Abstract
BACKGROUND: In mechanically ventilated patients with COPD, the response of the expiratory resistance of the respiratory system (expiratory RRS) to bronchodilators is virtually unknown.
OBJECTIVE: To examine the effect of inhaled albuterol on expiratory RRS, and the correlation of albuterol-induced changes in expiratory RRS 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 CRS) of each slice via regression analysis of the volume-flow and post-occlusion volume-tracheal pressure relationships, respectively. For each slice we calculated expiratory RRS as the time constant divided by the effective deflation CRS.
RESULTS: Albuterol significantly decreased the expiratory RRS (mean expiratory RRS 42.68 ± 17.8 cm H2O/L/s vs 38.08 ± 16.1 cm H2O/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 RRS 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 RRS 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.
Footnotes
- Correspondence: Eumorfia Kondili MD, Department of Intensive Care Medicine, University Hospital of Heraklion, Heraklion, Crete, Greece 71110. E-mail: konde{at}med.uoc.gr.
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The authors have disclosed no conflicts of interest.
- Copyright © 2011 by Daedalus Enterprises Inc.