title: Evaluation of the Effect of Hypercapnia on Vascular Function in Normal Tension Glaucoma.
abstract: BACKGROUND
  Altered ocular perfusion and vascular dysregulation have been reported in glaucoma. The aim of this paper was to evaluate the vascular response to a hypercapnic stimulus.
  
  
  METHODS
  Twenty normal tension glaucoma (NTG) patients and eighteen age- and gender-matched controls had pulsatile ocular blood flow (POBF) measurements, systemic cardiovascular assessment, and laser Doppler digital blood flow (DBF) assessed. Measurements were taken at baseline, after 10-minutes rest, in the stable sitting and supine positions and following induction and stabilization of hypercapnia, which induced a 15% increase in end-tidal pCO2. The POBF response to hypercapnia was divided into high (>20%) and low responders (<20%).
  
  
  RESULTS
  65% of NTG patients had a greater than 41% increase in POBF following CO2 rebreathing (high responders). These high responders had a lower baseline POBF, lower baseline DBF, and a greater DBF response to thermal stimulus.
  
  
  CONCLUSIONS
  NTG patients that have a greater than 20% increase in POBF after a hypercapnic stimulus have lower baseline POBF and DBF values. This suggests that there is impaired regulation of blood flow in a significant subgroup of NTG patients. This observation may reflect a generalised dysfunction of the vascular endothelium.
authors.affiliation: UCD School of Medicine and Medical Science, University College Dublin, Belfield, Dublin, Ireland.
authors.forename: B
authors.initials: B
authors.lastname: Quill
authors.affiliation: Princess Alexandra Eye Pavilion, Edinburgh, UK.
authors.forename: E
authors.initials: E
authors.lastname: Henry
authors.affiliation: Princess Alexandra Eye Pavilion, Edinburgh, UK.
authors.forename: E
authors.initials: E
authors.lastname: Simon
authors.affiliation: UCD School of Medicine and Medical Science, University College Dublin, Belfield, Dublin, Ireland.
authors.forename: C J
authors.initials: CJ
authors.lastname: O'Brien
mesh_terms: D001783:Blood Flow Velocity / Q000502:physiology; D016022:Case-Control Studies; D005123:Eye / Q000503:physiopathology; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D007429:Intraocular Pressure / Q000502:physiology; D057066:Low Tension Glaucoma / Q000097:blood* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D011673:Pulsatile Flow / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology