[An experiment on the pathogenesis of early biotrauma in ventilator-induced lung injury]

To investigate the pathogenesis of early biotrauma in ventilator-induced lung injury (VILI).

Twenty-four 8-week-old male specific-pathogen-free Sprague-Dawley (SD) rats weighing 250-300 g were randomly divided into sham group (S group), conventional mechanical ventilation group (L group) and high tidal volume (VT) mechanical ventilation group (H group) with 8 rats in each group. All rats received tracheostomy after anesthesia. Rats in S group received no mechanical ventilation but breathe room air spontaneously. All other parameters of the ventilator were the same in both mechanical ventilation groups, and the fraction of oxygen was set to 0.21, the rats in L group received 7 mL/kg VT, and those in H group received 28 mL/kg VT. Four hours after ventilation all rats were sacrificed and the lung tissues were harvested for wet/dry (W/D) ratio. Pathological injury score was evaluated by hematoxylin and eosin (HE) staining. Transferase-mediated deoxyuridine triphosphate-biotin nick end labeling stain (TUNEL) was performed to count the apoptosis cell in lung epithelial. Western Blot was performed to evaluate hemi-channel protein Pannexin-1 expression in lung homogenate. Bronchoalveolar lavage fluid (BALF) was collected, and the concentration of lactate dehydrogenase (LDH), isoprostane, adenosine triphosphate (ATP) and white cell count in BALF were measured. Yo-pro-1/propidium iodide (PI) double stain was performed to evaluate early apoptosis cell in BALF.

There was no significant difference in lung injury between S group and L group. Compared with S group and L group, rats in H group showed significant lung injury, represented as alveolar rupture, inflammatory cell infiltration, interstitial edema and airway epithelial exfoliation, and the lung W/D ratio was increased significantly (5.1±0.2 vs. 4.4±0.2, 4.3±0.4, both P < 0.01), pathological score was significantly increased [4.00 (4.00, 8.00) vs. 1.00 (0, 4.00), 2.00 (0, 4.75), both P < 0.01], the white cell in BALF was significantly increased (×10⁶/L: 2.97±0.46 vs. 1.03±0.26, 0.79±0.19, both P < 0.01), the level of LDH was significantly increased (U/L: 148.6±38.2 vs. 34.4±13.5, 78.6±13.9, both P < 0.01), and the expression of Pannexin-1 in lung homogenate was significantly increased (Pannexin-1/GAPDH: 0.89±0.21 vs. 0.48±0.25, 0.61±0.17, both P < 0.01), the ATP concentration in BALF was also significantly increased (nmol/L: 456.84±148.72 vs. 19.23±13.34, 113.26±57.90, both P < 0.01). There was no significant difference in the apoptosis cell in lung tissue or the apoptosis cell rate, isoprostane level in BALF among the three groups [apoptosis cell in lung (cells/HP): 4.00 (3.00, 5.00) vs. 5.00 (4.00, 6.00), 4.00 (3.25, 6.00); apoptosis cell rate in BALF: (0.57±0.20)% vs. (0.42±0.16)%, (0.58±0.19)%; isoprostane in BALF (μg/L): 3.85±0.46 vs. 3.83±0.60, 3.59±0.69, all P > 0.05].

The early pathogenesis of biotrauma in VILI is related to the release of inflammation mediator via membrane channel after activating by pressure stress, but not apoptosis and lipid peroxidation.