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Personalised Medicine - Cardiovascular > L4 - Physiology of the Heart III > Flashcards

L4 - Physiology of the Heart III Flashcards

1
Q

What is the aorta?

A

Large artery away from the heart
Supplies all other arteries
At the base is the aorta valve

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2
Q

What are the coronary arteries?

A

First branch of the aorta
Left and right
- These then branch further to supply the heart muscle
- The main arteries run over the surface of the heart
- Allow surgeons to reach them and allow bypass grafts to be stitched onto arteries
Big arteries – sit on top of heart
Smaller arteries – perforate into heart muscle

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3
Q

What drives blood flow down the coronary arteries?

A

Pressure at top end of coronaries is the same pressure as in the aorta

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4
Q

Why does there need to be a pressure gradient in the coronary arteries?

A

Pressure at far end of coronaries arteries need to be less that at the top
- The end of the coronary tree is basically the inner surface of the ventricle
- Pressure in the ventricle will determine pressure at bottom end of coronary artery
Pressure difference = aorta pressure – ventricular pressure

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5
Q

When are the aortic valves open and closed?

A

When the heart contracts the aortic valve opens in relation to flow
When the heart relaxes the aortic valve closes
- It then supports the blood above it
- Otherwise all the blood you have just ejected would rush back into the ventricle

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6
Q

How do you calculate coronary blood flow?

A

Perfusion pressure / resistance

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7
Q

How do coronary arteries change their blood flow?

A

Restrict and dilate

This changes their resistance

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8
Q

At what point in the cardiac cycle foes blood flow occur?

A

Diastole

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9
Q

Why does cardiac blood flow not occur in diastole?

A

When the heart muscle contracts it squeezes the smaller arteries

  • Can’t get blood flow them down
  • Every time heart contract it cuts of its own blood supply
  • Coronary arteries on the surface still patent –> but nowhere for blood to go –> no blood flow
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10
Q

What is the hearts oxygen consumption?

A

Heart is an active tissue – metabolically it takes up a lot of energy
One of the worst perfused organs
- No reserves / wasted blood flow
When we exercise the demand goes up and the flow goes up with it

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11
Q

Which organs have the least oxygen consumption?

A

Brain, kidney and skin

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12
Q

Which organs have the highest oxygen consumption?

A

Heart and contracting skeletal muscle

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13
Q

How do you calculate oxygen delivery?

A

Arterial oxygen concentration X Coronary blood flow

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14
Q

What is the arterial oxygen concentration?

A

Relatively little dissolved in plasma

97-100%

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15
Q

What is arterial oxygen concentration determined by?

A

Mainly determined by oxygen bound to haemoglobin
- Haem contains iron atoms – each atom binds one oxygen molecules
- Each haemoglobin carries 4 oxygen molecules
Anaemia will cause reduced oxygen delivery

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16
Q

Why is the ordinarily little change in the oxygen content of arterial blood?

A

97-100% normally
If already pretty much fully saturated - in exercise when hearts demand for oxygen goes up, you cannot carry more oxygen/change concentration
- Therefore primary determinant of oxygen delivery is coronary blood flow
- This is changed by pressure changes

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17
Q

In the aortic pressure trace what is the dichroic notch?

A

When the aortic valve closes

After it closes some blood continues to leach out into the system and pressure falls further

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18
Q

How and what do you measure when monitoring blood pressure?

A

Cuff around arm and monitor brachial artery pressure
Brachial artery is connected directly to aorta  measure of aortic pressure
Measure
- Systolic pressure - peak pressure generated by LV contraction
- Diastolic pressure - basal pressure after aortic valve is closed

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19
Q

Left ventricular pressure trace - why does systolic BP - aortic pressure?

A

If aortic valve opens fully the pressure generated in the ventricle during systole is exactly the same as the pressure generated in the aorta/brachial artery

  • Systolic pressures all the same
  • Systolic BP = aortic pressure
20
Q

Left ventricular pressure trace - why does the aortic valve not influence diastolic pressure in the ventricles?

A

In the ventricle you are proximal to the aortic valve – the aortic valve is not influencing the diastolic pressure

  • So when the ventricles stop contracting and starts relaxing the pressure drops to nearly 0
  • Then starts to fill again in diastole ready for the next cycle
  • End point of diastole –> LVEDP
21
Q

Is systolic BP always the same or always different?

A

The same

22
Q

Is diastolic BP always the same or always different?

A

Different

  • Arterial diastolic BP – 70-80 (supported by aortic valve)
  • Ventricle diastolic BP – LVEDP
23
Q

Does coronary perfusion occur during diastole or systole?

