Interdependence of bronchial circulation and clearance of ^99mTc-DTPA from the airway surface

The extent to which the systemic vasculature is involved in soluble-particle uptake in the conducting airways has not been studied extensively. In anesthetized, ventilated sheep, 6-10 μl of technetium-99m-labeled diethylenetriamine pentaacetic acid (^99mTc-DTPA) was delivered through a microspray nozzle to a fourth-generation airway. Perfusion of the cannulated bronchial artery was varied between control flow (0.6 ml · min^-1 · kg^-1), high flow (1.8 ml · min^-1 · kg^-1) or no flow (the infusion pump was stopped). Airway retention of the radioactive tracer was monitored using gamma camera imaging, and venous blood was sampled. During control perfusion, tracer retention at the site of deposition at 30 min averaged 20 ± 6% (n = 7). With no flow, retention was significantly elevated to 32 ± 8% (P = 0.03). In another group of sheep (n = 5) with a control retention of 13 ± 4%, high flow resulted in an increase in tracer (25 ± 4%; P = 0.04). Maximum blood uptake of tracer was calculated by estimating circulating blood volume and averaged 16% of total activity during control flow. Only during high-flow conditions was ^99mTc-DTPA in the blood decreased (10%; P = 0.04). Most of the tracer was cleared by mucociliary clearance as visualized by imaging. This component was substantially decreased during no flow. The results demonstrate that both decreased and increased airway perfusion limit removal of soluble tracer applied to the conducting airways.