Dependence of lung injury on inflation rate during low-volume ventilation in normal open-chest rabbits.
Lung mechanics and morphometry were assessed in two groups of nine normal open-chest rabbits mechanically ventilated (MV) for 3-4 h at zero end-expiratory pressure (ZEEP) with physiological tidal volumes (Vt; 11 ml/kg) and high (group A) or low (group B) inflation flow (44 and 6.1 ml x kg(-1) x s(-1), respectively). Relative to initial MV on positive end-expiratory pressure (PEEP; 2.3 cmH(2)O), MV on ZEEP increased quasi-static elastance and airway and viscoelastic resistance more in group A (+251, +393, and +225%, respectively) than in group B (+180, +247, and +183%, respectively), with no change in viscoelastic time constant. After restoration of PEEP, quasi-static elastance and viscoelastic resistance returned to control, whereas airway resistance, still relative to initial values, remained elevated more in group A (+86%) than in group B (+33%). In contrast, prolonged high-flow MV on PEEP had no effect on lung mechanics of seven open-chest rabbits (group C). Gas exchange on PEEP was equally preserved in all groups, and the lung wet-to-dry ratios were normal. Relative to group C, both groups A and B had an increased percentage of abnormal alveolar-bronchiolar attachments and number of polymorphonuclear leukocytes in alveolar septa, the latter being significantly larger in group A than in group B. Thus prolonged MV on ZEEP with cyclic opening-closing of peripheral airways causes alveolar-bronchiolar uncoupling and parenchymal inflammation with concurrent, persistent increase in airway resistance, which are worsened by high-inflation flow.
D'Angelo
Edgardo
E
Istituto di Fisiologia Umana I, via Mangiagalli 32, 20133 Milan, Italy. edgardo.dangelo@unimi.it
Pecchiari
Matteo
M
Saetta
Marina
M
Balestro
Elisabetta
E
Milic-Emili
Joseph
J
D000399:Air Pressure; D000465:Algorithms; D000758:Anesthesia; D000818:Animals; D001980:Bronchi / Q000502:physiology; D002452:Cell Count; D004548:Elasticity; D008168:Lung / Q000033:anatomy & histology / Q000473:pathology; D055370:Lung Injury; D008176:Lung Volume Measurements; D010243:Paralysis / Q000139:chemically induced / Q000503:physiopathology; D011014:Pneumonia / Q000473:pathology; D011175:Positive-Pressure Respiration; D011650:Pulmonary Alveoli / Q000502:physiology; D011817:Rabbits; D012121:Respiration, Artificial / Q000009:adverse effects*; D015656:Respiratory Mechanics / Q000502:physiology; D014132:Trachea / Q000502:physiology; D014783:Viscosity