Effect of alveolar hypercapnia on regional pulmonary perfusion

The effect of alveolar hypercapnia under a wide range of alveolar oxygen tensions was assessed in the right upper lobe of the normal dogs and the dogs with the reimplanted right lung. To induce alveolar hypercapnia by artificial ventilation of the right upper lobe, gas mixtures of differing oxygen fractions containing 10% or 20% CO2 were used as exchange gases for the right upper lobe. The concurrent alveolar hypercapnia had little superimposed effect on the regional vascular responses to a wide range of alveolar oxygen tensions in the normal and the reimplanted denervated lung lobe. Under an extreme alveolar hyperoxia, however, the concurrent alveolar hypercapnia somewhat suppressed regional hyperoxic vasodilation and/or recruitment of the pulmonary vascular beds, whereas in the reimplanted lung lobe it potentiated the hyperoxic pulmonary vascular response. The alveolar oxygen tension seems to be the main factor in the regulation of regional perfusion in the lungs.