Figure 10 - Effect of shunting.

Anatomic shunting results in transfer of venous blood into the arterial circulation. a:. Normal ventilation of lung (PCO₂, 40 mmHg). B:. Hyperventilation of lung (PCO₂, 20 mmHg). Increased ventilation in response to hypoxemia results in a fall in the PCO₂ in the ventilated regions of the lungs but cannot appreciably increase the saturation in the ventilated regions. Consequently, hyperventilation (B) can lower the PCO2 of the arterial blood to normal or below normal levels, but it has little effect on the arterial saturation. "Torr" represents partial pressure in millimeters of mercury.