Effect of Breathing a Mixture of 92% Oxygen (O2) + 8% Carbon Dioxide (CO2) on Flicker Induced Blood Flow Changes in Ocular Perfusion

Study Overview
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Brief Summary
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It has been shown that diffuse luminance flicker increases retinal and optic nerve head blood flow. This indicates that a neuro-vascular coupling between neural activity and blood flow exists in the retina as described previously for the brain. Although a lot of mediators such as NO, pO2, pCO2, H+ and K+ have been proposed, the mechanism of this coupling is still a matter of controversy. However, it has been shown in an animal experiment, that an increase in blood flow, evoked by diffuse luminance flicker stimulation is paralleled by decrease in pO2 in the tissue. In a recently performed study we could show that breathing of 100% O2 did not influence flicker induced changes in the retina and optic nerve head. However, breathing of 100% oxygen also leads to a pronounced vasoconstriction of the retinal vessels and in turn to a increased tension of the vessel wall. Recent evidence indicates that a combination of 92% O2 and 8% CO2 can, at least partially, counteract the vasoconstrictory effect of O2 and increases tissue pO2. Thus, in this study the investigators set out to investigate the flicker light induced increase in blood flow under a mixture of O2/CO2 .

Official Title
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Effect of Breathing a Mixture of 92% O2 + 8% CO2 on Flicker Induced Blood Flow Changes in Ocular Perfusion

Conditions
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Flicker-induced Vasodilatation

Intervention / Treatment
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* Drug: Oxygen + Carbondioxide
* Other: full field flickering light at 12.5 Hz


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Men and Women aged between 18 and 35 years, nonsmokers Body mass index between 15th and 85th percentile Normal findings in the medical history and physical examination unless the investigator considers an abnormality to be clinically irrelevant Normal laboratory values unless the investigator considers an abnormality to be clinically irrelevant Normal ophthalmic findings, ametropy < 3 Dpt. Exclusion Criteria: Regular use of medication, abuse of alcoholic beverages, participation in a clinical trial in the 3 weeks preceding the study Treatment in the previous 3 weeks with any drug Symptoms of a clinically relevant illness in the 3 weeks before the first study day Blood donation during the previous 3 weeks

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 35 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Double


Arms and Interventions

| Intervention/Treatment |
| --- |
|Drug: Oxygen + Carbondioxide|Mixture of 92 % oxygen and 8 % carbon dioxide for inhalation|
|Other: full field flickering light at 12.5 Hz|1 minute stimulation with full field flickering light at 12.5 Hz during measurement of vessel diameters and measurement of blood flow.|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Optic nerve head blood flow |  | 1 hour | 
| Retinal vessel diameters |  | 1 hour | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| blood pressure |  | 1 hour | 
| pulse rate |  | 1 hour | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Retinal vessel diameter, Flicker-induced vasodilatation, Optic nerve head blood flow, Ocular Physiology, Regional Blood Flow