Microcirculation Laboratory Site Menu
Microcirculation Factor: Shear Rate
As pressure gradients are reduced, as for example with onset of a low flow state such as shock, flow slows down.
With reductions in upstream to downstream pressure drop flow falls in a nonlinear manner. At very low pressure gradients, flow stops completely. The apparent viscosity of the blood rises as mean velocity falls (lower panel).
As shear rates are reduces, the number of WBCs adhering to the walls of postcapillary venules increases greatly. Shown above is the number of WBCs that are firmly adhered to the endothelium of postcapillary venules as flow is mechanically reduced by compressing the feeding vessel upstream and the endothelium is made "sticky" with fMLP.