Objective. Recent studies in respiratory system impedance (Zrs) with single-frequency
oscillometry have demonstrated the utility of novel intra-breath measures of Zrs in
the detection of pathological alterations in respiratory mechanics. In the present
work, we addressed the feasibility of extracting intra-breath information from Zrs
data sets obtained with conventional oscillometry. Approach. Multi-frequency recordings
obtained in a pulmonology practice were re-analysed to track the 11 Hz component of
Zrs during normal breathing and compare the intra-breath measures to that obtained
with a single 10 Hz signal in the same subjects. A nonlinear model was employed to
simulate changes in Zrs in the breathing cycle. The values of resistance (R) and reactance
(X) at end expiration and end inspiration and their corresponding differences (Delta
R and Delta X) were compared. Main results. All intra-breath measures exhibited similar
mean values at 10 and 11 Hz in each subject; however, the variabilities were higher
at 11 Hz, especially for Delta R and Delta X. The poorer quality of the 11 Hz data
was primarily caused by the overlapping of modulation side lobes of adjacent oscillation
frequencies. This cross-talk was enhanced by double breathing frequency components
due to flow nonlinearities. Significance. Retrospective intra-breath assessment of
large or special data bases of conventional oscillometry can be performed to better
characterise respiratory mechanics in different populations and disease groups. The
results also have implications in the optimum design of multiple-frequency oscillometry
(avoidance of densely spaced frequencies) and the use of filtering procedures that
preserve the intra-breath modulation information.
