A Simplified Three-Compartment Model of the Lung With A Representing Shunt; B an Ideal Gas Unit; and C Alveolar Dead Space (Vdalv) Physiologic Dead Space (Vdphys) is Filled With Air Containing No Co2, Shown As the White Area. Vdphys is the Sum of Airway Dead Space (Vdaw) and Vdalv. The Airway-Alveolar Interface is Demonstrated by the Dotted Line.

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

A simplified three-compartment model of the lung with A representing shunt; B an ideal gas unit; and C alveolar dead space (VDalv). Physiologic dead space (VDphys) is filled with air containing no CO2, shown as the white area. VDphys is the sum of airway dead space (VDaw) and VDalv. The airway-alveolar interface is demonstrated by the dotted line.