Li Yingxia, Cheng Haiying, Shen Qiang, Kim Moon, Thule Peter M, Olson Darin E, Pardue Machelle T, Duong Timothy Q
Yerkes Imaging Center, Emory University, Atlanta, Georgia, USA.
Invest Ophthalmol Vis Sci. 2009 Apr;50(4):1824-30. doi: 10.1167/iovs.08-2188. Epub 2008 Oct 24.
This study aims to investigate quantitative basal blood flow as well as hypercapnia- and hyperoxia-induced blood flow changes in the retinas of the Royal College of Surgeons (RCS) rats with spontaneous retinal degeneration, and to compare with those of normal rat retinas.
Experiments were performed on male RCS rats at post-natal days P90 (n=4) and P220 (n=5), and on age-matched controls at P90 (n=7) and P220 (n=6). Hyperoxic (100% O(2)) and hypercapnic (5% CO(2), 21% O(2), balance N(2)) challenges were used to modulate blood flow. Quantitative baseline blood flow, and hypercapnia- and hyperoxia-induced blood flow changes in the retinas were imaged using continuous arterial spin labeling MRI at 90 x 90 x 1500 microm.
In the normal rat retinas, basal blood flow of the whole-retina was 5.5 mL/gram per min, significantly higher than those reported in the brain (approximately 1 mL/gram per min). Hyperoxia decreased blood flow due to vasoconstriction and hypercapnia increased blood flow due to vasodilation in the normal retinas. In the RCS rat retinas, basal blood flow was diminished significantly (P<0.05). Interestingly, absolute hyperoxia- and hypercapnia-induced blood flow changes in the RCS retinas were not statistically different from those in the normal retinas (P>0.05). However, blood flow percent changes in RCS retinas were significantly larger than in normal retinas due to lower basal blood flow in the RCS retinas.
Retinal degeneration markedly reduces basal blood flow but does not appear to impair vascular reactivity. These data also suggest caution when interpreting relative stimulus-evoked functional MRI changes in diseased states where basal parameters are significantly perturbed. Quantitative blood flow MRI may serve as a valuable tool to study the retina without depth limitation.
本研究旨在调查患有自发性视网膜变性的皇家外科学院（RCS）大鼠视网膜的基础血流量以及高碳酸血症和高氧血症诱导的血流变化，并与正常大鼠视网膜进行比较。
对出生后第90天（n = 4）和第220天（n = 5）的雄性RCS大鼠以及年龄匹配的对照组（第90天，n = 7；第220天，n = 6）进行实验。使用高氧（100% O₂）和高碳酸血症（5% CO₂，21% O₂，其余为N₂）刺激来调节血流。在90×90×1500微米分辨率下，使用连续动脉自旋标记磁共振成像（MRI）对视网膜的基础血流量以及高碳酸血症和高氧血症诱导的血流变化进行成像。
在正常大鼠视网膜中，全视网膜的基础血流量为5.5毫升/克·分钟，显著高于大脑中的报道值（约1毫升/克·分钟）。在正常视网膜中，高氧血症由于血管收缩导致血流减少，高碳酸血症由于血管舒张导致血流增加。在RCS大鼠视网膜中，基础血流量显著减少（P<0.05）。有趣的是，RCS视网膜中高氧血症和高碳酸血症诱导的绝对血流变化与正常视网膜相比无统计学差异（P>0.05）。然而，由于RCS视网膜的基础血流量较低，其血流百分比变化显著大于正常视网膜。
视网膜变性显著降低基础血流量，但似乎并未损害血管反应性。这些数据还表明，在解释基础参数受到显著干扰的疾病状态下相对刺激诱发的功能MRI变化时应谨慎。定量血流MRI可能是一种研究视网膜且无深度限制的有价值工具。
