Fig. 1From: Volumetric capnography: lessons from the past and current clinical applicationsRiley three compartment model. Compartment A: shunt = perfused but not ventilated alveolae (V/Q = 0). Compartment B: ideal condition. Compartment C: dead space = ventilated but not perfused alveolae (V/Q = ∞). VDaw airway dead space, VDalv alveolar dead space, VDphys the sum of airway and alveolar dead spaceBack to article page