APK 2105C Lecture Notes - Lecture 31: Vascular Resistance, Hemorheology, Vasoconstriction
16 Jun 2018
School
Department
Course
Professor
Chapter 14, Part 2
Vessels & Blood Pressure
• Resistance in the CV system
o Resistance of individual vessels depends on
▪ Physical dimensions of tube
• Lots of branches in the “tubes” through the body
▪ Properties of the fluid
• Viscosity
o Factors impacting resistance
▪ Vessel radius = NUMBER ONE factor in impacting resistance
• Vasoconstriction
• Vasodilation
▪ Vessel length
• Longer vessels = far more resistance
• Not a factor in the body—vessels don’t just get longer instead in
periods of growth
▪ Blood viscosity
• Thicker blood = more resistance
• Determined by cell/protein conc
• Not normally factor in the body
o Poiseuille’s Law
▪ Fluid flowing through a tube encounters resistance from the walls of the
tube and the fluid itself
▪ Resistance = (8Ln)/(pi r^4)
• L = length of tube
• n = viscosity of fluid
• r = internal radius
o r is to ^4
▪ As r decreases, it impacts resistance to the ^4—
very big impact
▪ If radius is decreased by 1/2, resistance increases
16 fold
▪ Biggest impact on resistance
• L and n are directly proportional to resistance
o Total peripheral resistance (TPR) = combines resistances of all the vessels in the
network
▪ Vasoconstriction and dilation ANYWHERE changes the TOTAL
resistance of the network of vessels
▪ Flow = pressure gradient / resistance
▪ CO = MAP (mean arterial pressure) / TPR
• May need to be rearranged
• Refers to CO to a specific location/organ
find more resources at oneclass.com
find more resources at oneclass.com
