[Effect of Ca-antagonists on pulmonary blood flow during single-lung ventilation in the dog]

Experiments were conducted in 21 adult mongrel dogs to clarify the effects of Ca-antagonist (nifedipine sublingual administration 2.5 mg or 5 mg, or nicardipine intravenous administration 30 micrograms/kg or 60 micrograms/kg) on pulmonary blood flow under the condition of collapsed lung on the side of thoracotomy. Under anesthesia, an endotracheal tube with a movable blocker was used to intubate the trachea and the thoracotomized lung was collapsed. Subsequently, a Ca-antagonist was given and the ratio of the left main pulmonary artery/ascending thoracic aorta blood flow was used as an index of hypoxic pulmonary vasoconstriction (HPV). The following results were obtained. 1. Ca-antagonist administration under lung-collapse on the thoracotomy side resulted in inhibition of HPV of the collapsed lung, whereas, arterial blood oxygen tension (PaO2) remained in the acceptable range. 2. The maintenance of the lowered PaO2 within the acceptable range may have been due to the increase in cardiac output and the elevation of mixed venous blood oxygen tension resulting from Ca-antagonist administration, as well as the residual HPV even after administration of the Ca-antagonist.