title: Retrobulbar haemodynamics and contrast sensitivity improvements after CO2 breathing.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Ophthalmology, Rheinisch Westfaelische Technische Hochschule Aachen University, Germany. khuber@ukaachen.de
authors.forename: Klaudia K
authors.initials: KK
authors.lastname: Huber
authors.forename: Herbert
authors.initials: H
authors.lastname: Adams
authors.forename: Andreas
authors.initials: A
authors.lastname: Remky
authors.forename: Kay O
authors.initials: KO
authors.lastname: Arend
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D001794:Blood Pressure / Q000502:physiology; D002245:Carbon Dioxide / Q000008:administration & dosage*; D015350:Contrast Sensitivity / Q000502:physiology*; D005123:Eye / Q000098:blood supply*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D007429:Intraocular Pressure / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009880:Ophthalmic Artery / Q000502:physiology*; D010100:Oxygen / Q000097:blood; D011446:Prospective Studies; D012161:Retinal Artery / Q000502:physiology*; D018615:Ultrasonography, Doppler, Color; D014664:Vasodilation / Q000502:physiology
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen