Effect Of Breathing Pure Oxygen And A Mixture Of 92% O2 + 8% Co2 On Flicker Induced Vasodilatation

Abstract

Purpose: : Flicker light stimulation was shown to increase retinal and optic nerve head blood flow. It was suggested that higher oxygen demand, caused by increased neural activity due to flicker light stimulation might be the reason for the vascular flicker response. The aim of the present study was to investigate the effect of flicker light on the diameters of the vessels while breathing either 100% oxygen or a mixture of 92% oxygen plus 8% CO₂ compared to ambient air breathing.

Methods: : In total 34 subjects were included. 24 participants breathed ambient air first followed by inhaling pure oxygen. 10 subjects breathed air first followed by a mixture of 92% oxygen and 8% CO₂. Among these three groups measurements of the vessel diameters were done using the Dynamic Vessel Analyser. During the first 30 seconds baseline measurement was performed, followed by a 30 second flicker period (frequency 8 Hz). In addition, a blood gas sample was collected by capillary blood draw from the earlobe.

Results: : Flicker light stimulation significantly increased retinal venous diameters while breathing ambient air compared to baseline (p<0.05). Oxygen partial pressure (pO₂) was significantly increased, from 85±5 mmHg to 390±80 mmHg during 100% oxygen breathing. Inhaling of the gas mixture of 92% oxygen and 8% CO₂ increased the value from 88±18 mmHg to 277±71 mmHg. No change in flicker response compared to ambient air breathing could be observed in the 100% oxygen group. In contrast, breathing 92% oxygen + 8% CO₂ significantly increased flicker induced vasodilatation in retinal veins compared to room air (p < 0.05).

Conclusions: : Breathing pure oxygen does not alter the response of retinal vessels to stimulation with flicker light, whereas breathing 92% O₂ + 8% CO₂ significantly increases the flicker response.

Clinical Trial: : http://www.clinicaltrials.gov NCT00719342

Keywords: oxygen • retina • blood supply