Control of Cardiac Output Flashcards
Define afterload
the load the heart must eject against
Outline preload
amount the ventricles are stretched (filled) in diastole = related to end diastolic volume or central venous pressure
What is total peripheral resistance?
resistance to blood flow offered by all the system vasculature
What happens to the pressure of fluid in a tube as it encounters resistance?
Restriction = less outflow to the next chamber = pressure lowers
What will happen when constricting the arterioles?
arterioles offer the greatest resistance = constriction increases resistance = fall in pressure in capillaries and on venous side but rise in pressure on arterial side
Outline what happens if total peripheral resistance fall and cardiac output is unchanged
= arterial pressure fall + venous pressure will increase (less pinching = more blood can get through lowing arterial and raising venous)
What happens if total peripheral resistance increases and cardiac output is unchanged?
= arterial pressure will increase = venous pressure will fall (more pinching = even less can get through raising arterial and lowering venous)
If cardiac output increase and total peripheral resistance is unchanged what happens?
= arterial pressure will increase + venous pressure will fall (more kicked out = raising arterial, lowering venous as taken from there)
If cardiac output decreases and total peripheral resistance is unchanged what happens?
= arterial pressure will fall and venous pressure will rise (less kicked out = lowering arterial, raising venous as hasn’t been taken from there)
What happens if the tissues need more blood?
arterioles and precapillary sphincters will dilate = fall in peripheral resistance = heart need to pump more to maintain arterial pressure high and venous pressure low
What is the equation for cardiac output?
CO = SV X HR –> 70kg = 5L/min
What is the equation for stroke volume?
SV = EDV (end-diastolic vol) – ESV (end-systolic vol) = typically 70ml
What does the ventricular compliance curve show?
The higher the venous pressure the more the heart fills
Outline the frank-starling law of the heart
The more the heart fills, the harder it contracts (up to a limit)
If you stretch the fibres of the heart before contracting it will contract harder
Increased venous return leads to?
Increased left ventricular end-diastolic pressure and volume = increase in SV
What does the length tension curve for cardiac muscle show?
If sarcomere length is too short filament overlap interferes with contraction.
In cardiac muscle, also get an increase in Ca sensitivity as muscle fibres are stretched
Why does starlings law of the heart ensure both circulation loops are equal?
with increased fill there is increased stroke volume which is received by the other side of the heart and the same occurrence happens
Define contractility
Force of contraction for a given fibre length
What factors increase heart contractility?
Extrinsic such as sympathetic stim and circulating adrenaline
What is aortic impedance?
Pressure in the aorta
List the factors that determine cardiac output
How hard ventricle contracts (determined by EDV + contractility)
how hard it is to ejects blood (determined by aortic impedance)
If metabolism increases what happens to total peripheral resistance, arterial and venous pressure?
TPR falls = more blood supply = lowers arterial pressure and raised venous pressure
In what situation does both arterial and venous pressure change in the same direction?
Standing up and exercise
Increase SV with increased filling is what type of control mechanism?
Intrinsic
