Effects of overinflation on procollagen type III expression in experimental acute lung injury

Introduction In acute lung injury ( ALI), elevation of procollagen type III ( PC III) occurs early and has an adverse impact on outcome. We examined whether different high-inflation strategies of mechanical ventilation ( MV) in oleic acid ( OA) ALI alter regional expression of PC III. Methods We designed an experimental, randomized, and controlled protocol in which rats were allocated to two control groups ( no injury, recruited [ alveolar recruitment maneuver after tracheotomy without MV; n = 4 rats] and control [ n = 5 rats]) or four injured groups ( one exposed to OA only [ n = 10 rats] and three OA-injured and ventilated). The three OA-injured groups were ventilated for 1 hour according to the following strategies: LVHP-S ( low volume-high positive end-expiratory pressure [ PEEP], supine; n = 10 rats, tidal volume [ VT] = 8 ml/kg, PEEP = 12 cm H2O), HVLP-S ( high volume-low PEEP, supine; n = 10 rats, VT = 20 ml/kg, PEEP = 5 cm H2O), and HVLP-P ( high volume-low PEEP, prone; n = 10 rats). Northern blot analysis for PC III and interleukin-1-beta ( IL-1 beta) and polymorphonuclear infiltration index ( PMI) counting were performed in nondependent and dependent regions. Regional differences between groups were assessed by two-way analysis of variance after logarithmic transformation and post hoc tests. Results A significant interaction for group and region effects was observed for PC III ( p = 0.012) with higher expression in the nondependent region for HVLP-S and LVHP-S, intermediate for OA and HVLP-P, and lower for control ( group effect, p < 0.00001, partial eta(2) = 0.767; region effect, p = 0.0007, partial eta(2) = 0.091). We found high expression of IL-1 beta ( group effect, p < 0.00001, partial eta(2) = 0.944) in the OA, HVLP-S, and HVLP-P groups without regional differences ( p = 0.16). PMI behaved similarly ( group effect, p < 0.00001, partial eta(2) = 0.832). Conclusion PC III expression is higher in nondependent regions and in ventilatory strategies that caused overdistension. This response was partially attenuated by prone positioning.