title: Exploratory study into the effect of abdominal mass loading on airways resistance and ventilatory failure.
abstract: OBJECTIVE
  We hypothesised that the airway resistance during tidal breathing would correlate with a particular pattern of increasing obesity, particularly when supine, and would differ between participants with and without ventilatory failure.
  
  
  METHODS
  In our cross-sectional cohort study, 72 morbidly obese patients (40 males, 32 females, mean body mass index (BMI) 47.2) had measurements of both airways resistance (by impulse oscillometry (IOS)) and adiposity (by dual-energy X-ray absorptiometry (DXA)).
  
  
  RESULTS
  All measures of airways resistance increased in the supine position: total airways resistance (R5) +37% (p<0.0005); large airways resistance (R20) +29% (p<0.0005); and small airways resistance (R5-R20) +52% (p<0.0005). BMI was correlated with seated R5, seated R5-R20, supine R5 and supine R5-R20 (r=0.33 p<0.006, r=0.32 p<0.004, r=0.30 p<0.02 and r=0.36 p<0.04, respectively). Visceral adipose tissue mass was correlated with supine R5-20 (r=0.46 p<0.05). Supine measures of total airways resistance (R5) and large airways resistance (R20) differed between those with and without ventilatory failure, as did mean weight and BMI.
  
  
  CONCLUSIONS
  Our study identifies a potentially detrimental effect of the supine posture on tidal breathing airways resistance in obese patients. This change is correlated most with visceral adipose tissue mass and the small airways. We were able to demonstrate that supine increases in airways resistance during tidal breathing, within obese patients, are different between those with and without ventilatory failure.
  
  
  BACKGROUND
  NCT01380418; pre-results.
authors.affiliation: Oxford Respiratory Trials Unit, Experimental Medicine Division, Nuffield Department of Medicine, University of Oxford, Oxford, UK; St Peter's College, New Inn Hall Street, Oxford, UK; Centre for Altitude, Space and Extreme Environment Medicine (CASE Medicine), Institute of Sport Exercise and Health, University College London, London, UK.
authors.forename: Raj S
authors.initials: RS
authors.lastname: Dattani
authors.affiliation: University College London , London , UK.
authors.forename: Casey B
authors.initials: CB
authors.lastname: Swerner
authors.affiliation: Oxford Respiratory Trials Unit, Experimental Medicine Division, Nuffield Department of Medicine, University of Oxford, Oxford, UK; Oxford Centre for Respiratory Medicine, NIHR Oxford Biomedical Research Centre, The Churchill Hospital, Oxford University Hospitals NHS Trust, Oxford, UK.
authors.forename: John R
authors.initials: JR
authors.lastname: Stradling
authors.affiliation: Oxford Respiratory Trials Unit, Experimental Medicine Division, Nuffield Department of Medicine, University of Oxford, Oxford, UK; Oxford Centre for Respiratory Medicine, NIHR Oxford Biomedical Research Centre, The Churchill Hospital, Oxford University Hospitals NHS Trust, Oxford, UK.
authors.forename: Ari Rg
authors.initials: AR
authors.lastname: Manuel
keywords: Lung Physiology; Respiratory Measurement