Laser Doppler Velocimetry study of the effect of pure oxygen breathing on retinal blood flow

The noninvasive Laser Doppler Velocimetry (LDV) technique was used in normal volunteers to determine retinal blood flow, F, during pure oxygen breathing at atmospheric pressure. Changes in blood flow were calculated based on Poiseuille relation, F = (pi D2/4) X Vmax, where Vmax is the red blood cell maximum or center-line velocity and D, the diameter of the vessel at the site of the LDV recordings. After five minutes of pure oxygen breathing, Vmax decreased by about 53%, vessel diameter by 12%, and retinal blood flow by about 60%. In arteries, pulsatility of red blood cell velocity (Vmax, systole/Vmax, diastole) during the cardiac cycle increased by about 10%. Decrease in red blood cell velocity was detectable within 1-1 1/2 min. From these LDV flow measurements and the changes in retinal mean circulation time (MCT) reported by other investigators, based on the relation F = v/MCT, a 45% decrease in retinal blood volume (v) during 100% O2 breathing was obtained.