The Heavy Line Indicated All Possible Values of Alveolar O2 (Pao2) and Co2 (Paco2) With Ventilation Perfusion (V/Q) Ratios Ranging from Zero (to the Left, Lung Base) to Infinity (to the Right, Lung Apex) for a Person Breathing Air Mixed Expired Gas is a Mixture of Ideal Alveolar Gas and Dead Space. Arterial Blood is a Mixture of Blood With the Same Gas Tensions As Ideal Alveolar Gas and Shunt (Mixed Venous Blood)

(Reproduced with permission from Tusman G, Sipmann S, Bohm SH. Rationale of dead space measurement by volumetric capnography. Anesth Analg. 2012;114:866-874.)

The heavy line indicated all possible values of alveolar O2 (Pao2) and CO2 (Paco2) with ventilation perfusion (V/Q) ratios ranging from zero (to the left, lung base) to infinity (to the right, lung apex) for a person breathing air. Mixed expired gas is a mixture of ideal alveolar gas and dead space. Arterial blood is a mixture of blood with the same gas tensions as ideal alveolar gas and shunt (mixed venous blood)