 4.7]. The patient's arterial blood gases show increased pH, decreased $\mathrm{Pa}_{\mathrm{O}_{2}}$, and decreased $\mathrm{Pa}_{\mathrm{CO}_{2}}$. The decreased $\mathrm{Pa}_{\mathrm{O}_{2}}$ causes hyperventilation (stimulates breathing) via the peripheral chemoreceptors, but not via the central chemoreceptors. The decreased $\mathrm{Pa}_{\mathrm{CO}_{2}}$ results from hyperventilation (increased breathing) and causes increased $\mathrm{pH}$, which inhibits breathing via the peripheral and central chemoreceptors.

A 42-Year-Old Woman with Severe Pulmonary Fibrosis Is Evaluated by Her