PULMONARY BLOOD-FLOW AND VENTILATION-PERFUSION HETEROGENEITY

We studied the independent influence of changes in perfusion on pulmonary gas exchange in the left lower lobe (LLL) of anesthetized dogs. Blood flow to the LLL (Q(LLL)) was raised 50% (increased Q(LLL)) or reduced 50% (decreased Q(LLL)) from baseline by partial occlusion of the right or left pulmonary artery, respectively. Minute ventilation and alveolar PCO2 of the LLL remained constant throughout the study. We determined ventilation-perfusion distributions of the LLL using the multiple inert gas elimination technique. Increased Q(LLL) impaired LLL pulmonary gas exchange. All dispersion indexes and all arterial-alveolar difference areas increased (P < 0.01). Decreased Q(LLL) increased the log standard deviation of the perfusion distribution (P < 0.05) and reduced the log standard deviation of the ventilation distribution (P < 0.01) but did not affect the dispersion indexes or alveolar-arterial difference areas. We conclude that ventilation-perfusion heterogeneity is increased by independent changes in perfusion from normal baseline blood flow, even when ventilation and alveolar gas composition remain constant.