Forty-eight healthy clean male Sprague-Dawley (SD) rats were randomly divided into
sham operation (
Sham) group, low tidal volume (LVT)
mechanical ventilation group (LVT group), normal tidal volume (NVT)
mechanical ventilation group (NVT group) and high tidal volume (HVT)
mechanical ventilation group (HVT group) with 12 rats in each group. After
anesthesia, rats in the
Sham group were intubated and kept spontaneous breathing. The rats in different tidal volume (VT) groups were mechanically ventilated by endotracheal intubation with VT of 6 mL/kg (LVT group), 10 mL/kg (NVT group), and 20 mL/kg (HVT group), respectively. The inspiration-expiration ratio of the three groups was 1:1, the ventilation frequency was 40 times/min, and the ventilation time was 3 hours. At the end of the experiment, the bronchoalveolar lavage fluid (BALF) of rats was collected, and the levels of pro-inflammatory factors [
tumor necrosis factor-α (TNF-α),
interleukins (IL-1β and IL-6)] in BALF were detected by
enzyme-linked
immunosorbent assay (ELISA). The lung tissues of rats were collected, and the
lung wet/dry weight (W/D) ratio was calculated. The pathological changes of lung tissues were observed under light microscopy after
hematoxylin-
eosin (HE) staining, and
lung injury scores were performed. The brain tissue of rats was taken to measure the brain water content, and the
Evans blue (EB) content of brain tissue was measured to reflect the permeability of the blood-brain barrier. The
tight junction proteins in the brain tissues were detected by Western blotting.
RESULTS: After 3 hours of
mechanical ventilation, with the increase of VT, the degree of
lung injury in VILI rats gradually increased. When VT reached 20 mL/kg, lung tissue structure was significantly injured, alveolar wall
edema, alveolar congestion, lung interstitial thickening, a large number of inflammatory cells infiltrated, and the
lung injury score, lung W/D ratio, and the levels of TNF-α, IL-1β and
IL-6 in BALF were significantly higher than those in the
Sham group [
lung injury score: 10.6±1.1 vs. 1.4±1.0, lung W/D ratio: 6.6±0.8 vs. 3.7±0.6, TNF-α (ng/L): 832.9±97.9 vs. 103.8±23.3, IL-1β (ng/L): 68.9±14.1 vs. 15.7±2.6,
IL-6 (ng/L): 70.8±16.4 vs. 20.3±5.4, all P < 0.05].
Lung injury in rats was accompanied by aggravating
brain injury. When VT reached 20 mL/kg, brain water content and EB content in brain tissue were significantly higher than those in the
Sham group [brain water content: (85.4±3.6)% vs. (68.7±2.7)%, EB content in brain tissue (μg/g): 887±78 vs. 97±14, both P < 0.05], and the
protein expressions of
claudin-5, occluding and zonula occluden-1 (ZO-1) in the brain tissue were significantly lower than those in the
Sham group [
claudin-5 protein (
claudin-5/β-actin): 0.67±0.12 vs. 1.45±0.19,
occludin protein (
occludin/β-actin): 0.48±0.11 vs. 0.99±0.21, ZO-1
protein (ZO-1/β-actin): 0.13±0.03 vs. 0.63±0.12, all P < 0.05].
CONCLUSIONS: