control of cardiac output Flashcards
the cardiac output is controlled mainly by
the sum of all the local tissue flows
cardiac output
the quantity of blood pumped into the aorta each minute
venous return
the quantity of blood flowing from the veins into the right atrium each minute
CO =
HR x SV
SV =
EDV - ESV
EF =
SF/EDV = EDV-ESV/EDV
end diastolic volume - end systolic volume =
stroke volume
which affects CO more? HR or SV?
HR. changes in HR alone inversely affect stroke volume
at low HR, increase in HR is greater than
decrement in SV
Bowditch (Treppe or staircase phenomenon)
an increase in HR will also cause positive ionotrpy duets an increase in intracellular Ca+++ with a higher HR
preload
the initial stretching of the cardiac myocytes prior to contraction. it is related to the sarcomere length at the end of diastole.
what are the indirect ways to measure preload
LVEDV, LVEDP, PCWP, CVP
determinants of preload
venous BP, vasomotor tone, venous volume, venous retur, total blood volume, respiration, excerise, filling time (HR), ventricular compliance, atrial contraction, inflows outflow resistance, ventricular systolic failure
Frank-Starling Mechanism
When venous return to the heart is increased, ventricular filling increases, as does preload. This stretching of the myocytes causes an increase in force generation, which enables the heart to eject the additional venous return and thereby increase stroke volume.
(the heart pumps the blood that is returned it)
increasing venous return and ventricular preload leads to
increase in stroke volume
Afterload is closely related to
aortic pressure
afterload is
the “load” that the heart must eject blood against
LaPlace’s Law is for which concept
after load
what is LaPlace’s Law
wall stress = Pr/h. p is ventricular pressure, R is ventricular radius, h is wall thickness
aortic pressure does what to afterload
increased aortic pressure increases afterload
SVR does what to afterload
increased SVR increases afterload
aortic valve stenosis effect on afterload
increases
ventricular dilation effect on afterload
increases
Anrep effect
an abrupt increase in afterload can cause a modest increase in inotropy
contractility
the inherent capacity of the myocardium to contract independently of changes in afterload or preload.
alternative name for contractility
iontropy
changes in contractility are caused by
by intrinsic cellular mechanisms that regulate the interaction between actin and myosin independent of sarcomere length.
decreased iontropy does what to stroke volume and LVEDP?
decrease SV and increases LVEDP
increased iontropy does what to stroke volume and LVEDP
increase SV and decrease LVEDP
increased afterload does what to contractility
increases - anrep effect
what are the four major determinants of CO
contractility, stroke volume, HR, preload
to increase stroke volume, ____ End-diastolic volume
increase
to increase stroke volume ___, End-systolic volume
decrease
preload is directly related to _____ because of frank starling
CO. preload increases, CO increases. preload decreases, CO decreases
What physiologic relationship keeps cardiac output of the ventricle matched with venous return?
Frank starling mechanism – allows the heart to readily adapt to changes in venous return. Increasing venous return and preload leads to an increase in SV.
What physiologic relationship keeps the cardiac output of the right and left ventricles matched?
Frank starling – outputs of the two ventricles are matched over time, otherwise blood volume would shift between the pulm and systemic circulations
what parameter is on the y axis of starling curve
SV
what parameter is on the x axis
LVEDP
what factors can cause an increased after load?
Increased aortic pressure, increased SVR, aortic valve stenosis, ventricular dilation
Increasing afterload ____ SV
decreasese
decreasing afterload ______ sv
increases
q: during the phase of rapid ventricular filling
mitral valve open
q: rv preload is increased by ___ HR
decreased HR. more time is available for filling at reduced heart rates; therefore preload is increased.
effect on decreased atrial contractility, decreased blood volume, and decreased ventricular compliance on preload
reduced ventricular filling, reduced preload
increase in preload is a _____ in sarcomere length
increase
as the preload on a ventricular myocyte is increased,
active tension development increases
LVEDP is ____ by ventricular hypertrophy
increased
ventricular stroke volume is ____ by decreased ionotropy
reduced
ventricular stroke volume is ___ by reduced HR
increased - more filling
left ventricular end-systolic volume is ___ when iontrophy is impaired
increased
increasing afterload decreases ejection velocity and stroke volume, which leads to an ___ in end-systolic volume
increase
an increase in end diastolic volume will ____ SV, but stroke volume changes are about 1/4 as effective in changing myocardial oxygen consumption compared to changes in HR, MAP, or ventricular radius
increase
