Comparison of Rebreathing and Steady-State Pulmonary Do₂ in Dogs Ventilated by Body Respirator

Abstract

Alveolar gas exchange was studied com-paratively in anaesthetised dogs during spontaneous breathing and during artificial ventilation produced by a body respirator. The pulmonary O₂ diffusing capac- ity, D O₂, in particular, was measured, employing two different methods: the conventional steady-state method, using ideal alveolar P O₂ (D O₂SS) and a rebreathing method (Do_2RB). A considerable decrease (by a factor of 3) in both D o_2SS and D_O2RB was observed on transition from spontaneous breathing to artificial ventilation. Distributional inhomogeneities were found to be considerably increased during artificial ventilation as indicated by increased values of both alveolar dead space ventilation and venous admixture. The increased inhomogeneity was probably due to considerably decreased end-expiratory lung volume during artificial ventilation at mean intrapulmonary pressure zero. The observed reduction in D_O2 should, at least in part, be attributed to the enhanced distributional inhomogeneity during artificial ventilation at low lung volume. Apparently, D_O2SS and D_O2RB are affected about equally by distributional inequalities in the lung