Effect of low-level laser therapy on inflammatory response in an experimental model of ventilator-induced lung injury

Purpose: To evaluate the effect of low-level laser therapy (LLLT) on an experimental model of ventilator-induced lung injury (VILI). Methods: 24 adult Wistar rats were randomized in four groups: protective mechanical ventilation (PMV), PMV+laser, VILI and VILI+laser. The animals of the PMV and VILI groups were ventilated with tidal volume of 6 and 35 ml/Kg, respectively for 90 minutes. After the first 60 minutes of ventilation, the animals of the laser groups were irradiated (808 nm, 100 mW power density, 20 J/cm² energy density, continuous emission mode, and exposure time 5s) and after 30 minutes of irradiation, the animals were euthanized. Lung samples were removed to morphological analysis, bronchoalveolar lavage (BAL) and RT-qPCR technique. Results: The VILI group showed greater acute lung injury (ALI) score with an increase in neutrophil infiltration, higher neutrophil count in the BAL fluid and greater cytokine mRNA expression compared to the PMV groups (p<0.05). The VILI+laser group when compared to the VILI group showed lower ALI score (0.35 ± 0.08 vs. 0.54 ± 0.13, p<0.05), alveolar neutrophil infiltration (7.00 ± 5.73 vs. 21.50 ± 9.52, p<0.05), total cell count (1.90 ± 0.71 vs. 4.09 ± 0.96 x105, p<0.05) and neutrophil count in the BAL fluid (0.60 ± 0.37 vs. 2.28 ± 0.48 x105, p<0.05). Moreover, LLLT induced a decrease in pro-inflammatory and an increase of anti-inflammatory mRNA levels compared to the VILI group (p<0.05). Conclusion: LLLT reduced the inflammatory response in an experimental model of VILI.