Demonstration of interlobar collateral ventilation.

In an ongoing series of experiments on mongrel dogs, three dogs were observed to have incomplete lobar fissures (interlobar connection present) between the left upper and left lower lobes. With the interlobar connection unclamped, selective hypoxia of the left lower lobe caused the electromagnetically measured blood flow to the left lower lobe to decrease 41 +/- 4%, whereas with the interlobar connection clamped selective hypoxia of the left lower lobe caused a 52 +/- 4% decrease in left lower lobe flow (P less than 0.05). Following 100% O2 ventilation and with the interlobar connection unclamped, complete occlusion of the left lower lobe bronchus caused no atelectasis or decrease in left lower lobe blood flow, whereas with the interlobar connection clamped complete occlusion of the left lower lobe bronchus caused complete left lower lobe atelectasis and a 58 +/- 3% decrease in left lower lobe blood flow. Histological confirmation of interlobar pulmonary parenchymal connection was obtained in each dog. We conclude that a sufficient amount of interlobar collateral ventilation can occur in dogs with incomplete lobar fissures to prevent absorption atelectasis and alter lobar blood flow reduction usually caused by selective lobar hypoxia.