Velocity pulse measurements in the mesenteric arterioles of rabbits

The axial red blood cell velocity pulse was quantified throughout its period by a high-speed video microscopy method, using images of erythrocytes moving near the microvessel axis. In 10 mesenteric precapillary arterioles (8 to 12 microm in diameter) from six rabbits, axial velocities ranged from 0.46 (the minimum of all the end diastolic values) to 4.8 mm s(-1) (the maximum of all the peak systolic values). With the velocity pulse shape properly quantified, a correct estimation of the average velocity over time can be made and hence, appropriate quantification of blood flow. Average velocity ranged between 1.14 mm s(-1) (8 microm arterioles) and 1.98 mm s(-1) (9 microm arterioles). Also, with the velocity pulse shape known, an estimation of the magnitude of the pulsation can be made by introducing Pourcelot's resistive index (RI) in the microvascular haemodynamics (diameter less than 15 microm). The results of this study reveal that RI in the precapillary arterioles is quite high ranging between 0.56 (8 microm arterioles) and 0.74 (12 microm arterioles). Observing the velocity pulse diagrams in different diameters, quantitative information is obtained for the first time on how the velocity pulse shape flattens as it proceeds to the capillary bed.