Determining Medical Nebulizer’s Droplet Size Distribution with a Low-Cost Refrigeration System
Taewon Han, Michael Falvo, GEDIMINAS MAINELIS, Rutgers, The State University of New Jersey
Abstract Number: 296
Working Group: Health-Related Aerosols
Abstract
Medical nebulizers are crucial for respiratory drug delivery and bronchoprovocation testing. Their performance parameters include drug delivery rate and the size distribution of produced droplets. Our study evaluates a high-efficiency breath-actuated nebulizer (AeroEclipse® II BANTM), commonly used to deliver methacholine during bronchial challenge testing to assess airway hyperresponsiveness. In our earlier work, we investigated the nebulizer’s drug delivery rate. However, another important parameter of the nebulizer performance – droplet size distribution, is largely unknown. Measuring droplet size distribution is challenging because droplets begin to decrease in size due to evaporation as soon as they leave the nebulizer. Commercially available refrigerated multi-stage impactors alleviate this problem but are prohibitively expensive. We developed a low-cost test system where a nebulizer and an 8-stage Andersen impactor were placed inside a compact refrigerator (1.7 cu. ft.). Tests were performed with NaCl solution with the refrigeration system and at room temperature. The amount of material deposited on filters at different impactor stages was determined by eluting the material and measuring the conductivity of the eluent. Overall, we found that the operational temperature and drug concentration highly affected size distribution. When NaCl 1 mg/mL solution was aerosolized and measured at room temperature, most droplets were smaller than 1.1 µm (73% of collected material). When the same aerosol was measured using the refrigeration system, the size distribution peaked between 1.1 and 4.7 µm (57% of collected material). The all-important PM5 size fraction also differed substantially: it was 47% at room temperature and 70% when using our refrigeration system. The experiments are continuing with different drugs (methacholine) and concentrations (4 and 16 mg/mL). Overall, our developed low-cost refrigeration system and experimental protocol show promise to conveniently and inexpensively determine size distributions of aerosol droplets released by medical nebulizers.