Hypoxic, Hypercapnic, And Hyperoxic Responses Of The Optic Nerve Head And Subfoveal Choroid Blood Flow In Healthy Humans

PURPOSE. To investigate the impact of different gas mixtures (hyperoxia, hypoxia, and hypercapnia) on the optic nerve head (ONH) and choroidal (Ch) hemodynamics.METNODS. Twenty-three healthy subjects (28 +/- 6 years) took part in the study. Variations in inspired oxygen and carbon dioxide fraction were produced by a gas mixing device. Arterial oxygen saturation (SpO(2)) was measured continuously using a transcutaneous sensor and endtidal carbon dioxide partial pressure by capnography. The experiment comprised three successive periods: 3-minute baseline (room air breathing), 15-minute gas mixture inhalation (normocapnic hypoxia, hypercapnia, or hyperoxia), and 15-minute recovery (room air breathing). Laser Doppler flowmeter parameters-velocity (VEL), volume (VOL), and flow (BF) of red blood cells-were measured. Two-way ANOVAs were performed for statistical analysis.RESUTS. In response to hyperoxia, ONHBF significantly decreased by -18% +/- 6% (P = 0.04) from baseline, due to significant changes in VEL (-12% +/- 3% P = 0.0002). During hypoxia at 85% SpO(2) ONH VEL increased by + 12% +/- 3% (P = 0.0009), whereas VOL and BF did not change significantly. ChBF significantly increased by +7% +/- 2% (P = 0.004) in response to hypoxia, due to significant changes in VEL + 5% +/- 2% (P = 0.03). Both Ch and ONHBFs did not vary significantly in response to hypercapnia.CONCLUSIONS. The magnitude of the blood flow response is the most significant during hyperoxia for ONH and hypoxia for ChBE For ONHBF, a 37% difference between hyperoxia and hypoxia can be useful when vasoreactivity to O-2 will be tested in patients.