Hemodynamics

Question 1

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

Answer 1

the pressure gradient and radius to the fourth power

Question 2

Resistance is equal to…

Answer 2

pressure differential over blood flow

Question 3

For resistances in series, the total resistance of the entire system equals_________.

Answer 3

the sum of the individual resistances

Question 4

The primary site of arterial resistance is_______.

Answer 4

the arterioles

Question 5

What are examples of vessels in parallel in the circulatory system?

Answer 5

organs and vessels within a category of vessels (ex: the special circulations we discussed, including cerebral, coronary, renal, splanchnic, and cutaneous circulations)

Question 6

For resistances in parallel, the total resistance is____ than any individual resistance

Answer 6

less

Question 7

What is Reynold’s number?

Answer 7

it describes the propensity for turbulent blood flow (higher Reynold’s # = greater chance for turbulent flow)

Question 8

What is one of the most common places for turbulent blood flow to develop?

Answer 8

in the aorta, where the vessel diameter is large

Question 9

Is dense fluid more or less likely to exhibit turbulent flow?

Answer 9

more likely

Question 10

Is hematocrit higher or lower in smaller vessels compared to larger vessels? Why?

Answer 10

Hematocrit is lower in smaller vessels due to plasma skimming, in which blood from periphery of main vessel is shunted into a branching vessel (and the blood on the periphery contains less RBCs).

Question 11

What is axial streaming and what does it compensate for?

Answer 11

the tendency of RBCs to accumulate in axial laminae at high shear rates; compensates for the high viscosity expected to be experienced in small vessels (ie, capillaries) with low velocities

Question 12

What does the venous system vs. arterial system vs. lymphatic system vs. capillary network control?

Answer 12

• venous: volume
• arterial: pressure
• lymphatic: fluid drainage/return
• capillary: exchange

Question 13

Why is blood pressure on the arterial side NOT a good way to assess whether or not blood volume has been lost?

Answer 13

The arterial side controls blood pressure and has several mechanisms to maintain pressure; thus, even with a lower blood volume, the arterial side will maintain pressure. This is why central venous pressure is a much better indicator of blood volume.

Question 14

Muscular arteries serve as ______ resistance conduits that deliver blood quickly to tissues with _____ energy expenditure.

Answer 14

low; minimal

Question 15

Why are venous vessels known as capacitance vessels?

Answer 15

They are able to store large blood volumes without experiencing a large increase in blood pressure.

Question 16

Why is the right heart known as a “volume pump”?

Answer 16

It delivers large volumes of blood to the pulmonary circulation at low pressure.

Question 17

Define Bernoulli’s Principle and its application to the circulatory system.

Answer 17

Bernoulli’s states that in a constant flow system, the total energy (potential+kinetic+gravitational) remains constant. This principle can be applied to the circulatory system when considering stenosis. With stenosis, there is an abrupt decrease in vessel CSA, thus increasing velocity. Potential energy (pressure) is converted to kinetic energy (flow). Thus, transmural (static) pressure decreases as the velocity of blood flow increases in a stenotic area.

Question 18

What are other words we have used to refer to transmural pressure?

Answer 18

static pressure, lateral pressure, blood pressure (only when tissue pressure is negligible)

Question 19

Rather than understanding blood flow as movement from higher to lower pressure, it is more correct to understand blood flow as what?

Answer 19

flow from higher to lower total energy (and blood loses energy as it flows due to frictional forces against vessel wall)

Question 20

How does velocity of blood flow affect blood pressure?

Answer 20

higher velocity of flow = lower pressure

Question 21

How does Bernoulli’s Principle relate to heart sounds?

Answer 21

The smaller the aortic valve gets (ie, the more it closes, or the more stenotic it gets due to a pathological condition), the faster the blood flow through the valve and the louder the heart sound.

Question 22

What does Poiseuille’s Law state?

Answer 22

Flow is proportional to pressure gradient and inversely proportional to resistance.
R=(8Lη)/(πr^4)
Q=(πr^4)/(8Lη)

Question 23

Why are right and left ventricular pressures different if they generate the same cardiac output?

Answer 23

This is due to the vast change in resistance between the systemic and pulmonary circuits.

Question 24

What is the Reynold’s number needed to generate turbulent blood flow?

Answer 24

> 3000

Question 25

What are the determinants of turbulent flow?

Answer 25

• high density, large tube diameter, and high velocity all increase propensity for turbulent flow
• a more viscous fluid is less likely to exhibit turbulent flow

Question 26

Is an anemic patient more or less likely to exhibit turbulent flow? Why?

Answer 26

More likely- this is because less with anemia, there are less RBCs per volume of blood, which means the patient’s blood is less viscous. A decrease in viscosity increases the propensity for turbulent flow, based on Reynold’s equation.

Question 27

What is the difference b/t a Newtonian and non-Newtonian fluid?

Answer 27

A Newtonian fluid is one whose viscosity remains constant over a range of shear rates and shear stress (homogeneous). A non-Newtonian fluid is one whose viscosity changes over a range of shear rates and shear stress (non-homogeneous).

Question 28

What is the normal range for hematocrit?

Answer 28

35-50%