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Retinal arteriolar diameter, blood velocity, and blood flow response to an isocapnic hyperoxic provocation

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

Submitted 12 October 2004 ; accepted in final form 8 February 2005

The aim of this study was to simultaneously quantify the magnitude and response characteristics of retinal arteriolar diameter and blood velocity induced by an isocapnic hyperoxic provocation in a group of clinically normal subjects. The sample comprised 10 subjects (mean age, 25 yr; range, 21–40 yr). Subjects initially breathed air for 5–10 min, then breathed O₂ for 20 min, and then air for a final 10-min period via a sequential rebreathing circuit (Hi-Ox; Viasys) to maintain isocapnia. Retinal arteriolar diameter and blood velocity measurements were simultaneously acquired with a Canon laser blood flowmeter (CLBF-100). The response magnitude, time, and lag of diameter and velocity were calculated. In response to hyperoxic provocation, retinal diameter was reduced from control values of 111.6 (SD 13.1) to 99.8 (SD 10.6; P < 0.001) µm and recovered after withdrawal of hyperoxia. Retinal blood velocity and flow concomitantly declined from control values of 32.2 (SD 6.4) mm/s and 9.4 (SD 2.5) µl/min to 20.7 (SD 3.4) mm/s and 5.1 (SD 1.3) µl/min, respectively (P < 0.001 for both velocity and flow), and recovered after withdrawal of hyperoxia. The response times and response lags were not significantly different for each parameter between effect and recovery or between diameter and velocity. We conclude that arteriolar retinal vascular reactivity to hyperoxic provocation is rapid with a maximal vasoconstrictive effect occurring within a maximum of 4 min. Although there was a trend for diameter to respond before velocity to the isocapnic hyperoxic provocation, the response characteristics were not significantly different between diameter and velocity.

vascular reactivity; laser Doppler velocimetry; isocapnic hyperoxia

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