Cardiac output Flashcards
what is the LVOT? where is it located?
left ventricular outflow tract - where blood travels from LV, along the leaflet of the mitral valve, and out through the aorta
definition: cardiac index
volume of blood ejected from the heart (L) per unit time (min) per unit of body surface area (m2)
what are the determinants of SV?
EDV / preload
ventricular contractility
afterload
what parameter is a key determinant of ventricular contraction?
ventricular EDV
definition: preload
tension exerted on the cardiac venticular muscle when it begins to contract
definition: afterload
pressure that the ventricle has to win to produce SV
definition: ESV
intraventricular volume at the end of systole
what are the determinants of ESV?
preload
ventricular contractility
afterload
what is the effect of preload on SV?
within limits, SV increases as preload increases
the force of ventricular contraction is a function of what parameter of cardiac output? what is the name of this relationship?
ventricular end diastolic length of cardiac muscle
length dependent activation (frank starling law of the heart)
what mechanism explains the balancing of output between the ventricles?
length dependent activation - the length of myocardial sarcomere determines its sensitivity to calcium
what is the result of inadequate preload?
decrease in CO
hypotension
what is the result of an excessive initial stretch of cardiac muscle?
decompensation
decrease in CO
what is the effect of increasing afterload with preload and contractility remaining constant?
SV decreases with increasing afterload
what is the ANREP effect? what is the initial response?
when aortic pressure is elevated abruptly, a positive inotropic effect follows within 1 or 2 minutes
initial response - length dependent activation
what is the mechanism of the ANREP effect?
increased LV wall tension
increased cytosolic sodium level
increased myocardial cytosolic calcium level
increased myocardial contraction
what is the effect of increasing contractility with preload and afterload remaining constant?
increasing increases SV, and vice versa
what is the bowditch staircase phenomenon?
an increased HR progressively enhances the force of ventricular contraction (increasing HR intrinsically increases contraction as well)
what is the opposing factor of the bowditch staircase phenomenon?
decreased ventricular filling
is the effect of the bowditch phenomenon on CO rate-dependent or rate-independent?
rate-dependent
what effect does a decreased HR have on the bowditch staircase phenomenon?
decreased HR has a negative staircase effect
what is the most clinically common method of measuring CO?
pulmonary artery catheterization (PAC) thermodilution of with bolus injection of cold fluid
what is the relationship between thermodilution and CO?
the faster it takes the temperature to equilibrate, the larger the CO
small curve - larger CO
