Limited effect of supplemental oxygen on shunt

Because of the sigmoid shape of the oxygen-hemoglobin saturation curve, hyperventilating a normal region of lung (x) does not significantly increase the oxygen content of the blood leaving that unit; the binding sites on the hemoglobin are already nearly 100% saturated with oxygen. Therefore, hyperventilation will not compensate very well for the low oxygen content of blood leaving a poorly ventilated unit (y). The result is a final mixed oxygen content, and PaO₂, that is only slightly better (z) than prior to hyperventilation.

x: PaO₂ of blood exiting normal alveolus.

y: PaO₂ of blood exiting shunt alveolus.