title: Membrane diffusion in diseases of the pulmonary vasculature.
abstract: BACKGROUND
  We examined pulmonary diffusing capacity (D(LCO)) and its partition in pulmonary vascular diseases without evident parenchymal disease to assess the pattern and proportionality of change in membrane diffusion (D(m)) and capillary blood volume (V(c)). Disproportionate reduction in D(m) relative to V(c) (low D(m)/V(c)) in these diseases has been attributed to associated alveolar membrane/parenchymal disease, thus providing a potentially important diagnostic tool.
  
  
  METHODS
  Diseases included: idiopathic pulmonary arterial hypertension (n=6), chronic thromboembolic disease (n=5), and intravenous drug use (n=14), providing a spectrum of pulmonary vascular diseases. V(c) and D(m) were determined as described by Roughton and Forster.
  
  
  RESULTS
  All diseases showed a reduced V(c) (59+/-10, 69+/-14, 71+/-21 % predicted, respectively) and D(m) (76+/-22, 53+/-19, 63+/-16 % predicted, respectively) with no differences between groups (p>0.05). Disproportionate reduction of D(m) (D(m)/V(c) % predicted <1) was seen in all diseases (range 0.36-1.89). A mathematical analysis is presented to illustrate that changes in vascular geometry may additionally influence the proportionality of changes in D(m) and V(c). The mathematical analysis suggests that when reduction in patency of some vessels co-exits with compensatory dilatation of the remaining vasculature, a disproportionate reduction in D(m) relative to V(c) may result.
  
  
  CONCLUSIONS
  The balance between vascular curtailment and compensatory dilatation may contribute to the variability of the D(m)/V(c) relationship seen in pulmonary vascular disease. Disproportionate reduction in D(m) relative to V(c) may result from this imbalance and need not imply subclinical alveolar membrane and/or parenchymal disease.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Bellevue Hospital Chest Service, Department of Medicine, New York University School of Medicine, 462 First Ave 7W54, New York, NY 10016, USA. beno.oppenheimer@med.nyu.edu
authors.forename: Beno W
authors.initials: BW
authors.lastname: Oppenheimer
authors.forename: Kenneth I
authors.initials: KI
authors.lastname: Berger
authors.forename: Nicos P
authors.initials: NP
authors.lastname: Hadjiangelis
authors.forename: Robert G
authors.initials: RG
authors.lastname: Norman
authors.forename: David M
authors.initials: DM
authors.lastname: Rapoport
authors.forename: Roberta M
authors.initials: RM
authors.lastname: Goldring
mesh_terms: D000328:Adult; D001794:Blood Pressure; D005260:Female; D005652:Functional Residual Capacity; D006801:Humans; D006976:Hypertension, Pulmonary / Q000209:etiology / Q000503:physiopathology; D008171:Lung Diseases / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D011653:Pulmonary Diffusing Capacity; D011655:Pulmonary Embolism / Q000503:physiopathology; D012189:Retrospective Studies; D015819:Substance Abuse, Intravenous / Q000150:complications; D014109:Total Lung Capacity