Multiple different laminar velocity profiles in separate veins in the microvascular network of brain cortex in rats.

The orthogonal polarisation spectral (OPS) imaging technique is a method that enables intravital microscopy of the tissue microvasculature particularly including the erythrocytes and leucocytes. As a new finding we here report multi flow, i.e, several different laminar velocity profiles in each and separate veins (diameters < 200 μm) of the microcirculation of the rat brain cortex. The phenomenon was present in all 20 preparations studied and these different laminar velocity profiles were regularly maintained in length beyond 20 times the diameter of parent vessel. In single veins up to 9 different laminar velocity profiles were discernible, each with a different red blood cell velocity. These multi flow profiles may theoretically be anticipated based on what is known in rheological physiology as the Fahreus - Lindqvist effect. It may also be predicted in tissues that have both high and heterogeneous blood flows in conjunction with large local variations in metabolic activity as are present in the cortex of the brain. The new information is that the extent and magnitude of this multi laminar flow phenomenon especially in the venular network of the brain exceeds what has previously been known. The physiological importance of these finding warrants further studies.