Chorioretinal Vascular Oxygen Tension in Spontaneously Breathing Anesthetized Rats

Abstract

Purpose: To establish baseline and variability of oxygen tension (PO₂) measurements in the choroid, retinal arteries, capillaries, and veins of spontaneously breathing anesthetized rats and determine the effect of a moderate surgical procedure on the chorioretinal PO₂. Methods: Our previously established optical section phosphorescence imaging technique was utilized to measure PO₂ in the chorioretinal vasculatures. Imaging was performed in 29 spontaneously breathing rats under ketamine/xylazine anesthesia. In 7 rats, blood was drawn using a surgically implanted femoral arterial catheter and analyzed to determine the systemic arterial PO₂. The PO₂ measurements in 22 rats without surgery (group 1) and 7 surgically instrumented rats (group 2) were statistically compared. The intrasubject variability was calculated by the average standard deviation (SD) of repeated measurements. Results: The average systemic arterial PO₂ was 52 ± 7 mm Hg (mean ± SD) in group 2. In group 1, the average PO₂ measurements in the choroid, retinal arteries, capillaries, and veins were 50 ± 11, 40 ± 5, 39 ± 6, and 30 ± 5 mm Hg, respectively. No statistically significant PO₂ differences in any of the chorioretinal vasculatures were found between the two groups (p > 0.4). The intrasubject variability was 3 mm Hg in the choroid, retinal arteries, capillaries, and veins. Conclusions: Chorioretinal PO₂ measurements in spontaneously breathing anesthetized rats have a relatively low variability, indicating that PO₂ changes due to various physiological alterations can be reliably assessed.

Choroidal Oximetry With a Noninvasive Spectrophotometric Oximeter

“…Even though calculation of oxygen saturation from choroidal ODR has not been attempted, a low ODR is consistent with high oxygen saturation and high saturation in the choroid is in agreement with earlier studies on oxygenation in animals. 20,21 Shahidi et al 20 and Shakoor et al 21 used noninvasive phosphorescence imaging system to measure pO 2 in rat eyes and measured higher pO 2 in the choroid than in retinal arterioles under normal and increased oxygen breathing conditions; this agrees with our findings in the human eye.…”

A Method for Combined Retinal Vascular and Tissue Oxygen Tension Imaging

“…The mean inner retinal OEF was higher as compared to our previous study 16 and maximum outer retinal tPO 2 in the current study was slightly lower than previous reports 14 , 15 . Both of these results are consistent with the presence of reduced systemic oxygenation 26 , which likely resulted from the effect of anesthesia while the rats were under spontaneous breathing conditions 27 . Furthermore, the variability of tPO 2 adjacent to the chorioretinal interface along the tPO 2 image may, at least in part, be attributed to presumed anesthesia-induced systemic hypotension.…”

Three-Dimensional Mapping of Chorioretinal Vascular Oxygen Tension in the Rat

“…As previously reported, the hypoxic condition of the rats in our study might have resulted from the respiratory depressant effect of the anesthetics because the rats were not intubated or ventilated and they breathed spontaneously 46. Previous studies performed under systemic arterial PO 2 greater than 80 mm Hg in rat, monkey, miniature pig, and cat have reported choroidal PO 2 measurements that were approximately 60% of the systemic arterial PO 2 4,43,47,48.…”