C8: Hemodynamics

Question 1

define hemodynamics

Answer 1

the study of blood flow in the circulatory system, it refers to both blood and power

Question 2

which muscles in the body are referred to as the venous heart

Answer 2

calf muscles

Question 3

what are the 4 items that blood is composed of

Answer 3

• plasma (55%) - made of water and protein
• RBCs (45%)
• WBCs (~1%)
• platelets (~1%)

Question 4

what does the term hematocrit refer to

Answer 4

the % of blood volume that is composed of cells

Question 5

define density

Answer 5

the mass per unit volume or the resistance of an object to accelerate

Question 6

define viscosity

Answer 6

resistance to flow

Question 7

what vessels control vascular resistance of blood flow

Answer 7

arterioles

Question 8

is the largest amount of blood located in which vessels in the body?

Answer 8

veins

Question 9

how is the pressure difference that is need for blood to flow created in the body

Answer 9

by the heart or gravity

Question 10

how are pressure and flow rate related

Answer 10

directly

Question 11

formula for pressure gradient

Answer 11

P gradient = P1 - P2 / Length

Question 12

basic formula for volume flow rate

Answer 12

V flow rate (Q) = delta Pressure / Resistance

Question 13

what is Poiseuille’s resistance formula for a long straight tube

Answer 13

R = 8 x length x viscosity / pie x (r)^4

…w/ radius being the most dominant factor

Question 14

formula for volume flow rate for a long straight tube only (when considering resistance)

Answer 14

Q = delta pressure x pie x (d)^4 / 128 x length x viscosity

Question 15

if the size of a vessel is constant, will a thin or large vessel produce slow flow

Answer 15

thinner = slower

but if theres a stenosis, then thinner means faster velocity

Question 16

describe plug flow, where is it seen?

Answer 16

flow pattern that has almost all RBCs travelling at the same velocity…. will have a thin envelope

-seen at the opening of larger vessels like the AO

Question 17

describe laminar parabolic flow, where is it seen?

Answer 17

flow pattern where the RBCs move in concentric layers w/ the fastest velocity at the centre… will have fairly thin envelope and clear window

-most common flow pattern in normal arteries

Question 18

describe jet flow, where is it seen?

Answer 18

flow pattern seen at areas of significant reduction in vessel diameter… e.g. stenosis

Question 19

describe disturbed flow, where is it seen?

Answer 19

flow pattern that natural occurs at bifurcations, curves or tapering of vessels…. not all layers of blood move in laminar fashion

• may see spectral broadening and/or reversal
• eg carotid bulb

Question 20

describe turbulent flow, where is it seen?

Answer 20

flow pattern that is seen just past a stenosis

-flow velocities and direction vary greatly.

Question 21

what type of spectral waveform would you get w/ turbulent flow
is turbulent flow normal?

Answer 21

1. filled in spectral tracing since there are many velocities
2. not normal except near the heart

Question 22

what does a Reynolds number (RN) predict

Answer 22

can predict onset of turbulence in a vessel

Question 23

having an RN greater than what value indicates turbulence?

Answer 23

2000

Question 24

what is the continuity rule?

what does it explain

Answer 24

it says: in the presence of a stenosis, the volume of flow must remain constant proximal to, at, and distal to the stenosis

it explains why we get a ‘jet’ when we have a stenosis… the velocity of blood must increase in a stenosis in order to keep the volume flow constant

Question 25

if the diameter of a stenosis is 1/2 of the vessel, what happens to the velocity of blood flow in this area

Answer 25

the velocity will double to maintain volume flow rate

Question 26

whats the relationship b/w pressure and velocity

Answer 26

inversely related

Question 27

when is a stenosis considered hemodynamically significant

Answer 27

if it causes a reduction of 50% or > in diameter of the vessel

Question 28

total fluid energy is composed of what 2 factors

Answer 28

``` potential energy (PE) kinetic energy ```

Question 29

formula for PE

Answer 29

intravascular pressure plus gravitational potential energy

Question 30

how is intravascular pressure produced

Answer 30

by the contraction of the heart, hydrostatic pressure and static filing pressure

Question 31

describe the changes of pressure experienced at a stenosis

Answer 31

at a stenosis theres a pressure drop in order to accommodate the acceleration of blood through the stenosis... after the stenosis blood decelerates

Question 32

describe the changes of PE experienced at a stenosis

Answer 32

PE is converted to KE when it enters the stenosis and then is converted pack to PE after the stenosis

Question 33

what is the simplified Bernoulli's equation

Answer 33

change in pressure = 4 (v2)^2

Question 34

what is tradus parvus | why does it occur

Answer 34

the drop in acceleration time and peak systolic velocity of arterial flow after a stenosis..... .... the stenosis detracts from the pressure gradient that was created by the heart

Question 35

does tardus parvus indicate proximal or distal stenosis

Answer 35

proximal

Question 36

what type of spectral trace will you get if theres a stenosis distally

Answer 36

you'll have a smaller peak velocity and you'll lose diastole because blood cant get through the stenosis as easily

Question 37

what is the windkessel effect | why does it occur?

Answer 37

the continued forward flow in the AO during diastole... occurs as a result of the elasticity of the vessel walls contracting back to their original shape

Question 38

why isnt there any backwards flow in the AO during diastole

Answer 38

the AO valve has closed

Question 39

which phenomenon is responsible for creating the dicrotic notch

Answer 39

windkessel effect

Question 40

why does flow reversal in arteries happen

Answer 40

the pressure wave travels along the walls of the vessel faster than the blood flowing in the vessel.... the wave reaches the end of the arterial system and causes the wave to be reflected backwards..... this causes the vessel wall to expand and contract against the flow of blood causing reversal reversal also occurs due to the increased pressure down stream and the heart relaxing

Question 41

what is a subclavian steal?

Answer 41

occurs when a stenosis is located at the origin of the vertebral artery... the stenosis causes a decrease in pressure which allows blood to instead flow retrogradely and into the subclavian artery rather than the vertebral... ... this 'steal' occurs in peak systole when the velocity is the highest and causes the other vertebral artery to have to work much harder and deliver the majority of the blood to the brain