title: Monitoring the Inhalation Flow Rate of Nebulized Aerosols Using an Ultrasonic Flow Meter: In Vitro Assessment.
abstract: BACKGROUND
  The measurement of aerosol flow rates without obscuration of the flow is of particular concern with in vivo lung deposition studies, where precise knowledge of aerosol particle size distributions is a necessary requirement for the development of predictive correlations. This study examines the utility of an ultrasonic flow meter for such measurements and determines if a valved system can be attached to the flow meter for sampling exhaled aerosols.
  
  
  METHODS
  The flow rate across a D-30 flow meter was compared with and without nebulization of 0.9% saline aerosols from a PARI LC Sprint nebulizer. Particle size distributions of the nebulized aerosol before and after adding the D-30 flow meter and duckbill valve were measured using a Spraytec laser diffraction system. Finally, the ability of the Thor D-30 to capture a realistic breathing profile was assessed.
  
  
  RESULTS
  The mean ± standard error flow rates measured by the D-30 flow meter with and without nebulization were 10.4 ± 0.1 versus 10.4 ± 0.1 L/min, 66.4 ± 0.1 versus 67.2 ± 0.1 L/min, and 89.9 ± 0.1 versus 91.4 ± 0.1 L/min. The D-30 flow meter did not considerably affect the volumetric median diameter (VMD) of the aerosols, while the VMD reduced slightly by 0.65 μm at 10 L/min and 0.69 μm at 72 L/min upon the inclusion of a duckbill valve. Time-weighted average inhalation flow rates measured by D-30 flow meters placed upstream and downstream of the one-way valve agreed well, 31.9 versus 32.6 L/min, respectively.
  
  
  CONCLUSIONS
  The D-30 flow meter can be used to accurately measure inhalation flow rates of nebulized aerosols without significantly impacting particle size distributions, and one-way duckbill valves can be used to isolate the inhalation portion of a breathing pattern to facilitate collection of exhaled doses.
authors.affiliation: Advanced Drug Delivery Group, Faculty of Pharmacy, University of Sydney , Sydney, Australia .
authors.forename: Michael Y
authors.initials: MY
authors.lastname: Yang
authors.affiliation: Advanced Drug Delivery Group, Faculty of Pharmacy, University of Sydney , Sydney, Australia .
authors.forename: Hak-Kim
authors.initials: HK
authors.lastname: Chan
mesh_terms: D000280:Administration, Inhalation; D000336:Aerosols; D004867:Equipment Design; D045268:Flowmeters; D006801:Humans; D009330:Nebulizers and Vaporizers; D010316:Particle Size; D012119:Respiration; D012965:Sodium Chloride / Q000008:administration & dosage*; D014465:Ultrasonics
chemical_list: D000336:Aerosols; D012965:Sodium Chloride
keywords: aerosol flow rate; flow meter; inhalation flow rate; nebulizer