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
