title: Retinal arteriolar hemodynamic response to a combined isocapnic hyperoxia and glucose provocation in early sight-threatening diabetic retinopathy.
abstract: OBJECTIVE
  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 < or = 0.001 and P < or = 0.0002, respectively) in response to a combined isocapnic hyperoxia and glucose provocation. The maximum-to-minimum velocity ratio significantly increased (P < or = 0.005), and wall shear rate (WSR) significantly decreased (P < or = 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.
authors.affiliation: Multi-Disciplinary Laboratory for the Research of Sight-Threatening Diabetic Retinopathy, Department of Ophthalmology and Vision Science, University of Toronto, Toronto, ON, Canada.
authors.forename: Edward D
authors.initials: ED
authors.lastname: Gilmore
authors.forename: Chris
authors.initials: C
authors.lastname: Hudson
authors.forename: Ravi K
authors.initials: RK
authors.lastname: Nrusimhadevara
authors.forename: Rowena
authors.initials: R
authors.lastname: Ridout
authors.forename: Patricia T
authors.initials: PT
authors.lastname: Harvey
authors.forename: Mark
authors.initials: M
authors.lastname: Mandelcorn
authors.forename: Wai-Ching
authors.initials: WC
authors.lastname: Lam
authors.forename: Robert G
authors.initials: RG
authors.lastname: Devenyi
mesh_terms: D001160:Arterioles / Q000502:physiology; D001783:Blood Flow Velocity; D001786:Blood Glucose / Q000032:analysis; D003930:Diabetic Retinopathy / Q000503:physiopathology*; D005260:Female; D005947:Glucose / Q000008:administration & dosage*; D005951:Glucose Tolerance Test; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D006943:Hyperglycemia / Q000503:physiopathology*; D018496:Hyperoxia / Q000503:physiopathology*; D017078:Laser-Doppler Flowmetry; D008269:Macular Edema / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D012039:Regional Blood Flow / Q000502:physiology; D012161:Retinal Artery / Q000502:physiology*
chemical_list: D001786:Blood Glucose; D005947:Glucose