Rationale: In de novo acute respiratory failure (ARF), the worsening of underlying pulmonary injuries could be related to the risk of P-SILI (patient-self inflicted lung injury) during spontaneous breathing.

Objectives: To design a model of de novo ARF and to assess P-SILI favoring conditions.

Methods and measurements: Based on our previously described model of ventilation in healthy subjects and patients with lung fibrosis (altered compliance (C)) on an artificial mechanical lung with 2 compartments (A1 and A2), we simulated de novo ARF. Worsening of ARF was simulated by increasing the proportion of altered alveoli. The model consisted of a proportion (X) of alveoli with basal C (C1=200 ml/cmH₂O) and a proportion (Y) of alveoli with altered C (C2=50 ml/cmH₂O), such as X+Y=100%. Tidal volume (TV), end-expiratory lung volume (EELV), driving pressure (?P), driving transpulmonary pressure (?P_tp), dynamic alveolar strain (Strain_alv), mechanical power (MP), time lag between inspiratory flow in A1 and A2 (?t _(Q1-Q2)), were measured.

Results: During ARF worsening,TV remained stable but was higher in the compartment with higher C. EELV decreased dramatically (min 167 ml) especially in the compartment with lowest C. From mild to very severe AF, ?P increased (11.9 to 14.4 cmH2O), ?P_tp increased (5.9 to 14.2 cmH₂O), Strain_alv increased (0.8 to 1.2), MP increased (27.8 to 45.1 J/min). ?t _(Q1-Q2) was correlated with the difference in C between A1 and A2 (r=0.98, CI_95%(0.7783; 0.9990), p=0.002).     

Conclusion: This physiological bench study designed for the first time a mechanical ventilation model that reproduces lung inhomogeneity and mechanisms of volo- and atelec-trauma in de novo ARF.