Effects of changing small airway mechanics and inspiratory flow waveforms on pulmonary ventilation: A modeling study

For patients with chronic obstructive pulmonary disease (COPD), pathological changes of small airways can cause air trapping and lung overinflation, which can easily be aggravated during mechanical ventilation. To evaluate how properties of small airways influence pulmonary ventilation during mechanical ventilation, a nonlinear model of breathing mechanics with two parallel alveolar compartments was developed. Each of the alveolar compartments was in series with a collapsible airway segment and a lower airway segment, whose parameters represented different pathological changes in the small airways of COPD patients. Four inspiratory flow waveforms were studied. We found that the collapsible airways played an important role in air trapping and the lower airways had a large effect on ventilation distribution. In addition, the decelerating flow resulted in the most even distribution, but the flow patterns had little influence on air trapping.