Circulation Resistance to flow Guyton Chapter 1.2

1. Resistance to Flow
Dr. Sara Sadiq
(MBBS, M.Phil)

2. Surprise Test
1. What are the factors affecting
hemodynamics?
2. What are different types of blood
flow?

3. Factors Affecting Hemodynamics
1. Velocity of blood flow (Viscosity)
2. Size of blood vessel
3. Resistance
4. Elasticity of muscular layer (tunica media)

4. Resistance

5. Vascular Resistance
• Friction between blood and the walls of blood
vessels: resists to blood flow

6. • Vascular resistance depends on
three factors:
(1) Size of the blood vessels
(2) Blood viscosity
(3) Total blood vessels length

7. What Determines Resistance in the
Vessels?
• Poiseuille’s Law relates these factors to resistance:
• R  Lη/r4
• if the tube length increases, resistance increases
• if the viscosity increases, resistance increases
• if the tube’s radius increases, resistance decreases

9. Shear
• Is a consequence of the fact that
blood travel at different velocities
within a blood vessel.
• Velocity of blood is zero at the wall
and highest at the center of the
vessel
• So shear is highest at the wall where
the difference in blood velocity is
greatest and lowest at the center of
the vessel where blood velocity is
constant.

10. Thank You