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Flashcards in Shock ✅ Deck (148)
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1

What does cardiac output determine?

Blood pressure, hence tissue perfusion

2

How is cardiac output calculated?

Heart rate x stroke volume

3

What can control of cardiac output be divided into?

- Intracardiac
- Extracardiac

4

What does the intracardiac mechanism of controlling CO depend on?

Physical properties of the cardiac muscle

5

What happens when the cardiac muscle fibres are stretched?

They respond with more forceful contraction until the sarcomeres become overstretched

6

What is the relationship between cardiac muscle fibres stretching and contraction described by?

The Frank-Starling curve

7

What initially happens in the Frank-Starling curve?

Increases in ventricular end-diastolic volume result in an increase in stroke volume, and hence cardiac output

8

What is the increase in cardiac output with increased ventricular end-diastolic volume the rationale for?

Volume resuscitation in shock

9

What happens to the Frank-Starling curve as there is stretching beyond the optimal sarcomere length?

There is reduction in stroke volume

10

What is the clinical relevance of stroke volume decreasing as sarcomeres become overstretched?

It means that excessive volume resuscitation has a negative effect

11

What does the intracardiac mechanism of control of cardiac output ensure?

The right and left ventricles perform equally, and fluid does not accumulate in the lungs

12

What is the extracardiac mechanism of control of cardiac output?

The autonomous nervous system

13

What effect does the SNS have on cardiac output?

Increases heart rate and contractility, increasing CO

14

What effect does the PNS have on CO?

Reduces heart rate and contractility, reducing CO

15

How does the SNS increase cardiac output?

The SNS causes a release of adrenaline from the adrenal glands, and noradrenaline from sympathetic nerve fibres innervating the heart and blood vessels. This causes vasoconstriction of arterioles and veins, and increase heart rate and contractility via stimulation of alpha and beta adrenergic receptors

16

How does the parasympathetic nervous system affect CO?

Fibres innervate the blood vessels of the head, viscera, and heart. They release ACh, which causes vasodilation and reduction in heart rate and contractility via muscarinic M3 and M2 receptors respectively.

17

Where are baroreceptors located?

In the carotid sinus and aortic arch

18

What do baroreceptors respond to?

Stretch

19

Where do baroreceptors send impulses to?

They send impulses to the autonomic vasomotor centre in the brainstem

20

What does baroreceptor stimulation result in?

Vasoconstriction and and increases in HR, BP, and CO

21

Via what system do baroreceptors lead to an increase in HR, BP, and CO?

The SNS

22

Where are chemoreceptors located?

Carotid body and aortic arch

23

What do chemoreceptors respond to?

- Hypoxaemia
- CO2
- Acidosis

24

What do chemoreceptors stimulate?

- Vasoconstrictor response
- Respiratory rate

25

What does chemoreceptor stimulation of the vasoconstrictor response result in?

Increase in arterial pressure

26

What does chemoreceptor stimulation of the respiratory rate result in?

Provides respiratory compensation of metabolic acidosis

27

What is the vasomotor centre?

An intense controller of BP

28

When is the strongest response by the vasomotor centre seen?

When it is subjected to ischaemia, i.e. cerebral ischaemia

29

What secretes renin?

The juxtaglomerular cells of the kidney

30

When is renin secreted?

In response to a fall in BP