Retrobulbar haemodynamics and contrast sensitivity improvements after CO₂ breathing

Abstract

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 ¼ 0.0054). In the ophthalmic artery, the mean PSV increased by 13% (p < 0.0001) and the mean EDV by 26% (p ¼ 0.0002). Furthermore, there was a significant increase of contrast sensitivity (spatial frequency: 3cpd: p ¼ 0.0016; 6cpd: p ¼ 0.005; 12cpd: p ¼ 0.0012). Systolic blood pressure (p ¼ 0.0225), mean arterial blood pressure (p ¼ 0.0097) and ocular perfusion pressure (p ¼ 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.

Farbduplexsonographie der retrobulbären Gefäße und Hyperkapnie bei Normaldruckglaukom

“…ophthalmica und centralis retinae wurden mithilfe der Farbduplexsonographie ( Der experimentelle Aufbau zur Durchführung der CO 2 -Provokation zur Erhö-hung des endexspiratorischen pCO 2 ist bereits mehrfach publiziert [16,17,18,21]. Alle Untersuchungen unter Normokapnie und unter Hyperkapnie wurden in derselben Reihenfolge am selben Tag durchgeführt.…”

“…Bei Gesunden führt eine CO 2 -Provokation zu einem Anstieg von Blutflussparametern am Sehnerv, in der Netzhaut und in der Choroidea [11,12,13,14,15]. Des Weiteren wurde über einen Anstieg der retrobulbären Blutfließge-schwindigkeiten unter Hyperkapnie berichtet [16,17]. Diese Veränderungen wurden aufgrund einer Reduktion des peripheren Gefäßwiderstands unter CO 2 -Provokation als Hinweis auf einen vermehrten Blutfluss der jeweiligen Gefäß-abschnitte interpretiert.…”

“…centralis retinae und ophthalmica von Gesunden bei Hyperkapnie signifikant erhöht [17]. Andere Studien mit kleineren Kohorten haben jedoch auch über ausbleibende Effekte der CO 2 -Inhalation auf die retrobulbären Fließgeschwindig-keiten bei Gesunden berichtet [14,22].…”

“…Ein Anstieg der Blutdrucks, der Respirationsrate und ein Abfall des IOD sind bekannte Reaktionen auf eine CO 2 -Inhalation [10,16,17,29].…”

Blood flow in non-muscle tissues and organs during exercise: Nature of splanchnic and ocular circulation

“…Increases in ocular blood flow induced by either inhalation of high concentrations of CO2 or administration of sildenafil was shown to improve static visual acuity and contrast sensitivity 53,54) . In addition, an increase in the retrobulbar circulation -which supplies blood to the ocular circulation -by CO2 inhalation, was associated with improved contrast sensitivity 55) . Nevertheless, the effects of acute changes in ocular blood flow on visual function have yet to be established, in part because these changes in ocular flow are also associated with changes in cerebral blood flow, which is strongly related to brain function, including visual information processing 53) .…”