title: The nonallergic asthma of obesity. A matter of distal lung compliance.
abstract: BACKGROUND
  The pathogenesis of asthma in obesity is poorly understood, but may be related to breathing at low lung volumes.
  
  
  OBJECTIVE
  To determine if lung function in obese patients with asthma and control subjects would respond differently to weight loss.
  
  
  METHODS
  Lung function was evaluated by conventional clinical tests and by impulse oscillometry in female late-onset, nonallergic patients with asthma and control subjects before, and 12 months after, bariatric surgery.
  
  
  RESULTS
  Patients with asthma (n = 10) had significantly lower FEV1 (79.8 ± 10.6 vs. 95.5 ± 7.0%) and FVC (82.4 ± 13.2 vs. 93.7 ± 8.9%) compared with control subjects (n = 13). There were no significant differences in FRC or TLC at baseline. Twelve months after surgery, control subjects had significant increases in FEV1 (95.5 ± 7.0 to 100.7 ± 5.9), FVC (93.6 ± 8.9 to 98.6 ± 8.3%), FRC (45.4 ± 18.5 to 62.1 ± 15.3%), and TLC (84.8 ± 15.0 to 103.1 ± 15.3%), whereas patients with asthma had improvement only in FEV1 (79.8 ± 10.6 to 87.2 ± 11.5). Control subjects and patients with asthma had a significantly different change in respiratory system resistance with weight loss: control subjects exhibited a uniform decrease in respiratory system resistance at all frequencies, whereas patients with asthma exhibited a decrease in frequency dependence of resistance. Fits of a mathematical model of lung mechanics to these impedance spectra suggest that the lung periphery was more collapsed by obesity in patients with asthma compared with control subjects.
  
  
  CONCLUSIONS
  Weight loss decompresses the lung in both obese control subjects and patients with asthma, but the more pronounced effects of weight loss on lung elastance suggest that the distal lung is inherently more collapsible in people with asthma.
authors.affiliation: 1 Deparment of Medicine and.
authors.forename: Ali
authors.initials: A
authors.lastname: Al-Alwan
authors.forename: Jason H T
authors.initials: JH
authors.lastname: Bates
authors.forename: David G
authors.initials: DG
authors.lastname: Chapman
authors.forename: David A
authors.initials: DA
authors.lastname: Kaminsky
authors.forename: Michael J
authors.initials: MJ
authors.lastname: DeSarno
authors.forename: Charles G
authors.initials: CG
authors.lastname: Irvin
authors.forename: Anne E
authors.initials: AE
authors.lastname: Dixon
mesh_terms: D000328:Adult; D001249:Asthma / Q000209:etiology* / Q000503:physiopathology; D050110:Bariatric Surgery; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D005541:Forced Expiratory Volume; D006801:Humans; D008168:Lung / Q000503:physiopathology*; D008170:Lung Compliance; D008875:Middle Aged; D015233:Models, Statistical; D009765:Obesity / Q000150:complications* / Q000503:physiopathology / Q000601:surgery; D011446:Prospective Studies; D016896:Treatment Outcome; D014797:Vital Capacity; D015431:Weight Loss / Q000502:physiology*
keywords: bariatric surgery; forced oscillation technique; impedance; lung volume