Table 3– Overall recommendations for washout systems
Instantaneous flow within 5%, and VT and CEV measurement accuracy within 3%.
Quality of gas signals allowing determination of FRC, end-tidal gas concentration and SIII down to 1/40 of the starting inert-gas concentration with sufficient accuracy and resolution (see below).
FRC measurement accuracy within 5% of the true FRC value (for 95% of values),using a realistic lung model incorporating BTPS conditions across the intended volume range and breathing pattern of the system. Commercial systems manufacturers should perform this validation both prior to sale and whenever significant hardware or software modifications are made to existing devices. Re-evaluation should be performed as necessary if marked variation occurs beyond the normal observed pattern for biological controls during clinical research use.
The static and dynamic properties of the gas analyser (accuracy, response time and signal-to-noise ratio) should ensure a linear and accurate gas signal. End-tidal inert-gas concentrations should be within 1% relative to inert-gas concentrations at the start and 5% relative to inert-gas concentrations at the end of the washout (i.e. at 1/40 of the starting concentration).
  • The manufacturers of commercial inert-gas washout systems should demonstrate these features prior to commercial release, with data being included within supporting documentation. VT: tidal volume; CEV: cumulative expired volume; FRC: forced residual capacity; SIII: phase III slope; BTPS: body temperature, ambient pressure, saturated with water.