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Hélène Kergoat, Caroline Faucher; Effects of Oxygen and Carbogen Breathing on Choroidal Hemodynamics in Humans. Invest. Ophthalmol. Vis. Sci. 1999;40(12):2906-2911.
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purpose. Previous studies in humans have demonstrated that oxygen
(O2) reduces retinal vessel caliber and blood flow, whereas
carbon dioxide (CO2) usually has opposite effects. The
influence of O2 and CO2 on choroidal
circulation is not fully understood, however. This study was conducted
to determine the effects of systemic hyperoxia and hypercapnia on
global choroidal hemodynamics, as evaluated by pulsatile ocular blood
flow (POBF) tonography.
methods. In this experiment, 16 and 22 healthy volunteers breathed 100%
O2 and carbogen, respectively. POBF and intraocular
pressure (IOP) were measured twice with a UK OBF tonograph for each of
the following conditions: in ambient room air breathing, after
breathing pure O2 or carbogen through a face mask, and in
ambient room air 10 minutes after mask removal. Heart rate (HR),
hemoglobin oxygen saturation level (SaO2), and systemic
arterial blood pressure (BP) were monitored throughout testing. The
end-tidal CO2 (EtCO2) level and respiratory
rate (RR) were also recorded during carbogen breathing.
results. Results revealed that HR was reduced (P < 0.004)
and SaO2 was increased (P = 0.0001) by
both oxygen and carbogen breathing. Systemic arterial BP remained
stable throughout the experiment. EtCO2 was increased
during carbogen breathing (P = 0.0001), whereas RR
was reduced (P = 0.0175). IOP was significantly
decreased during both phases of the experiment (P =
0.0001). Finally, POBF was not altered by pure O2 breathing, but it increased on average by 7.7% during carbogen
breathing (P = 0.0222).
conclusions. The data obtained with POBF tonography indicate that the choroid reacts
to increased blood CO2 concentration, but not to systemic
hyperoxia, in a manner similar to that in retinal and brain
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