title: Response of choroidal blood flow in the foveal region to hyperoxia and hyperoxia-hypercapnia.
abstract: OBJECTIVE
  Arterial carbon dioxide tension and arterial oxygen tension are important determinants of retinal and cerebral blood flow. In the present study the hypothesis that changes in arterial blood gases also influence choroidal blood flow was tested.
  
  
  METHODS
  The effect of breathing different mixtures of oxygen (O(2)) and carbon dioxide (CO(2)) on choroidal blood flow in the foveal region was investigated in healthy subjects. The study was performed in a randomized, double-masked four way cross-over design in 16 subjects. Using a compact laser Doppler flowmeter, red blood cell velocity (ChBVel), volume (ChBVol), and flow (ChBF) in the choroidal vasculature were measured during the breathing of various mixtures of O(2)and CO(2) (hyperoxia-hypercapnia): 100% O(2), 97%O(2)+3%CO(2), 95%O(2)+5%CO(2) (carbogen) and 92%O(2)+8%CO( 2). Arterial oxygen tension (pO(2)) and carbon dioxide tension (pCO(2)) were measured from arterialized blood samples from the earlobe.
  
  
  RESULTS
  Breathing 100% O(2) had no significant effect on ChBVel (-3.7%), ChBVol (+1.7%) and ChBF (-4.3%). Addition of 3% CO(2) to O(2) also produced no significant change on these blood flow parameters. In contrast, carbogen significantly increased ChBVel (10.0 +/- 4.4%, 95% CI, p < 0.001) and ChBF (12.5 +/- 11.7%, p = 0.002). The effect of 92% O(2) + 8% CO(2) was more pronounced since it significantly increased ChBVel and ChBF by 15.5 +/- 7.5% (p < 0.001) and 16.2 +/- 11.0% (p < 0.001), respectively. None of the gas mixtures induced a significant change in ChBVol. The increase in ChBF was approximately 1.5% per 1 mmHg increase in pCO(2).
  
  
  CONCLUSIONS
  This study demonstrates that, in healthy subjects, pCO(2) is an important determinant of foveal choroidal blood flow, whereas pO(2) has little impact on it.
authors.affiliation: Institute de Recherche en Ophthalmologie, Sion, Switzerland.
authors.forename: M H
authors.initials: MH
authors.lastname: Geiser
authors.forename: C E
authors.initials: CE
authors.lastname: Riva
authors.forename: G T
authors.initials: GT
authors.lastname: Dorner
authors.forename: U
authors.initials: U
authors.lastname: Diermann
authors.forename: A
authors.initials: A
authors.lastname: Luksch
authors.forename: L
authors.initials: L
authors.lastname: Schmetterer
mesh_terms: D000280:Administration, Inhalation; D000328:Adult; D001783:Blood Flow Velocity / Q000187:drug effects; D002245:Carbon Dioxide / Q000097:blood / Q000494:pharmacology; D002829:Choroid / Q000098:blood supply*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004338:Drug Combinations; D004912:Erythrocytes / Q000187:drug effects / Q000502:physiology; D005584:Fovea Centralis / Q000098:blood supply*; D006801:Humans; D006935:Hypercapnia / Q000150:complications* / Q000503:physiopathology*; D018496:Hyperoxia / Q000150:complications* / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000097:blood / Q000494:pharmacology; D010313:Partial Pressure; D012016:Reference Values; D012039:Regional Blood Flow / Q000187:drug effects
chemical_list: D004338:Drug Combinations; D002245:Carbon Dioxide; D010100:Oxygen