Inspiratory Muscle Unloading by Neurally Adjusted Ventilatory Assist During Maximal Inspiratory Efforts in Healthy Subjects

摘要

Background: Neurally adjusted ventilatory assist (NAVA) is a mode of mechanical ventilation innwhich the ventilator is controlled by the electrical activity of the diaphragm (EAdi). Duringnmaximal inspirations, the pressure delivered can theoretically reach extreme levels that mayncause harm to the lungs. The aims of this study were to evaluate whether NAVA could efficientlynunload the respiratory muscles during maximal inspiratory efforts, and if a high level of NAVAnwould suppress EAdi without increasing lung-distending pressures.nMethod: In awake healthy subjects (n u0001 9), NAVA was applied at increasing levels in a stepwisenfashion during quiet breathing and maximal inspirations. EAdi and airway pressure (Paw),nesophageal pressure (Pes), and gastric pressure, flow, and volume were measured.nResults: During maximal inspirations with a high NAVA level, peak Paw was 37.1 u0002 11.0 cm H2On(mean u0002 SD). This reduced Pes deflections from u0003 14.2 u0002 2.7 to 2.3 u0002 2.3 cm H2O(p < 0.001)nand EAdi to 43 u0002 7% (p < 0.001), compared to maximal inspirations with no assist. At high NAVAnlevels, inspiratory capacity showed a modest increase of 11 u0002 11% (p u0001 0.024).nConclusion: In healthy subjects, NAVA can safely and efficiently unload the respiratory musclesnduring maximal inspiratory maneuvers, without failing to cycle-off ventilatory assist and withoutncausing excessive lung distention. Despite maximal unloading of the diaphragm at high levels ofnNAVA, EAdi is still present and able to control the ventilator. (CHEST 2007; 131:711–717)