title: Increased diaphragmatic contribution to inspiratory effort during neurally adjusted ventilatory assistance versus pressure support: an electromyographic study.
abstract: BACKGROUND
  Neurally adjusted ventilatory assist (NAVA), regulated exclusively by the electromyographic activity (EA) of the diaphragm (EAdi), could affect the distribution of neural drive to the various inspiratory muscles. The objective of this study was to compare EAdi, EA of the scalene (EAscal), and EA of the alae nasi (EAan), according to the ventilatory mode and assist level in 12 mechanically ventilated patients.
  
  
  METHODS
  Seven assist levels of pressure support ventilation (PSV) and NAVA were sequentially applied. EAdi, EAscal, and EAan were quantified and expressed as a percentage of their maximum values. The relative contributions of extradiaphragmatic muscles to inspiratory efforts were assessed by calculating EAscal/EAdi and EAan/EAdi ratios. Three assist levels for each of the two ventilatory modes that resulted in EAdi values of 80 to 100%, 60 to 80%, and 40 to 60% were assigned to three groups (N1, N2, and N3). Results are expressed as median and interquartile range.
  
  
  RESULTS
  EA of inspiratory muscles decreased during PSV and NAVA (P < 0.0001). Although EAdi remained constant within groups (P = 0.9), EAscal was reduced during NAVA compared with PSV in N1 and N3 (65% [62 to 64] and 27% [18 to 34] in NAVA vs. 90% [81 to 100] and 49% [40 to 55] in PSV, P = 0.007). Altogether, EAscal/EAdi and EAan/EAdi ratios were lower in NAVA than PSV (0.7 [0.6 to 0.7] and 0.7 [0.6 to 0.8] in NAVA vs. 0.9 [0.8 to 1.1] and 0.9 [0.7 to 1.1] in PSV, P < 0.05).
  
  
  CONCLUSIONS
  NAVA and PSV both reduced extradiaphragmatic inspiratory muscle activity, in proportion to the level of assistance. Compared with PSV, NAVA resulted in a predominant contribution of the diaphragm to inspiratory effort.
authors.affiliation: From the Sorbonne Universités, UPMC Univ Paris 06, INSERM, UMR_S 1158 "Neurophysiologie Respiratoire Expérimentale et Clinique," Paris, France (J.C., M.S., T.S.); INSERM, UMR_S 1158 "Neurophysiologie Respiratoire Expérimentale et Clinique," Paris, France (J.C., M.S., T.S.); AP-HP, Groupe Hospitalier Pitié-Salpêtrière Charles Foix, Service de Pneumologie et Réanimation Médicale (Département "R3S"), Paris, France (M.S., A.D., T.S.); and UMR_S 974, Inserm-Université Paris 6, Paris, France (A.D.).
authors.forename: Jérôme
authors.initials: J
authors.lastname: Cecchini
authors.forename: Matthieu
authors.initials: M
authors.lastname: Schmidt
authors.forename: Alexandre
authors.initials: A
authors.lastname: Demoule
authors.forename: Thomas
authors.initials: T
authors.lastname: Similowski
mesh_terms: D000368:Aged; D003964:Diaphragm / Q000502:physiology*; D004576:Electromyography; D005260:Female; D006801:Humans; D059725:Interactive Ventilatory Support / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012121:Respiration, Artificial / Q000379:methods*; D015656:Respiratory Mechanics / Q000502:physiology; D012132:Respiratory Muscles / Q000502:physiology; D014939:Work of Breathing / Q000502:physiology*