Patient - Haemodynamics(unfinished) Flashcards Preview

Pharmacy Year 2 Semester 1 > Patient - Haemodynamics(unfinished) > Flashcards

Flashcards in Patient - Haemodynamics(unfinished) Deck (32):
1

Cardiac output depends on what 2 factors?

Autonomic nervous input
Venous filling pressure

2

CO=?

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

3

What drives filling of ventricles during diastole?

Venous pressure

4

What does the aortic pressure resist during systole?

Aortic pressure resists flow out of left ventricle during systole

5

Define preload

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

6

Define afterload

The arterial pressure the ventricle must push against
-greater contractile force = more energy (and oxygen) use

7

What sets energy consumption?

Preload and afterload

8

What do both preload and afterload depend on?

The vascular system

9

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

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

10

Define haemodynamics

The physics of blood flow

11

What is flow resistance?

The relationship between pressure and flow

12

How is flow resistance controlled?

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

13

Define resistance in haemodynamics

R= Pressure/Flow

14

What can resistance be applied to?

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

15

What is Poiseuille's Law?

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

16

What is flow resistance proportional to?
What is it inversely proportional to?

Proportional to blood viscosity and length
Inversely proportional to diameter

17

What is blood viscosity dependent on?

Haematocrit and protein content

18

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

-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)

19

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

R is lower in parallel

20

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

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

21

What is total peripheral resistance?
Give the PRU formula

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)

22

What is the normal physiological range of PRU?

0.2-4 PRU (peripheral resistance units)

23

Total pulmonary resistance=

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

24

Normal physiological range of the pulmonary resistance?

0.03 to 1 PRU

25

Vessel structure from inside to outside

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

26

Increase in vascular smooth muscle tone causes..

reduction in diameter

27

Reduction in diameter causes..

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

28

Greater flow resistance means

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

29

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

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

30

What is critical closing pressure

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

31

What is flow autoregulation?

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

32

If pressure gets to low, what happens?

Reach critical closing pressure
Vessel will collapse