Figure 17-10 Schematic drawing of regional hypoxic pulmonary vasoconstriction (HPV); one-lung ventilation is a common clinical example of regional HPV. HPV in the hypoxic atelectatic lung causes redistribution of blood flow away from the hypoxic lung to the normoxic lung, thereby diminishing the amount of shunt flow (S/T) that can occur through the hypoxic lung. Inhibition of hypoxic lung HPV causes an increase in the amount of shunt flow through the hypoxic lung, thereby decreasing PaO₂ .