Inhaled aerosols may have reflex or local effects on airway smooth muscle. Reflex bronchoconstriction occurs when chemically inert particulates deposit on large airways (by stimulating "cough" receptors) or when materials (especially chemical irritants) deposit on smaller airways (by stimulating "irritant" receptors). When small particles of broncho-active materials are inhaled, they deposit in bronchioles that they contract by a local action. The physiological effects of these two forms of airway constriction are markedly different.
There is a new roentgenologic technique for studying airways by using insufflated powdered tantalum as roentgenographic contrast material. The method allows the examination of airway dimensions and abnormalities (including bronchioles) in vivo. The patterns of deposition can be studied, using tantalum particles of different sizes. Topographic study of lung clearance mechanisms can also be studied with this technique.