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Retinal Arteriolar Hemodynamic Response to a Combined Isocapnic Hyperoxia and Glucose Provocation in Early Sight-Threatening Diabetic Retinopathy

¹From the Multi-Disciplinary Laboratory for the Research of Sight-Threatening Diabetic Retinopathy, Department of Ophthalmology and Vision Science, and the ³Department of Endocrinology, University of Toronto, Toronto, Ontario, Canada; and the ²School of Optometry, University of Waterloo, Waterloo, Ontario, Canada.

PURPOSE. To quantify the magnitude of change of retinal arteriolar hemodynamics induced by a combined isocapnic hyperoxia and glucose provocation in diabetic patients with early sight-threatening diabetic retinopathy (DR) and in age-matched control subjects and to compare the response to that of an isocapnic hyperoxia provocation alone. The study hypothesis was that hyperglycemia reduces the retinal vascular reactivity response to a hyperoxic stimulus.

METHODS. The sample comprised 17 control subjects (group 1), 15 patients with no clinically visible DR (group 2), 16 patients with mild-to-moderate nonproliferative DR (group 3), and 15 patients with diabetic macular edema (group 4). Retinal hemodynamic measurements were acquired in the subjects, at baseline and 1 hour after consuming a standardized oral glucose load drink while breathing oxygen isocapnic with baseline.

RESULTS. Retinal blood velocity and flow significantly decreased in all groups (P 0.001 and P 0.0002, respectively) in response to a combined isocapnic hyperoxia and glucose provocation. The maximum-to-minimum velocity ratio significantly increased (P 0.005), and wall shear rate (WSR) significantly decreased (P 0.0002), in groups 1, 2, and 3, but not in group 4. The vascular reactivity response was not significantly different across the groups. The control group demonstrated a reduced change in flow (P = 0.009) and WSR (P = 0.010) to the combined isocapnic hyperoxia and glucose provocation compared with that of hyperoxia alone.

CONCLUSIONS. The vascular reactivity response to a combined isocapnic hyperoxia and glucose provocation produced a pronounced reduction in blood flow. Unlike the response to hyperoxia alone, the vascular reactivity response was not significantly different across the groups. Hyperglycemia reduced the retinal vascular reactivity response to hyperoxia in age-matched control subjects.