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.
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.
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.
We have demonstrated that central airway obstruction alone will not generate frequency dependence of resistance using patient specific printed and computational airway models.