The evolution of the meaning of blood hyperviscosity in cardiovascular physiopathology: should we reinterpret Poiseuille?

In the 1960s and 1970s, a number of researchers (including ourselves) involved in the study of cardiovascular pathophysiology and particularly in the development of techniques to quantify blood flow, came across the observation that, along with vessel diameter, also blood viscosity plays an important role not only in theory but also in practice. Until then, viscosity was thought to play only a marginal role in determining blood flow, a concept which was based on the 1828 theories of Jean Louis Marie Poiseuille (Fig. 1, and [1]).1 In his well-known formula, named after its fathers Hagen2 and Poiseuille,