title: Assessing respiratory mechanics using pressure reconstruction method in mechanically ventilated spontaneous breathing patient.
abstract: BACKGROUND
  Respiratory system modelling can aid clinical decision making during mechanical ventilation (MV) in intensive care. However, spontaneous breathing (SB) efforts can produce entrained "M-wave" airway pressure waveforms that inhibit identification of accurate values for respiratory system elastance and airway resistance. A pressure wave reconstruction method is proposed to accurately identify respiratory mechanics, assess the level of SB effort, and quantify the incidence of SB effort without uncommon measuring devices or interruption to care.
  
  
  METHODS
  Data from 275 breaths aggregated from all mechanically ventilated patients at Christchurch Hospital were used in this study. The breath specific respiratory elastance is calculated using a time-varying elastance model. A pressure reconstruction method is proposed to reconstruct pressure waves identified as being affected by SB effort. The area under the curve of the time-varying respiratory elastance (AUC Edrs) are calculated and compared, where unreconstructed waves yield lower AUC Edrs. The difference between the reconstructed and unreconstructed pressure is denoted as a surrogate measure of SB effort.
  
  
  RESULTS
  The pressure reconstruction method yielded a median AUC Edrs of 19.21 [IQR: 16.30-22.47]cmH2Os/l. In contrast, the median AUC Edrs for unreconstructed M-wave data was 20.41 [IQR: 16.68-22.81]cmH2Os/l. The pressure reconstruction method had the least variability in AUC Edrs assessed by the robust coefficient of variation (RCV)=0.04 versus 0.05 for unreconstructed data. Each patient exhibited different levels of SB effort, independent from MV setting, indicating the need for non-invasive, real time assessment of SB effort.
  
  
  CONCLUSIONS
  A simple reconstruction method enables more consistent real-time estimation of the true, underlying respiratory system mechanics of a SB patient and provides the surrogate of SB effort, which may be clinically useful for clinicians in determining optimal ventilator settings to improve patient care.
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch 8041, New Zealand; Faculty of Electrical Engineering, Universiti Teknologi MARA (UiTM), Malaysia. Electronic address: norsalwa071@ppinang.uitm.edu.my.
authors.forename: Nor Salwa
authors.initials: NS
authors.lastname: Damanhuri
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch 8041, New Zealand; Monash University, Malaysia. Electronic address: yeongshiong.chiew@canterbury.ac.nz.
authors.forename: Yeong Shiong
authors.initials: YS
authors.lastname: Chiew
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch 8041, New Zealand; Faculty of Electrical Engineering, Universiti Teknologi MARA (UiTM), Malaysia. Electronic address: azlan.othman@pg.canterbury.ac.nz.
authors.forename: Nor Azlan
authors.initials: NA
authors.lastname: Othman
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch 8041, New Zealand. Electronic address: paul.docherty@canterbury.ac.nz.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Docherty
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch 8041, New Zealand. Electronic address: chris.pretty@canterbury.ac.nz.
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Pretty
authors.affiliation: Department of Intensive Care, Christchurch Hospital, Christchurch, New Zealand. Electronic address: Geoff.Shaw@cdhb.health.nz.
authors.forename: Geoffrey M
authors.initials: GM
authors.lastname: Shaw
authors.affiliation: University of Liège, Liège, Belgium. Electronic address: tdesaive@ulg.ac.be.
authors.forename: Thomas
authors.initials: T
authors.lastname: Desaive
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch 8041, New Zealand. Electronic address: geoff.chase@canterbury.ac.nz.
authors.forename: J Geoffrey
authors.initials: JG
authors.lastname: Chase
mesh_terms: D006801:Humans; D012121:Respiration, Artificial; D015656:Respiratory Mechanics; D014939:Work of Breathing
keywords: ARDS; Airway pressure reconstruction; Asynchrony; Mechanical ventilation; Respiratory mathematical modelling; Spontaneous breathing