title: Pressure attenuation during high-frequency airway clearance therapy across different size endotracheal tubes: An in vitro study.
abstract: High-frequency airway clearance therapy is a positive pressure secretion clearance modality used in pediatric and adult applications. However, pressure attenuation across different size endotracheal tubes (ETT) has not been adequately described. This study quantifies attenuation in an in vitro model.
  
  
  
  The MetaNeb® System was used to deliver high-frequency pressure pulses to 3.0, 4.0, 6.0 and 8.0mm ID ETTs connected to a test lung during mechanical ventilation. The experimental setup included a 3D-printed trachea model and imbedded pressure sensors. The pressure attenuation (Patt%) was calculated: Patt%=[(Pproximal-Pdistal)/Pproximal]x100. The effect of pulse frequency on Pdistal and Pproximal was quantified.
  
  
  
  Patt% was inversely and linearly related to ETT ID and (y=-7.924x+74.36; R(2)=0.9917, P=.0042 for 4.0Hz pulse frequency and y=-7.382+9.445, R(2)=0.9964, P=.0018 for 3.0Hz pulse frequency). Patt% across the 3.0, 4.0, 6.0 and 8.0mm I.D. ETTs was 48.88±10.25%, 40.87±5.22%, 27.97±5.29%, and 9.90±1.9% respectively. Selecting the 4.0Hz frequency mode demonstrated higher Pproximal and Pdistal compared to the 3.0Hz frequency mode (P=.0049 and P=.0065). Observed Pdistal was <30cmH2O for all experiments.
  
  
  
  In an in vitro model, pressure attenuation was linearly related to the inner diameter of the endotracheal tube; with decreasing attenuation as the ETT size increased.
authors.affiliation: Division of Critical Care Medicine, Department of Anesthesiology, Perioperative and Pain Medicine, Boston Children's Hospital, Boston, MA; Department of Bioengineering, Northeastern University, Boston, MA; Harvard Medical School, Boston, MA. Electronic address: craig.smallwood@childrens.harvard.edu.
authors.forename: Craig D
authors.initials: CD
authors.lastname: Smallwood
authors.affiliation: Respiratory Care Department, Boston Children's Hospital, Boston, MA.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Bullock
authors.affiliation: Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Gouldstone
mesh_terms: D035641:Chest Wall Oscillation / Q000379:methods*; D006801:Humans; D066298:In Vitro Techniques; D007442:Intubation, Intratracheal / Q000295:instrumentation*; D008954:Models, Biological; D011312:Pressure; D012121:Respiration, Artificial / Q000379:methods*; D014132:Trachea
keywords: Endotracheal tube; High-frequency; Pressure attenuation; Secretion clearance