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  • Title: Retrobulbar haemodynamics and contrast sensitivity improvements after CO2 breathing.
    Author: Huber KK, Adams H, Remky A, Arend KO.
    Journal: Acta Ophthalmol Scand; 2006 Aug; 84(4):481-7. PubMed ID: 16879568.
    Abstract:
    PURPOSE: Effects of gas mixtures have been widely studied. Carbon dioxide (CO(2)) is known to act as a vasodilator, whereas oxygen (O(2)) acts as a vasoconstrictor. Therefore, the interpretation of results is difficult. In this study, only the effect of an elevated CO(2) level on retrobulbar hemodynamics and contrast sensitivity was investigated. METHODS: Thirty adults (age 31 +/- 7) were examined under normocapnic and hypercapnic conditions. Colour Doppler imaging was used to measure the velocity in the ophthalmic and central retinal artery. Moreover, contrast sensitivity using the CSV-1000 was investigated. Blood pressure, heart rate and intraocular pressure (IOP) were measured and ocular perfusion was calculated. RESULTS: Under hypercapnia, mean end tidal CO(2) increased from 36.4 mmHg to 42.5 mmHg and blood oxygen saturation increased from 98.3% to 98.6% (p < 0.0001). Hypercapnia significantly reduced IOP by 0.94 mmHg (p < 0.0008). In the central retinal artery, the mean PSV increased by 18% (p < 0.0001) and the mean EDV by 21% (p = 0.0054). In the ophthalmic artery, the mean PSV increased by 13% (p < 0.0001) and the mean EDV by 26% (p = 0.0002). Furthermore, there was a significant increase of contrast sensitivity (spatial frequency: 3cpd: p = 0.0016; 6cpd: p = 0.005; 12cpd: p = 0.0012). Systolic blood pressure (p = 0.0225), mean arterial blood pressure (p = 0.0097) and ocular perfusion pressure (p = 0.0013) increased significantly. CONCLUSION: This setting was able to detect an increase in blood flow velocity in normal subjects under hypercapnia. Furthermore, hypercapnia results in a functional improvement in contrast sensitivity, possible due to the increased blood flow or the increase in blood oxygen levels.
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