Purchase this article with an account.
J. K. Adleman, S. Dorner, J. A. Fisher, T. Wong, G. E. Trope, C. Hudson; Vascular Reactivity Reserve and Resting Tonus in Retinal Arterioles of Healthy Subjects. Invest. Ophthalmol. Vis. Sci. 2009;50(13):402.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To determine the magnitude of retinal arteriolar vascular reactivity reserve in relation to the resting tonus of healthy subjects.
The retinal arteriolar vascular reactivity was assessed in either eye of five healthy subjects (mean 28, range: 23-32 years). All subjects had a visual acuity of 20/20 or better, no history of ocular disease or refractive surgery and were non-smokers. Vascular reactivity was defined as change from baseline in arteriolar diameter, blood velocity, max:min velocity ratio, and blood flow as assessed by the Canon Laser Blood Flowmeter. Baseline conditions were measured at an end-tidal PCO2 (PETCO2) of 38mmHg and end-tidal PO2 (PETO2) of 100mmHg to determine resting tonus.Two graded vasodilatory stimuli were applied in the form of hypoxic hypercapnia (PETO2 = 83 / PETCO2 = 46 mmHg; and PETO2 = 65 / PETCO2 = 46 mmHg) and a single maximal constrictor stimulus was applied in the form of hyperoxic hypocapnia (PETO2 = 300mmHg / PETCO2 = 30mmHg) in randomized order. A 15 minute interval was employed following hyperoxic hypercapnia to avoid any persistent effects of inhaled oxygen. End-tidal gases were actuated by providing predetermined gas flows of specific PCO2 and PO2 to a sequential gas delivery breathing circuit via an automated gas blender (RespiractTM TRI, Toronto, Canada). Following a 3 minute stabilization period at the beginning of each phase, 3 hemodynamic measurements were acquired in the superior temporal arteriole at approximately 1 disc diameter from the optic nerve head.
Flow was unchanged during the first and second phase of the dilatory stimuli (+10.0%, SD = 7.9, p=0.558, and +7.7%, SD = 8.5, p=0.693, respectively). Flow was reduced by -32.9% (SD = 0.6, p=0.007) during the constrictor stimulus. There was a non-significant trend for the max:min velocity ratio to increase during the constrictor stimulus and to decrease during the dilatory stimuli.
Relative to the resting tonus position, the retinal arterioles demonstrated a greater capacity for vasoconstriction than vasodilation in response to the gas stimuli used in this study.
This PDF is available to Subscribers Only