Patient - Haemodynamics(unfinished)

Question 1

Cardiac output depends on what 2 factors?

Answer 1

Autonomic nervous input

Venous filling pressure

Question 2

CO=?

Answer 2

CO=Cardiac output=HRxSV
HR=heart rate
SV=stroke volume

Question 3

What drives filling of ventricles during diastole?

Answer 3

Venous pressure

Question 4

What does the aortic pressure resist during systole?

Answer 4

Aortic pressure resists flow out of left ventricle during systole

Question 5

Define preload

Answer 5

The amount of stretch in the heart prior to contraction

i. e.
- Tension in expanded ventricle (due to venous filling)
- Greater stretch = myocytes need more energy (and oxygen) per contraction

Question 6

Define afterload

Answer 6

The arterial pressure the ventricle must push against

-greater contractile force = more energy (and oxygen) use

Question 7

What sets energy consumption?

Answer 7

Preload and afterload

Question 8

What do both preload and afterload depend on?

Answer 8

The vascular system

Question 9

Apart from transporting blood to all tissues, what else does the vascular system do? What is haemodynamics?

Answer 9

• interacts with cardiac function to control blood flows and pressures throughout the body
• This aspect - the physics of blood flow - is called haemodynamics

Question 10

Define haemodynamics

Answer 10

The physics of blood flow

Question 11

What is flow resistance?

Answer 11

The relationship between pressure and flow

Question 12

How is flow resistance controlled?

Answer 12

By changing vessel diameter (by constriction and relaxation of vascular smooth muscle)

Question 13

Define resistance in haemodynamics

Answer 13

R= Pressure/Flow

Question 14

What can resistance be applied to?

Answer 14

An individual vessel/tube
or
An entire vascular branch e.g.
The peripheral circulation or the pulmonary circulation

Question 15

What is Poiseuille’s Law?

Answer 15

R= change in P/F = 128/pi x nL/D^4 
It describes flow resistance (R) of an individual vessel or tube 
where n=blood viscosity 
L=length
D=diameter

Question 16

What is flow resistance proportional to?

What is it inversely proportional to?

Answer 16

Proportional to blood viscosity and length

Inversely proportional to diameter

Question 17

What is blood viscosity dependent on?

Answer 17

Haematocrit and protein content

Question 18

Describe how the haemodynamics of resistance differs when in networks of vessels

Answer 18

• resistance is additive in series (sum of all section)

- resistance within a section (in parallel) is inversely proportional to the number of vessels (~1/n)

Question 19

Is resistance lower in parallel or series? (of blood vessels)

Answer 19

R is lower in parallel

Question 20

The smallest vessels have the most or greatest resistance to flow?

Answer 20

The greatest resistance to flow because pressure drops across each section from the aorta to the capillaries, but flow is the same
Lower resistance is due to the smaller diameter

Question 21

What is total peripheral resistance?

Give the PRU formula

Answer 21

Also called systemic vascular resistance
1PRU = 100mmHg/100ml/s =~ (MAP-RAP)/CO
Where PRU= peripheral resistance unit
MAP= mean arterial pressure =~100mmHg
RAP= Right atrial pressure =~ 0 (relative to atmospheric)

Question 22

What is the normal physiological range of PRU?

Answer 22

0.2-4 PRU (peripheral resistance units)

Question 23

Total pulmonary resistance=

Answer 23

Pulmonary circulation is a low resistance (low pressure) system
0.12PRU
i.e. 10% of the TPR
Mean pulmonary artery pressure minus left atrial pressure~12mmHg=12PRU

Question 24

Normal physiological range of the pulmonary resistance?

Answer 24

0.03 to 1 PRU

Question 25

Vessel structure from inside to outside

Answer 25

1 - Endothelium (all vessels) 2 - Smooth muscle (arteries-thick, veins-thinner, not in capillaries) 3 - Connective tissue (adventitia), arteries and veins, not in capillaries

Question 26

Increase in vascular smooth muscle tone causes..

Answer 26

reduction in diameter

Question 27

Reduction in diameter causes..

Answer 27

greater flow resistance (only really significant in the smallest vessels, arterioles, capillaries, venules)

Question 28

Greater flow resistance means

Answer 28

Reduced volume increase in venous pressure and cardiac filling Particularly important effect in large veins

Question 29

Vessel diameter affected by balance between what 2 factors? | What do these factors affect?

Answer 29

2 factors = internal pressure and tension in vessel wall | They affect the volume of blood and resistance to flow

Question 30

What is critical closing pressure

Answer 30

When arterial pressure falls to <20mmHg, tension in the artery wall collapses the vessel and shuts down flow

Question 31

What is flow autoregulation?

Answer 31

If pressure surges, stretch-gated receptors in smooth muscle react to increase tone (acting to increase flow resistance and minimise changes in flow)

Question 32

If pressure gets to low, what happens?

Answer 32

Reach critical closing pressure | Vessel will collapse