Wall shear stress quantification in the human conjunctival pre-capillary arterioles in vivo.

Blood volume flow (Q), wall shear rate (WSR) and wall shear stress (WSS) were quantified, for the first time, in the conjunctival pre-capillary arterioles of normal human volunteers with diameters (D) between 6 and 12 μm. The variation of the blood velocity throughout the cardiac cycle was taken into account using high speed video microcinematography. The dual effect of arteriolar diameter, firstly on the WSR and secondly on the dynamic viscosity of blood, was taken into account in the estimation of WSS. The average Q, WSR and WSS, throughout the cardiac cycle ranged from 13 to 202 pl/s, 587 to 3515 s(-1) and 1.7 to 21.1 N/m(2) respectively. The best fit power law equations, giving the increase of Q and the decrease of WSR and WSS with diameter, are presented for the systolic and diastolic phase as well as for the averages throughout the cardiac cycle. According to the WSS best fit equation, the average WSS decreases from 10.5 N/m(2) at D=6 μm down to 2.1 N/m(2) at D=12 μm.