On-line measurement of the dynamic velocity of erythrocytes in the cerebral microvessels in the rat

Velocity-diameter relationships of the microcirculation

An analytical expression for the relationship between velocity (and blood flow) and diameter for vessels in the microcirculatory range up to 900 mum diameter is presented. Both the arterial and venous systems are considered. The analytical expression for these relationships has been derived from computer analysis of data obtained from individual measurements reported in the literature. Computer analysis shows that blood velocity is a nearly linear function of diameter of blood vessels for the arteriolar tree. The relationship for blood flow as a function of diameter is Q = 108d3.101 for arteries, arterioles and capillaries in the diameter range 5 to 900 mum and for the venous system in the range 5 to 115 mum is Q = 334d2.388 where Q is in mum3 per second and d is in mum. Comparison of the results of this study for the arterial system to the Hagen-Poiseuille Law reveals close agreement, if correction is made for geometric factors of blood vessels and for the variation of viscosity with diameter for blood.

Hepatic sinusoidal responses to intraportal injections of phenylephrine and isoprenaline in the rat

1. Specific alpha- and beta-adrenoreceptor agonists, phenylephrine and isoprenaline, were injected intraportally into the intact rat liver under direct microscopic observation by an in vivo transillumination technique. 2. The diameter of a hepatic sinusoid and the intra-sinusoidal erythrocyte velocity were quantitatively measured, and the sinusoidal volume flow was calculated from these two parameters. 3. Results show that phenylephrine causes a sinusoidal constriction and an increased sinusoidal blood flow, whereas isoprenaline causes the opposite effects on the sinusoids. 4. All the sinusoidal responses to phenylephrine and isoprenaline were dose-dependent and were possibly related to the direct effect of these drugs on the sinusoids.