Animal model construction
The experimental group (n = 40, FiO2 = 60%) and the control group (n = 40, FiO2 = 21%) were divided into two groups by random numbering method after weighing 80 newborn SD rats (purchased from Beijing Huatai Yikang Biotechnology Co., LTD, China). Rats in the experimental group were placed in a sealed 60cm x 50cm x 40cm oxygen chamber (temperature 21°C to 27°C, humidity 55% to 65%) with a constant oxygen intake, oxygen concentration maintained at 60% and CO2 concentration <0.5%. The control group of neonatal rats was placed in a standard rearing bin (FiO2 = 21%) in the same rearing room, with the same experimental conditions as the experimental group, except for the difference in oxygen concentration. All animal procedures were approved by the Committee on the Ethics of Animal Experiments of the Affiliated Hospital of Inner Mongolia Medical University, Inner Mongolia, China. All surgeries were performed under chloral hydrate anesthesia via intraperitoneal injection.