Inertial Aerosol Deposition in Neonatal Infant Nasal Airways

Abstract

The inertial filtration properties of neonatal infant nasal airways are the focus of this thesis. Nasal replicas based on computed tomography (CT) scan images of seven infants between the ages of 5 and 79 days were created using three-dimensional printing. Deposition of inertial sized aerosol particles in these models was measured using an electrical low pressure impactor (ELPI). The aerosol entering the nasal replica is characterized with the ELPI by sampling through a blank line. The reduction in concentration of aerosol after passing through the nasal replica is the deposited fraction. The ELPI bin geometric centres were used as a single particle size for deposition data. Deposition was recorded for particles with aerodynamic diameters between 0.53 and 5.54 μm. A filtration efficiency correlation was developed through non-linear least squares fitting. This correlation collapsed intersubject variability in the data onto a single curve capable of describing deposition in all the nasal replicas studied. A non-dimensional pressure drop, the Euler number, was required as an input variable in addition to the Reynolds and Stokes numbers to achieve satisfactory collapse of the data. These dimensionless parameters were evaluated with a characteristic dimension defined as the nasal airway volume divided by its surface area. An analysis of expected in-vivo intersubject variability of aerosol filtration was also performed. Further, the ability to scale a previously developed idealized infant nasal airway to produce a model which mimics nasal filtration in the neonatal population was explored. Inertial deposition in three scaled models of the original full scale geometry was measured using the same method used to quantify deposition in the nasal replica models. Comparison of deposition in the scaled idealized models to deposition in the replica models led to the identification of the appropriate scale factor. Non-linear least squares fitting produced a correlation which uses Reynolds and Stokes numbers to describe deposition in this geometry for all scales considered. It is hoped that the results of this thesis will aid future research into aerosol devices specifically for neonatal infants and their unique extrathoracic airways.