Humidified and Heated Cascade Impactor for Aerosol Sizing

Area of Science:

• Pharmaceutical Sciences
• Aerosol Science and Technology
• Respiratory Drug Delivery

Background:

• Aerosol particle sizing is typically performed under ambient conditions.
• Human airways present a unique environment of 37°C and 100% relative humidity (HPTH).
• Ambient condition measurements may not accurately reflect particle behavior and deposition in the airways.

Purpose of the Study:

• To develop and validate a novel method for measuring aerosol particle size distribution at HPTH.
• To assess the impact of HPTH conditions on particle size for various medical aerosol devices.
• To evaluate the relevance of HPTH measurements for improving aerosol deposition predictions.

Main Methods:

• Construction of a heated and humidified artificial trachea model.
• Adaptation of a cascade impactor to operate at 37°C and 100% relative humidity.
• Testing of four medical aerosol types (jet nebulizer, mesh nebulizer, pMDI, DPI) under both ambient and HPTH conditions.

Main Results:

• Lower Mass Median Aerodynamic Diameter (MMAD) was observed at HPTH for jet and mesh nebulizers.
• pMDI particle size remained similar between ambient and HPTH conditions.
• DPI showed a reduced mass of particles <5 μm at HPTH (51.9 vs. 82.8 μg/puff).

Conclusions:

• A new method for measuring aerosol particle size at HPTH was successfully developed and evaluated.
• HPTH conditions significantly influence particle size and distribution for certain inhalation devices.
• This method has relevance for enhancing the precision of aerosol deposition predictions in respiratory airways.