title: The deflation limb of the pressure-volume relationship in infants during high-frequency ventilation.
abstract: BACKGROUND
  The importance of applying high-frequency oscillatory ventilation with a high lung volume strategy in infants is well established. Currently, a lack of reliable methods for assessing lung volume limits clinicians' ability to achieve the optimum volume range.
  
  
  OBJECTIVE
  To map the pressure-volume relationship of the lung during high-frequency oscillatory ventilation in infants, to determine at what point ventilation is being applied clinically, and to describe the relationship between airway pressure, lung volume, and oxygenation.
  
  
  METHODS
  In 12 infants, a partial inflation limb and the deflation limb of the pressure-volume relationship were mapped using a quasi-static lung volume optimization maneuver. This involved stepwise airway pressure increments to total lung capacity, followed by decrements until the closing pressure of the lung was identified.
  
  
  RESULTS
  Lung volume and oxygen saturation were recorded at each airway pressure. Lung volume was measured using respiratory inductive plethysmography. A distinct deflation limb could be mapped in each infant. Overall, oxygenation and lung volume were improved by applying ventilation on the deflation limb. Maximal lung volume and oxygenation occurred on the deflation limb at a mean airway pressure of 3 and 5 cm H(2)O below the airway pressure approximating total lung capacity, respectively.
  
  
  CONCLUSIONS
  Using current ventilation strategies, all infants were being ventilated near the inflation limb. It is possible to delineate the deflation limb in infants receiving high-frequency oscillatory ventilation; in doing so, greater lung volume and oxygenation can be achieved, often at lower airway pressures.
authors.affiliation: Department of Neonatology, Royal Children's Hospital, Flemington Road, Parkville, Victoria 3052, Australia. david.tingay@rch.org.au
authors.forename: David G
authors.initials: DG
authors.lastname: Tingay
authors.forename: John F
authors.initials: JF
authors.lastname: Mills
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Morley
authors.forename: Anastasia
authors.initials: A
authors.lastname: Pellicano
authors.forename: Peter A
authors.initials: PA
authors.lastname: Dargaville
mesh_terms: D006612:High-Frequency Ventilation / Q000379:methods*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008168:Lung / Q000502:physiology*; D008176:Lung Volume Measurements; D011312:Pressure