Background. The forced oscillation technique (FOT) may be useful in a wide range of lung diseases. Interpretation of FOT requires caution in the absence of data on how global or regional alterations in airway resistance (Raw) and lung compliance (CL), two key pathophysiological characteristics of lung disease, translate into variation of FOT measurements.
Methods. A 2-compartment physical model of the respiratory system allowed to simulate variations in Raw (1.495 to 29.025 cmH2O.L-1.s), CL (0.026 to 0.312 L.cmH2O-1), 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 (Fres) and intrabreath variation in Rrs5 and Xrs5 were measured by FOT. Relationships between model characteristics (Raw, CL, and their 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, respectively). By contrast, associations of Xrs5, AX, and Fresp with model characteristics were weak (R2=0.214, 0.349 and 0.076, respectively). 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. Xrs5 did not strongly associate with model characteristics.