Performance evaluation of nebulizers based on aerodynamic droplet diameter characterization using the Direct Laminar Incidence (DLI)

ABSTRACT

Abstract Introduction Optical microscope images can be useful to evaluate nebulizers considering the size of droplets produced by these devices. From this perspective, the proposed method was compared to the classic concept of Mass Median Aerodynamic Diameter (MMAD) for the ideal droplet size between 0.5-5.5 µm. Methods We tested a sample of five home nebulizers sold on the Brazilian market. A high-speed camera coupled to a microscope obtained images of the droplets during the nebulization process, which allowed us to characterize the diameter of the aero-dispersed droplets. The Count Median Aerodynamic Diameter (CMAD) was used as measurement parameter. Results The images obtained during the nebulization process with the five different nebulizers provided data to determine the frequency distribution of the aero-dispersed droplet population. Successive images were obtained in the range of 2.0s to evaluate the dynamic behavior of the droplets. The generated data also allowed the elaboration of histograms emphasizing the ideal diameter range of droplets between 0.5 and 5.5 μm. Conclusion The Direct Laminar Incidence (DLI) model using digital image processing technique allowed the characterization of respirable particles. This model proposes the creation of a range of optimum absorption of the droplets by the respiratory tract. Although there is a technical limitation in the direct acquisition of images due to the depth of focus, presenting an error of 9.3%, the described method provides consistent results when compared to other droplets characterization techniques. Thus, the authors believe that Direct Laminar Incidence (DLI) is a viable method to assess the performance of nebulizers despite the requirement of adjustments and possible improvements required to minimize measurement errors.