This study compares an Impulse Oscillometry System (IOS; CareFusion) and an Airwave Oscillometry System (tremoFlo; THORASYS) in phantoms and humans.
We built and characterized 3 phantoms representative of normal and obstructed human respiratory systems. Each was measured thrice per device, and averages of resistance (R) and reactance (X) versus frequency (IOS: 5-35 Hz; tremoFlo: 5-37 Hz) were calculated. We computed derived parameters and maximum deviations from predicted values (εmax). Six volunteers (4 normal, 2 asthmatic) were also measured per device.
The IOS overestimated predicted R of phantoms up to 36% (Table), or 26% after supplemental filter compensation (FC), and the area under the reactance curve (AX) by 31%. For tremoFlo, εmax peaked at 5.3%. In subjects, IOS resistance at 5 Hz (R5) was higher than tremoFlo pre-FC (21% p=0.066). No significant differences were observed post-FC.
IOS results may be affected by anti-bacterial filters. Once this was compensated, we observed no significant differences between IOS and tremoFlo in our small group of normal and mildly abnormal subjects. However, measurements of higher impedance phantoms suggest that the IOS may over-estimate R, AX and Fres in presence of more severe obstruction.