Normobaric Hyperoxia Induces Time-Dependent Hemodynamic Fluctuations in the Middle Cerebral Artery and Cortical Damage in Neonatal Rats.

Objective: To assess the feasibility of cranial color Doppler flow imaging (CDFI) for monitoring the middle cerebral artery (MCA) hemodynamics and its correlation with histopathological changes in neonatal rats under persistent hyperoxia.

Methods: On postnatal day 1, 48 neonatal Sprague-Dawley rats were randomly divided into control and hyperoxia groups. MCA hemodynamic parameters were assessed by color Doppler ultrasound at 0 h, 24 h, 48 h, and 72 h post-exposure, followed by systematic analysis of hyperoxia-induced pathological changes in collected brain tissues in the hyperoxia group.

Results: The hyperoxia group exhibited time-dependent fluctuations in MCA hemodynamic parameters compared to controls. Both peak systolic velocity (PSV) and resistance index demonstrated a biphasic pattern: significant increases at 24 h, decreases at 48 h, and subsequent rises at 72 h (p < 0.05). In contrast, EDV peaked at 24 h and progressively declined thereafter (p < 0.05).Simultaneously, histopathological analysis revealed that short-term hyperoxia exposure (≤24 h) significantly alleviated cortical neuronal damage and microvascular density loss compared to 0 h (p < 0.05). However, prolonged exposure (≥48 h) induced progressive oxygen toxicity, exacerbating cortical neuronal injury, with maximal severity observed at 72 h (p < 0.05). Notably, from 0 to 72 h of hyperoxia, the PSV of the MCA exhibited a consistent correlation with both neuronal count and microvascular density in the cerebral cortex.

Conclusion: CDFI sensitively detects significant hemodynamic fluctuations in the MCA induced by prolonged hyperoxia, which correlate with cortical damage. This establishes CDFI as a reliable, non-invasive tool for dynamic MCA hemodynamic monitoring and early prediction of hyperoxia-induced neonatal brain injury.