title: Validating Whole-Airway CFD Predictions of DPI Aerosol Deposition at Multiple Flow Rates.
abstract: The objective of this study was to compare aerosol deposition predictions of a new whole-airway CFD model with available in vivo data for a dry powder inhaler (DPI) considered across multiple inhalation waveforms, which affect both the particle size distribution (PSD) and particle deposition.
  
  
  
  The Novolizer DPI with a budesonide formulation was selected based on the availability of 2D gamma scintigraphy data in humans for three different well-defined inhalation waveforms. Initial in vitro cascade impaction experiments were conducted at multiple constant (square-wave) particle sizing flow rates to characterize PSDs. The whole-airway CFD modeling approach implemented the experimentally determined PSDs at the point of aerosol formation in the inhaler. Complete characteristic airway geometries for an adult were evaluated through the lobar bronchi, followed by stochastic individual pathway (SIP) approximations through the tracheobronchial region and new acinar moving wall models of the alveolar region.
  
  
  
  It was determined that the PSD used for each inhalation waveform should be based on a constant particle sizing flow rate equal to the average of the inhalation waveform's peak inspiratory flow rate (PIFR) and mean flow rate [i.e., AVG(PIFR, Mean)]. Using this technique, agreement with the in vivo data was acceptable with <15% relative differences averaged across the three regions considered for all inhalation waveforms. Defining a peripheral to central deposition ratio (P/C) based on alveolar and tracheobronchial compartments, respectively, large flow-rate-dependent differences were observed, which were not evident in the original 2D in vivo data.
  
  
  
  The agreement between the CFD predictions and in vivo data was dependent on accurate initial estimates of the PSD, emphasizing the need for a combination in vitro-in silico approach. Furthermore, use of the AVG(PIFR, Mean) value was identified as a potentially useful method for characterizing a DPI aerosol at a constant flow rate.
authors.affiliation: 1 Department of Mechanical and Nuclear Engineering, Virginia Commonwealth University , Richmond, Virginia.|2 Department of Pharmaceutics, Virginia Commonwealth University , Richmond, Virginia.
authors.forename: P Worth
authors.initials: PW
authors.lastname: Longest
authors.affiliation: 1 Department of Mechanical and Nuclear Engineering, Virginia Commonwealth University , Richmond, Virginia.
authors.forename: Geng
authors.initials: G
authors.lastname: Tian
authors.affiliation: 1 Department of Mechanical and Nuclear Engineering, Virginia Commonwealth University , Richmond, Virginia.
authors.forename: Navvab
authors.initials: N
authors.lastname: Khajeh-Hosseini-Dalasm
authors.affiliation: 2 Department of Pharmaceutics, Virginia Commonwealth University , Richmond, Virginia.
authors.forename: Michael
authors.initials: M
authors.lastname: Hindle
mesh_terms: D000280:Administration, Inhalation; D000328:Adult; D000336:Aerosols; D001993:Bronchodilator Agents / Q000008:administration & dosage* / Q000737:chemistry / Q000378:metabolism; D019819:Budesonide / Q000008:administration & dosage* / Q000737:chemistry / Q000378:metabolism; D003198:Computer Simulation; D004339:Drug Compounding; D058995:Dry Powder Inhalers; D005938:Glucocorticoids / Q000008:administration & dosage* / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008953:Models, Anatomic; D010316:Particle Size; D015203:Reproducibility of Results; D012119:Respiration; D012137:Respiratory System / Q000033:anatomy & histology / Q000378:metabolism*; D013269:Stochastic Processes; D014018:Tissue Distribution
chemical_list: D000336:Aerosols; D001993:Bronchodilator Agents; D005938:Glucocorticoids; D019819:Budesonide
keywords: computational fluid dynamics (CFD); pharmaceutical aerosols; predictions of aerosol deposition; respiratory drug delivery; stochastic individual pathway model