Table 6– Factors that lead to variation in measured indices between centres and recording systems
FactorExamples
Equipment relatedAnalyser rise time
Analyser linearity
Flow measurement linearity
Size of equipment related deadspace volume, including distance between gas and flow measurement points
Procedure relatedInert gas used (and concentration)
Breathing stability
Age of subjects tested
Analysis relatedAlgorithms used for calculation of indices
BTPS correction applied
Corrections applied for equipment-related deadspace
Drift correction algorithms
Synchronisation of flow and gas concentration signals
Acceptability criteria applied (e.g. FRC values within 10%)

  • BTPS: body temperature, ambient pressure, saturated with water; FRC: functional residual capacity.