Determination Of Pulmonary Parameters (V̇A, \( {D_{{L_{{O^2}}}}} \)) From Arterial O2 and CO2 Partial Pressures During Exercise

The arterial O2 and CO2 partial pressures mainly depend on the ventilation-perfusion ratio VA/Q and on the O2 diffusing capacity-perfusion ratio DLO2/Q. According to RAHN’s VA/Q concept, the dependence of the alveolar O2 and CO2 partial pressures on the ventilation-perfusion ratio can be determined graphically, and displayed in the form of a diagram (2,3). However, the application of the RAHN diagram is limited by the fact that during the passage of the blood through the lung capillaries, a complete adjustment of the capillary O2 partial pressure to the alveolar value frequently does not occur. This is particularly valid for gas exchange during exercise. For this case, the alveolar-endcapillary O2 partial pressure difference, PAO2 — PC’O2, can be calculated on the basis of an exponential increase of PO2 in the lung capillaries. The existence of such a course can be concluded from various theoretical and experimental results (1,5,6).