Hemodynamics Flashcards
(49 cards)
What is Poiseuille’s Law?
F = (change)P/R
How is blood flow affected by diff variables?
-blood flow is directly proportional to the pressure gradient
(better gradient, better flow)
-blood flow proportional to r^4
(lil increase in diameter increases blood flow dramatically)
-blood flow inversely proportional to resistance
(higher resistance, harder to flow)
-blood flow inversely prop to length and viscosity
(the longer the tube and the thicker the fluid, the slower the blood will flow)
How is resistance affected by diff variables?
proportional to length and viscosity
(cuz the longer the thicker, the higher the resistance)
inversely proportional to r^4
(the bigger the vessel, the lower the resistance)
What is the most important determinant of blood flow/
pressure gradient and r^4
pressure usually constant, so change in radius = major!
What is viscosity?
internal frictional resistance b/w adjacent layers of a fluid
What is a non-Newtonian fluid?
fluid whose viscosity changes over a range of shear rates and shear stress
aka blood! the diff layers [hetero: RBC, proteins etc] have diff velocities (higher in the middle)
so u get parabola!
How does hematocrit affect viscosity?
as hematocrit increases, have higher viscosity
normal: b/w 35-50%
What is anemia?
low hematocrit aka low viscocity
What is polycythemia?
high hematocrit aka high viscosity!
How is blood flow affected by viscosity?
as it slows down, viscosity goes up cuz higher chance of interaction b/w components
What is axial streaming?
RBC accumulate in the middle, line up
What is plasma skimming?
since RBC accumulate in middle, get more plasma to the sides
so this plasma is the one that goes into the smaller vessels
=hematocrit lower in smaller vessels
What is laminar flow?
fluid moves in parallel concentric layers within a tube
parabola!
fastest at middle and slower @ sides
What is turbulent flow?
disorderly pattern of fluid movement
When can you get turbulent flow?
murmurs, damage to endothelial lining (smoking), thrombi, korotkoff sounds
What is Reynold’s number?
indicates propensity for turbulent blood flow
What are the determinants of Rey’s #?
NR = DV/viscosity
the larger the vessel and velocity, the higher the chance
Velocity of blood flow varies inversely with cross sectional area.
What does that mean?
the smaller the vessel, the faster it goes
the larger the vessel or the larger the total cross sectional area, the slower the blood will flow (e.g. capillaries)
What is the Bernoulli principle?
in a constant flow system, the total energy remains constant
What happens to the flow when there is an abrupt decrease in cross sectional area?
potential energy (pressure) is converted to kinetic energy (flow) so! the velocity of blood increases
How do you explain blood flowing from lower to higher pressure after stenoic region??
blood flows from a higher to a lower total energy
-total energy continuously decreases
What is the Laplace relationship?
Tension = Pressure x Radius / wall thickness
How does Laplace explain why aneurisms rupture?
@ the aneurysm there is a buldge
-bigger radius!
-thinner wall! (cuz stretching)
-higher are so blood slows down => higher potential energy! (lateral P)
all those add up to a higher tension so distends a lil more
+ feedback
how do you explain that capillaries don’t rupture when jump too hard?
They have small radius so low tension: can withstand large pressures ^^
