Exam 3 Kirk Lecture 1 : Hemodynamics 1

Question 1

What is the function of the venous system? Is it low or high pressure? Type of valves?

What is the function of the lymphatic system?

What is the function of the arterial system? Low or high pressure?

Answer 1

Venous system: low pressure, controls volume (has veins, low resistance vessels, uni directional valves, right heart)

Lymphatic System: drainage

Arterial System: high pressure, controls pressure, left heart

Question 2

Function of the capillaries

Answer 2

Capillaries: network exchange vessels, O2 and nutrients to tissues and organs

Question 3

Explain the function of the following:

Left Heart

Elastic arteries

Muscular arteries

Arterioles

Capillary network

Answer 3

Left heart: pressure pump, delivers blood to elastic arteries

Elastic arteries: serve as surge pump in which energy is stored during systole and released during diastole… positive pressure in aorta ensyres flow in capillaries during cardiac cycle (120/80 mmHg)

Muscular arteries: serve as low resistance conduits that deliver blood quickly to tissues with minimal energy expenditure

Arterioles: variable resistors, change diameter and regulate the blood flow into the capillaries

Capillary network: exchange vessels deliver O2 to target organs

Question 4

Explain the function of the following:

Venous vessels

Right heart

Pulmonary vessels

Lymphatic vessels

Blood

Answer 4

Venous vessels: capitance vessles, variable capacitors, change the volume of the vascular system to match the volume blood needed, one way valves

Right heart: serves as volume pump, delivers large volumes of blood to the pulmonary circulation at low pressure

Pulmonary vessels: gas exchange and volume reservoir

Lymphatic vessels: drainage system, returns fluids to bloodstream

Blood: carries nutrients, signaling molecules

Question 5

Describe the three types of pressure in the circulatory system:

Hydrostatic Pressure

Driving Pressure

Transmural Pressure

Answer 5

Hydrostatic Pressure: pressure from gravity (example: why you get dizy when you stand up from couch)

Driving pressure: pressure driving blood flow (high to low)

Transmural pressure: pressure of fluid pushing on a wall (what is normally measured as blood pressure)

Question 6

The circulatory system maintains constant blood flow

Define the velocity of blood flow

Define “flow rate”

Does flow increase or decrease with cross sectional area

Answer 6

Velocity of blood flow: distance that a particle travels with respect to time, cm/sec

Flow Rate: volume of blood moving per unit time

Flow Rate: v = Q/A

or

velocity = flow rate / cross sectional area

Flow is slower over a wider sectional area (think putting your hand over a water hose spout

Question 7

Bernoulli’s Principle:

In a ________, the total energy (____ + _____+ ____) remains constant.

What is the equation?

Answer 7

In a constant flow system, the total energy (potential, kinetic, gravitational) remains constant

Question 8

Bernoulli’s Equation:

In stenosis: ______ increases and _____ decreases

Thus, transmural pressure _______ as the velocity of the blood flow increases in the stenotic region

Answer 8

In stenosis (an abrupt decrease in vessel cross-sectional area), kinetic energy/flow increases, while potential energy decreases.

Thus, transmural pressure decreases as the velocity of blood flow increases in the stenotic region.

Therefore, there is less pressure pushing against eh stenotic region, making it even worse.

Question 9

In stenotic regions, blood flow technically does what?

What is a better way to think about blood flow

Answer 9

In stenotic regions, the pressure in the stenotic region is lower than in a downstream segment. Therefore, blood in that case is moving from low to high pressure.

THUS, it is more correct to understand that blood flow moves from higher to lower TOTAL energy.

Total energy made up of potential and kinetic.

Total energy in stenotic region is higher because of how much higher the kinetic energy is.

Question 10

Blood flow moves from what to what

Answer 10

Blood flows from high total energy to lower total energy

Also, friction causes a loss of total energy as blood flows through the vessels

Question 11

Explain blood pressure measurements at the ascending aorta: side port catheter vs end port catheter measurements

Answer 11

There are two catheters: a side port (measures PE)

and a end port (measures KE + PE)

If a cathetor has an end port sensor that is facing the flowing stream of blood, it will measure a pressure that is higher than the pressure measured by the side port sensor on the same cathetor.

Side port measures only potential energy - therefore is more accurate

Question 12

What is Poiseuille’s Law?

Answer 12

It is analogous to ohm’s law

Equation: Q = deltaP/ R (DeltaP = QR)

Pressure = flow x resistance

Question 13

Poiseuille’s Law:

Blood flow is ______ to pressure gradient

Blood flow is ______ to vessel radius to 4th power

Blood flow is ______ to vessel length and blood viscosity

Resistance is _____ to vessel length and viscosity

Resistance is _____ to vessel radius to 4th power

Answer 13

Blood flow: directly proportional to pressure gradient and radius to the 4th…. inversely proportional to vessel length and blood viscosity

Resistance is directly proportional to vessel length and blood viscosity

Resistance is inversely proportional to vessel radius to 4th power

Question 14

The most important determinants of blood flow are the ______ and the ______

Answer 14

Most important determinants of blood flow in the CV system are pressure gradient and the radius to the 4th power…………… pressure gradients are generally held constant by feedback mechanisms

Question 15

Relationship between blood flow and radius

(what happens when radius doubles?)

