title: Tidal volume single breath washout of two tracer gases--a practical and promising lung function test.
abstract: BACKGROUND
  Small airway disease frequently occurs in chronic lung diseases and may cause ventilation inhomogeneity (VI), which can be assessed by washout tests of inert tracer gas. Using two tracer gases with unequal molar mass (MM) and diffusivity increases specificity for VI in different lung zones. Currently washout tests are underutilised due to the time and effort required for measurements. The aim of this study was to develop and validate a simple technique for a new tidal single breath washout test (SBW) of sulfur hexafluoride (SF(6)) and helium (He) using an ultrasonic flowmeter (USFM).
  
  
  METHODS
  The tracer gas mixture contained 5% SF(6) and 26.3% He, had similar total MM as air, and was applied for a single tidal breath in 13 healthy adults. The USFM measured MM, which was then plotted against expired volume. USFM and mass spectrometer signals were compared in six subjects performing three SBW. Repeatability and reproducibility of SBW, i.e., area under the MM curve (AUC), were determined in seven subjects performing three SBW 24 hours apart.
  
  
  RESULTS
  USFM reliably measured MM during all SBW tests (n = 60). MM from USFM reflected SF(6) and He washout patterns measured by mass spectrometer. USFM signals were highly associated with mass spectrometer signals, e.g., for MM, linear regression r-squared was 0.98. Intra-subject coefficient of variation of AUC was 6.8%, and coefficient of repeatability was 11.8%.
  
  
  CONCLUSIONS
  The USFM accurately measured relative changes in SF(6) and He washout. SBW tests were repeatable and reproducible in healthy adults. We have developed a fast, reliable, and straightforward USFM based SBW method, which provides valid information on SF(6) and He washout patterns during tidal breathing.
authors.affiliation: Division of Respiratory Medicine, Department of Paediatrics, University Children's Hospital of Bern, Bern, Switzerland.
authors.forename: Florian
authors.initials: F
authors.lastname: Singer
authors.forename: Georgette
authors.initials: G
authors.lastname: Stern
authors.forename: Cindy
authors.initials: C
authors.lastname: Thamrin
authors.forename: Oliver
authors.initials: O
authors.lastname: Fuchs
authors.forename: Thomas
authors.initials: T
authors.lastname: Riedel
authors.forename: Per
authors.initials: P
authors.lastname: Gustafsson
authors.forename: Urs
authors.initials: U
authors.lastname: Frey
authors.forename: Philipp
authors.initials: P
authors.lastname: Latzin
mesh_terms: D000328:Adult; D019540:Area Under Curve; D001944:Breath Tests / Q000379:methods*; D005260:Female; D045268:Flowmeters; D005740:Gases / Q000032:analysis*; D006371:Helium / Q000032:analysis; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D012119:Respiration; D013459:Sulfur Hexafluoride / Q000032:analysis; D013990:Tidal Volume / Q000502:physiology; D014465:Ultrasonics
chemical_list: D005740:Gases; D006371:Helium; D013459:Sulfur Hexafluoride