title: Effect of albuterol on expiratory resistance in mechanically ventilated patients.
abstract: BACKGROUND
  In mechanically ventilated patients with COPD, the response of the expiratory resistance of the respiratory system (expiratory R(RS)) to bronchodilators is virtually unknown.
  
  
  OBJECTIVE
  To examine the effect of inhaled albuterol on expiratory R(RS), and the correlation of albuterol-induced changes in expiratory R(RS) with end-inspiratory resistance and the expiratory flow-volume relationship.
  
  
  METHODS
  We studied 10 mechanically ventilated patients with COPD exacerbation, before and 30 min after administration of albuterol. We obtained flow-volume curves during passive expiration, divided the expired volume into 5 equal volume slices, and then calculated the time constant and dynamic effective deflation compliance of the respiratory system (effective deflation C(RS)) of each slice via regression analysis of the volume-flow and post-occlusion volume-tracheal pressure relationships, respectively. For each slice we calculated expiratory R(RS) as the time constant divided by the effective deflation C(RS).
  
  
  RESULTS
  Albuterol significantly decreased the expiratory R(RS) (mean expiratory R(RS) 42.68 ± 17.8 cm H(2)O/L/s vs 38.08 ± 16.1 cm H(2)O/L/s) and increased the rate of lung emptying toward the end of expiration (mean time constant 2.51 ± 1.2 s vs 2.21 ± 1.2 s). No correlation was found between the albuterol-induced changes in expiratory R(RS) and that of end-inspiratory resistance. Only at the end of expiration did albuterol-induced changes in the expiratory flow-volume relationship correlate with changes in expiratory R(RS) in all patients.
  
  
  CONCLUSIONS
  In patients with COPD, albuterol significantly decreases expiratory resistance at the end of expiration. In mechanically ventilated patients, neither inspiratory resistance nor the whole expiratory flow-volume curve may be used to evaluate the bronchodilator response of expiratory resistance.
authors.affiliation: Department of Intensive Care Medicine, University of Crete, Heraklion, Crete, Greece. konde@med.uoc.gr
authors.forename: Eumorfia
authors.initials: E
authors.lastname: Kondili
authors.forename: Christina
authors.initials: C
authors.lastname: Alexopoulou
authors.forename: George
authors.initials: G
authors.lastname: Prinianakis
authors.forename: Nektaria
authors.initials: N
authors.lastname: Xirouchaki
authors.forename: Katerina
authors.initials: K
authors.lastname: Vaporidi
authors.forename: Dimitris
authors.initials: D
authors.lastname: Georgopoulos
mesh_terms: D000280:Administration, Inhalation; D000368:Aged; D000403:Airway Resistance / Q000187:drug effects* / Q000502:physiology; D000420:Albuterol / Q000008:administration & dosage*; D001993:Bronchodilator Agents / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D005260:Female; D005500:Follow-Up Studies; D005540:Forced Expiratory Flow Rates / Q000187:drug effects; D006801:Humans; D008297:Male; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology / Q000628:therapy*; D012121:Respiration, Artificial
chemical_list: D001993:Bronchodilator Agents; D000420:Albuterol