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Cardiovascular system > Haemodynamics - L9 > Flashcards

Haemodynamics - L9 Flashcards

1
Q

The Q posed is to explain the physiological mechanisms underlying this change in blood flow

A

Active hyperaemia - when we increase activity locally at any organ such as digestive system after eating

If we have a reduction in O2 and increase in CO2 and build up of metabolites - those local changes cause increase in vasoactivity

Reactive hyperaemia - sudden influx of blood into area, reacting to something
exaggerated blood flow response post-occlusion - this reactive hyperaemia due to myogenically and chemically induced vasodilation
Body responds to try and overide it

endothelin issues some people can have

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2
Q

What is Haemodynamics - William R. Milnor (1982) Haemodynamics 1st Ed.?

A

Hemodynamics is concerned with the forces
generated by the heart and the motion of blood
through the cardiovascular system.”

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3
Q

Haemodynamics is important because:

A

Flow is always continuous, despite periods of diastole. Continuous flow: arteries as pressure reservoirs; valves
and muscle activity influence veins

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4
Q

Flow is continuous, despite periods of diastole, where

A

no blood enters the arterial tree - not being ejected from ventricles, peripheral circulation is maintained - organs are full of blood and perfused and diastolic pressure does not fall to zero - always an element of pressure within the vascular tree

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5
Q

What allows this flow?

A

Structural features of arteries and veins
Arteries work as pressure reservoirs with combination of muscle and elastic tissue that allows it to extend to accept influx of blood and contract and propel the blood forward
Valves and muscle activity influence veins under skeletal muscle pump

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6
Q

What is blood flow calculated as?

A

Flow per unit time

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7
Q

Physical laws governing blood flow are dictated by?

A

Pressure Gradients in the vasculature
Resistance in the vasculature

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8
Q

F?

A

Change in pressure / Resistance
Delta G / R

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9
Q

What does flow occur from areas in terms of pressure?

A

High pressure to low pressure

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10
Q

Why does the heart initially create for the bulk flow of blood?

A

Heart creates pressure gradient for bulk flow of blood.

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11
Q

What do we then need after heart creates pressure gradient for bulk flow of blood?

A

A gradient must exist throughout circulatory system to
maintain blood flow.

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12
Q

MAP = ?
MABP = ?

A

They are the same thing
MAP = (SV X HR) XT PR
MABP = CO X TPR

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13
Q

Are the pressures throughout the vasculature constant?

A

No, the systemic circuit is at higher pressure than pulmonary circuit but same patterns just at lower absolute values

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14
Q

Where does the greatest drop in pressure occur?

A

Greatest drop in pressure occurs in arterioles as they are major resistance vessels - they’re constantly under sympathetic nervous discharge that ensures that vasculature tone

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15
Q

Is MAP just an average of systolic and diastolic pressure?

A

No, the heart spends less time in systole than diastole

MAP = Diastolic + 1/3 pulse pressure
= 70 + (40/3)
= 83.3 mmHg

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16
Q

Pulse pressure?

A

Difference between systolic and diastolic

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17
Q

MAP is the average of?

A

Average across the cardiac cycle or the heartbeat and throughout the body
pressure constant throughout the whole system

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18
Q

Flow in high resistance?
Flow in moderate resistance?
Flow in low resistance?

A

No flow
Moderate flow
Large flow

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19
Q

What are the control valves?

A

The arterioles

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20
Q

Poiseuille’s Law what is it, what does each stand for and what behaviour does it describe?

A

Flow = (Pi x Delta P x r^4)/ (8 x weird n x L)

Where:
1. Delta P = pressure gradient along a vessel
2. r^4 = (vessel radius)^4
3. weird n = blood viscosity
4. L = vessel length

2,3+4= Resistance

This Law describes the behaviour of a perfect fluid in a rigid tube

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21
Q

1 Key role of CVS explained via Poiseuille’s Law?

A

Level of capillary where we have to offload the oxygen and nutrients - this regulation flow for surviving and living and maintaining homeostasis of CVS for the body

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22
Q

Under Poiseuille’s law - the longer the vessel… and capillaries…

A

The longer the vessel, the greater the resistance to flow.
As the longer the vessel, the more blood that is in it
Capillaries tend to be short compared with larger vessels. Resistance within capillaries is minimal and we need minimal resistance as the whole point of capillaries is to offload these nutrients, etc

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23
Q

Poiseuille’s Law describes the behaviour of a perfect fluid in a rigid tube BUT:

A

Blood vessels are not rigid - capillaries as an example are 1 cell wall thick
Blood is a 2-phase system (both cells and plasma and plasma is 90% water)
Must have variation within the formula

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24
Q

Laplace’s law ?

