Control of Cardiac Output Flashcards
What is afterload
the load the heart must eject blood again (roughly equivalent to aortic pressure/impedance)
What is preload
amount the ventricles are stretched/filled in diastole. related to EDV or central venous pressure
what is total peripheral resistance (systemic vascular resistance)?
resistance to blood flow by all systemic vasculature
what happens to the pressure of fluid in a tube as it encounters resistance
the pressure decreases.
what does constriction of the arterioles do?
increases the resistance causing venous and capillary pressure to fall and arterial pressure to rise.
what will happen to arterial pressure and venous pressure if TPR falls and cardiac output remains the same
arterial pressure will decrease and venous pressure would increase
what will happen to arterial pressure and venous pressure if TPR increases and cardiac output remains the same
arterial pressure will increase and venous pressure will decrease
what effect does changing cardiac output have on arterial and venous pressures if TPR remains the same
if CO increases arterial pressure will increase and venous will decrease. Vice versa if CO decreases
How does the heart react to changes in tissue demand for blood
by detecting changes in the arterial BP and central venous pressure through intrinsic and extrinsic mechanisms.
what is cardiac output
the amount of blood pumped by the heart per unit of time. Usually litres per min. stroke vol x heart rate
what is stroke volume
the amount of blood pumped by the ventricles during systole. end diastolic volume- end systolic volume
what percentage of the normal EDV is the SV
67%
how can the SV change
by increasing the EDV or decreasing the ESV
what causes the ventricles to stop filling
when the venous pressure (pulmonary veins) is equal to the intraventricular pressure
what does the frank-starling law say
stretching a muscle before contraction leads to a greater force of contraction up until a point
why is the frank-starling law important to the heart
the more the heart fills the harder it contracts. increases venous pressure will increase ventricular filling depending on the compliance. leading to bigger stroke volume
what measurement is used for filling pressure and what is the normal value
left ventricle end diastolic pressure (LVEDP) 8mmHg
why is sarcomere length important
if length is too short overlap of contractile proteins interferes with contraction
what happens to calcium sensitivity in cardiac muscle as it is stretched
it increases
what is contractility
the force of contraction for a given fibre length. change in the stroke volume for a given left ventricular end diastolic pressure
what extrinsic factors can change contractility
sympathetic stimulation (inc or dec) and circulating adrenaline
what is the effect of increases TPR on aortic impedance and venous pressure
increases aortic pressure so harder for the heart to pump out blood and also reduces venous pressure so reduced filling of the heart.
what factors affect CO
how hard it contracts- EDV and contractility
aortic impedance
heart rate (sympathetic nervous system)
what effect does metabolism have on the heart
increase in metabolism leads to decrease in TPR to supply more blood resulting in decrease aBP and increased vBP causing positive inotropy
how does postural hypotension arise
standing up decreases vBP due to gravity, reducing filling and decreasing aBP baroreceptor reflex and autonomic nervous system don’t increase heart rate and TPR.
what effect does excercise have on the heart
initial muscle pumping and venoconstriction increases venous return as does later decreased TPR. increased sympathetic drive and contractility.
