Passage of aerosol around or through a facemask can result in deposition on the face and in the eyes. The present study quantified facial and eye deposition in a model simulating drug delivery to a young child. Aerosol delivery and facial deposition of radiolabeled saline test aerosols were studied in vitro with filters and a gamma camera. A child's face facsimile, attached to a piston pump, was used to simulate the patient receiving aerosol therapy. A filter placed in the oropharynx of the face facsimile measured aerosol delivery (inhaled mass). Seven commercially available facemasks in combination with three jet nebulizers were studied for aerosol delivery to the "patient" as well as for deposition on the face and in the eyes. Inhaled mass varied from 2.24-5.96% of nebulizer charge (drug placed in the nebulizer). Facial deposition varied from 0.44-2.34% of nebulizer charge, with eye deposition at 0.09-1.78%. All facemasks leaked aerosol, with significant facial and eye deposition approaching in magnitude delivery to the lung. Factors affecting facial and eye deposition include the interactive design characteristics of the facemask and nebulizer, as well as the aerodynamic properties of the aerosol.
Aerosols produced by nebulizers are often characterized on the bench using cascade impactors. We studied the effects of connecting tubing, breathing pattern, and temperature on mass-weighted aerodynamic particle size aerosol distributions (APSD) measured by cascade impaction. Our experimental setup consisted of a piston ventilator, low-flow (1.0 L/min) cascade impactor, two commercially available nebulizers that produced large and small particles, and two "T"-shaped tubes called "Tconnector(cascade)" and "Tconnector(nebulizer)" placed above the impactor and the nebulizer, respectively. Radiolabeled normal saline was nebulized using an airtank at 50 PSIG; APSD, mass balance, and Tconnector(cascade) deposition were measured with a gamma camera and radioisotope calibrator. Flow through the circuit was defined by the air tank (standing cloud, 10 L/min) with or without a piston pump, which superimposed a sinusoidal flow on the flow from the air tank (tidal volume and frequency of breathing). Experiments were performed at room temperature and in a cooled environment. With increasing tidal volume and frequency, smaller particles entered the cascade impactor (decreasing MMAD; e.g., Misty-Neb, 4.2 +/- 0.9 microm at lowest ventilation and 2.7 +/- 0.1 microm at highest, p = 0.042). These effects were reduced in magnitude for the nebulizer that produced smaller particles (AeroTech II, MMAD 1.8 +/- 0.1 to 1.3 +/- 0.1 microm; p = 0.0044). Deposition on Tconnector(cascade) increased with ventilation but was independent of cascade impactor flow. Imaging of the Tconnector(cascade) revealed a pattern of deposition unaffected by cascade impactor flow. These measurements suggest that changes in MMAD with ventilation were not artifacts of tubing deposition in the Tconnector(cascade). At lower temperatures, APSD distributions were more polydisperse. Our data suggest that, during patient inhalation, changes in particle distribution occur that are related to conditions in the tubing and may reduce the diameters of particles entering the patient. This effect is more significant for nebulizers producing large particles. Changes in ambient temperature did not affect these observations.
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