Reduction of lung perfusion increases VA/Q heterogeneity.

This study addresses the hypothesis that decreases in lung perfusion rate independently worsen gas exchange efficiency in an isolated left lower lobe in zone 2 conditions. In seven anesthetized dogs, the left lower lobe was isolated, leaving the bronchus and bronchial vasculature intact. Blood was taken from the femoral arteries and reinfused at a controlled rate into the pulmonary artery of the left lower lobe. The flow rate was varied between 100 and 400 ml/min. The multiple inert gas elimination technique was used to quantitate the matching of ventilation to perfusion. Reduction in lobe blood flow resulted in a significant increase in perfusion-related indexes of alveolar ventilation-perfusion heterogeneity, such as the log standard deviation of the perfusion distribution, the retention component of the arterial-alveolar difference area, and the retention dispersion index. The increased heterogeneity suggests a worsening of the intraregional matching between the ventilation and the perfusion when perfusion is less than normal.