New assessment of small and large airway responsiveness to inhalation aerosol

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To examine the role of small and large airway responsiveness to inhalation aerosols, we developed a new system which continuously measures both pulmonary resistance (R1) and frequency dependence of dynamic compliance (Cdyn.f.), calculated by Fourier-series analysis of flow and transpulmonary pressure in a single-cycle of breathing. R1 was obtained from fundamental harmonics. Cdyn.f was calculated from the linear regression line obtained from the fundamental to the third hermonics, and Cdyn at 0.5 Hz ( <C_(0.5)> ) and Cdyn at 0 Hz ( <C_0> ) were obtained. In house dust allergen inhalation, we observed that in some asthmatic patients the decrease in <C_0> and <C_(0.5)> preced the increase in R1 or <C_0> and <C_(0.5)> decreased progressively even if R1 did not change significantly. In some asthmatic subjects, after <beta_2> stimulant aerosol inhalation <C_0> and <C_(0.5)> continued to increase even after R1 decreased to minimum value. These results mean that small airway response to house dust aerosol may be earlier than the large airway response, and that <beta_2> stimulant aerosol may first dilate the large airway and then continue to dilate the small airways. Furthermore, we studied measurement of the amount of aerosol deposition in the airways using a laser scattering method. However, we could not yet establish the continuous measurement of the amount of aerosol deposition in the airways during two years. Further studies are needed.