Measurement of airway mucosal blood flow with dimethylether: validation with microspheres

We have recently developed a noninvasive dimethylether (DME) uptake technique to estimate airway mucosal blood flow (Qaw) in humans (12). Because it was not feasible to validate the technique directly, we undertook the present study to compare Qaw as measured by DME (QDME) and by color-coded microspheres (QM) as a standard in seven anesthetized sheep prepared with a carotid and a left atrial catheter. QDME was determined by measuring DME uptake with multiple breath holds after passive inflation with a DME-helium gas mixture, simulating the technique used in humans. After the microspheres were injected into the left atrium, the sheep were killed and the tracheal segment corresponding to the dead space from which DME uptake was determined was removed, and its mucosa was stripped and processed for microsphere counts. Mean QDME was 35.6 ml.min-1.100 g-1 wet tissue (range 9.6-98.0 ml.min-1.100 g-1) and mean QM was 29.1 ml.min-1.100 g-1 (range 7.7-91.5 ml.min-1.100 g-1). There was a strong correlation between QDME and QM (r = 0.89; P = 0.01). Intravenous nitroglycerin and vasopressin caused comparable increases and/or decreases in QDME and QM (r = 0.87; P = 0.02). This suggests that the noninvasive DME uptake method measures Qaw accurately and supports its validity in human studies.