Haemodynamics and microcirculation

Question 1

What is the calculation for MAP?

Answer 1

CO x TPR
Cardiac output x total peripheral resistance
CO = HR x SV
MAP = HR x SV x TPR

Question 2

What does Darcy’s law state?

Answer 2

Flow in steady state is linearly proportional to the pressure difference between two points, concerns fluid flow (volume/time)

Question 3

What is mean velocity?

Answer 3

Flow divided by total cross sectional area, as total cross sectional area increases as the blood enters the microcirculation, mean velocity falls progressively

Question 4

Is total flow altered?

Answer 4

No remains equal to cardiac output at each level of the vascular system

Question 5

Where does laminar flow happen?

Answer 5

Arteries and veins

Question 6

Where does turbulent flow happen?

Answer 6

Ventricles and in ascending aorta of healthy subjects

Question 7

Where does single file flow occur?

Answer 7

In capillaries

Question 8

What did Jean Poiseuille find about resistance to flow?

Answer 8

Resistance to steady flow along a straight cylindrical tube is proportional to tube length and fluid viscosity and inversely proportional to tube radius raised to the 4th power

Question 9

Why are arterioles the main site of resistance in the circulation?

Answer 9

Flow is extremely sensitive to vessel radius, resistance increases with a decrease in radius

Question 10

What venules collectively are arranged in series?

Answer 10

Arteries, arterioles, capillaries, venules and veins

Question 11

Does total resistance increase or decrease if series units are added?

Answer 11

Increase

Question 12

Does total resistance increase or decrease if parallel units are added?

Answer 12

Decrease

Question 13

What is distending pressure?

Answer 13

Pressure acting on a vessel inside minus the pressure outside

Question 14

What is the compliance of a vessel defined as

Answer 14

The change in volume per unit change in distending pressure

Question 15

Do veins have a higher compliance than arteries?

Answer 15

Yes, they are thin walled and easily stretched

Question 16

Veins act as volume reservoirs while arteries act as … reservoirs/

Answer 16

Pressure

Question 17

What is the law of LaPlace?

Answer 17

Magnitude of force or tension (T) necessary to withstand the transmural pressure (Pt) is influenced both by the vessel radius (r) and wall thickness (u)
T = Pt x r / u

Question 18

In large arteries is Pt large or small

Answer 18

Large so wall needs to be thick to compensate

Question 19

In veins is there tension generated?

Answer 19

Yes Pt is low, r is still large though

Question 20

Why are capillaries walls very thin?

Answer 20

Pt and r very small

Question 21

Where is the likelihood of vessel rupture the greatest?

Answer 21

Aorta

Question 22

What is the definition of microcirculation?

Answer 22

Circulation of blood through the smallest blood vessels - arterioles, capillaries and venules

Question 23

Where is the density of capillaries the highest?

Answer 23

Metabolically active tissues - skeletal muscle

Question 24

What does blood flow in capillaries depend on?

Answer 24

Not uniform - depends on contractile state of the arteriolar smooth muscle

Question 25

what is auto regulation?

Answer 25

Intrinsic adjustment of blood flow to a tissue or vascular bed so the flow meets the requirements at a give time

Question 26

How are changes in blood flow occurring?

Answer 26

Change in diameter of arterioles and altering the contraction of precapillary sphincters

Question 27

What are intrinsic control mechanisms classed as?

Answer 27

Myogenic or metabolic

Question 28

What is the relationship between metabolism and blood flow?

Answer 28

As rate of metabolism increases so does blood flow as long as perfusion pressure is constant and maintained in the absence of autonomic nerve input

Question 29

When the metabolic rate of a tissue increases such that local oxygen consumption exceeds delivery, what happens?

Answer 29

Vasodilation and relaxation of an arteriolar smooth muscle, less resistance, more oxygen in capillary beds causes metabolic rate to decrease and less oxygen consumption

Question 30

What products of metabolism cause relaxation of smooth muscle?

Answer 30

CO2, H+, K+ and adenosine

Question 31

Which products mediate vasodilation?

Answer 31

Prostacyclin and nitric oxide

Question 32

What is the endothelium derived relaxing factor that causes relaxation of vascular smooth muscle?

Answer 32

Nitric oxide

Question 33

In myogenic control what is flow?

Answer 33

Pressure gradient / resistance

Question 34

If myogenic flow is to remain constant what has to happen?

Answer 34

Increased pressure gradient met by an increase resistance in flow

Question 35

How does the myogenic response occur?

Answer 35

Perfusion pressure increases, stretch of muscle, constriction increases, increased resistance, decreased flow/increased flow according to pressure

Question 36

What is long term autoregulation?

Answer 36

If nutritional/oxygen demands chronically exceed delivery this occurs. Due to both an increase in microcirculatory vessels supplying blood to tissue and provoked by partial occlusion of a coronary vessel

Question 37

How do lipophilic solutes enter or leave the capillary bed?

Answer 37

Via transcellular route

Question 38

How do hydrophilic solutes cross capillaries?

Answer 38

Intercellular clefts (albumin and other plasma proteins cannot)

Question 39

Where is hydrostatic pressure the greatest?

Answer 39

Arterial end

Question 40

How do hydrostatic pressures result?

Answer 40

Capillary blood pressure

Question 41

How do osmotic pressure gradients result in the capillary bed?

Answer 41

Presence of large, non diffusible plasma proteins, net osmotic pressure favours fluid absorption