A 60-year-old man comes to your office complaining of dyspnea (difficult breathing). His laboratory values are as follows: $\begin{array}{|l|l|l|}
\hline& \text {Breathing}& \text {Breathing $ 100 \% $}\
& \text {air}& \text {$\mathrm{O}_{2} \text { for } 7 \text { minutes }$} \
\hline \text { Arterial } \mathrm{PO}_{2}(\mathrm{mmHg}) & 76 & 500 \
\hline \text { Arterial } \mathrm{PCO}_{2}(\mathrm{mmHg}) & 55 & 65 \
\hline \text { Arterial } \mathrm{Hb}(\mathrm{g} / 100 \mathrm{~mL}) & 18 & 18 \
\hline \text { Arterial } \mathrm{O}_{2} \text { saturation (\%) } & 85 & 100 \
\hline \text { Arterial } \mathrm{pH} & 7.35 & 7.20\
\hline
\end{array}$
Which of the following diagnoses best explains the laboratory test findings?

Question

A 60-year-old man comes to your office complaining of dyspnea (difficult breathing). His laboratory values are as follows: $\begin{array}{|l|l|l|}
\hline& \text {Breathing}& \text {Breathing $ 100 \% $}\
& \text {air}& \text {$\mathrm{O}_{2} \text { for } 7 \text { minutes }$} \
\hline \text { Arterial } \mathrm{PO}_{2}(\mathrm{mmHg}) & 76 & 500 \
\hline \text { Arterial } \mathrm{PCO}_{2}(\mathrm{mmHg}) & 55 & 65 \
\hline \text { Arterial } \mathrm{Hb}(\mathrm{g} / 100 \mathrm{~mL}) & 18 & 18 \
\hline \text { Arterial } \mathrm{O}_{2} \text { saturation (\%) } & 85 & 100 \
\hline \text { Arterial } \mathrm{pH} & 7.35 & 7.20\
\hline
\end{array}$
 Which of the following diagnoses best explains the laboratory test findings?

Quizplus · Accepted Answer

The laboratory findings indicate a significant increase in arterial PO2 when breathing 100% O2, but not to the expected level (>600 mmHg), suggesting a diffusion problem across the alveolar membrane, which is consistent with a thickened alveolar membrane impairing diffusion.

A 60-Year-Old Man Comes to Your Office Complaining of Dyspnea