Optimal level of pressure support ventilation for recovery from diaphragmatic fatigue in rabbits

Objective: To determine whether there is an optimal level of pressure support ventilation (PSV) for recovery from acute diaphragmatic fatigue, Design: Prospective laboratory trial. Setting: Experimental laboratory, Subjects: Twenty healthy adult New Zealand White rabbits, Interventions: Diaphragmatic fatigue was induced with 50 Hz of phrenic nerve stimulation for 30 mins, Recovery was compared between inspiratory load + PSV of 0 cm H2O (LO), inspiratory load + PSV of 60 cm H2O (L60), inspiratory load + PSV of 80 cm H2O (L80), and PSV of 0 cm H2O without inspiratory load (SB) for 90 mins immediately after the end of the fatigue-inducing procedure. To add inspiratory load during the recovery phase, three pressure threshold valves, each having an opening pressure of -20 cm H2O2 were used. Measurements and Main Results: After the fatigue-inducing procedure, diaphragmatic electromyogram and transdiaphragmatic pressure remained at baseline in both SE and L60, decreased in L80, and increased in LO, Recovery was assessed by abdominal cavity pressure (Pabd) generated by high-frequency (100 Hz) and low-frequency (20 Hz) stimulation, Pabd at 100 Hz recovered to baseline in L60 and SE but not in LO and L80 (69.1%, 81.3%, 100.3%, and 100.7% of the baseline at 90 mins for LO, L80, L60, and SE, respectively), Pabd at 20 Hz did not differ among ventilatory settings, Conclusion: There is an optimal range of PSV assist level to improve recovery from diaphragmatic fatigue, Recovery was hampered not only by inadequate PSV but also by excessive PSV.