Mean alveolar gases and alveolar-arterial gradients in pulmonary patients

the best way to estimate mean alveolar gases in patients with ventilation-perfusion inequalities, three different methods were evaluated on 54 patients. 1) O2 and CO2 were recorded by mass spectrometer on an 02 (x)-CO2 ( y) diagram. The coordinates at the intersect of the expiratory record with the mixed expired R line (Ra) gives the mean alveolar values (PAo, and P&o,. 2) PA&, was calculated with the Bohr equation using a predicted anatomic dead space and PA’o, was derived with the alveolar equation. 3) End-tidal (ET) Paz and Pco, were averaged over 1 min at rest in steady state. Mean RET calculated from 3 was identical with RE. Mean values for PTi;co2, PA’<:~~, and PETIT, differed by less than 1 Torr, but the variance was least with the end-tidal method. There was a highly significant correlation between AaAPco, using PETIT, and VD/VT, better than with either of the other methods. The end-tidal measurement ap