Abstract
In 58 patients with pulmonary emphysema and/or chronic bronchitis (mean age=60.5±SD 10.6 years, EEVl/FVC=49.8±15.2%, and VC=72.4±21.2% of predicted), mixed venous and arterial blood gases obtained during cardiac catheterization were used to calculate an efficiency index (EI) of the pulmonary gas exchange, a newly defined word. The patients were classified into 9 groups according to the severity of arterial hypoxemia. PaO2 ranged from 90.0 to 35.3mmHg (mean=60.5mmHg) and PaCO2 from 25.3 to 60.5mmHg (mean=42.2mmHg).
The EI was calculated by the equation: EI=avDO2/AvDO2, where, avDO2: arterial to mixed venous difference in PO2 (mmHg) and AvDO2: alveolar to mixed venous difference in PO2 (mmHg). Alveolar PO2 (PAO2) was calculated from the standard alveolar air equation.
The El correlated with PaO2 (r=0.83), AaDO2 (r=-0.726), and PaO2 (predicted-observed values, r=-0.704). The EI did not correlate with DLCO/VA which was measured in separate occasions. Right to left shunt correlated weakly with EI.
avDO2 and AvDO2 decreased and AaDO2 increased as PaO2 decreased. The EI decreased progressively as PaO2 decreased and it was 0.5 at PaO2 70mmHg indicating that inefficient part for the pulmonary gas exchange overcame the efficient part at this critical point.
These results indicate that the efficiency of pulmonary gas exchange is best reflected by PaO2, AaDO2, and PaO2. Patients with PaO2 less than 70mmHg may be defined as pulmonary failure.
