Effects of the intermittent intrapulmonary deflation technique on expiratory flow limitation: an in vitro study

The intermittent intrapulmonary deflation (IID) technique is a recent airway clearance technique that intends to delay the onset of expiratory flow limitation (EFL) during exhalation. We showed in a previous study that IID increased the expiratory volume of COPD patients compared to quiet breathing and positive expiratory pressure (PEP) therapy. We hypothesized that it was due to the attenuation of the EFL. To verify the physiologic effects of IID and PEP techniques on EFL with a mechanical lung model. A mechanical lung model was created to assess the effects of IID and PEP techniques. The thorax was simulated by a plexiglas box in which an adult test lung was connected. A calibration syringe simulated the inspiratory phase. Later, with activation of the IID, the expiratory phase was driven by the deflation generated by the device. With PEP, the expiration occurred maintaining an expiratory pressure between 5 and 10 cmH2O. A pneumotachograph and a pressure transducer were placed in series for flow, volumes and pressure measurements. The model reproduced physiological characteristics of EFL. However, the deflation of the model was slowed by IID and PEP, and flow remained almost constant, so flow limitation was reduced. The IID and PEP attenuate EFL and increase exhaled volume in the in vitro model.