title: Inspiratory muscle unloading by neurally adjusted ventilatory assist during maximal inspiratory efforts in healthy subjects.
abstract: BACKGROUND
  Neurally adjusted ventilatory assist (NAVA) is a mode of mechanical ventilation in which the ventilator is controlled by the electrical activity of the diaphragm (EAdi). During maximal inspirations, the pressure delivered can theoretically reach extreme levels that may cause harm to the lungs. The aims of this study were to evaluate whether NAVA could efficiently unload the respiratory muscles during maximal inspiratory efforts, and if a high level of NAVA would suppress EAdi without increasing lung-distending pressures.
  
  
  METHODS
  In awake healthy subjects (n = 9), NAVA was applied at increasing levels in a stepwise fashion during quiet breathing and maximal inspirations. EAdi and airway pressure (Paw), esophageal pressure (Pes), and gastric pressure, flow, and volume were measured.
  
  
  RESULTS
  During maximal inspirations with a high NAVA level, peak Paw was 37.1 +/- 11.0 cm H(2)O (mean +/- SD). This reduced Pes deflections from - 14.2 +/- 2.7 to 2.3 +/- 2.3 cm H(2)O (p < 0.001) and EAdi to 43 +/- 7% (p < 0.001), compared to maximal inspirations with no assist. At high NAVA levels, inspiratory capacity showed a modest increase of 11 +/- 11% (p = 0.024).
  
  
  CONCLUSIONS
  In healthy subjects, NAVA can safely and efficiently unload the respiratory muscles during maximal inspiratory maneuvers, without failing to cycle-off ventilatory assist and without causing excessive lung distention. Despite maximal unloading of the diaphragm at high levels of NAVA, EAdi is still present and able to control the ventilator.
authors.affiliation: Department of Critical Care Medicine, St. Michael's Hospital, Department of Medicine, University of Toronto, Toronto, ON, Canada. Electronic address: sinderby@rogers.com.
authors.forename: Christer
authors.initials: C
authors.lastname: Sinderby
authors.affiliation: Department of Newborn and Developmental Pediatrics, Sunnybrook Health Sciences Centre, Department of Pediatrics, University of Toronto, Toronto, ON, Canada.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Beck
authors.affiliation: Sacré-Coeur Hospital Research Center, Department of Medicine, University of Montreal, Montreal, QC, Canada.
authors.forename: Jadranka
authors.initials: J
authors.lastname: Spahija
authors.affiliation: Sir Mortimer B. Davis Jewish General Hospital, McGill University, Montreal, QC, Canada.
authors.forename: Michel
authors.initials: M
authors.lastname: de Marchie
authors.affiliation: Pediatric Intensive Care Unit, Department of Pediatrics, Hôpital Sainte-Justine Research Center, Université de Montréal, Montreal, QC, Canada.
authors.forename: Jacques
authors.initials: J
authors.lastname: Lacroix
authors.affiliation: Pulmonary Rehabilitation and Respiratory Intensive Care Unit, Fondazione S. Maugeri, Pavia, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Navalesi
authors.affiliation: Department of Critical Care Medicine, St. Michael's Hospital, Department of Medicine, University of Toronto, Toronto, ON, Canada.
authors.forename: Arthur S
authors.initials: AS
authors.lastname: Slutsky
mesh_terms: D000328:Adult; D003964:Diaphragm / Q000503:physiopathology*; D005260:Female; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D008297:Male; D008451:Maximal Voluntary Ventilation / Q000502:physiology*; D011175:Positive-Pressure Respiration / Q000295:instrumentation*; D012129:Respiratory Function Tests; D012132:Respiratory Muscles / Q000503:physiopathology*; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D012984:Software; D013813:Therapy, Computer-Assisted / Q000295:instrumentation*; D014939:Work of Breathing / Q000502:physiology*