A person with a ventilation/perfusion (V/Q) defect has hypoxemia and is treated with supplemental $\mathrm{O}_{2}$. The supplemental $\mathrm{O}_{2}$ will be most helpful if the person's predominant $\mathrm{V} / \mathrm{Q}$ defect is

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[VII]. Supplemental $\mathrm{O}_{2}$ (breathing inspired air with a high $\mathrm{Po}_{2}$ ) is most helpful in treating hypoxemia associated with a ventilation/perfusion (V/Q) defect if the predominant defect is low V/Q. Regions of low V/Q have the highest blood flow. Thus, breathing high $\mathrm{PO}_{2}$ air will raise the $\mathrm{PO}_{2}$ of a large volume of blood and have the greatest influence on the total blood flow leaving the lungs (which becomes systemic arterial blood). Dead space (i.e., $\mathrm{V} / \mathrm{Q}=\infty$ ) has no blood flow, so supplemental $\mathrm{O}_{2}$ has no effect on these regions. Shunt (i.e., $\mathrm{V} / \mathrm{Q}=0$ ) has no ventilation, so supplemental $\mathrm{O}_{2}$ has no effect. Regions of high V/Q have little blood flow, thus raising the $\mathrm{PO}_{2}$ of a small volume of blood will have little overall effect on systemic arterial blood.

A Person with a Ventilation/perfusion (V/Q) Defect Has Hypoxemia and Is