title: Spirometric changes in obstructive disease: after all, how much is significant?
abstract: OBJECTIVE
  To establish the upper limits for changes in FEV1, slow vital capacity (SVC), FVC, and inspiratory capacity (IC) after placebo administration in patients with airflow obstruction.
  
  
  METHODS
  One hundred and two adults with airflow obstruction (FEV1 = 62 ± 19% of predicted) were included in the study. All of the participants performed SVC and FVC maneuvers before and after the administration of placebo spray. The changes in FEV1, SVC, FVC, and IC were expressed as absolute values, percentage of change from baseline values, and percentage of predicted values, 95% CIs and 95th percentiles being calculated. Factor analysis was performed in order to determine how those changes clustered.
  
  
  RESULTS
  Considering the 95% CIs and 95th percentiles and after rounding the values, we found that the upper limits for a significant response were as follows: FEV1 = 0.20 L, FVC = 0.20 L, SVC = 0.25 L, and IC = 0.30 L (expressed as absolute values); FEV1 = 12%, FVC = 7%, SVC = 10%, and IC = 15% (expressed as percentage of change from baseline values); and FEV1 = 7%, FVC = 6%, SVC = 7%, and IC = 12% (expressed as percentage of predicted values).
  
  
  CONCLUSIONS
  In patients with airflow obstruction, IC varies more widely than do FVC and SVC. For IC, values greater than 0.30 L and 15% of change from the baseline value can be considered significant. For FVC, values greater than 0.20 L and 7% of change from the baseline value are significant. Alternatively, changes exceeding 0.20 L and 7% of the predicted value can be considered significant for FEV1 and FVC. On factor analysis, spirometric parameters clustered into three dimensions, expressing changes in flows, volumes, and dynamic hyperinflation.
authors.affiliation: Federal University of Rio Grande do Norte, Natal, Brazil. drandrepinto@globo.com
authors.forename: André Luis Pinto
authors.initials: AL
authors.lastname: Soares
authors.forename: Carlos Alberto de Castro
authors.initials: CA
authors.lastname: Pereira
authors.forename: Silvia Carla
authors.initials: SC
authors.lastname: Rodrigues
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001993:Bronchodilator Agents / Q000008:administration & dosage* / Q000627:therapeutic use; D005163:Factor Analysis, Statistical; D005260:Female; D005541:Forced Expiratory Volume / Q000187:drug effects; D006801:Humans; D007320:Inspiratory Capacity / Q000187:drug effects; D008173:Lung Diseases, Obstructive / Q000188:drug therapy* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D059085:Nasal Sprays; D010919:Placebos / Q000008:administration & dosage / Q000494:pharmacology*; D013147:Spirometry; D018709:Statistics, Nonparametric; D014797:Vital Capacity / Q000187:drug effects*
chemical_list: D001993:Bronchodilator Agents; D059085:Nasal Sprays; D010919:Placebos