Abstract
Laser Doppler velocimetry (LDV) is a technique which can be applied to determine the maximum velocity, V max, of red blood cells (RBCs) in retinal arteries. Under conditions of constant flow, the flow rate can be accurately derived from V max and the vessel diameter through the assumption of a parabolic velocity profile. Our in vitro study of pulsatile flow evaluated the validity of integrating the instantaneous LDV-measured V max over the flow cycle to derive a mean flow rate. Measurements were made on suspensions of polystyrene spheres in water and RBCs in physiological saline perfusing glass capillary tubes (70–200 μm diameter) at velocities in the range of retinal artery blood velocities. The LDV-determined flow rate differed from an independently measured flow rate by less than 1% for the spheres and by less than 12% for the RBCs. Whether the velocity profile of blood remains parabolic at every phase of the flow cycle, as is the case for the spheres in water, cannot be concluded from this study.
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