Answer 15

Blood flow = radius ^ 4

So if blood flow doubles, radius increases x 16

Question 16

What in the CV system are in series with each other?

Explain resistances in series

Answer 16

The aorta, large and small arteries, arterioles, capillaries, venules, veins, vena cava are all in series

Rt = R1 + R2+ R3

For resistances in series, the total resistance of the entire system equals the sum of the individual resistances

Therefore, each resistance is less than the entire system

Question 17

Where is the primary site of arterial resistance?

Answer 17

Arterioles are the primary site of arterial resistance

Question 18

What in the CV system is arranged in parallel?

Explain the resistances in parallel

Answer 18

Organs and vessels within a category of vessels (capillaries, etc) are arranged in parallel

For resistances in parallel, the total resistance is less than any individual resistance

1/Rt = (1/R1)+ (1/R2)+ etc

Question 19

________ indicates the propensity for turbulent blood flow

The higher the _____ the greater change for turbulent blood flow to develop

Eqn:

Answer 19

Reynold’s number indivates the propensity for turbulent blood flow

Higher the Nr, the greater change for turbulent flood flow to develop

Eqn: Nr = (density)(diameter)(velocity) / (viscosity)

Question 20

What would increase Reynold’s number vs decrease it

Answer 20

Increase Nr : density, velocity, tube diamter

Decrease Nr = viscosity

Question 21

Explain the difference between laminar and turbulent blood flow

The larger the diameter, the ____ the chance to develop turbulent flow

Answer 21

Laminar Flow: fluid moves in parallel layers within tube (laminar is silent)

Turbulent/ non linear flow: disorderly pattern, results in : murmurs/bruits, damage to endothelial lining, thrombi, Korokoff sounds

The LARGER the diameter, the higher change to develop turbulent flor (aorta)

Question 22

A person who has anemia has an ________

Aka where could you hear a bruit in someone with anemia

Answer 22

Person with anemia : check for bruit in aorta

Anemia: lower than normal RBCs in blood, hemtacrit is lower than normal, viscosity is lower, so renoyld’s number goes UP

Question 23

Define the following terms in how they relate to viscosity:

Shear stress

Shear rate

Viscosity =

Answer 23

Shear stress : resistance to movement between layers aka pressure

Shear rate: relative velocities between layers (velocity of blood flow)

Viscosity = shear stress / shear rate

THEREFORE, viscosity = pressure over velocity

so velocity is equal to pressure/viscosity

Question 24

Explain viscosity in a newtonian vs nonnewtonian fluid

As velocity of blood flow increases, viscosity _____ due to less interactions between components

Answer 24

Newtonian fluid: fluid whose viscosity remains constant (water or plasma)

Non-newtonian fluid: fluid whose viscosity changes

As velocity of blood flow increases, viscosity decreases due to less interactions between components

Question 25

What is the normal range of hematocrit?

Answer 25

Normal range of hematocrit : 35-50%

Question 26

Define Axial streaming and plasma skimming

As you go from the aorta down, hematocrit _____

As blood flow slows down from larger to smaller vessels, the viscosity should increase, but it DOES NOT because of ______

Answer 26

Axial Streaming: tendency for RBCs to cluster in axial/innermost and fastest layer, which creates a large cell free area around the outside, thus in smaller vessels they have a larger cell free area and thus a lower viscosity

Plasma skimming: tendency of smaller vessels to contain more plasma and less RBCs due to axial streaming (branching off effect)

Hematacrit is lower in smaller vessels due to plasma skimming

As blood slows down from larger to smaller vessels, the viscosity should increase, but it doesn’t in small vessles because of axial streaming and plasma skimming offset the shear thinning fluid effect of blood (they offset the slow velocity)

Question 27

Capallaries can withstand incredibly high pressures without bursing.

What is the Laplace Equation that explains tension in a vessel wall

Answer 27

Tension = (pressure x radius)/ wall thickness

Or wall tension is directly related to pressure and radius, inversely related to wall thickness

Question 28

Explain the following physiological concequences of Laplace:

Capallaries with a small radius can withstand _____

Answer 28

Laplace:

Capallaries with small radius can withstand very large transmural pressures

Question 29

Explain the following due to the laplace relationship:

Arteriolar Vasoconstriction will ____ wall tension and provide _____

Answer 29

Arteriolar vasoconstriction will decrease wall tension and provide greater control over blood flow

(think, constrict means smaller radius, smaller radius means less tension)

Question 30

Explain the following due to the Laplace equation:

Aneurysms result in a section of a vessel with a _____ radius, increasing the wall tension and creating a higher risk of bursting

Answer 30

Aneursyms result in a section of a vessel with a large radius, which will increase the wall tension and be at risk of bursing

Question 31

Explain this using the laplace equation:

Dilated hearts have a larger radius and ______ wall tension and thus require more _________ to overcome

Answer 31

Dilated hearts have a larger radius and higher wall tension, thus requiring more systolic work and higher oxygen consumption to overcome

Question 32

What is the equation for the laplace relationship aka the equation to calculate wall tension

Answer 32

T = P x radius / wall thickness

aka wall tension = [(pressure)(radius)]/ wall tension