title: Effect of tidal volume and positive end-expiratory pressure on expiratory time constants in experimental lung injury.
abstract: We utilized a multicompartment model to describe the effects of changes in tidal volume (VT) and positive end-expiratory pressure (PEEP) on lung emptying during passive deflation before and after experimental lung injury. Expiratory time constants (τE) were determined by partitioning the expiratory flow-volume (V˙EV) curve into multiple discrete segments and individually calculating τE for each segment. Under all conditions of PEEP and VT, τE increased throughout expiration both before and after injury. Segmented τE values increased throughout expiration with a slope that was different than zero (P < 0. 01). On average, τE increased by 45.08 msec per segment. When an interaction between injury status and τE segment was included in the model, it was significant (P < 0.05), indicating that later segments had higher τE values post injury than early τE segments. Higher PEEP and VT values were associated with higher τE values. No evidence was found for an interaction between injury status and VT, or PEEP. The current experiment confirms previous observations that τE values are smaller in subjects with injured lungs when compared to controls. We are the first to demonstrate changes in the pattern of τE before and after injury when examined with a multiple compartment model. Finally, increases in PEEP or VT increased τE throughout expiration, but did not appear to have effects that differed between the uninjured and injured state.
authors.affiliation: Division of Critical Care Medicine, Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada william.henderson@vch.ca.
authors.forename: William R
authors.initials: WR
authors.lastname: Henderson
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Paolo B
authors.initials: PB
authors.lastname: Dominelli
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Yannick
authors.initials: Y
authors.lastname: Molgat-Seon
authors.affiliation: Emmes Canada, Burnaby, British Columbia, Canada.
authors.forename: Rachel
authors.initials: R
authors.lastname: Lipson
authors.affiliation: Division of Critical Care Medicine, Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada Department of Anesthesiology, Pharmacology & Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Donald E G
authors.initials: DE
authors.lastname: Griesdale
authors.affiliation: Division of Critical Care Medicine, Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Mypinder
authors.initials: M
authors.lastname: Sekhon
authors.affiliation: Division of Critical Care Medicine, Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Najib
authors.initials: N
authors.lastname: Ayas
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: A William
authors.initials: AW
authors.lastname: Sheel
mesh_terms: D000818:Animals; D045853:Exhalation / Q000502:physiology*; D005260:Female; D055370:Lung Injury / Q000503:physiopathology* / Q000628:therapy*; D011175:Positive-Pressure Respiration / Q000379:methods*; D013552:Swine; D013990:Tidal Volume / Q000502:physiology*; D013997:Time Factors
keywords: Acute respiratory distress syndrome; pulmonary alveoli; respiration