Physical properties of flowing blood

Abstract

The viscosity and electrical resistivity changes of blood due to the flow are dependent on the orientation and deformation of red cells. From an electrical point of view, it can be assumed that blood is a suspension of small insulating particles (red cells) in conducting fluid (plasma) when the frequency of supplied voltage is lower than several hundreds kHz. When blood flows, red cells deform and orient in the flow direction. Therefore, flowing blood shows anisotropic resistivity. In the steady flow, blood resistivity longitudinal to flow decreases with the flow rate, and transverse one increase. Blood flow in living body is not steady but pulsatile. We measured both longitudinal and transverse resistivity change and viscosity change of sinusoidally flowing blood in a rectangular conduit.
The results are 1) during one period of flow the direction of longitudinal resistivity change is opposite to that of transverse one, and 2) minimum points of both longitudinal resistivity and viscosity changes during one period do not occur at the moment when flow is being zero but are delayed.
In case of amplitude of sinusoidal flow is small and oscillation frequency is high, the phase difference between the zero crossing period of flow and the priod of minimum change of resistivity, increases up to 90°. Viscosity of blood decreases with increase of amplitude of sinusoidal flow and increase of oscillation frequency