Neonatal hyperoxia exposure resulted in decreased growth and lung structural and functional alterations. Body weights of mice exposed to hyperoxia for 7 days from birth compared to neonates exposed to normoxia (A). n = 9 & 13 mice/treatment. Morphometric estimation of mean linear intercept (B), percentage tissue (C) and percentage airspace (D) in lungs exposed to hyperoxia and normoxia. n = 4 & 5 lungs/treatment. Data were analysed using two-tailed unpaired t-tests. *p < 0.05. Normoxia (E) and hyperoxia-exposed (F) lungs at P7 demonstrated the decrease in tissue percentage and increase in alveolar size due to hyperoxia. Respiratory trace recordings revealed that mice exposed to hyperoxia (H) display abnormal breath patterns compared to normoxic mice (G).