Blood Flow Pressure/Resistance Flashcards
What major factors affect Blood flow and pressure?
- Cardiac Output
- Compliance
- Volume
- Resistance
- Vessel Length
- Vessel Diameter
Define Perfusion.
∆P along a vessel access.
Pressure difference upstream to
downstream. Pressure loss.
Compare Laminar and Turbulent flow?
Laminar Flow: Fluid elements in any given lamina remain in that lamina as fluid moves longitudinally along the tube.
Turbulent: Fluid elements in any given lamina remain in that lamina as fluid moves longitudinally along the tube.
What is Reynolds numb Er, and how is it calculated?
- Ratio of inertial to viscous forces for a fluid flowing through a cylinder
- Determines laminar vs Turbulent flow
- N = pDv/n
- > 3000 turbulent
- <2000 laminar
Murmur
when turbulence occurs in the heart
Bruit
when turbulence occurs in the vessel.
What is Shear Stress?
As blood flows through a vessel, it exerts a force on the vessel wall
parallel to the wall.
What is the Two plates model of Viscosity?
provides there are two
plates with fluid in-between.
• Two criteria: 1. fluid does not glide along but is in contact. An
adhesive force operates between fluid + plates. 2. flow is laminar. Thin layers + no turbulence
• Lower plate does not move + upper plate drifts aside
How are Velocity and Flow of a fluid related in a rigid tube?
V = Q/A (A = SA)
What is the determining factor for how erythrocytes flow in vessels?
- Flexibility of RBCs
- At low flow rates like in microcirculation rigid particles do not migrate toward the central axis of a tube and flexible
particles do.
How are viscosity and shear rate related?
apparent viscosity of blood diminishes as the
shear rate is increased
How does Fibrinogen affect flow?
- Large plasma protein
- High fibrinogen causes aggregation —> more viscous blood —> change in flow
What law is used to determine flow of a fluid through cylindrical tube?
- Poiseulle’s law
- Q = piPr^4 / 8nl
What are the two categories of superficial stress to blood vessels?
Circumferential: due to pulse pressure variation inside the vessel. Intravascular hydrostatic pressure produces not only
circumferential but also normal tensions
Shear Stress: Due to blood flow
What are major vasodilators and vasoconstrictors?
Vasodilators:
- Low O2, High CO2, INC metabolic acids, High NO, High L, High H+
- Inflammation
- INC blood flow
- relaxed precapilary sphincters
Vasoconstrictors:
- Prostaglandins; Activated platelets; Leukocytes, endothelium
- Cinricted precapilary sphincters
- DEC blood flow