title: Time-varying respiratory system elastance: a physiological model for patients who are spontaneously breathing.
abstract: BACKGROUND
  Respiratory mechanics models can aid in optimising patient-specific mechanical ventilation (MV), but the applications are limited to fully sedated MV patients who have little or no spontaneously breathing efforts. This research presents a time-varying elastance (E(drs)) model that can be used in spontaneously breathing patients to determine their respiratory mechanics.
  
  
  METHODS
  A time-varying respiratory elastance model is developed with a negative elastic component (E(demand)), to describe the driving pressure generated during a patient initiated breathing cycle. Data from 22 patients who are partially mechanically ventilated using Pressure Support (PS) and Neurally Adjusted Ventilatory Assist (NAVA) are used to investigate the physiology relevance of the time-varying elastance model and its clinical potential. E(drs) of every breathing cycle for each patient at different ventilation modes are presented for comparison.
  
  
  RESULTS
  At the start of every breathing cycle initiated by patient, E(drs) is < 0. This negativity is attributed from the E(demand) due to a positive lung volume intake at through negative pressure in the lung compartment. The mapping of E(drs) trajectories was able to give unique information to patients' breathing variability under different ventilation modes. The area under the curve of E(drs) (AUCE(drs)) for most patients is > 25 cmH2Os/l and thus can be used as an acute respiratory distress syndrome (ARDS) severity indicator.
  
  
  CONCLUSIONS
  The E(drs) model captures unique dynamic respiratory mechanics for spontaneously breathing patients with respiratory failure. The model is fully general and is applicable to both fully controlled and partially assisted MV modes.
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch, New Zealand.
authors.forename: Yeong Shiong
authors.initials: YS
authors.lastname: Chiew
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch, New Zealand.
authors.forename: Christopher
authors.initials: C
authors.lastname: Pretty
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch, New Zealand.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Docherty
authors.affiliation: GIGA Cardiovascular Science, University of Liege, Liege, Belgium.
authors.forename: Bernard
authors.initials: B
authors.lastname: Lambermont
authors.affiliation: Department of Intensive Care, Christchurch Hospital, Christchurch, New Zealand.
authors.forename: Geoffrey M
authors.initials: GM
authors.lastname: Shaw
authors.affiliation: GIGA Cardiovascular Science, University of Liege, Liege, Belgium.
authors.forename: Thomas
authors.initials: T
authors.lastname: Desaive
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch, New Zealand.
authors.forename: J Geoffrey
authors.initials: JG
authors.lastname: Chase
mesh_terms: D004548:Elasticity; D006801:Humans; D008954:Models, Biological; D012128:Respiratory Distress Syndrome / Q000503:physiopathology*; D015656:Respiratory Mechanics; D013995:Time