A

Wall tension = Pressure x radius / wall thickness

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25
Q

Wall tension of aorta?

A

High - Pressure is high relative to the radius

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26
Q

What determines blood flow?

A

MAP / Resistance

27
Q

In chronic hypertension what happens to the aortic wall?

A

In chronic hypertension, aortic wall thickness increases in compensation

28
Q

Why must large arteries have strong walls?

A

Large arteries must have strong walls - an artery of twice the radius needs to withstand twice the tension at any given blood pressure

29
Q

Where do aneurysms tend to develop in?

A

Larger arteries

30
Q

Viscosity ?

A

Resistance of a fluid to change in shape or movement of neighbouring portions relative to one another.
Viscosity denotes opposition to flow

31
Q

Is viscosity constant?
Which is more viscous plasma or water?
What about whole blood, what is the main contributing factor here?
What does viscosity depend on?

A

Viscosity mostly remains constant
Plasma almost twice as viscous as water
Whole blood is 3-4 times as viscous as water, red blood cells
Viscosity depends on haematocrit

32
Q

What is viscosity of a fluid?

A

How thick a particular fluid is

33
Q

Red blood cells tend to flow in…?

A

Centre Stream - concept of plasma skimming
We have this cyclindrical volume - blood flows in concentric blood cells and tends to flow in concentric laminar layers
RBCs come to centre part as the pressure is front loaded at level of RBCs - actual plasma content is then more skimming off the actual blood vessel as it travels through as RBCs are in the centre of the flow flow as this increases the speed of blood travelling through the vessel, the velocity

34
Q

What is hematocrit?

A

% of RBCs within total blood volume

35
Q

Laminar flow vs turbulent flow?
Normal/irregular - what kind of flow?

A

Laminar Flow (silent): Streamlined parallel flow and Turbulent Flow (murmurs): Irregular, random flow

36
Q

What kind of flow does blood typically flow in?

A

Laminar flow

37
Q

Does laminar flow make a sound?
Does turbulent flow make a sound?

A

No
Yes it can be heard

38
Q

Is laminar flow slow or fast and central or distal?

A

Laminar flow is fast centrally as RBCs congregate here and drive the blood here and slow/stationary at the surface which is useful for sites of offloading for capillaries as there is greater time for them to get drop nutrients, etc

39
Q

Laminar flow is more likely with?

A

Small tubes and slow flow velocity

40
Q

Turbulent flow is more likely with?

A

Large tubes, high flow velocity and low viscocity

41
Q

Which type of flow is used for measurements of BP?

A

Turbulent flow

42
Q

Flow rate remains constant but does the speed?

A

Yes the speed, the velocity of flow can change

43
Q

Vasoconstriction is ?

A

Increased contraction of circular smooth muscle in the arteriolar wall, which leads to increased resistance and decreased flow through the vessel

44
Q

Vasodilation is?

A

Decreased contraction of circular smooth muscle in the arteriolar wall, which leads to decreased resistance and increased flow through the vessel

45
Q

Vasodilation is caused by?

A

Decreased myogenic activity, decreased O2, increased CO2 and other metabolites, increased nitric oxide, decreased sympathetic stimulation: histamine release, in the heat

46
Q

Vasoconstriction is caused by?

A

Increased myogenic activity, increased O2, Decreased CO2 and other metabolites, increased endothelin, increased sympathetic stimulation: vasopressin, angiotensin 2, in the cold

47
Q

Why regulate vessel radius?

A

Regulation of MAP and to regulate blood flow to individual organs

48
Q

Vessel radius is controlled via?

A

Controlled via Intrinsic & Extrinsic mechanisms

49
Q

Is the vessel radius the most significant influence on blood flow?
Normal control - Pathological conditions?

A

Yes, the vessel radius is vital for powerful normal control
e.g. 25% ↑radius → 140% ↑flow
Also critical in pathological conditions (atherosclerosis)
e.g. 25% ↓radius → 60% ↓flow

50
Q

Extrinisic regulation of vessel radius?

A

Generalised sympathetic outflow → constriction to all arterioles (except brain; lack of beta1 adrenoreceptors )
No parasympathetic innervation of arterioles (except genitalia)
Dilation via sympathetic withdrawal
Catecholamines → generalised constriction

51
Q

Intrinisic regulation of the vessel radius?

