One major factor influencing blood viscosity is hematocrit. You may be interested in using the analogy of ketchup outlined a few months ago in my article for students Blood viscosity and peripheral resistance at theAPstudent.org
Recently, researchers also looked at the viscosity of the blood plasma alone (without the formed elements). They found that blood plasma has unique characteristics of flow found only in non-Newtonian fluids, becoming less viscous with increasing pressure. Again, just like ketchup. Plasma, unlike plain water, exhibits both viscous and elastic behaviors.
Researchers found in recent experiments that this characteristic of plasma may promote swirling where blood vessels diameters change—both at the beginning and end of a narrowed segment. Thus, this could have an effect on formation of clots at stenoses or where a stent has been placed.
So, as you may have suspected all along, blood is not only thicker than water—it's weirder than water.
Want to know more?
- Blood viscosity and peripheral resistance
- Kevin Patton
- The A&P Student 12 September 2012
- [Analogy of ketchup flow for students. Includes video.]
- Blood Is Thicker Than Water – And Blood Plasma Is, Too
- Science Daily Feb. 18, 2013
- [Brief, plain-language article outlining the recent research.]
- Rheology of human blood plasma: Viscoelastic versus Newtonian behavior.
- M. Brust, et al.
- Phys. Rev. Lett, 110, 078305 (2013) DOI: 10.1103/PhysRevLett.110.078305
- [Original journal article. See photos from the experiments below.]
Photo: Christof Schaefer, Phys. Rev. Lett. 110, 2013, 078305th Copyright (2013) by the American Physical Society
Photo: Mathias chest, Phys. Rev. Lett. 110, 2013, 078305th Copyright (2013) by the American Physical Society