BACKGROUND: Collapsibility of upper airways may impair the efficacy of mechanical insufflation-exsufflation (MI-E) devices. The aim of this study was to determine the effect of a collapsible tube on peak expiratory flow (PEF) when using an MI-E device. METHODS: An MI-E device was attached to a lung simulator. Resistance was set at 5 and 20 cm H2O/L/s (R5, R20) for compliance settings of 20, 40, and 60 mL/cm H2O (C20, C40, C60). A series of 5 cycles were delivered at 3 pressures in the following order: +30/−30, +40/−40, and +50/−50 cm H2O for each compliance/resistance combination with and without the collapsible tube. Each respiratory mechanics profile was tested in random order. Pressure and flow were measured upstream of the MI-E device, and the primary outcome measure was PEF. The relationships of PEF to maximum expiratory pressure were compared with and without the collapsible tube using a linear regression model. RESULTS: For the C20-R5 condition, the effect of the collapsible tube on the intercept (−0.35 cm H2O) was not significant, but this was offset by a significant (and the largest) increase in slope (+0.12 L/s/cm H2O). For the C60-R20 condition, the effect of the collapsible tube on the slope (−0.003 L/s/cm H2O) was not significant, but this was offset by a significant (and the largest) increase of the intercept (+3.16 cm H2O) at 30 cm H2O expiratory pressure. For the other conditions, the collapsible tube significantly increased PEF at 30 cm H2O expiratory pressure, and the gap further increased above this pressure as the slope increased with the collapsible tube. CONCLUSIONS: The collapsible tube resulted in a higher PEF for all respiratory mechanics profiles tested.