Pulmonary lobe blood flow during ventilation hypoxia and lobar collapse in the dog

The aim of the present study was to determine whether the diversion of blood flow away from a collapsed pulmonary lobe is due to hypoxic pulmonary vasoconstriction alone, or whether hypercapnia and mechanical factors also contribute. Hypoxic pulmonary vasoconstriction was tested in a canine pulmonary left lower lobe. Alveolar hypoxia was produced by absorption collapse or by ventilation with 7% oxygen, which has previously been shown to produce an end-pulmonary capillary pO2 similar to mixed venous pO2. The proportion of the cardiac output flowing to the lobe was reduced in both hypoxic states but was significantly lower during collapse than during ventilation hypoxia. The beta 1-adrenergic agonist dobutamine hydrochloride (30 micrograms X kg-1 X min-1 iv) produced a significant increase in the proportion of the cardiac output flowing to the lobe during collapse but no significant change during ventilation hypoxia. It is concluded that changes in local pCO2 during collapse may account for the greater diversion of blood flow from the lobe when compared with ventilation hypoxia.