Even in healthy young subjects, regional differences in pulmonary ventilation and blood flow result in the PaO₂ being lower than the PAO₂. Why is this so?

Question

Quizplus · Accepted Answer

Most blood flows through the bases of the lung, which have a higher perfusion relative to ventilation ($\dot { V }$ / $\dot { Q }$ ratio) compared to the apexes. This results in a lower PaO2 compared to PAO2 due to the gravitational effects on blood flow, leading to more efficient gas exchange in the lower parts of the lungs.

Even in Healthy Young Subjects, Regional Differences in Pulmonary Ventilation V˙\dot { V }V˙

Even in Healthy Young Subjects, Regional Differences in Pulmonary Ventilation $\dot { V }$