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Pang-yu Teng, Norman P. Blair, Justin M. Wanek, Isa Yildirim, Mahnaz Shahidi; Longitudinal Gradients of Oxygen Tension in the Retinal Vasculature of Rat. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1732.
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© ARVO (1962-2015); The Authors (2016-present)
Oxygen transport in the retinal vasculature plays a crucial role in maintaining normal retinal metabolic function. Therefore, study of changes in oxygen tension (PO2) along retinal blood vessels is helpful to gain fundamental knowledge of retinal physiology. The purpose of this study is to report measurements of PO2 longitudinal gradients in retinal capillaries, arteries and veins in the rat, using our previously established phosphorescence lifetime imaging technique.
Phosphorescence lifetime imaging was performed in 12 rats under normoxia. A narrow vertical laser line was scanned horizontally across the retina in small steps after injection of an oxygen-sensitive molecular probe and three-dimensional retinal vascular PO2 maps were constructed. Retinal blood vessels were segmented semi-automatically and vessel centerlines were identified using distance transformations. PO2 was quantified within cross sectional areas along each blood vessel path. An average PO2 measurement in each blood vessel was calculated. Linear regression analysis was used to determine PO2 gradients in retinal capillaries, arteries and veins. Statistical significance was accepted at p < 0.05.
Systemic arterial PO2 was 100 ± 22 mmHg (mean ± SD, N=12). PO2 measurements in retinal capillaries, arteries and veins were 32 ± 6 mmHg (N = 8), 42 ± 9 mmHg (N = 12) and 28 ± 6 mmHg (N =12), respectively. Statistically significant negative PO2 longitudinal gradients (decrease from upstream to downstream) were found in 6 of 8 retinal capillaries and 5 of 12 retinal arteries. Mean PO2 longitudinal gradients in these retinal capillaries and arteries were -5.26 ± 1.35 mmHg/100µm (N = 6) and -1.47 ± 0.64 mmHg/100µm (N = 5), respectively. Statistically significant positive PO2 longitudinal gradients (increase from upstream to downstream) were found in 7 of 12 retinal veins with a mean PO2 longitudinal gradient of 0.48 ± 0.35 mmHg/100µm (N = 7).
Quantitative measurements of PO2 longitudinal gradients in retinal blood vessels of the rat demonstrated retinal tissue oxygen extraction occurs predominantly in the capillaries. This method has the potential to help elucidate retinal capillary oxygen transport in health and disease.
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