Use of a lung model to assess mechanical in-exsufflator therapy in infants with tracheostomy

The mechanical in-exsufflator (MIE) is commonly used to augment cough in patients with neuromuscular disease from infancy to adulthood. Little is known about the alveolar pressures, lung volumes, and expiratory flow rates generated by the MIE when used via tracheostomy tube in infants and children.

A high-fidelity mechanical lung model was programmed to simulate infants with tracheostomy tubes. Generated pressures, volumes, and expiratory flows using the MIE device at variable insufflation/exsufflation pressures and times were recorded. The primary measure of interest was maximal expiratory flow (MEF).

Pressure equilibration across the tracheostomy tube did not occur with insufflation time <1 sec. Longer insufflation time significantly increased measured alveolar pressures, lung volume, and MEF until TLC was reached. Longer exsufflation time did not significantly increase MEF. Higher insufflation pressures resulted in greater lung volumes, with >70% vital capacity attained at insufflation pressures as low as 20 cmH2 O. Though higher insufflation pressures resulted in increased expiratory flow rates, more negative exsufflation pressure had a greater absolute impact on MEF.

Using the MIE via tracheostomy tube in an infant lung model, we found that an insufflation time of >1 sec is required for equilibration of insufflation pressure and alveolar pressure. Longer exsufflation time does not significantly alter MEF. Higher insufflation and exsufflation pressures both increased MEF, but greater exsufflation pressure had more substantial impact.