control of cardiac output Flashcards
define after load
load heart must eject blood against (aortic pressure)
define preload
amount ventricles are stretched in diastole
define TPR (total peripheral resistance)
resistance to blood flow offered by all systematic vascuculture
what happens when you increase the resistance in the blood vessel
the greater the resistance the more pressure decreases on the venous side (after the pressure increase) and the more it increases on the atrial side (before pressure increase)
in which vessel does pressure most decrease in the CVS
decreases most in the arterioles due to them offering the most resistance. largest decrease in size of lumen
how decreasing TPR affects venous pressure, arterial pressure and cardiac output
arterial pressure decreases, venous pressure increases and cardiac output does not change
how increasing TPR affects venous pressure, arterial pressure and cardiac output
arterial pressure increases, venous pressure decreases and cardiac output does not change
what happens to arterial and venous pressure when you increase cardiac output
arterial pressure increases and venous pressure decreases because more blood pumped out of the venous system (TPR doesnt change)
what happens to arterial and venous pressure when you decrease cardiac output
arterial presure decreases because less blood being pumped into venous system and venous pressure increases
what happens when demand for blood in tissues increases
sphincters dilate and resistance falls. the heart therefore needs to pump more so arterial pressure doesnt fall and venous pressure doesnt rise. this is a response coordinated by intrinsic and extrinsic mechanisms
equation for cardiac output
stroke volume (usually 70ml) x heart rate
how to calculate stroke volume
end disatolic volume - end systolic volume
how to increase stroke volume
increase EDV by filling ventricles more and decrease ESV by emptying ventricles more
explain the ventricular compliance curve
shows that ventricular volume increases as ventricular pressure increases. this is because the heart fills more if there is a higher venous pressure and the therefore there is a higher ventricular pressure. DRAW GRAPH
what is the frank starling law
if you stretch the fibre of the heart before contraction it will contract harder and therefore the heart fills more and it contracts harder. therefore increasing venous pressure increases contraction
describe and draw the starling curve
increasing venous return leads to higher LVEDP and an increased stroke volume. shows sigmoidal curve with stroke volume down y axis and LVEDP across x axis
describe and draw the length tension curve for cardiac muscle
if the sarcomere has too much overlap it interferes with contraction and also muscle is more sensitive to calcium if muscle fibres are stretched. is sigmoidal curve with contraction force down y and resisting sarcomere length across x axis
why do the right and left sides of the heart both have same amounts of blood
explained by starlings law. its under intrinsic control if the stroke volume increases. if stroke volume increases more blood pumped to opposite side of the heart increasing its stroke volume too
how contractility force is controlled by extrinsic factors
more sympathetic and adrenaline means increased contractility and therefore higher stroke volume and PVEDP and it decreases with less sympathetic stimulations
how increased arterial pressure decreases stroke volume
aortic pressure increases when TPR increases. This decreases venous pressure and stroke volume goes down due to decreased filling of ventricles. overtime this causes hypertension and hypertrophy
how CVS responds to eating a meal and vasodilation in the gut to supply extra blood supply to gut
TPR decreases due to vasodilation this decreases arterial which increases heart rate pressure and decreases venous pressure which increases stroke volume. both these increase cardiac output which decreases arterial pressure and increase venous pressure
how CVS responds to standing up
blood pools in venous system when you stand up decreasing venous pressure and therefore cardiac output which in turn decreases arterial pressure. can’t adjust these consequences by intrinsic mechanisms.
how CVS responds to exercise
vasocontriction and muscle pumping increases blood returning to heart. in response heart rate increase and TPR decreases to increase venous return. also contractility increased by sympathetic nervous system. all of these increase cardiac output
what is the jugular venous pulse
it measures venous pressure and seen along neck muscle. its an important exam to evaluate cardiac contains because there are no valves in this vein. both a and v waves observed as pulses in the physical exam
draw an explain the graph
a- atrial contraction increases pressure
x- atrial relaxation decreases pressure
c- eluding of tricuspid valve with ventricular contraction
x’- downaward movement of tricuspid valve with ventricular contraction decreases atrial pressure
v- pressure increases as atria fill
y - atrial emptying as tricuspid valve opens. pressure decreases
what is an elevated JVP caused by
too much fluid from an IV infusion, obstruction of superior vena cava, inability to pump blood (bradycardia, right ventricular failure and more) and hyper dynamic circulation all cause an elevated JVP.
