title: Expiratory air trapping during asthma exacerbation: Relationships with clinical indices and proximal airway morphology.
abstract: OBJECTIVE
  To semi-quantitatively assess expiratory air trapping (AT(exp)) and structural changes in the proximal airways in asthma during asthma exacerbation (AE) and to explore the relationships among AT(exp), clinical indices, and proximal airway changes.
  
  
  METHODS
  Paired inspiratory-dynamic forced expiratory CT scans of 36 asthmatics (30 women, 6 men; mean age, 49.2±18.9 years) performed during AE were retrospectively reviewed for the total AT(exp) score (summed scores [extent grading (0-4)×pattern grading (1-4)] of the twelve lung zones), morphologic parameters and expiratory bronchial collapse (BC(exp)) of the proximal airways. The relationships of the score with clinical indices and proximal airway morphology (normalized by body surface area [BSA]) were analyzed. A p value of <0.05 was considered statistically significant.
  
  
  RESULTS
  The mean total AT(exp) score was 110.1±43.4 (range, 8-166). It was higher in the lower zones and in patients older than 60 years, having BMI of <27.5 kg/m(2), and peak expiratory flow rate (PEFR) of <60% predicted. Correlation existed between the score and age (r=0.331), BMI (r=-0.375), BSA (r=-0.442), % predicted PEFR (r=-0.332), right upper lobe apical segmental bronchus (RB1)-wall area (WA)/BSA (r=0.467), %RB1-WA (r=0.395), and RB1-bronchial wall thickness (BWT)/BSA (r=0.378). The score showed no correlation with BC(exp) and other morphologic bronchial parameters. Area under receiver-operating-characteristic curve 0.724 (95% CI) showed that the score of 110 could discriminate patients with PEFR of <60% predicted from those with PEFR of ≥60% predicted.
  
  
  CONCLUSIONS
  During AE, there was a high prevalence of extensive AT(exp) which was correlated with patient's age, BMI, BSA, AE severity and RB1 morphology but not correlated with BC(exp).
authors.affiliation: Division of Diagnostic Radiology, Department of Diagnostic and Therapeutic Radiology, Mahidol University, Bangkok, Thailand. Electronic address: ratrspoom@yahoo.com.
authors.forename: Thitiporn
authors.initials: T
authors.lastname: Suwatanapongched
authors.affiliation: Division of Diagnostic Radiology, Department of Diagnostic and Therapeutic Radiology, Mahidol University, Bangkok, Thailand. Electronic address: airtikky652@hotmail.com.
authors.forename: Chayanin
authors.initials: C
authors.lastname: Thongprasert
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Medicine, Mahidol University, Bangkok, Thailand. Electronic address: siwaporn083@gmail.com.
authors.forename: Siwaporn
authors.initials: S
authors.lastname: Lertpongpiroon
authors.affiliation: Section of Clinical Epidemiology and Biostatistics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand. Electronic address: dittapol.mun@gmail.com.
authors.forename: Dittapol
authors.initials: D
authors.lastname: Muntham
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Medicine, Mahidol University, Bangkok, Thailand. Electronic address: sml_kt2@yahoo.com.
authors.forename: Sumalee
authors.initials: S
authors.lastname: Kiatboonsri
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001249:Asthma / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D015992:Body Mass Index; D001830:Body Surface Area; D001980:Bronchi / Q000503:physiopathology; D001995:Bronchography; D045853:Exhalation / Q000502:physiology*; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012720:Severity of Illness Index; D014057:Tomography, X-Ray Computed; D055815:Young Adult
keywords: Air trapping; Asthma; Asthma exacerbation; Bronchial collapse; Bronchial wall thickness; CT