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

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.

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“…Before and in between tasks, the mask was evacuated using the suction pump, and new baseline measurements were obtained while the volunteer breathed normally. Finally, the volunteer underwent both rigid and flexible endoscopy to ensure that all relevant anatomy could be reached using a 3-pass rigid endoscopy method 9 and a flexible endoscopy method to visualize the vocal folds and both piriform sinuses. At the conclusion of the trial, the scoping surgeon filled out a Likert-scale survey regarding the ability to see all relevant anatomy, and the volunteer filled out a survey regarding comfort with and without suction.…”

COVID‐19 in the Clinic: Aerosol Containment Mask for Endoscopic Otolaryngologic Clinic Procedures

“…The nebulizer was loaded with 2% sterile saline at a flow rate of 10 L/min. 14 , 15 Aerosols were measured by an optical particle counter (Particles Plus) at approximately 2 cm anterior to the mask (sensor 1) and at 2 cm lateral to the mask near the area where its edge was against the face of the mannequin (sensor 2).…”

“…Two mannequin heads, with and without facial hair, were attached to a nebulizer device (DeVilbiss) via a tube running through the back of the mannequin to the nose. The nebulizer was loaded with 2% sterile saline at a flow rate of 10 L/min 14 , 15 . Aerosols were measured by an optical particle counter (Particles Plus) at approximately 2 cm anterior to the mask (sensor 1) and at 2 cm lateral to the mask near the area where its edge was against the face of the mannequin (sensor 2).…”

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“…A luz não difratada é focada no detector central. Desta forma, um padrão de difração de todas as partículas contribuintes é registrado como uma função do ângulo de dispersão [24], [25].…”