Neural control of ventilation prevents both over-distension and de-recruitment of experimentally injured lungs.

BACKGROUND: Endogenous pulmonary reflexes may protect the lungs during mechanical ventilation. We aimed to assess integration of continuous neurally adjusted ventilatory assist (cNAVA), delivering assist in proportion to diaphragm's electrical activity during inspiration and expiration, and Hering-Breuer inflation and deflation reflexes on lung recruitment, distension, and aeration before and after acute lung injury (ALI).

METHODS: In 7 anesthetised rabbits with bilateral pneumothoraces, we identified adequate cNAVA level (cNAVAAL ) at the plateau in peak ventilator pressure during titration procedures before (healthy lungs with endotracheal tube, [HLETT ]) and after ALI (endotracheal tube [ALIETT ] and during non-invasive ventilation [ALINIV ]). Following titration, cNAVAAL was maintained for 5min. In 2 rabbits, procedures were repeated after vagotomy (ALIETT+VAG ). In 3 rabbits delivery of assist was temporarily modulated to provide assist on inspiration only. Computed tomography was performed before intubation, before ALI, during cNAVA titration, and after maintenance at cNAVAAL .

RESULTS: During ALIETT and ALINIV , normally aerated lung-regions doubled and poorly aerated lung-regions decreased to less than a third (p<0.05) compared to HLETT ; no over-distension was observed. Tidal volumes were<5ml/kg throughout. Removing assist during expiration resulted in lung de-recruitment during ALIETT , but not during ALINIV . During ALIETT+VAG the expiratory portion of EAdi disappeared, resulting in cyclic lung collapse and recruitment.

CONCLUSIONS: When using cNAVA in ALI, vagally mediated reflexes regulated lung recruitment preventing both lung over-distension and atelectasis. During non-invasive cNAVA the upper airway muscles play a role in preventing atelectasis. Future studies should be performed to compare these findings with conventional lung-protective approaches.