title: What are ventilation defects in asthma?
abstract: BACKGROUND
  Hyperpolarised (3)He MRI provides a way to visualise regional pulmonary functional abnormalities that in asthma are thought to be related to airway morphological abnormalities. However, the exact aetiology of ventilation defects in asthma is not well understood.
  
  
  OBJECTIVE
  To better understand the determinants of ventilation defects in asthma, we evaluated well-established clinical as well as (3)He MRI and X-ray CT airway measurements in healthy subjects and subjects with asthma.
  
  
  METHODS
  Thirty-four subjects (n=26 subjects with asthma, n=8 healthy volunteers) underwent MRI, spirometry, plethysmography, fraction of exhaled nitric oxide analysis, methacholine challenge and CT for a region-of-interest proximal to ventilation defects. For subjects who consented to CT (n=18 subjects with asthma, n=5 healthy volunteers), we evaluated 3(rd) to 5th generation airway wall area and wall thickness per cent and lumen area.
  
  
  RESULTS
  Seventeen subjects with asthma (17/26=65%) had visually obvious evidence of (3)He ventilation defects prior to bronchoprovocation and nine subjects with asthma had no ventilation defects prior to bronchoprovocation (9/26=35%). Subjects with asthma with defects were older (p=0.01) with worse forced expiratory volume in 1 s (FEV1)/forced vital capacity (p=0.0003), airways resistance (p=0.004), fraction of exhaled nitric oxide (p=0.03), greater bronchoprovocation concentration of methacholine that reduced FEV1 by 20% (p=0.008) and wall thickness per cent (p=0.02) compared with subjects with asthma without defects. There was a moderate correlation for wall area per cent with ventilation defect per cent (r=0.43, p=0.04).
  
  
  CONCLUSIONS
  Subjects with asthma with (3)He ventilation defects were older with significantly worse airway hyper-responsiveness, inflammation and airway remodelling but similar FEV1 as subjects with asthma without defects; hyperpolarised (3)He ventilation abnormalities were spatially and quantitatively related to abnormally remodelled airways.
authors: Imaging Research Laboratories, Robarts Research Institute, , London, Ontario, Canada.
authors: Sarah
authors: S
authors: Svenningsen
authors: Miranda
authors: M
authors: Kirby
authors: Danielle
authors: D
authors: Starr
authors: Harvey O
authors: HO
authors: Coxson
authors: Nigel A M
authors: NA
authors: Paterson
authors: David G
authors: DG
authors: McCormack
authors: Grace
authors: G
authors: Parraga
mesh_terms: D000328:Adult; D000402:Airway Obstruction / Q000473:pathology / Q000503:physiopathology; D001249:Asthma / Q000473:pathology / Q000503:physiopathology*; D001980:Bronchi / Q000473:pathology* / Q000503:physiopathology*; D001985:Bronchial Provocation Tests; D005260:Female; D006371:Helium; D006801:Humans; D008168:Lung / Q000503:physiopathology; D008279:Magnetic Resonance Imaging; D008297:Male; D016210:Methacholine Chloride; D008875:Middle Aged; D010991:Plethysmography; D012123:Pulmonary Ventilation / Q000502:physiology*; D013147:Spirometry; D014057:Tomography, X-Ray Computed; D055815:Young Adult
chemical_list: D016210:Methacholine Chloride; D006371:Helium
keywords: Asthma; Imaging/CT MRI etc