Hemodynamics

Question 1

What is Poiseuille’s Law?

Answer 1

analogous to Ohm’s Law

F = (P1-P2)/R

Question 2

What are the most important determinants of blood flow in the cardiovascular system?

Which of those are most dynamic?

Answer 2

pressure gradient and radius to the FOURTH power

radius (pressure is relatively constant)

Question 3

If the left and right ventricle generate the same cardiac output, why does the left ventricle create such a massive flow?

Answer 3

RESISTANCE

Question 4

What is the definition of Shear Stress?

Answer 4

the resistance to movement between laminae (pressure)

Question 5

What is the definition of Shear Rate?

Answer 5

the relative velocities between laminae (velocity of blood flow)

Question 6

What is the definition of viscosity?

Answer 6

Shear Stress/ Shear Rate

aka pressure/ velocity

Question 7

What is a Newtonian fluid and how does it differ from a non-Newtonian fluid?

Answer 7

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

Question 8

What is the relationship between hematocrit and viscosity?

Answer 8

directly proportional (as hematocrit increases, so does viscosity)

Question 9

What are 2 effects of vessel diameter on viscosity:hematocrit ratio?

Answer 9

1) axial streaming

2) plasma skimming

Question 10

What occurs in axial streaming?

Answer 10

RBCs accumulate in axial laminae

Question 11

What does plasma skimming mean?

Answer 11

describes the tendency of smaller vessels to contain relatively more plasma and less RBCs due to axial streaming

Question 12

Hematocrit is typically _______ in smaller vessels compared to larger vessels

Answer 12

LOWER

Question 13

Viscosity is typically ______ in smaller vessels

Answer 13

LOWER

Question 14

Why is there MORE plasma in smaller vessels?

Answer 14

axial streaming

Question 15

Why is the hematocrit LOWER in smaller vessels?

Answer 15

plasma skimming

Question 16

What are 4 clinical scenarios with turbulent flow?

Answer 16

1) murmurs
2) damage to endothelial lining
3) thrombi
4) Korotkoff sounds (not pathological)

Question 17

What does Reynold’s number indicate?

Answer 17

the propensity for turbulent flow

Question 18

What 4 factors influence Reynold’s number?

Answer 18

1) Diameter of tube
2) velocity
3) density
4) viscosity

Question 19

What is the only factor related to Reynold’s number that varies inversely?

Answer 19

viscosity

lower viscosity, higher Reynold’s number (larger propensity for turbulence

Question 20

Propensity for turbulence (Reynold’s number) increases with increasing _______, ________, and ________

Answer 20

diameter, velocity, and density

Question 21

Blood flow _____(slows down/speeds up) as it moves further from the heart?

Answer 21

slows down

cross sectional area gets larger even though individual vessels are smaller

Question 22

With regards to blood flow, total energy only remains constant in a……

Answer 22

constant flow system

Question 23

What happens to total energy in a stenotic region?

Answer 23

It is increases (because KE component is significantly higher than in downstream segment)

Question 24

With respect to blood flow, what is kinetic energy defined as?

Answer 24

velocity of blood flow

Question 25

What is potential energy defined as?

Answer 25

transmural (lateral) pressure

Question 26

What is the formula for the LaPlace relationship?

Answer 26

Wall Tension = (Pressure x Radius)/ Wall Thickness

Question 27

How can capillaries withstand large transmural pressures? (like jumping off of a ledge?)

Answer 27

because their small radius generates a low wall tension

Question 28

Why are aneurysms dangerous?

Answer 28

They have a HIGH wall tension because of a large radius

Question 29

For resistance in series, the total resistance of the entire system equals the ____________________

Answer 29

sum of the individual resistances

Question 30

For resistance in parallel, the total resistance of the entire system is (reduced/increased)

Answer 30

reduced (why resistance is lower through capillary beds)

Question 31

Where is resistance the largest?

Answer 31

arterioles

Question 32

As blood moves further and further away from the heart, what happens to resistance of the vessel?

Answer 32

increases

Question 33

Where is the largest drop in arterial pressure?

Answer 33

across the arterioles (right before the capillaries)

Question 34

What happens to blood pressure as you move further and further from the heart?

Answer 34

Diastolic decreases

Systolic increases

Question 35

Which has higher compliance, veins or arteries?

Answer 35

veins

arteries are stiff

Question 36

Which vessel has the closest to a 1:1 ratio on cross-sectional area and blood volume?

Answer 36

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)