Session 2- Control of cardiac output Flashcards
afterload
the load the heart must eject blood against roughly equivalent to aortic pressure
preload
amount the ventricles are stretched (filled) in diastole- related to the end diastolic volume or central venous pressure
what is central venous pressure
pressure of large veins draining into the heart
arterial pressure
pressure in large arteries
total peripheral pressure
sometimes referred to as systemic vascular resistance- resistance to blood flow offered by all the systemic vasculature
what happens to pressure of fluid in a tube as it encounters resistance
the pressure the blood exerts drops as it flows through a resistance
which vessels offer the greater resistance
arterioles
what does more resistance lead to
higher pressure upstream from the arterioles, but a bigger drop in pressure as blood reaches the venous side
what happens if TPR falls and CO is unchanged
arterial pressure will fall
venous pressure will increase
A fall in peripheral resistance will mean it is easier for blood to flow through the resistance vessels to the venous side so arterial pressure will drop but venous pressure will increase as it easier to flow through
what happens when TPR increases and CO is unchanged
arterial pressure will increase
venous pressure will fall
an increase in TPR means it is harder for blood to flow through but CO stays the same so arterial pressure will increase as the heart is still pumping out the same amount of blood. Bigger drop in pressure this resistance so central venous drops
what happens in CO increases ans TPR is unchanged
arterial pressure will increase
venous pressure will fall
if you increase cardiac output arterial pressure will go up and this will go through TPR which is unchanged. Because you’re pumping out more blood less blood is left in the heart so it is easier for blood to flow back in as there is a drop in central venous pressure
what happens if CO decreases and TPR is unchanged
arterial pressure will fall
venous pressure will rise
if you reduce CO less blood is being pumped so arterial pressure will fall. However since you aren’t emptying the heart as much it is harder to fill it up so central venous pressure increases
how is peripheral resistance controlled
precapillary sphincters- dilate to reduce resistance
how does the heart respond to a drop in resistance
it pumps more to make sure arterial pressure doesn’t fall and venous pressure doesn’t rise
this is done through extrinsic and intrinsic mechanism
calculate stroke volume
end diastolic volume - end systolic volume
volume of blood ejected in each heart beat
when does ventricular filling occur
diastole
AV valves are open but the aortic and pulmonic valves closed
what is the ventricular compliance curve
the higher the venous pressure the more the heart fills
the more the heart fills the higher the left ventricular pressure
frank-starling law of the heart
the more the heart fills the harder it contracts
the harder the heart contracts, the bigger the stroke volume
an increase in venous pressure will fill the heart more
what does increasing venous return do
increased LVEDP and volume
this causes an increase in stroke volume, so that the extra blood pumped out of the ventricle
LVEDP- left ventricular end-diastolic pressure
what is contractility
the force of contraction for a given fibre length
effects of increasing arterial pressure
increased when peripheral resistance is increased- makes it harder for the heart to pump out
increased TPR also reduces venous pressure and therefore reduces filling of the heart
what determines cardiac output
how hard it contracts- determined by end diastolic volume and contractility
how hard it is to eject blood - determined by aortic impedance - aortic pressure
where is right atrial pressure measured
right internal jugular vein
direct column of blood connected to right atrium
