title: Relationship between the baseline alveolar volume-to-total lung capacity ratio and airway responsiveness.
abstract: OBJECTIVE
  Ventilation heterogeneity (VH) has been linked to airway responsiveness (AR) based on various measures of VH involving inert gas washout, forced oscillation and lung imaging. We explore whether VH at baseline, as measured by the simple ratio of single breath alveolar volume to plethysmographically determined total lung capacity (VA/TLC), would correlate with AR as measured by methacholine challenge testing.
  
  
  METHODS
  We analysed data from spirometry, lung volumes, diffusing capacity and methacholine challenge to derive the VA/TLC and the dose-response slope (DRS) of forced expiratory volume in 1 s (DRS-FEV1) during methacholine challenge from 136 patients. We separated out airway closure versus narrowing by examining the DRS for forced vital capacity (DRS-FVC) and the DRS for FEV1/FVC (DRS-FEV1/FVC), respectively. Similarly, we calculated the DRS for sGaw (DRS-sGaw) as another measure of airway narrowing. We performed statistical analysis using Spearman rank correlation and multifactor linear regression using a backward stepwise modelling procedure.
  
  
  RESULTS
  We found that the DRS-FEV1 correlated with baseline VA/TLC (rho = -0.26, P < 0.01), and VA/TLC and FEV1 were independently associated with DRS-FEV1 (R(2)  = 0.14, P = 0.01). In addition, VA/TLC was associated with both airway narrowing and closure in response to methacholine.
  
  
  CONCLUSIONS
  These results confirm that baseline VA/TLC is associated with AR, and reflects both airway closure and airway narrowing following methacholine challenge.
authors.affiliation: Vermont Lung Center, Pulmonary Disease and Critical Care Medicine, University of Vermont College of Medicine, Burlington, Vermont, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Kaminsky
authors.forename: Anees
authors.initials: A
authors.lastname: Daud
authors.forename: David G
authors.initials: DG
authors.lastname: Chapman
mesh_terms: D000328:Adult; D000368:Aged; D056151:Airway Remodeling; D000403:Airway Resistance / Q000187:drug effects* / Q000502:physiology; D001249:Asthma / Q000150:complications / Q000503:physiopathology*; D016535:Bronchial Hyperreactivity / Q000503:physiopathology*; D001985:Bronchial Provocation Tests; D016085:Bronchoconstrictor Agents / Q000494:pharmacology*; D015331:Cohort Studies; D005260:Female; D005541:Forced Expiratory Volume / Q000187:drug effects; D006801:Humans; D008297:Male; D016210:Methacholine Chloride / Q000494:pharmacology*; D008875:Middle Aged; D011653:Pulmonary Diffusing Capacity / Q000187:drug effects; D013147:Spirometry; D014109:Total Lung Capacity / Q000187:drug effects* / Q000502:physiology
chemical_list: D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride
keywords: asthma; clinical respiratory medicine; respiratory function test; respiratory mechanics; respiratory structure and function