Evaluation of impulse oscillation system: comparison with forced oscillation technique and body plethysmography

The impulse oscillation system (IOS) has been developed recently to measure respiratory system resistance (Rrs) and reactance (Xrs) at different frequencies up to greater than or equal to 25 Hz. IOS has, however, not been validated against established techniques. This study compared IOS with the classical pseudorandom noise forced oscillation technique (FOT) and body plethysmographic airway resistance (Ra) in 49 subjects with a variety of lung disorders and a wide range of Raw (0.10-1.28 kPa.L-1.s). Rrs,IOS was slightly greater than Rrs,FOT, especially at lower frequencies, with a mean-SD difference at 5-6 Hz of 0.14 +/-0.09 kPa.L-1.s. Comparisons with the wave-tube technique applied on two analogues indicated an overestimation by IOS. Xrs,los and Xrs,FOT were very similar, with a slightly higher resonant frequency with IOS than with FOT (mean difference +/- sD 1.35 +/-3.40 Hz). Rm was only moderately correlated with Rrs-FOT and Rrs-IOS; although the mean differences were small (0.04 +/-0.14 kPa.L-1.s for Rrs(6),FOT and -0.10 +/-0.14 kPa.L-1.s for Rrs(5),IOS), IOS and FOT markedly underestimated high resistance values. In conclusion, the impulse oscillation system yields respiratory system resistance and reactance values similar, but not identical to those provided by the forced oscillation technique.