Bench Assessment of the Effect of a Collapsible Tube on the Efficiency of a Mechanical Insufflation-Exsufflation Device

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 H 2 O/L/s (R5, R20) for compliance settings of 20, 40, and 60 mL/cm H 2 O (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 H 2 O 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 H 2 O) was not significant, but this was offset by a significant (and the largest) increase in slope (+0.12 L/s/cm H 2 O). For the C60-R20 condition, the effect of the collapsible tube on the slope (−0.003 L/s/cm H 2 O) was not significant, but this was offset by a significant (and the largest) increase of the intercept (+3.16 cm H 2 O) at 30 cm H 2 O expiratory pressure. For the other conditions, the collapsible tube significantly increased PEF at 30 cm H 2 O 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.