Fig. 2.
Top: PaCO2 and PaO2 as a function of regional v̇/q̇. Middle: feedback loop gains for the regulation of regional v̇/q̇ by hypercapnic and hypoxic pulmonary vasoconstriction. Bottom: efficiencies of regulation of regional v̇/q̇ by hypercapnic and hypoxic pulmonary vasoconstriction. Dashed lines, responses relating to CO2; dotted lines, responses relating to O2; solid lines, combined responses to both CO2 and O2. Note that the regulatory effect of O2 is greater than that for CO2 at low values for v̇/q̇, that the regulatory effect of CO2 is greater than that for O2 at higher values of v̇/q̇, and that the total regulatory efficiency remains relatively constant over the range of values displayed for v̇/q̇.