title: Mechanism of bronchodilator effect in chronic airflow limitation.
abstract: OBJECTIVE
  To examine the mechanisms through which two bronchodilators (theophylline and salbutamol) influence dyspnea during daily activities.
  
  
  METHODS
  Twenty-four patients with chronic airflow limitation participated in a multiple crossover, randomized, placebo-controlled trial. The effect of theophylline and salbutamol, alone or combined, on pulmonary function and dyspnea during daily activities was examined. Correlations of changes in forced expiratory volume in 1 second (FEV1) and maximum expiratory pressures (MIPs) (independent variables) and changes in dyspnea score during daily activities (dependent variable) were also examined.
  
  
  RESULTS
  The two drugs proved to be beneficial the effects in general were additive rather than synergistic. The drugs improved the FEV1; theophylline significantly improved the MIPs. The correlation between the changes in FEV1 and those in dyspnea score, after adjustment for the changes in MIPs, was 0.55 (p less than 0.001). The correlation between the changes in MIPs and those in dyspnea score, after adjustment for the changes in FEV1, was 0.39 (p less than 0.001).
  
  
  CONCLUSIONS
  Changes in airway calibre and in respiratory muscle strength play an independent and important role in dyspnea during daily activities in patients with chronic airflow limitation. Changes in airway calibre may be of greater importance.
authors.affiliation: Department of Clinical Epidemiology, McMaster University, Hamilton, Ont.
authors.forename: R
authors.initials: R
authors.lastname: Jaeschke
authors.forename: G H
authors.initials: GH
authors.lastname: Guyatt
authors.forename: J
authors.initials: J
authors.lastname: Singer
authors.forename: J
authors.initials: J
authors.lastname: Keller
authors.forename: M T
authors.initials: MT
authors.lastname: Newhouse
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D000420:Albuterol / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D004359:Drug Therapy, Combination; D004417:Dyspnea / Q000188:drug therapy* / Q000209:etiology / Q000503:physiopathology; D005541:Forced Expiratory Volume / Q000187:drug effects; D005652:Functional Residual Capacity / Q000187:drug effects; D006801:Humans; D008173:Lung Diseases, Obstructive / Q000150:complications*; D012132:Respiratory Muscles / Q000187:drug effects; D013806:Theophylline / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: D013806:Theophylline; D000420:Albuterol