Retinal and Cerebral Oxygenation Response to Graded Hypoxia

Abstract

Purpose: To determine whether major retinal vessel oxygen saturation (SO2) and frontal cortex tissue oxygenation (StO2) changes with controlled manipulation of inhaled oxygen (ETO2) occur alongside one another.

Methods: Non-invasive hyperspectral retinal imaging (Photon HRC, Photon etc, QC, Canada) and cortical near-infrared spectroscopy (FORE-SIGHT™ Cerebral Oximeter, CasMed, CT, USA) measurements were acquired in 11 healthy volunteers (29±4 yrs, 8M). Continuous readings were acquired during normoxia and graded hypoxic conditions (i.e., end-tidal [ET] O2 80mmHg, 60mmHg and 50mmHg), whilst end-tidal CO2 tensions were stabilized at homeostatic baseline values, using a computer-controlled sequential gas blender system (RespirAct™, Thornhill Research, ON, Canada).

Results: There was a marked decrease in retinal artery SO2 (Friedman analysis; p=0.006) and cerebral StO2 (p=0.001) during hypoxia which was most pronounced during ETO2 50mmHg (95±8% vs. 77±10% and 70±3% vs. 61±3%).

Conclusions: This novel preliminary study demonstrated a significant decrease in SO2 and StO2 of healthy individuals that occur concurrently during controlled isocapnic hypoxia.

Keywords: 548 hypoxia • 688 retina • 550 imaging/image analysis: clinical