Objective: To determine whether pathological alterations in alveolar mechanics (i.e., the dynamic change in alveolar size and shape with ventilation) at a similar level of lung injury vary depending on the cause of injury.
Design and setting: Prospective controlled animal study in a university laboratory.
Subjects: 30 male Sprague-Dawley rats (300-550 g).
Interventions: Rats were separated into one of four lung injury models or control (n=6): (a) 2% Tween-20 (Tween, n=6), (b) oleic acid (OA, n=6), (c) ventilator-induced lung injury (VILI, PIP 40/ZEEP, n=6), (d) endotoxin (LPS, n=6). Alveolar mechanics were assessed at baseline and after injury (PaO2/FIO2 <300 mmHg) by in vivo microscopy.
Measurements: Alveolar instability (proportional change in alveolar size during ventilation) was used as a measurement of alveolar mechanics.
Results: Alveoli were unstable in Tween, OA, and VILI as hypoxemia developed (baseline vs. injury: Tween, 7+/-2% vs. 67+/-5%; OA: 3+/-2% vs. 82+/-9%; VILI, 4+/-2% vs. 72+/-5%). Hypoxemia after LPS was not associated with significant alveolar instability (baseline vs. injury: LPS, 3+/-2 vs. 8+/-5%).
Conclusions: These data demonstrate that multiple pathological changes occur in dynamic alveolar mechanics. The nature of these changes depends upon the mechanism of lung injury.