CPR Contractility & Cardiac Output Flashcards
What is cardiac output dependent on?
Heart rate
Contractility
Preload
Afterload
How do cardiac glycosides work?
used to treat heart failure by
inhibition of K+ binding on Na/K ATPase increases Na+ conc decreases Ca2+ efflux thru Ca2+/Na+ exhanger increases intracell Ca2+ positive inotropic effect
How do you calculate cardiac output?
CO=HR x SV
SV relates to myocardial contractility
What is left ventricular end-diastolic volume?
amount of blood ready to be pumped
wall tension in LV just before contraction is initiated
What is the Frank-Starling relationship?
volume of blood ejected by ventricle depends on volume present in ventricle @ end of diastole
How do CO & venous return relate?
CO=venous rate (steady state)
What is afterload?
for LV, is related to aortic pressure
the force opposing contraction/pressure required to eject blood from LV
Preload v Afterload w/ in cardiac cycle
Preload=LV end-diastolic volume (fiber length from where muscle contracts)
Afterload=aortic pressure (what is needed to open aortic valve)
What is stroke volume?
volume of blood ejected by ventricle w/ each beat
SV=EDV - ESV
Usually about 70ml
What is ejection fraction?
fraction of EDV ejected in each stroke volume
(measure of efficiency and contractility)
EF = SV/EDV, approx 55%
What is cardiac output?
total volume of blood ejected by ventricle per min
CO (Q) = SV x HR
usually is 5 L/min
What happens to CO if preload increases?
increases CO & contractility in a healthy heart
What happens to CO if afterload increases?
decrease CO (must increase contractility or increase HR)
What is the effect of HR on contractility?
increased HR increases contractility (more Ca2+ enters cells & taken up into SR)
What is the effect of sympathetic stimulation on CO?
positive ionotropic effect
inhibits troponin I & stimulates phospholamban & sarcolemma Ca2+ channels
What is the effect of parasympathetic stimulation on CO?
negative ionotropic effect in ATRIA only (no influence on ventricular myocytes)
activation of muscarinic receptor decreases inward Ca+ current & increase K+ efflux
What does phase 1 to 2 on vent pressure-volume loop represent?
isovolumetric contraction
What does phase 2 to 3 on pressure volume loop represent?
ventricular ejection
What does phase 3 to 4 on pressure volume loop represent?
isovolumetric relaxation
What does phase 4 to 1 on pressure volume loop represent?
ventricular filling
What compensation occurs with increased preload?
more venous return, more blood volume
increased SV
What compensation occurs with increased afterload?
aortic stenosis, hypertension
greater pressure needed w/ reduced SV & EF%
What compensation occurs with increased contractility?
adrenergic stimulation
increased SV & EF%
less blood left in heart
What is pressure work?
aortic pressure
What is minute work?
CO x aortic pressure
What is stroke work?
performed by LV (area w/ in pressure-volume loop)
stroke volume x aortic pressure
What is the Fick Principle?
describes O2 consumption
O2 consumption= CO x (O2 in pulmonary vein - (CO)(O2 in pulmonary artery))
What does the cardiac function curve describe?
relationship between CO & venous return
as venous return increases, RA pressure increases & EDV & end-diastolic fiber length increases
What does equilibrium on cardiac function curve indicate?
CO = venous return (will vary depending on state of CV system)
What is a vascular function curve?
mean circulatory filling pressure
when there is no CO & depends entirely on vascular compliance & blood volume
Cardiac Failure
decreased ionotropy
decreased vascular compliance
increased blood volume
increased SVR/TPR
