title: Pulmonary function characteristics in patients with different patterns of methacholine airway hyperresponsiveness.
abstract: OBJECTIVE
  The American Thoracic Society guidelines for methacholine-induced airway hyperresponsiveness include a > or = 20% reduction in FEV(1) or a > or = 40% reduction in specific airway conductance (sGaw). The objectives of the current study are to assess the concordance between these two criteria and to characterize the pulmonary function and respiratory symptoms of patients with different patterns of methacholine hyperresponsiveness.
  
  
  METHODS
  A prospective study of 248 consecutive patients referred for methacholine bronchoprovocation testing.
  
  
  RESULTS
  Positive methacholine hyperresponsiveness was noted in 179 patients; 139 patients (78%) had a > or = 20% reduction in FEV(1), whereas 40 patients (22%) had a > or = 40% reduction in sGaw alone without a significant change in FEV(1). The former group had the following: (1) higher baseline lung volumes, (2) lower baseline values of FEV(1) and sGaw, (3) forced expiratory flow between 25% and 75% of vital capacity (FEF(25-75))/FVC ratios compared to patients with a reduction in sGaw alone (0.72 +/- 0.26 vs 0.97 +/- 0.28, mean +/- SD; p < 0.0001), and (4) more frequent presence of wheezing and chest tightness (p < 0.05).
  
  
  CONCLUSIONS
  First, a substantial number of patients have a reduction in SGaw alone in response to methacholine, and secondly, this response is seen in patients with a higher FEF(25-75)/FVC ratio. Since the FEF(25-75)/FVC ratio is thought to be an index of airway size relative to lung size, we speculate that the larger intrinsic airway size relative to lung size may explain the differences in baseline parameters and patterns of methacholine hyperresponsiveness.
authors.affiliation: Department of Pulmonary and Critical Care Medicine, Memorial Hospital of Rhode Island and Brown Medical School, Providence, RI 02860, USA. Annie_Parker@brown.edu
authors.forename: Annie Lin
authors.initials: AL
authors.lastname: Parker
authors.forename: F Dennis
authors.initials: FD
authors.lastname: McCool
mesh_terms: D000328:Adult; D001249:Asthma / Q000175:diagnosis / Q000503:physiopathology; D016535:Bronchial Hyperreactivity / Q000175:diagnosis* / Q000503:physiopathology*; D001985:Bronchial Provocation Tests; D016085:Bronchoconstrictor Agents; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D016210:Methacholine Chloride; D008875:Middle Aged; D011446:Prospective Studies
chemical_list: D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride