Rheology is the study of the deformation and flow of matter under the influence of an applied stress. The term was coined by Eugene Bingham, a professor at Lehigh University, in 1920, from a suggestion by a colleague, Markus Reiner. The term was inspired by Heraclitus's famous expression panta rei, "everything flows".
In practice, rheology is principally concerned with extending the "classical" disciplines of elasticity and (Newtonian) fluid mechanics to materials whose mechanical behaviour cannot be described with the classical theories. It is also concerned with establishing predictions for mechanical behaviour (on the continuum mechanical scale) based on the micro- or nanostructure of the material, e.g. the molecular size and architecture of polymers in solution or the particle size distribution in a solid suspension.
Rheology unites the seemingly unrelated fields of plasticity and non-Newtonian fluids by recognising that both these types of materials are unable to support a shear stress in static equilibrium. In this sense, a plastic solid is a fluid. Granular rheology refers to the continuum mechanical description of granular materials.
One of the tasks of rheology is to empirically establish the relationships between deformations and stresses, respectively their derivatives by adequate measurements. These experimental techniques are known as rheometry. Such relationships are then amenable to mathematical treatment by the established methods of continuum mechanics.
ABO polymorphism and effect on blood rheology
ABO blood group is one of the most significant polymorphic influences on blood haemorrheology (clotting and viscosity). ()
Associations between the ABO phenotype and variations in blood rheology have been also reported in high blood pressure (), stress, diabetes (), heart attack, cancer and thyroid disease, kidney failure () and malignant melanoma (). Virtually all have shown greater coagulation in blood group A versus other groups.()
There is evidence that the rheology of blood may play a role in a variety of chronic anxiety states. When compared to normal subjects, chronic depressive () and schizoid patients had very significant differences in their blood rheology and in the ability of their red blood cells to aggregate. When patients having schizoid anxiety were compared to those having depressive anxiety, their ratio of albumin to globulin was increased. When patients were divided according to their ABO blood groups, significant differences were found in their albumin to fibrinogen ratio and their blood viscosity. This was particularly true for women who were type A and who suffered from depressive anxiety: their blood tended to be substantially ‘thicker’ and have higher amounts of serum proteins in it than women with similar depression who were blood type O. ()