Circulatory 1 Flashcards
Poiseuille’s law
Steady laminar flow of Newtonian fluids through uniform cylindrical tubes
Poiseuille’s law is analogous to . . .
Ohm’s law
Equation for Poiseuille’s law
Force = change in pressure / resistance
Flow is directly proportional to . . .
Radius to the fourth and pressure difference
Flow is inversly proportional to . . .
length and viscosity
Resistance is directly proportional to . . .
length and viscosity
Resistance is inversely proportional to . . .
radius to the fourth power
Most important determinants of blood flow in the CV system
Pressure gradient and the radius to the fourth power
Viscosity
“Lack of slipperness”
Shear stress
Resistance to movement between laminae
Shear rate
Relative velocities between laminae
Viscosity equation
Shear stress divided by shear rate
Pressure over velocity
Newtonian fluid
A fluid whose viscosity remains constant over a range of shear rates and shear stress
Non-Newtonian fluid
A fluid whose viscosity changes over a range of shear rates and shear stress
Relationship between viscosity and hematocrit
As hematocrit increases, the viscosity increases (hyperbolic relationship: concave upward)
Axial streaming
Tendency of red blood cells to accumulate in the axial laminae
Plasma skimming
Tendency of smaller vessels to contain relatively more plasma and less red blood cells due to axial streaming
Laminar flow
Fluid moves in parallel concentric layers within a tube
Turbulent flow
Disorderly pattern of fluid movement. Non-laminar
What sounds can turbulent flow cause/ what can they be a cause of?
Murmurs, damage to endothelial lining, thrombi, and Korotkoff sounds
Reynold’s number
Dimensionless number indicating propensity for turbulent blood flow
Determinants of Reynold’s number
Tube diameter, velocity, density, and viscosity
Bernoulli Principle
In a constant flow system, the total energy (potential + kinetic) remains constant
Describe what happens when there is an abrupt decrease in vessel cross-sectional area
Potential energy is converted into kinetic energy. Transmural pressure decreases as the velocity of blood flow increases in a stenotic region
Laplace relationship
wall tension is equal to the pressure multiplied by the wall thickness or radius
Laplace relationship - capillaries
Small radius, low wall tension. Can withstand very large transmural pressures
Arterial vasoconstriction - Laplace relationship
Relatively large wall thickness/lumen diameter ratio; low wall tension. Provides greater control of vessel diameter and blood flow
Aneurysm: Laplace relationship
Lage radius and high wall tension; cannot withstand transmural pressures and therefore will eventually rupture
Dilated heart: Laplace relationship
Large radius, high wall tension, higher afterload. More systolic work, higher oxygen consumption to overcome higher wall tension
Do veins or arteries have a higher cross-sectional area?
Veins
Percentage of blood in veins
60%
Percentage of blood in arteries
18%
