Capturing the efficiency of vibrating mesh nebulizers: minimizing upper airway deposition

Background: Vibrating mesh devices are portable nebulizer systems with reported high efficiency. Losses occur during expiration, and particle size distributions vary. We describe an aerosol chamber designed to capture and condition aerosols from a typical vibrating mesh nebulizer, the Omron U22. The goal was to improve inhaled mass (IM) and respirable fraction (RF) and shorten treatment time.

Methods: With test solutions of radiolabeled saline, we characterized the Omron U22 (three examples) vibrating mesh nebulizer measuring aerosol output with different breathing patterns, with and without manual breath synchronization. Particle size distributions were measured by cascade impaction as a "standing cloud" and during ventilation with a piston respirator. IM (percentage of nebulizer charge), respirable mass (RM), particle size distribution, and breathing time were measured with and without use of the chamber. Breathing patterns were designed to simulate tidal breathing with a "COPD" (chronic obstructive pulmonary disease) pattern (450 mL, rate 15, duty cycle 0.35) and "slow and deep" breathing for maximal lung deposition (1,500 mL, rate 5, duty cycle 0.70). Patterns of deposition were confirmed in a human volunteer using a gamma camera.

Results: IM was significantly affected by breathing pattern and averaged 30.0±2.91% and 53.9±7.99% for COPD and slow and deep patterns, respectively. With the chamber, IM was less sensitive to breathing pattern (57.4±6.97%, 57.9±4.69%, respectively). Particle size distributions varied widely between devices and were markedly affected by both ventilating the device and addition of the chamber. With the chamber, RF and RM increased, and differences in particle size distributions between individual devices were minimized. Compared with breath synchronization, treatment time was reduced. Gamma camera images revealed reduced upper airway deposition consistent with predictions from in vitro cascade distributions.

Conclusions: Our prototype chamber allowed for capture and conditioning of nebulized aerosol by mixing with room air and removal of large particles by impaction, providing better control of IM, RF, RM, and lung deposition, without the need for breath synchronization.