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editorial
. 2023 Jan 26;61(1):2201962. doi: 10.1183/13993003.01962-2022

FIGURE 1.

FIGURE 1

Graphical analysis of the calculation of ideal alveolar air (Ai; ideal point) modified from Riley and Cournand [2]. Blood or gas carbon dioxide tension (PCO2) is plotted against oxygen tension (PO2) (in mmHg) with the gas inspired (I; air) set at PO2 150 and PCO2 0 mmHg (see text). Curved line joining point I to point v̅ (the PCO2–PO2 of mixed venous blood) is the V̇A/Q̇ line, reflecting all possible alveolar PCO2 and PO2 values for V̇A/Q̇ ratios from zero (at v̅) to infinity (at I) at a lung and body respiratory quotient (RQ or R) of 0.8. Gas and blood R lines, constructed for R=0.8, intersect at the “ideal” point. “art” is the PCO2–PO2 of mixed arterial blood in a healthy subject, “c” is the composition of mixed blood leaving alveolar capillaries (arterial minus anatomic shunt), alv of mixed alveolar gas, and E̅ads of mixed expired air corrected for apparatus dead space.