title: Comparison of total-breath and single-breath diffusing capacity in healthy volunteers and COPD patients.
abstract: BACKGROUND
  The measurement of single-breath diffusing capacity (Dlco(SB)) assumes that diffusing capacity per liter of alveolar volume (Dlco/VA) determined in a 750-mL gas sample represents the diffusing capacity (Dlco) of the entire lung. Fast-responding gas analyzers provide the opportunity to verify this assumption because of the possibility to measure CO and CH(4) fractions continuously throughout the entire expiration. Continuous gas sampling provides more information per measurement, but this information cannot be expressed in the traditional parameters. Our goals were to find new parameters to express the extra information of the continuous gas sampling, and to compare these new parameters with the traditional parameters.
  
  
  METHODS
  We compared a new method to determine Dlco with the traditional method in 62 healthy volunteers and 26 COPD patients. Traditionally, Dlco(SB) is determined by multiplying Dlco/VA with alveolar volume, both calculated from gas concentrations in a 750-mL gas sample. The new method calculates total-breath Dlco (Dlco(TB)) by integration of Dlco/VA against exhaled volume.
  
  
  RESULTS
  In healthy volunteers, Dlco/VA shows a slight upward slope during exhalation, while in COPD patients Dlco/VA shows a horizontal line. Total-breath total lung capacity (TLC) is larger than single-breath TLC both in healthy volunteers and in COPD patients, leading to a Dlco(TB) that is significantly larger than Dlco(SB) in both groups (p < 0.001).
  
  
  CONCLUSIONS
  The assumption that a 750-mL gas sample represents the entire lung seems to be correct for Dlco/VA but not for the CH(4) fraction in case of ventilation inhomogeneity.
authors.affiliation: Department of Pulmonary Diseases, Erasmus University, V203, PO Box 2040, 3000 CA Rotterdam, the Netherlands. m.horstman@erasmusmc.nl
authors.forename: Maartje J M
authors.initials: MJ
authors.lastname: Horstman
authors.forename: Frans W
authors.initials: FW
authors.lastname: Mertens
authors.forename: Daniel
authors.initials: D
authors.lastname: Schotborg
authors.forename: Henk C
authors.initials: HC
authors.lastname: Hoogsteden
authors.forename: Henk
authors.initials: H
authors.lastname: Stam
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011653:Pulmonary Diffusing Capacity / Q000502:physiology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D011659:Pulmonary Gas Exchange / Q000502:physiology; D013147:Spirometry