Retinal Oxygen Metabolism and Delivery Response to Hyperoxia During Bilateral Common Carotid Artery Occlusion in Rats

Abstract

Purpose : Hyperoxia has been shown to diminish injury induced by ischemia. We previously reported reduced inner retinal oxygen metabolism (MO₂) and delivery (DO₂) as well as increased oxygen extraction fraction (OEF) after permanent bilateral common carotid artery occlusion (BCCAO). The effect of hyperoxia on these oxygen metrics has not been investigated. We hypothesized that hyperoxia improves MO₂ and DO₂ under ischemia induced by BCCAO in rats.

Methods : Thirteen rats underwent BCCAO and were imaged in one eye either immediately or 3 days later under both spontaneous breathing condition (normoxia) and 15 minutes of 100% O₂ inspiration (hyperoxia). In 6 of these rats, baseline imaging was performed before BCCAO. Phosphorescence lifetime, microsphere fluorescence, and reflectance images were acquired to derive MO₂, DO₂, and OEF.

Results : MO₂, DO₂ and OEF were impaired immediately after BCCAO compared to baseline (P≤0.03; N=6). On average, MO₂ and DO₂ decreased to 52% and 19% of baseline values, respectively, and OEF increased to 301% of baseline value. Immediately after BCCAO, MO₂ and DO₂ increased under hyperoxia (220±96 and 260±140 nLO/min, respectively) compared to that under normoxia (120±82 and 120±83 nLO/min, respectively) (P≤0.04; N=9). OEF was not significantly different under hyperoxia (0.90±0.11) compared to that under normoxia (0.98±0.02) (P=0.06). MO₂ and DO₂ under normoxia were inversely correlated to changes in the corresponding measurement under hyperoxia (r≥0.88; P≤0.002; N=9). After 3 days of BCCAO, there were no significant differences in MO₂, DO₂, and OEF under normoxia (230±110 nLO/min, 300±81 nLO/min, and 0.74±0.16, respectively) compared to that under hyperoxia (170±51 nLO/min, 440±300 nLO/min, 0.53±0.31, respectively) (P≥0.17; N=4). MO₂ and DO₂ under normoxia were not correlated with changes in the corresponding measurement under hyperoxia (r≤0.91; P≥0.09; N=4).

Conclusions : MO₂ and DO₂ increased with hyperoxia immediately after BCCAO, and the increases were inversely related to their levels under normoxia. However, after 3 days of BCCAO, there was no detectable effect of hyperoxia on MO₂ and DO₂. OEF did not respond to hyperoxia at either time point. These results suggest that improvement in MO₂ and DO₂ by hyperoxia may be most effective shortly after ischemia, rather than after longer durations of ischemia.

This is a 2020 ARVO Annual Meeting abstract.