title: Effects of different levels of pressure support on intra-individual breath-to-breath variability.
abstract: BACKGROUND
  Evidence exists that during pressure support ventilation (PSV), the addition of an extrinsic (ie, ventilator-generated) breath-to-breath variability (BBV) of breathing pattern improves respiratory function. If BBV is beneficial per se, choosing the PS level that maximizes it could be considered a valid strategy for conventional PSV. In this study, we evaluated the effect of different PS levels on intrinsic BBV in acutely ill, mechanically ventilated subjects to determine whether a significant relationship exists between PS level and BBV magnitude.
  
  
  METHODS
  Fourteen invasively mechanically ventilated subjects were prospectively studied. PS was adjusted at 20 cm H2O and sequentially reduced to 15, 10, and 5 cm H2O. Arterial blood gas analysis and pressure at 0.1 s after the onset of inspiration (P0.1) were measured at each PS level. Airway and esophageal pressure and air flow were continuously recorded. Peak inspiratory flow, tidal volume (VT), breathing frequency, and pressure-time product (PTP) were calculated on a breath-by-breath basis. The breathing pattern variability was assessed by the coefficient of variation of the time series of VT, peak inspiratory flow, and breathing frequency from ∼ 60 consecutive breath cycles at each PS level. A general linear model for repeated measures was applied, with PS as an independent factor. A significance level of .05 was considered.
  
  
  RESULTS
  Despite a large inter-individual difference in all measured variables (P < .001), the coefficient of variation was as low as 30%, and no significant differences in the coefficient of variation of peak inspiratory flow, breathing frequency, and VT between PS levels were observed (P > .15). Additionally, a significant increase in P0.1, PTP, and breathing frequency (P < .01) and a reduction in VT (P < .001) were observed with PS reduction.
  
  
  CONCLUSIONS
  Despite a significant increase in spontaneous activity with PS reduction, BBV was not influenced by the PS level and was as low as 30% for all evaluated parameters.
authors.affiliation: Laboratory of Clinical Research in Intensive Care Medicine, National Institute of Infectious Disease, Oswaldo Cruz Foundation, Rio de Janeiro, Brazil.
authors.forename: Monica R
authors.initials: MR
authors.lastname: Cruz
authors.affiliation: Laboratory of Respiration Physiology, Carlos Chagas Filho Institute of Biophysics, Universidade Federal do Rio de Janeiro, Brazil.
authors.forename: Luciana M
authors.initials: LM
authors.lastname: Camilo
authors.affiliation: Laboratory of Respiration Physiology, Carlos Chagas Filho Institute of Biophysics, Universidade Federal do Rio de Janeiro, Brazil.
authors.forename: Luis Felipe S C
authors.initials: LF
authors.lastname: Paula
authors.affiliation: Laboratory of Clinical Research in Intensive Care Medicine, National Institute of Infectious Disease, Oswaldo Cruz Foundation, Rio de Janeiro, Brazil.
authors.forename: Andre M
authors.initials: AM
authors.lastname: Japiassú
authors.affiliation: Department of Electronics, Federal University of Minas Gerais, Belo Horizonte, Brazil.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Beda
authors.affiliation: Laboratory of Respiration Physiology, Carlos Chagas Filho Institute of Biophysics, Universidade Federal do Rio de Janeiro, Brazil.
authors.forename: Alysson R
authors.initials: AR
authors.lastname: Carvalho
authors.affiliation: Laboratory of Clinical Research in Intensive Care Medicine, National Institute of Infectious Disease, Oswaldo Cruz Foundation, Rio de Janeiro, Brazil. D'Or Institute for Research and Education, Rio de Janeiro, Brazil. denise.medeiros@ipec.fiocruz.br bozza.fernando@gmail.com fernando.bozza@ipec.fiocruz.br.
authors.forename: Fernando A
authors.initials: FA
authors.lastname: Bozza
authors.affiliation: Laboratory of Clinical Research in Intensive Care Medicine, National Institute of Infectious Disease, Oswaldo Cruz Foundation, Rio de Janeiro, Brazil. denise.medeiros@ipec.fiocruz.br bozza.fernando@gmail.com fernando.bozza@ipec.fiocruz.br.
authors.forename: Denise M
authors.initials: DM
authors.lastname: Medeiros
mesh_terms: D000328:Adult; D000368:Aged; D001784:Blood Gas Analysis; D004947:Esophagus; D006801:Humans; D008875:Middle Aged; D011312:Pressure; D011446:Prospective Studies; D012123:Pulmonary Ventilation; D012119:Respiration; D012121:Respiration, Artificial / Q000379:methods*; D012131:Respiratory Insufficiency / Q000503:physiopathology / Q000628:therapy*; D056152:Respiratory Rate; D013990:Tidal Volume; D013997:Time Factors
keywords: breath-to-breath variability; coefficient of variation; patient-ventilator interaction; pressure support ventilation