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

As shown in Table 12-1, because of gravity most blood flows to the lung bases, where the PO₂ is lower and the PCO₂ is higher than normal. After leaving the lung, this relatively large volume of blood combines with the smaller volume coming from the middle and apical regions. The result is a mixture of blood with less O₂ and more carbon dioxide than would come from an ideal gas exchange unit.

Even in Healthy Young Subjects, Regional Differences in Pulmonary Ventilation