Background: Frequency dependence of resistance derived from forced oscillation technique is a potential small airways dysfunction/early airways obstruction tool. However the structural basis of this measurement has not been fully elucidated.
Methods: We sought to evaluate the central airway contribution to frequency dependence of resistance, measured with Impulse Oscillometry (IOS: R5-R20) and Sinusoidal Forced Oscillations (TremoFlo C-100: R5-R19). We derived a patient specific 3D printed airway model of the central airways (Clear Flex (r) 50 water clear urethane rubber, Smooth-On Inc), from a CT segementation in a mild asthmatic (age=64, FEV1/FVC=71%, FEV1%=95%). Systematic obstruction of the model outlets was achieved by heterogeneous occlusion (sequence generated by a Matlab algorithm), whilst IOS and FOT was applied to the model in triplicate for each occlusion. Additionally a computer simulation was applied to the same model under the same conditions.
Results: Sequential occlusion of the printed model was not associated with frequency dependence of resistance, which was further validated by the computational model (Figure 1). In contrast there was a non-linear and exponential increase in R20/R19 and R5.
Conclusions: We have demonstrated that central airway obstruction alone will not generate frequency dependence of resistance using patient specific printed and computational airway models.
