title: Validation of a photoacoustic gas analyser for the measurement of functional residual capacity using multiple-breath inert gas washout.
abstract: BACKGROUND
  The respiratory mass spectrometer is the current gold-standard technique for performing multiple-breath inert gas washout (MBW), but is expensive and lacks portability. A number of alternative techniques have recently been described.
  
  
  OBJECTIVE
  We aimed to validate, using an in vitro lung model, an open-circuit MBW system that utilises a portable photoacoustic gas analyser, with sulphur hexafluoride (SF6) as the inert tracer gas.
  
  
  METHODS
  An acrylic glass lung model was utilised to assess the accuracy of functional residual capacity (FRC) measurements derived from MBW. Measurements were performed in triplicate at 20 combinations of simulated FRC, tidal volume and respiratory rate. FRC measured using MBW (FRCmbw) was compared to FRC calculated from the known dimensions of the model (FRCcalc). MBW was also performed in 10 healthy subjects and 14 patients with asthma.
  
  
  RESULTS
  The MBW system measured FRC with high precision. The mean bias of FRCmbw with respect to FRCcalc was -0.4% (95% limits of agreement of -4.6 and 3.9%). The mean coefficient of variation of triplicate FRC measurements was 4.0% in vivo and 1.0% in vitro. MBW slightly underestimated low lung volumes and overestimated high lung volumes, but this did not cause a significant error in lung clearance index except at lung volumes below 1,500 ml.
  
  
  CONCLUSIONS
  The open-circuit MBW system utilising SF6 as the inert tracer gas and a photoacoustic gas analyser is both accurate and repeatable within the adult range of lung volumes. Further modifications would be required before its use in young children or infants.
authors: Institute for Lung Health, University of Leicester, Leicester, UK.
authors: Sherif
authors: S
authors: Gonem
authors: Florian
authors: F
authors: Singer
authors: Steven
authors: S
authors: Corkill
authors: Amisha
authors: A
authors: Singapuri
authors: Salman
authors: S
authors: Siddiqui
authors: Per
authors: P
authors: Gustafsson
mesh_terms: D001944:Breath Tests / Q000379:methods; D004867:Equipment Design; D005652:Functional Residual Capacity / Q000502:physiology*; D006801:Humans; D008954:Models, Biological; D061088:Photoacoustic Techniques / Q000379:methods / Q000592:standards; D015203:Reproducibility of Results; D012129:Respiratory Function Tests / Q000379:methods*; D013459:Sulfur Hexafluoride
chemical_list: D013459:Sulfur Hexafluoride