Nonlinear recruitment model with viscoelastic component fit respiratory mechanics in ARDS
© BioMed Central Ltd. 2010
Published: 1 March 2010
Alveolar recruitment/de-recruitment (R/D) seems to play an important role in the development of VILI . Many clinicians base their determination of PEEP settings during mechanical ventilation of ARDS/ALI patients on an estimate of alveolar recruitability . This project aims to establish an online tool that provides estimates of R/D in patients at the bedside.
In volume-controlled ventilated piglets as ARDS models, the airway pressure Paw (SI-Special Instruments, Nördlingen, Germany) and the flow rate Q (F + G GmbH, Hechingen Germany) were continuously recorded at 200 Hz. The pressure curve shows high nonlinearity being a suspect of recruitment effects during inspiration and a relaxation process during the end inspiratory pause. Based on the obtained data, the parameters of the linear viscoelastic model  are calculated by a LSE fitting process. As the parameter C1 represents a static constant compliance of the lung, this model is not capable of reproducing the nonlinear effects during inspiration. To improve on this, the constant compliance C1 is replaced by a nonlinear pressure-dependent compliance describing recruitment and dilatation as proposed by Hickling .
Using this new model it is possible to fit nonlinear behavior due to alveolar recruitment separately from viscoelastic effects with minimized error.