L14 Circulation- Hemodynamics Flashcards
Explain Poiseuille’s law.
Applies to laminar flow of Newtonian fluids through uniform cylindrical tubes (blood is non-Newtonian and circulatory system isn’t uniform)
- Flow is direction proportional to pressure gradient and inversely proportional to resistance
- Flow is also directly proportional to radius^4= diameter double give flow increase by 16
How does Poiseuille’s law relate to blood flow?
It puts flow in relationship to resistance, pressure gradient and radius of vessel
How does Poiseuille’s law related to BP?
Flow is directly proportional to pressure gradient
How does Poiseuille’s law related to resistance?
Flow is indirectly proportional to resistance
Define viscosity.
Internal frictional resistance between adjacent layers of fluid
-viscosity= shear stress/ shear rate (pressure/velocity)
How does viscosity change with vessel diameter?
Increasing vessel diameter increases viscosity b/c of increase in hematocrit
How does hematocrit change viscosity?
Increase in hematocrit= increase in viscosity
How does hematocrit change with vessel diameter?
Hematocrit is lesser in smaller vessels than in larger b/c of plasma skimming and axial streaming
Define laminar blood flow.
Fluid moves in parallel concentric layers within a tube
-Laminar flow is silent
Define turbulent blood flow.
Fluid moves in a disorderly pattern
- Murmurs, bruit, thrombi
- Korotkoff sounds- based on changes in V of blood flow
Define Reynold’s number.
Dimensionless number indicating propensity of turbulent blood flow
- Higher Reynold’s number= greater chance for turbulent blood flow
- N(R)= (density x Diameter x velocity)/ viscosity
- Larger diameter = higher chance for turbulence (aorta, smokers)
Define Bernoulli’s principle.
In a constant flow system, total energy (potential + kinetic) remains constant
- Energy conserved by velocity of flow (kinetic) or lateral pressure (potential)
- Total energy (E)= potential energy (P) + velocity of blood flow (pv^2 / 2)
- When velocity of blood flow increases, lateral pressure decreases
How does Bernoulli’s apply to the circulation system?
- Blood flow moves from higher to lower total energy, not from higher to lower pressure
- Abrupt decreases in vessel size (stenosis) converts potential energy into kinetic= lateral pressure decreases and velocity of blood flow increases
Define the Laplace relationship.
Wall Tension= Pressure x Radius / Wall Thickness
How does wall tension affect fxn of dilated hearts?
Large radius= high wall tension, more systolic work/higher oxygen consumption to overcome tension
-High wall tension opposes shortening