Module 8 : Hemodynamics

Question 1

what is hemodynamics

Answer 1

• study of blood flow in the circulatory system

Question 2

what is the circulatory system comprised of and what type of circuit is it

Answer 2

• closed circuit

- heart, arteries, capillaries, veins

Question 3

what is the venous heart

Answer 3

• contracting muscles that help pump blood back to the heart especially in the lower extremity

Question 4

what is blood composed of

Answer 4

• plasma
• erythrocytes
• leukocytes
• platelets

Question 5

what is the hematocrit

Answer 5

• the amount of blood that is made up by cells

Question 6

in which portion of the circulatory system is the most blood contained

Answer 6

• veins

Question 7

what type of flow is seen in the capillaries

Answer 7

• low volume and velocity

Question 8

what is required for any fluid to flow

Answer 8

• pressure different / gradient

Question 9

what results from an increase in the pressure

Answer 9

• increased flow rate

Question 10

what is a pressure gradient

Answer 10

• pressure difference divided by the distance between two pressure locations

Question 11

what is the volume flow rate

Answer 11

• volume of blood passing a point per unit time

Question 12

what happens to the volume flow rate if the pressure gradient increases

Answer 12

• flow increases

Question 13

what happens to volume flow rate is the resistance increases

Answer 13

• flow decreases

Question 14

what is pouselles equation for resistance

Answer 14

• R = 8 x length x viscosity / ii x radius ^4

Question 15

what will increase resistance to flow

Answer 15

• longer length
• increased viscosity
• decreased radius

Question 16

what factor will have the greatest effect on the resistance to flow

Answer 16

• change in radius because of exponent

Question 17

what are the 5 different flow patterns

Answer 17

• plug
• laminar
• jet
• disturbed
• turbulent

Question 18

characteristics of plug flow

Answer 18

• seen at opening of large vessels

- all RBCs travelling at same velocity

Question 19

characteristics of laminar parabolic flow

Answer 19

• most common

- RBC move in concentric layers with the ones at the centre moving the fastest

Question 20

characteristics of jet flow

Answer 20

• seen when there is significant reduction in diameter

- velocities within narrowing are the fastest

Question 21

characteristics of disturbed flow

Answer 21

• occur naturally with tapering curves and bif

- not all layers moving in laminar fashion

Question 22

characteristics of turbulent flow

Answer 22

• type of flow just past stenosis
• flow velocities vary in velocity and direction
• not normal except near the heart

Question 23

what is Reynolds number

Answer 23

• can predict the onset of turbulence in a vessel

Question 24

what is the number that must be exceeded for turbulence to occur

Answer 24

• 2000

Question 25

what is the continuity rule

Answer 25

- in the presence of a stenosis the volume of flow must stay the same proximal, within and distal to stenosis

Question 26

what must happen to the velocity of blood is a stenosis reduced the vessel diameter to less than 50%

Answer 26

- velocity must double within stenosis

Question 27

what is Bernoulli describing

Answer 27

- pressure and energy must also remain the same through a vessel with a. stenosis

Question 28

what is Bernoulli's principle

Answer 28

- at a stenosis a pressure drop is necessary for the fluid to accelerate through the stenosis and decelerate past stenosis - pressure/ potential energy is converted to kinetic energy at the stenosis then back to potenital after stenosis

Question 29

what is the simplified Bernoulli equation

Answer 29

- P = 4(v^2)

Question 30

what is tardus parvus flow

Answer 30

- flow afer a stenosis where there is a drop in acceleration time and PSV - stenosis detracts from pressure gradient that was created by the heart

Question 31

what is the windkessel effect

Answer 31

- continued forward flow in diastole because of the elasticity of the vessel walls contracting to its original diameter

Question 32

what can cause flow reversal in the vessels other than disease

Answer 32

- the pressure wave along the walls of the vessel travels faster than the blood - when wave reaches en dog arterial system there is a reflected wave that causes the vessel to expand and contract against blood flow