[Effects of O2 inhalation on the partial arterial-alveolar pressure of CO2 in healthy patients and in patients suffering from chronic bronchitis (author's transl)].

The increase in arterial-alveolar CO2 difference (D[a-A]CO2) on 100% O2 breathing was studied in healthy subjects and in chronic bronchitic patients with or without hypoxemia. This increase in D(a-A)CO2 showing the enhancement of the dead-space effect (i.e. of the ventilation/perfusion ratio; VA/Q,), resulted from increase in PaCO2 or/and from decrease in PACO2 and was only found in hypoxic bronchitic subjects. In such subjects D(a-A)CO2 increased by about 50%. This phenomenon seems to arise from the vasomotor effect of pure O2 on pulmonary circulation and the role played by the Haldane effect in increasing PaCO2 and thus D(a-A)CO2 in some subjects is very weak. In subjects where inhalation of pure O2 produced the greatest increase in D(a-A)CO2 and in VA/Q, the calculated value of the venous admixture (QSh/QT) after measurement of D(A-a)O2 at the 30th min of hyperoxia was overestimated. Indeed D(A-a) O2 was enlarged by increasing the dead-space effect under 100% O2 breathing.