Association of forced oscillation technique measurements with respiratory system compliance and resistance in a 2-compartment physical model

Abstract

Background: The forced oscillation technique (FOT) may be useful for diagnosis and follow-up of respiratory diseases. It is unclear how global or regional alterations in airway resistance (Raw) and lung compliance (C_L) alter FOT measurements.

Methods: A 2-compartment physical model of the respiratory system allowed to simulate variations in Raw, C_L, and their heterogeneity during tidal breathing in an adult human. Five-Hz respiratory system resistance (Rrs5) and reactance (Xrs5), area of reactance (AX), resonance frequency (Fresp) and intrabreath variation in Rrs5 and Xrs5 were measured by FOT. Frequency dependance of resistance could not be studied in this model. Relationships between model characteristics (Raw, C_L, and heterogeneity) and FOT measurements were explored by multiple regression.

Results: Rrs5 and intrabreath variation in Rrs5 and Xrs5 strongly associated with model characteristics (R²=0.753, 0.5 and 0.658). Associations of Xrs5, AX, and Fresp with model characteristics were weak (R²=0.214, 0.349 and 0.076). Raw heterogeneity was the main determinant of Rrs5 (Coeff=0.594), AX (Coeff=0.566) and intrabreath variation in Rrs5 and Xrs5 (Coeff=0.586 and 0.732). Regional extremes in Raw strongly determined Rrs5 (Coeff=1.006). Xrs5 did not strongly associate with any model characteristic.

Conclusion: Raw heterogeneity and maximal regional Raw were the main determinants of FOT measurements, in particular Rrs5. Associations between C_L and FOT measurements were weak.

Keywords: COPD; Impulse oscillometry; Interstitial lung disease; Lung function; Pulmonary fibrosis.