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K. Huber, H. Adams, A. Remky, O. Arend; Retrobulbar hemodynamics and contrast sensitivity after CO2 breathing . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2617.
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Purpose: CO2 is known as a vasodilator in the brain. In clinical routine the effect of gas mixtures (Carbogen) of CO2 and O2 are studied. The results are in a wide interindividual respiratory response. We investigated effects of CO2 on retrobulbar hemodynamics and contrast sensitivity in young adults to establish a vasodilatatory response test. Methods: Thirty healthy adults (age 31 ± 7 years, from 21 to 48, 15 male, 15 female) were studied under normo– and hypercapnic conditions. Color Doppler imaging (Siemens Sonoline Sienna) was used to measure vasoreactivity in the ophthalmic and central retinal artery. Under both conditions the peak systolic (PSV) and end–diastolic velocities (EDV) as well as Resistive Index (RI) were determined. Furthermore, we studied contrast sensitivity (CSV 1000). Results: Hypercapnia lowered the intraocular pressure significantly (p< 0.0001). Hypercapnia increased PSV by 17% and EDV by 23% in the central retinal artery. In the ophthalmic artery PSV raised by 14% and EDV by 21% under hypercapnia. There was no significant change of the RI of the central retinal and the ophthalmic artery. Vasoreactivity in healthy subjects (velocity CO2 – velocity baseline) was independent of smoking habits or history of migraine headache. There was a significant increase of contrast sensitivity under hypercapnia (spatial frequency: 3cpd: p< 0.0001; 6cpd: p< 0.0001; 12cpd: p< 0.0002; 18cpd: p< 0.03). Conclusion: Hypercapnia resulted in functional improvements of contrast sensitivity and led to decreased IOP. Flow velocity in the central retinal and ophthalmic artery are affected by CO2. Therefore, responsiveness of vasoreactivity could have an impact on therapy regimen.
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