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 in diastole
what is central venous pressure
pressure in large veins draining into the heart
if the pressure is high then heart will fill more and end diastolic vol will be greater
what is total peripheral resistance (aka systemic vascular resistance )
resistance to blood flow offered by the systemic vasculature
where is the greatest resistance in the vascular system and how does this affect pressure elsewhere
arterioles
causes pressure in capillaries and venous side to fall but pressure in arterial side to increase
what happens if TPR falls and cardiac output is unchanged
arterial pressure decreases easier for blood to get to venous side.
venous pressure increases
what are the effects of increasing total peripheral resistance
increase in arterial pressure
decrease in central venous pressure
what are the effects of increasing cardiac output if TPR is unchanged
more blood is being pumped out so arterial pressure increases and central venous pressure decreases.
what are the effects of decreasing CO and keeping TPR unchanged
less blood ejected so arterial pressure decreases and venous pressure increases.
what happens when there is a higher demand for blood in tissues
arterioles and precapillary sphincters will dilate. Therefore TPR falls. The heart needs to pump more so that the arterial pressure doesn’t fall and the venous pressure doesn’t rise
what is the relationship between intraventricular pressure and venous pressure
the higher the venues pressure the more the heart fills. the more the heart fills the higher the left ventricular pressure
displayed in ventricular compliance curve
what is the Frank-starling Law of the heart
the more the heart fills the harder it contracts(up to a limit)
as its beings stretched more
what happens in cardiac muscle when it stretches in relation to calcium sensitivity
calcium sensitivity increases which is why the length tension curve is steeper in cardiac muscle than skeletal muscle
what is an intrinsic control mechanism on the heart
increased stroke vol with increased filling
same vol of blood pumped to body must also be pumped to lungs
example of extrinsic factors on starling curve
sympathetic stimulation
circulating adrenaline
what factors determine cardiac output
how much the ventricle empties- determined by how hard it contracts, how hard it is to eject blood
stroke vol, heart rate
contractility and heart rate are controlled by the autonomic nervous system.
how arterial blood pressure affects nervous system
stretch receptors in aorta and carotid arteries sense arterial bp and alter parasmpathetic and sympathetic ns activity to control heart rate and contractility.
decrease in arterial bp reduces parasympathetic ns and stimulates sympathetic ns to increase heart rate and contractility
what are the effects of increase in metabolism on TPR,CO,arterial pressure and venous pressure
TPR falls to supply more blood
results in a decrease of arterial pressure and increase in venous pressure
heart responds by pumping more
how the cvs responds to eating a meal (local vasodilation of gut-needs blood supply)
TPR decreases, arterial pressure decreases
this is detected by stretch receptors in arteries stimulating increase in sympathetic NS increasing contractility which increases stroke vol & heart rate.
overall increasing cardiac output
how standing up affects CNS
standing up causes pooling of blood in legs due to effect of gravity on a column of liquid.
venous pressure , cardiac output and arterial pressure decrease.
cannot be adjusted by intrinsic factors.
baroreceptor reflex and autonomic NS increase heart rate, contractility and increase TPR.
if these reflexes don’t work you get postural hypotension ( not enough blood going to brain causing dizziness and faint).
why is there higher cardiac output during exercise
calf muscle pumping and venoconstriction(Smooth muscle cells in veins contract) returns more blood to the heart.
Decreased TPR increases venous return
increased contractility and heart rate due to increased sympathetic drive
why is the internal jugular vein important
is in direct contact with superior vena cava which drains into right atrium. therefore changes in pressure in right atrium transmit back to the internal jugular vein.
biphasic pulse
conditions that will increase jugular venous pressure
if right sided of heart doesn’t pump blood out properly
volume overload with IV infusion
if anything impairs filling of the heart e.g stabbing
