Figure 2.

Effect of alveolar dead space (VD_alv). The right lung compartment receives no perfusion and contains no carbon dioxide (ignoring interlung unit ventilation). By mass balance for carbon dioxide, VD_alv/VT_alv = (PaCO₂ - PETCO₂)/PaCO₂. For the sample condition shown, VD_alv/VT_alv = (40-20)/40= 50%. PaCO₂, arterial PCO₂; PACO₂, alveolar PCO₂; PETCO₂, end-tidal PCO₂; P CO₂, mixed venous PCO₂;VT_alv, alveolar tidal volume.Adapted from Breen [61].