Effects of increased cardiac output on pulmonary blood flow distribution during lobar ventilation hypoxia and collapse.

Electromagnetic flow probes were placed around the pulmonary artery and left lower lobe artery in anaesthetized open-chest dogs in order to measure possible changes in the ratio of lobar-to-total pulmonary blood flow (Ql/Qt) in response to changes in cardiac output produced by the opening of arterio-venous fistulae or fluid loading. Ventilation of the lobe with 7% oxygen or lobar collapse reduced Ql/Qt by 35% and 42%, respectively, but there were no significant changes in Ql/Qt in response to increases in Qt of 29-133%. It is concluded that the changes in Qt, pulmonary vascular pressures and mixed venous PO2 within the range studied did not influence Ql/Qt.