Feasibility of neurally synchronized and proportional negative pressure ventilation in a small animal model

RATIONALE: Synchronized positive pressure ventilation is possible using diaphragm electrical activity (EAdi) to control the ventilator. It is unknown whether EAdi can be used to control negative pressure ventilation. AIM: To evaluate the feasibility of using EAdi to control negative pressure ventilation. METHODS: Fourteen anesthetized rats were studied (380–590 g) during control, resistive breathing, acute lung injury or CO(2) rebreathing. Positive pressure continuous neurally adjusted ventilatory assist (cNAVA(P+)) was applied via intubation. Negative pressure cNAVA (cNAVA(P−)) was applied with the animal placed in a sealed box. In part 1, automatic stepwise increments in cNAVA level by 0.2 cmH(2)O/µV every 30 s was applied for cNAVA(P+), cNAVA(P−), and a 50/50 combination of the two (cNAVA(P±)). In part 2: During 5‐min ventilation with cNAVA(P+) or cNAVA(P−) we measured circuit, box, and esophageal (Pes) pressure, EAdi, blood pressure, and arterial blood gases. RESULTS: Part 1: During cNAVA(P+), pressure in the circuit increased with increasing cNAVA levels, reaching a plateau, and similarly for cNAVA(P−), albeit reversed in sign. This was associated with downregulation of the EAdi. Pes swings became less negative with cNAVA(P+) but, in contrast, Pes swings were more negative during increasing cNAVA(P−) levels. Increasing the cNAVA level during cNAVA(P±) resulted in an intermediate response. Part 2: no significant differences were observed for box/circuit pressures, EAdi, blood pressure, or arterial blood gases. Pes swings during cNAVA(P−) were significantly more negative than during cNAVA(P+). CONCLUSION: Negative pressure ventilation synchronized and proportional to the diaphragm activity is feasible in small animals.