title: Mild loss of lung aeration augments stretch in healthy lung regions.
abstract: Inspiratory stretch by mechanical ventilation worsens lung injury. However, it is not clear whether and how the ventilator damages lungs in the absence of preexisting injury. We hypothesized that subtle loss of lung aeration during general anesthesia regionally augments ventilation and distension of ventilated air spaces. In eight supine anesthetized and intubated rats, hyperpolarized gas MRI was performed after a recruitment maneuver following 1 h of volume-controlled ventilation with zero positive end-expiratory pressure (ZEEP), FiO2 0.5, and tidal volume 10 ml/kg, and after a second recruitment maneuver. Regional fractional ventilation (FV), apparent diffusion coefficient (ADC) of (3)He (a measurement of ventilated peripheral air space dimensions), and gas volume were measured in lung quadrants of ventral and dorsal regions of the lungs. In six additional rats, computed tomography (CT) images were obtained at each time point. Ventilation with ZEEP decreased total lung gas volume and increased both FV and ADC in all studied regions. Increases in FV were more evident in the dorsal slices. In each lung quadrant, higher ADC was predicted by lower gas volume and by increased mean values (and heterogeneity) of FV distribution. CT scans documented 10% loss of whole-lung aeration and increased density in the dorsal lung, but no macroscopic atelectasis. Loss of pulmonary gas at ZEEP increased fractional ventilation and inspiratory dimensions of ventilated peripheral air spaces. Such regional changes could help explain a propensity for mechanical ventilation to contribute to lung injury in previously uninjured lungs.
authors.affiliation: Department of Anesthesiology and Critical Care, University of Pennsylvania, Philadelphia, Pennsylvania; maurizio.cereda@uphs.upenn.edu.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Cereda
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania; and.
authors.forename: Yi
authors.initials: Y
authors.lastname: Xin
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania; and.
authors.forename: Hooman
authors.initials: H
authors.lastname: Hamedani
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania; and.
authors.forename: Justin
authors.initials: J
authors.lastname: Clapp
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania; and.
authors.forename: Stephen
authors.initials: S
authors.lastname: Kadlecek
authors.affiliation: Department of Anesthesiology and Critical Care, University of Pennsylvania, Philadelphia, Pennsylvania;
authors.forename: Natalie
authors.initials: N
authors.lastname: Meeder
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania; and.
authors.forename: Johnathan
authors.initials: J
authors.lastname: Zeng
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania; and.
authors.forename: Harrilla
authors.initials: H
authors.lastname: Profka
authors.affiliation: Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Brian P
authors.initials: BP
authors.lastname: Kavanagh
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania; and.
authors.forename: Rahim R
authors.initials: RR
authors.lastname: Rizi
mesh_terms: D000818:Animals; D008168:Lung / Q000502:physiology*; D055370:Lung Injury / Q000503:physiopathology; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D011175:Positive-Pressure Respiration / Q000379:methods; D001261:Pulmonary Atelectasis / Q000503:physiopathology; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012121:Respiration, Artificial / Q000379:methods; D013990:Tidal Volume / Q000502:physiology; D014057:Tomography, X-Ray Computed / Q000379:methods
keywords: alveolar recruitment; atelectasis; computed tomography; hyperpolarized gas MRI; ventilator-induced lung injury