Modeling ventilation of patients with interstitial lung disease at rest and exercise: a bench study

Background: The ventilatory physiopathology of patients with interstitial lung disease (ILD) remains poorly understood. We aimed to personalize a mechanical simulator to model healthy and ILD profiles ventilation, and to evaluate the effect of spontaneous breathing on respiratory mechanics at rest and during exercise.

Methods: In a 2-compartment lung simulator (ASL 5000^®), we modeled 1 healthy and 3 ILD profiles, at rest and during exercise, based on physiological data from literature and patients. Measurements were: tidal volume, end-expiratory lung volume, driving pressure, transpulmonary driving pressure, dynamic alveolar strain, mechanical power, and time lag of inspiratory flow between compartments 1 and 2.

Results: Healthy and ILD models were validated: maximum differences between real and simulated tidal volume were 5% (96 ml) and 6% (54 ml) at rest and during exercise respectively, considered clinically negligible. When we simulated lung inhomogeneity (compliance in compartment 1 > compartment 2), tidal volume, end-expiratory lung volume, driving pressure and mechanical power increased in compartment 1 and decreased in compartment 2. Driving transpulmonary pressure and dynamic alveolar strain increased in compartment 2 and decreased in compartment 1. Time lag of inspiratory flow between compartments 1 and 2 was positively correlated with a difference of compliance between compartments (r = 0.98, CI95% (0.9106; 0.9962), p < 0.0001).

Conclusion: In this bench study, we personalized a mechanical simulator thatmodels the lung inhomogeneity and spontaneous breathing of healthy subjects and ILD patients at rest and during exercise. Our results suggest that lung inhomogeneity could increase lung vulnerability to volo-atelec-trauma mechanisms in ILD. Further physiological studies are needed to evaluate the impact of this vulnerability on acute or chronic ILD worsening.