Bronchial edema alters Tc-99m-DTPA clearance from the airway surface in sheep

Airway wall edema, prominent in inflammatory airways disease, may alter bar rier properties at the airway air-liquid interface such that normal absorpt ion of soluble substances into the airway circulation is altered. We studie d the effects of bradykinin-induced airway wall edema on the clearance of t he soluble tracer technetium-99m-labeled diethylenetriamine pentaacetic aci d (Tc-99m-DTPA) from subcarinal airways in sheep (n = 8). (99m)-Tc-DTPA (6- 10 mul) was delivered by a microspray nozzle inserted through a bronchoscop e to a fourth-generation bronchus both before and 1 h after bradykinin (20 ml; 10(-6) M) had been infused through a cannulated and perfused bronchial artery. Airway retention (by scintigraphy) and blood levels of radiolabel w ere monitored for 30 min after the local deposition of Tc-99m-DTPA. During control conditions, 85-90% of the tracer cleared from the deposition site w ithin 30 min. The maximum blood level during that time was 17% of the total delivered tracer. However, 1 h after bradykinin infusion, there was signif icant retention of the marker at the deposition site with clearance within 30 min reduced to 63-70% and decreased blood levels of radiolabel (8%; both P < 0.05). These results demonstrate that moderate airway wall edema alter s blood uptake and removal of soluble substances delivered to the subcarina l airways. We suggest that the interplay between vascular and mucociliary c learance routes will impact the resident time for clearance of soluble air toxins and/or therapeutic agents from the epithelial surface.