[Effects of neurally adjusted ventilatory assist on prevention of ventilator-induced diaphragmatic dysfunction in acute respiratory distress syndrome rabbits].

OBJECTIVE: To evaluate the effect of neurally adjusted ventilatory assist (NAVA) on prevention of ventilator-induced diaphragmatic dysfunction (VIDD) in ARDS rabbits.

METHODS: Twenty New Zealand white rabbits were randomly divided into 4 groups: (1) control group (n = 5); (2) Volume control (VC) group (n = 5); (3) Pressure support (PSV) group (n = 5); (4) NAVA group (n = 5). In VC, PSV and NAVA groups, the rabbits were killed and the diaphragm was removed after 4 hours of ventilation. Animals in the control group were not mechanically ventilated, and the diaphragm was also removed immediately after anesthetizing. In all rabbits, malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione (GSH) of diaphragm were measured. Structure of diaphragm was observed by light microscope, electron microscope, constituent ratio and mean cross-sectional area (CSA) of diaphragm fiber.

RESULTS: (1) MDA: Compared with the control [(0.15 ± 0.06) nmol/mg], PSV group [(0.30 ± 0.11) nmol/mg], there was no significant difference in MDA of diaphragm in NAVA group [(0.28 ± 0.19) nmol/mg] (F = 2.730, P > 0.05). MDA in VC group [(0.40 ± 0.16) nmol/mg] was significantly higher than the control group (P < 0.05). (2) SOD: Compared with control [(111 ± 12) U/mg], PSV group [(93 ± 4) U/mg], there was no significant difference in SOD of diaphragm in NAVA group [(94 ± 9) U/mg] (F = 4.422, P > 0.05). SOD in VC group [(80 ± 21) U/mg] was significantly lower than the control group (P < 0.05). (3) GSH: Compared with control [(5.3 ± 1.0) mg/g] and PSV group [(4.5 ± 1.2) mg/g], there was no significant difference in GSH of diaphragm in NAVA group [(5.6 ± 1.0) mg/g] (F = 3.001, P > 0.05). GSH in VC group [(3.3 ± 1.7) mg/g] is significantly lower than control and NAVA groups (P < 0.05). (4) Light microscope: In VC group, many changes were observed in the muscle, such as myelofibrosis, necrosis, and some of muscle fibers became atrophy, but these were no obvious changes of pathological structure in control, PSV or NAVA groups. (5) Electron microscope: In control, PSV and NAVA groups, the ultrastructure of diaphragm was normal. Different from the above 3 groups, some abnormal ultrastructure was observed in VC group, including disrupted myofibrils, swollen mitochondria. (6) CSA of diaphragm fiber: Compared with control and PSV group, there was no significant difference in CSA of diaphragm fiber in NAVA group (P > 0.05); The CSA of type II fibers in VC group was markedly lower than control group (P < 0.05).

CONCLUSIONS: Compared with volume control ventilation, NAVA may mitigate diaphragmatic oxidative stress, atrophy and injury, and prevent VIDD better than VC.