The following equation relates the percentage of blood flow that is not exposed to inhaled gas, called the shunt fraction Q s / Q t PO2 is the partial pressure of oxygen and reflects the amount of oxygen gas dissolved in the blood.

Some references refer to “shunt-effect” or “dead space-effect” to designate the ventilation/perfusion mismatch states that are less extreme than absolute shunt or dead space. These terms can also be used to describe areas or effects where blood flow and ventilation are not properly matched, though both may be present to varying degrees. “Shunt” and “ dead space“ are terms used to describe conditions where either blood flow or ventilation do not interact with each other in the lung, as they should for efficient gas exchange to take place. The Shunt equation (also known as the Berggren equation) quantifies the extent to which venous blood bypasses oxygenation in the capillaries of the lung. In Medicine shunt may also refer to Cardiac shunts, Cerebral shunts, Lumbar-peritoneal shunts, or Peritoneovenous shunts, for additional shunts in medicine see Shunt (medical).

Physiologic shunting and dead space