The relationship between resistance, blood vessel diameter, and blood viscosity is expressed by the Poiseuille equation (R=8nl/πr4), with resistance (R), viscosity of blood(n), length of blood vessel (l), and radius of blood vessel raised to the fourth power (r4). Resistance to flow is directly proportional to blood viscosity and vessel length, and inversely related to the fourth power of the radius of the blood vessel. Resistance can be series, the sum of resistance of blood vessels within an organ, or parallel, the sum total resistance among the various major arteries branching off the aorta. When blood flow is distributed through parallel resistances, the flow through each organ is a fraction of the total blood flow.
- "Medical Physiology" Elsevier (2016)
- "Physiology" Elsevier (2017)
- "Principles of Anatomy and Physiology" Wiley (2014)
- "Rheology" Biology and Mechanics of Blood Flows, Part II: Mechanics and Medical Aspects. Springer. pp. 119–123 (2007)
- "Human Anatomy & Physiology" Pearson (2018)