Hemodynamics Flashcards
What is Poiseuille’s Law?
analogous to Ohm’s Law
F = (P1-P2)/R
What are the most important determinants of blood flow in the cardiovascular system?
Which of those are most dynamic?
pressure gradient and radius to the FOURTH power
radius (pressure is relatively constant)
If the left and right ventricle generate the same cardiac output, why does the left ventricle create such a massive flow?
RESISTANCE
What is the definition of Shear Stress?
the resistance to movement between laminae (pressure)
What is the definition of Shear Rate?
the relative velocities between laminae (velocity of blood flow)
What is the definition of viscosity?
Shear Stress/ Shear Rate
aka pressure/ velocity
What is a Newtonian fluid and how does it differ from a non-Newtonian fluid?
a Newtonian fluid’s viscosity remains constant over a range of shear stresses and rates while a non-Newtonian fluid’s viscosity changes
Newtonian: homogenous
non-Newtonian: heterogenous
What is the relationship between hematocrit and viscosity?
directly proportional (as hematocrit increases, so does viscosity)
What are 2 effects of vessel diameter on viscosity:hematocrit ratio?
1) axial streaming
2) plasma skimming
What occurs in axial streaming?
RBCs accumulate in axial laminae
What does plasma skimming mean?
describes the tendency of smaller vessels to contain relatively more plasma and less RBCs due to axial streaming
Hematocrit is typically _______ in smaller vessels compared to larger vessels
LOWER
Viscosity is typically ______ in smaller vessels
LOWER
Why is there MORE plasma in smaller vessels?
axial streaming
Why is the hematocrit LOWER in smaller vessels?
plasma skimming
What are 4 clinical scenarios with turbulent flow?
1) murmurs
2) damage to endothelial lining
3) thrombi
4) Korotkoff sounds (not pathological)
What does Reynold’s number indicate?
the propensity for turbulent flow
What 4 factors influence Reynold’s number?
1) Diameter of tube
2) velocity
3) density
4) viscosity
What is the only factor related to Reynold’s number that varies inversely?
viscosity
lower viscosity, higher Reynold’s number (larger propensity for turbulence
Propensity for turbulence (Reynold’s number) increases with increasing _______, ________, and ________
diameter, velocity, and density
Blood flow _____(slows down/speeds up) as it moves further from the heart?
slows down
cross sectional area gets larger even though individual vessels are smaller
With regards to blood flow, total energy only remains constant in a……
constant flow system
What happens to total energy in a stenotic region?
It is increases (because KE component is significantly higher than in downstream segment)
With respect to blood flow, what is kinetic energy defined as?
velocity of blood flow
What is potential energy defined as?
transmural (lateral) pressure
What is the formula for the LaPlace relationship?
Wall Tension = (Pressure x Radius)/ Wall Thickness
How can capillaries withstand large transmural pressures? (like jumping off of a ledge?)
because their small radius generates a low wall tension
Why are aneurysms dangerous?
They have a HIGH wall tension because of a large radius
For resistance in series, the total resistance of the entire system equals the ____________________
sum of the individual resistances
For resistance in parallel, the total resistance of the entire system is (reduced/increased)
reduced (why resistance is lower through capillary beds)
Where is resistance the largest?
arterioles
As blood moves further and further away from the heart, what happens to resistance of the vessel?
increases
Where is the largest drop in arterial pressure?
across the arterioles (right before the capillaries)
What happens to blood pressure as you move further and further from the heart?
Diastolic decreases
Systolic increases
Which has higher compliance, veins or arteries?
veins
arteries are stiff
Which vessel has the closest to a 1:1 ratio on cross-sectional area and blood volume?
veins
(capillaries have a huge cross sectional area but do not hold a lot of blood; arteries hold more blood than they have cross sectional area)
