Flashcards in Shock ✅ Deck (148)
What does cardiac output determine?
Blood pressure, hence tissue perfusion
How is cardiac output calculated?
Heart rate x stroke volume
What can control of cardiac output be divided into?
What does the intracardiac mechanism of controlling CO depend on?
Physical properties of the cardiac muscle
What happens when the cardiac muscle fibres are stretched?
They respond with more forceful contraction until the sarcomeres become overstretched
What is the relationship between cardiac muscle fibres stretching and contraction described by?
The Frank-Starling curve
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
What is the increase in cardiac output with increased ventricular end-diastolic volume the rationale for?
Volume resuscitation in shock
What happens to the Frank-Starling curve as there is stretching beyond the optimal sarcomere length?
There is reduction in stroke volume
What is the clinical relevance of stroke volume decreasing as sarcomeres become overstretched?
It means that excessive volume resuscitation has a negative effect
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
What is the extracardiac mechanism of control of cardiac output?
The autonomous nervous system
What effect does the SNS have on cardiac output?
Increases heart rate and contractility, increasing CO
What effect does the PNS have on CO?
Reduces heart rate and contractility, reducing CO
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
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.
Where are baroreceptors located?
In the carotid sinus and aortic arch
What do baroreceptors respond to?
Where do baroreceptors send impulses to?
They send impulses to the autonomic vasomotor centre in the brainstem
What does baroreceptor stimulation result in?
Vasoconstriction and and increases in HR, BP, and CO
Via what system do baroreceptors lead to an increase in HR, BP, and CO?
Where are chemoreceptors located?
Carotid body and aortic arch
What do chemoreceptors respond to?
What do chemoreceptors stimulate?
- Vasoconstrictor response
- Respiratory rate
What does chemoreceptor stimulation of the vasoconstrictor response result in?
Increase in arterial pressure
What does chemoreceptor stimulation of the respiratory rate result in?
Provides respiratory compensation of metabolic acidosis
What is the vasomotor centre?
An intense controller of BP
When is the strongest response by the vasomotor centre seen?
When it is subjected to ischaemia, i.e. cerebral ischaemia
What secretes renin?
The juxtaglomerular cells of the kidney