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 CO2 rebreathing. Positive pressure continuous neurally adjusted ventilatory assist (cNAVAP+ ) was applied via intubation. Negative pressure cNAVA (cNAVAP- ) was applied with the animal placed in a sealed box. In part 1, automatic stepwise increments in cNAVA level by 0.2 cmH2 O/µV every 30 s was applied for cNAVAP+ , cNAVAP- , and a 50/50 combination of the two (cNAVAP± ). In part 2: During 5-min ventilation with cNAVAP+ or cNAVAP- we measured circuit, box, and esophageal (Pes) pressure, EAdi, blood pressure, and arterial blood gases.

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

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