Lec 10 Hemodynamics

Question 1

4 Hemodynamic principles

Answer 1

• pressure
• flow
• resistance
• capicitance

Question 2

What primarily determines resistance of blood vessel?

Answer 2

radius

Question 3

What does connecting blood vessels in series do to overall system resistance?

Answer 3

increase resistance

Question 4

What does connecting blood vessels in parallel do to overall system resistance?

Answer 4

decrease resistance

Question 5

What does Q stand for?

Answer 5

flow

Question 6

what does C stand for?

Answer 6

vessel compliance

Question 7

Does blood flow up or down pressure gradients? What does this mean for vascular pressure [in aorta vs arterioles vs capillaries vs venules vs veins]

Answer 7

• blood flows down pressure gradients
• pressure must decrease through circulation
• aorta&raquo_space; arteries&raquo_space; arterioles&raquo_space; capillaries&raquo_space; venules&raquo_space; veins&raquo_space; vena cava

Question 8

What are 4 examples in body of flow down gradients?

Answer 8

• ions cross cell membrane to create action potential
• blood moving through circulatory system
• plasma crossing capillary wall
• solutes reabsorbed in kidney

Question 9

What is ohm’s law?

Answer 9

Q = (P[final] - P [initial]) / R = delta P /R

Q = flow
P = hydrostatic pressure
R = resistance

Question 10

What is relationship between velocity and vessel area?

Answer 10

• velocity is proportional to flow, inversely to area

Q = vA

Q = flow
A = cross sectional area
v = blood velocity

Question 11

What is definition of flow vs velocity?

Answer 11

• flow = how many RBCs pass a particular point

- velocity = how fast does a single RBC move

Question 12

What is poiseuille’s equation?

Answer 12

Determines blood vessel resistance
R = 8ηl/πr^4

R = vessel resistance
l = vessel length
η = blood viscosity
r = vessel radius

Question 13

What is significance of poiseuille’s equation – what type of vessels have biggest resistance?

Answer 13

longer vessels, smaller radius, more blood viscosity

Question 14

Do shorter or longer vessels have more resistance?

Answer 14

longer vessels

Question 15

does more or less blood viscosity cause more resistance?

Answer 15

more blood viscosity

Question 16

Does large or smaller vessel radius cause more resistance?

Answer 16

smaller vessel radius

Question 17

Does blood viscosity increase or decrease with hematocrit?

Answer 17

increases

Question 18

What is viscosity?

Answer 18

How easy for fluid to move

if large force required to move fluid = high viscosity

Question 19

What is compliance [definition, equation]

Answer 19

C = V/P –> compliance = volume/ pressure
low compliance = stiff, difficult to fill with fluid
high compliance = loose, easy to fill with fluid

Question 20

How can you find compliance in a graph of pressure vs Volume % increase?

Answer 20

slope!

higher slope = higher V/P so higher C

Question 21

Is compliance of veins or arteries higher?

Answer 21

veins have high compliance

arteries have low compliance

Question 22

Do veins or arteries hold most of the blood? Why?

Answer 22

Veins because they have high compliance which means they are loose and easy to fill with fluid

Question 23

How does flow change between vessels in series?

Answer 23

flow must be identical

Question 24

How to calculate flow of vessels in parallel?

Answer 24

• total flow is divided into parallel vessels

Q tot = Q1 + Q2 + Q3

Question 25

Are pressure drop and flow same or different between parallel vessels

Answer 25

• pressure drop through parallel vessels is the same

- flow through parallel vessels can be different [total flow is sum of parallel flows]

Question 26

How to calculate resistance in series?

Answer 26

• overall resistance is sum of individuals
  R tot = R1 + R2 + R3
  if R2&raquo_space; R2 and R3 then R tot = R2

Question 27

How to calculate resistance in parallel?

Answer 27

Overall resistance is less than each individual

1/Rtot = 1/R1 + 1/R2 + 1/R3

Question 28

Do capillaries have high or low resistance – individually? as a system?

Answer 28

Capillaries each have high resistance

BUT body has 3 billion capillaries in parallel, so v. low overall resistance

Question 29

Which section of vasculature has greatest resistance? How can you calculate?

Answer 29

arterioles
Q = deltaP/R so –> R = delta P /Q
THUS: since same Q [flow] same for all parts of vasculature [in series], arterioles have highest delta P so highest R

Question 30

Is blood flow through capillaries slow or fast [v]? Why?

Answer 30

Very slow flow in each capillary
Vcap = Q total/A total
Qtot = overall CO
Atot = overall cross sectional area
since Atot is very big --> v must be small

Question 31

What is radius of capillary?

Answer 31

3.5 x 10 e -6 m [micro m]

Question 32

What is flow through single capillary?

Answer 32

CO / 3x10^9 [since theres 3 billion capillaries in parallel]

Question 33

How does body control flow to different regions?

Answer 33

• if resistance increased in one region/organ system –> divert flow from this region and increase flow to other organs

Question 34

What is the TPR?

Answer 34

total peripheral resistance

Question 35

What is significance of smooth muscle in arterioles?

Answer 35

• means resistance can be regulated [in capillary one cell thick so can’t do anything to make individual capillary greater or smaller]