Use of aerosols to estimate pulmonary air-space dimensions.

Single-breath inhalations of monodisperse aerosols were performed with a group of normal subjects to determine aerosol recovery from the human lung after periods of breath holding. Aerosols of monodisperse nonhygroscopic droplets of bis(2-ethylhexyl) sebacate of between 0.5 and about 2.5 μm diam were used for the inhalation. The inhalation apparatus allows continuous monitoring of particle number concentration and flow rate close to the mouth. Experiments were designed to find the optimum experimental conditions for the principal concept of Palmes et al. (In: Inhaled Particles and Vapours. London: Pergamon, 1976, vol. II, p. 339-347) to evaluate pulmonary airspace dimensions by means of aerosols. The experimental results obtained for various respiratory flow rates (125, 250, and 500 cm 3.s -1), settling velocities of the particles (10 -3 to 1.5 x 10 -2 cm.s -1), and volumes of inspired aerosols (500, 1,000, and 2,000 cm 3) are compared with the results derived from a mathematical model for the particle deposition during respiratory pauses. Monodisperse aerosols with particles between 1 and about 1.5 μm diam, inspired for breath holding into the lung region of interest, may provide optimum conditions for the sizing of air spaces by means of aerosols