A

Intrinsic regulation: Local control
Changes within tissues which affect the arteriolar smooth muscle
Important in matching blood flow with the metabolic needs of tissues (e.g. active hyperaemia) - moment by moment influence
Local influences are chemical or physical

52
Q

Endothelial cells release vasoactive substances such as?

A

EDRF (Nitric Oxide) & endothelin

53
Q

What are the chemical local influences on the regulation of vessel radius?
O2? CO2? pH? K^+ions?

A

Decreased oxygen (hypoxia)
Increased CO2 -More is produced as a result of increased metabolism.
Decreased pH: Carbonic acid is generated from CO2, lactic acid is produced from anaerobic metabolism of ATP production.
Increased potassium ions eg. in exercising muscle: repeated action potentials (K+out, Na+ in) may outpace Na+ /K+ pump activity, causing accumulation of K+ in tissue fluid.

54
Q

What physical local influences exist for vessel raidus regulation?

A

Heat or cold
Myogenic responses to stretch: autoregulation

55
Q

Physical local influences on vessel radius - what happens with heat and with the cold

A

Heat increases blood flow to an area by causing localised vasodilation.
Cold causes vasoconstriction and therefore decreased blood flow

56
Q

Do the arterioles in the brain have vasoconstriction or vasodilation?

A

We never want the arterioles within the brain to be vasoconstricting or vasodilating as there is no beta 1 adrenergic receptors for that sympathetic discharge, so the brain is an exception

57
Q

We don’t typically have parasympathetic innervation of these arterioles all over the body as it is sympathetic discharge instead and when we want vasodilation it occur it is due to sympathetic withdrawal however the only place within the body for this parasympathetic innervation of arterioles is the?

A

Both male and female genitalia, whilst they are inactive

58
Q

Physical local influences on intrinsic regulation of vessel radius is also due to myogenic responses to stretch (NB. Autoregulation - see later lecture) explain:

  1. What is nerve - independent contractile activity initiated by…
  2. Arteriolar smooth muscle responds to being stretched by…
  3. What does a decrease in stretch result in…
  4. Do vasoactive substances contribute to these responses…
A
  1. Nerve-independent contractile activity is initiated by the muscle itself.
  2. Arteriolar smooth muscle responds to being stretched by myogenically increasing its tone (contracting), therefore resisting the stretch.
  3. Conversely, a decrease in stretch results in decreased myogenic tone.
  4. Vasoactive substances may also contribute to these responses
59
Q

Do arterioles have much elastic tissue?

A

Remember: Arterioles do not contain much elastic tissue – not very stretchy, so will respond to this mechanical strain.

60
Q

What type of relationship exists between Cross Sectional Area and velocity?

A

Inverse relationship
Flow is constant - what changes is velocity, the speed at which flow travels through a particular vessel - This is determined by number of active capillary beds, so the more capillary beds that need to be supplied by O2 and nutrients, the slower the velocity

Example - The velocity within aorta and larger arteries is greater than smaller vasculature

61
Q

There is complementary action of precapillary sphincters and arterioles in adjusting blood flow

What are the steps of increased tissue metabolic activity to the end increased exchange between blood and tissue to support increased metabolic activity?

A

Increased tissue metabolic activity leads to:
- Increased O2 and decreased CO2 and other metabolites
- Relaxation of precapillary sphincters and arteriolar vasodilation
- Increased number of open capillaries and increased capillary blood flow
- Increased delivery of O2, more rapid removal of CO2 and other metabolites
- Increased surface area available for exchange, decreased diffusion distance from cell to open capillary, increased concentration gradient for these materials between blood and tissue cells
All leads to increase in exchange between blood and tissue to support increased metabolic activity

62
Q

See diagram on factors affecting TPR

A

Short term - increased sympathetic activity is what she is most focused on
Which is reinforced by catecholamines that are released
Less of an effect of long term b.p controls: vasopressin and angiotensin 2 that are vasoconstrictors

=> Sympathetic activity most important

Local control of the myogenic response to stretch plays a minor role in active and reactive hyperaemia where we have to meet demands of active tissue - regular moment of moment i. alteration in CO and reactive - acclusion to blood flow how does the body respond

63
Q

What influences TPR SAQ wise?

A

Mention all from diagram at end of slides
You can say they don’t all contribute as greatly
Say that the main role or main contributer is this sympathetic activity and also what happens locally - intrinsic local control with regards to changes vasoactivity at level fo that smooth muscle but must still discuss the others such as heat and cold, stress, histamine release, etc.

Cardiovascular system (13 decks)

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