Cross sectional images recorded byaOCT in a proximal and distal airway. Proximal airway is Gen #3 and distal airway Gen #9. The airway epithelium (AE), probe catheter (PR) and cartilage plates (CP) are indentified. The airway preparation was scanned initially in its relaxed state and then 5, 15 and 30 min after addition of carbachol administered to the adventitial airway surface. Airway narrowing was typically greater and more rapid in distal airways.