Multi-frequency Forced Oscillation Technique Using Impulse Oscillations: Can It Give Mechanical Information about the Lung Periphery?

Abstract

Forced oscillation techniques (FOTs) using sine curved oscillatory waves are used for assessing the lung periphery, but measure only overall respiratory mechanics. Therefore, mathematical models of the respiratory system serve as vehicles to obtain detailed mechanics. Although the simplest model of respiratory mechanics is a simple 3-element series (RIC) model, the constant phase (CP) model is recently used for characterizing respiratory mechanics, which has the advantage of partitioning of respiratory mechanics into airway and tissue components. Meanwhile, FOTs using non-sine curved oscillatory waves are easily applied in patients with severe respiratory diseases because they do not require voluntary apnea. If the latter type of FOTs is as informative as the former, the question arises whether a FOT using non-sine curved oscillatory waves (IOS) could be used to study mechanical properties of the lung periphery. And the CP model should fit the impedance spectra. To answer this, subjects with lymphangioleiomyomatosis (LAM) were recruited as a cohort of patients with lung parenchymal disease. Impedance spectra obtained by the IOS were fitted to the CP and RIC models. Mean values of goodness of fit from the CP and RIC models were 0.978 ± 0.022 and 0.968 ± 0.026, respectively. The extra sum-of-squares F test was used to compare the two mathematical models. The F ratio was 2.37 ± 1.40 and the p-value was 0.29 ± 0.21. Unfortunately, there was no compelling evidence for adopting the CP model for the evaluation of impedance spectra obtained by IOS. This result might relate to the uncertainty of IOS for detecting mechanical properties of the lung periphery.