Charting human thoracic airways by aerosols

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Abstract
A non-invasive method is described which permits the estimation of average airway calibre as a function of the volumetric depth in the human respiratory tract. It is basd upon the measurement of gravitational particle losses during breath-holding from boli of monodisperse aerosols inspired to different depths in the respiratory tract. Aerosol boli comprising particles of 1.5 mu m aerodynamic diameter and 45 mu m settling velocity were inspired to depths between 80 and 820 cm3. The number of particles recovered decreased exponentially with the period of breath-holding, and an average airway radius was calculated for each lung depth from the slope of these exponential functions. The average airway radius changes rapidly with depth. Among six subjects it varies between 630 and 1400 mu m at 120 cm3 lung depth and between 165 and 280 mu m at 600 cm3 lung depth. The average airway radii evaluated in this study are within the range covered by current lung models.