Session 2: Control Of Cardiac Output Flashcards
What is afterload?
The load the heart must eject blood against (roughly equivalent to aortic pressure)
What is preload?
Amount the ventricles are stretched (filled) in diastole - related to EDV or CVP
What is total peripheral resistance?
Resistance to blood flow offered by all the systemic vasculature (also referred to as systemic vascular resistance)
What happens to pressure of fluid in a tube as it encounters resistance?
- ‘Resistance’ is associated with vasoconstriction
- pressure on arterial side increases
- Pressure of fluid in the capillaries and on venous side fall
What is the effect of decreasing TPR (CO unchanged)?
Arterial pressure falls
Venous pressure rises
What is the effect of increasing TPR (CO unchanged)?
Arterial pressure rises
Venous pressure falls
What is the effect of increasing CO (TPR unchanged)?
Arterial pressure rises
Venous pressure falls
What is effect of decreasing CO (TPR unchanged)?
Arterial pressure falls
Venous pressure rises
What happens if the demand for blood in tissues increases?
Arterioles and precapillary sphincters dilate
Therefore TPR falls
How did cardiac output calculated?
CO = Stroke volume x heart rate
How is stroke volume calculated?
SV = EDV - ESV
What is the typical stroke volume for a 70kg man?
70ml
What is the relationship between venous pressure and filling of the heart?
The higher the venous pressure the more the heart fills
What does the Frank-Starling law of the heart state?
If you stretch the fibres of the heart before contracting, force of contraction increases
What does compliance mean?
How easily a chamber of the heart or the lumen of a blood vessel expands when it is filled with a volume of blood
What does the Starling curve show?
LV end-diastolic pressure and stroke volume have a direct relationship
What is the intrinsic control mechanism of the heart?
Increased stroke volume with increased filling of the heart
What is contractility?
Force of contraction for a given fibre length
What is the effect of increasing arterial pressure on stroke volume?
- arterial pressure is increased when TPR is increased
- therefore venous pressure is reduced
- reduced filing of the heart
- Stroke volume decreases
What factors determine cardiac output?
- Stroke volume
- Heart rate
- End-systolic volume
- end-diastolic volume
- arterial blood pressure
- aortic impedance
- contractility
- autonomic nervous system
What does increased metabolism of the body result in?
TPR falls
Arterial pressure falls
Venous pressure rises
Heart pumps more blood
How does the CVS respond to eating a meal?
Local vasodilation in the gut
- TPR falls
- arterial pressure falls
- Venous pressure rises
- stroke volume increases
- heart rate increases
- cardiac output increases
- arterial pressure rises
- venous pressure falls
What effect does standing up have on the CVS?
- ‘pooling’ of blood in legs
- venous pressure falls
- arterial pressure falls
- baroreceptor reflex and ANS increase heart rate and TPR
What happens if baroreceptor and ANS reflexes don’t work when standing up?
Postural/orthostatic hypotension
What changes occur in the CVS when exercising?
- initially: venoconstriction returns more blood to the heart (because venous pressure rises)
- later: decreased TPR also increases venous return
- very early response of increased heart rate
- increased contractility
- INCREASED CARDIAC OUTPUT