A

Only occurs during diastole
Perfusion pressure in diastole is dependent on aortic diastolic pressure and LVEDP
- The difference between the two is the pressure gradient - determines blood flow

24
Q

Overview of left ventricular pressure trace

A

Increases during systole

Falls back to nearly 0 during diastole

25
Q

Overview of aortic pressure trace

A

Increases during systole

Falls back to arterial diastolic pressure – supported by aortic valve

26
Q

The bigger the diastolic pressure the greater?

A

The perfusion

27
Q

What are 3 physical factors that influence diastolic coronary flow?

A

Length of diastole
Raised LVEDP
Reduced diastolic pressure

28
Q

How does raised LVEDP affect diastolic coronary flow?

A

Raised LVEDP –> decreases perfusion pressure
Failing hearts tend to run on high LVEDP
LVEDP stretches the muscle leading to more contraction

29
Q

How does the length of diastole affect diastolic coronary flow?

A

Length of diastole –> tachycardia –> disproportionately reduces diastole
Systole is relatively fixed in terms of its duration

30
Q

How does reduced diastolic pressure affect diastolic coronary flow?

A

Reduced diastolic pressure –>decreases perfusion pressure

31
Q

What is auto regulation of coronary blood flow?

A

Ability of an organ to maintain a constant blood flow despite changes in perfusion pressure

  • Protection mechanism
  • Occurs by changing resistance
32
Q

What can cause a fall in perfusion pressure?

A

Loss of blood –> coronary blood flow drops

33
Q

When a fall in perfusion pressure occurs due to loss of blood how does the body respond?

A

Pressure stays low
Blood flow would also stay low if nothing else happened
- Autoregulation kicks in and resistance in the tissue drops
– Due to local metabolite effect
- Allows greater blood flow

34
Q

What are the two ways coronary blood flow can be regulated?

A

Vascular control - metabolites and mediators
- Most important
Mechanical control

35
Q

What does hypoxia cause in the coronary arteries?

A

Causes coronary vasodilatation in situ but not in isolated coronary artery

  • Coronaries being present in whole organ needed for local effects
  • Suggests caused by local metabolite – adenosine
36
Q

What increases if metabolism in the heart is happening anaerobically?

A 
Potassium ions
Carbon dioxide
Hydrogen ions
Lactic acid
These themselves cause coronary vasodilation
37
Q

How does the sympathetic nervous system control coronary arteries?

A

Neural and humoral control

  • Less important
  • Large vessel α-adrenoceptor vasoconstriction
  • Smaller vessel β2 vasodilatation
38
Q

What is the main symptom of coronary artery disease?

A

Narrowing of the coronary artery –> cholesterol plaques

Overpowers all mechanisms coronary arteiers have to increase blood flow

39
Q

How do patients with coronary disease know they aren’t getting enough blood flow to the heart?

A

Get accumulation of metabolites –> angina/pain in chest
May be fine at rest - heart demands not too high
On exercise –> heart rate increases –> blood pressure increases –> when narrowing of arteries becomes an issue (don’t have the oxygen reserve)

40
Q

What two hormones does the heart release?

A

Heart is an endocrine organ - releases hormones which travel in the blood and act somewhere else
Atrial natriuretic peptide
B-natriuretic peptide

41
Q

Where does atrial natriuretic peptide come from and cause?

A

Comes from the atria

Released during stretch / raised atrial pressure / volume overload

42
Q

Where does B-natriuretic peptide come from and cause?

A

Comes from the ventricles

Released during stretch / raised ventricular pressure / volume overload

43
Q

What are the main effects of atrial natriuretic peptide and B-natriuretic peptide?

A

Increase renal excretion of sodium and water (diuresis)
- Try to get rid of fluid to lower the pressure
Relax vascular smooth muscle (except efferent arterioles of renal glomeruli)
- Still increase perfusion pressure in glomeruli
- Increase Na and water filtration into kidney
Increased vascular permeability
Inhibit the release or actions of
- Aldosterone
- Angiotensin II
- Endothelin
- Anti-diuretic hormone

44
Q

What is the importance of atrial natriuretic peptide and B-natriuretic peptide inhibiting aldosterone, angiotensin II, endothelin and ADH?

A

These hormones all cause vasconstriction, water retention and salt retention
- Counter-regulatory system to the renin-angiotensin system

45
Q

What are cardiac natriuretic peptide metabolised by?

A

Neutral Endopeptidase (NEP - neprilysin)

46
Q

What can NEP be inhibited by?

A

A combination drug
- Sacubitril – neprilysin inhibitor
- Valsartan – angiotensin II blocker
Novel therapy for heart failure –> allows increased levels of cardiac natriuretic peptides

Personalised Medicine - Cardiovascular (11 decks)

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