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 rebreathing. Positive pressure continuous neurally adjusted ventilatory assist (cNAVA ) was applied via intubation. Negative pressure cNAVA (cNAVA ) was applied with the animal placed in a sealed box. In part 1, automatic stepwise increments in cNAVA level by 0.2 cmH O/µV every 30 s was applied for cNAVA , cNAVA , and a 50/50 combination of the two (cNAVA ). In part 2: During 5-min ventilation with cNAVA or cNAVA we measured circuit, box, and esophageal (Pes) pressure, EAdi, blood pressure, and arterial blood gases.

Results: Part 1: During cNAVA , pressure in the circuit increased with increasing cNAVA levels, reaching a plateau, and similarly for cNAVA , albeit reversed in sign. This was associated with downregulation of the EAdi. Pes swings became less negative with cNAVA but, in contrast, Pes swings were more negative during increasing cNAVA levels. Increasing the cNAVA level during cNAVA 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 were significantly more negative than during cNAVA .

Conclusion: Negative pressure ventilation synchronized and proportional to the diaphragm activity is feasible in small animals.