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

Objective: To determine whether there is an optimal level of pressure suppo rt 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 nerv e stimulation for 30 mins, Recovery was compared between inspiratory load PSV of 0 cm H2O (LO), inspiratory load + PSV of 60 cm H2O (L60), inspirato ry load + PSV of 80 cm H2O (L80), and PSV of 0 cm H2O without inspiratory l oad (SB) for 90 mins immediately after the end of the fatigue-inducing proc edure. To add inspiratory load during the recovery phase, three pressure th reshold valves, each having an opening pressure of -20 cm H2O2 were used. Measurements and Main Results: After the fatigue-inducing procedure, diaphr agmatic electromyogram and transdiaphragmatic pressure remained at baseline in both SE and L60, decreased in L80, and increased in LO, Recovery was as sessed by abdominal cavity pressure (Pabd) generated by high-frequency (100 Hz) and low-frequency (20 Hz) stimulation, Pabd at 100 Hz recovered to bas eline 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 a t 20 Hz did not differ among ventilatory settings, Conclusion: There is an optimal range of PSV assist level to improve recove ry from diaphragmatic fatigue, Recovery was hampered not only by inadequate PSV but also by excessive PSV.