title: Resistivities of placebo and active Diskus inhalers compared.
abstract: OBJECTIVE
  Verbal instruction and demonstration of inhalation technique are essential to enhance the effectiveness of inhalation therapy. Placebo devices are commonly used to instruct patients. It is not obvious that patients, who inhale with an adequate flow through an empty placebo Diskus, would also be able to do so with active inhalers containing a strip with powder. The presence of powder may result in a change in resistivity. We compared the resistivities of a placebo Diskus being empty; a powder filled Diskus inhaler and a Diskus inhaler with an empty blister.
  
  
  METHODS
  A Diskus inhaler was placed in a box, which enabled measurement of pressure drop and flow rates. Ten placebo and ten Ventolin Diskus inhalers were measured. Twelve pressure- and flow-profiles were recorded through each device. After each simulated inhalation through a powder filled blister, a second inhalation was performed through the empty blister. The resistivity was calculated by pressure-flow equation.
  
  
  RESULTS
  The resistivity of the empty placebo Diskus inhaler was slightly but significantly higher than both blister filled inhalers, with or without powder (0.0215 vs. 0.0211 and 0.0211 (kPa)(0.5) (l min(-1))(-1)) (P<0.001).
  
  
  CONCLUSIONS
  Patients who are capable of generating sufficient flow through a placebo Diskus will surely be capable of generating equivalent flows through a Diskus inhaler containing a strip with active drug substance.
authors.affiliation: Department of Pulmonology Dekkerswald, University of Nijmegen, P.O. Box 9001, 6560 GB, Groesbeek, The Netherlands. m.broeders@mailbox.kun.nl
authors.forename: M E
authors.initials: ME
authors.lastname: Broeders
authors.forename: J
authors.initials: J
authors.lastname: Molema
authors.forename: H T
authors.initials: HT
authors.lastname: Folgering
mesh_terms: D000399:Air Pressure; D000465:Algorithms; D009330:Nebulizers and Vaporizers; D011208:Powders
chemical_list: D011208:Powders