title: Postural changes in nasal and pulmonary resistance in subjects with asthma.
abstract: BACKGROUND
  Subjects with asthma frequently have nasal symptoms and complain of orthopnoea but airflow resistance is usually only assessed during oral breathing and while seated.
  
  
  METHODS
  We have used a forced oscillation technique to measure total respiratory resistance (Rrs) at 6Hz during mouth breathing (Rrs,mo) and during nose breathing (Rrs,na) in the sitting and supine postures; resistance of the nasal airway (Rnaw) was estimated as Rrs,na--Rrs,mo. Forced oscillations were applied during normal tidal breathing and the mid-tidal lung volume (MTLV) was determined for each breathing route and posture.
  
  
  METHODS
  Three groups of subjects were studied: 10 normal subjects without lung or nasal disease (N; five males, mean age 33.5 [range 23-58] years, mean FEV1 105%pred, FEV1/VC 86%); seven subjects with asthma alone (A; four males, 40.3 [23-57] years, mean FEV1 66%pred, FEV1/VC 74%); 10 asthmatic subjects with nasal obstructive symptoms (AN; six males, 62.8 [38-80] years, mean FEV1 56%pred, FEV1/VC 75%).
  
  
  RESULTS
  In all three groups of subjects, mean Rrs,mo and Rrs,na were higher in the supine than sitting posture. In normal subjects the increase in supine Rrs,mo was associated with a 0.6 liter fall in MTLV. In asthma supine Rrs,mo increased despite a much smaller fall in MTLV; supine increases in Rrs,na were particularly large in presence of nasal disease.
  
  
  CONCLUSIONS
  Values of airflow resistance are 2-3 times higher in both normal and asthmatic subjects when breathing via the nose and supine than under normal laboratory conditions of oral breathing and seated.
authors.affiliation: Respiratory Medicine, Faculty of Medicine, Imperial College, London, UK.
authors.forename: C J
authors.initials: CJ
authors.lastname: Duggan
authors.forename: R A
authors.initials: RA
authors.lastname: Watson
authors.forename: N B
authors.initials: NB
authors.lastname: Pride
mesh_terms: D000328:Adult; D000403:Airway Resistance / Q000502:physiology*; D001249:Asthma / Q000503:physiopathology*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009055:Mouth; D009666:Nose / Q000503:physiopathology*; D010865:Pilot Projects; D011187:Posture; D012016:Reference Values; D012119:Respiration; D015656:Respiratory Mechanics; D012680:Sensitivity and Specificity