Effets de l’inhalation d’O₂ pur sur la difference artério-alvéolaire de pression partielle de CO₂ chez le sujet normal et le bronchiteux chronique

Abstract

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; V_A/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 02 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 02 produced the greatest increase in D(a-A)CO₂ and in VA/Q, the calculated value of the venous admixture (O_sh/O_τ) 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 % O₂breathing.