12.1 B Flashcards
Sympathetic nerves have what effect on preload?
sympathetic firing increases preload
Sympathetic nerves have what effect on afterload?
sympathetic firing increases afterload
Sympathetic nerves have what effect on inotropic state?
sympathetic firing increases the inotropic state
Increased afterload has what affect on stroke volume and cardiac output?
increased afterload decreases stroke volume
What is preload?
- stretch on the myocardial fibers before contraction
- related to ventricular filling
- EDV, EDP, and venous return are indices of preload
What is afterload?
- the ventricular wall tension during ejection
- the resistance that must be overcome to eject blood
- aortic systolic or diastolic pressure are indices
Inotropic state represents what?
the force of contraction
Inotropic state is dependent on what?
the cytosolic calcium level within contracting myocytes
In contracting ventricles, cytosolic calcium levels are ____ under normal conditions.
submaximal, leaving room for an increase in inotropic state
What neurotransmitter will enhance calcium entry into myocytes and increase inotropic state?
norepinephrine
Starling’s law states what about the heart?
stroke volume increases when preload increases because stretch leads to improved force of contraction
Starling’s law says that the increased force of contraction at greater preload is due to what?
stretch which results in more favorable overlap of thin and thick filaments, not a change in calcium levels
Stretch, increases sarcomere length and does what to the force of contractino?
increases contraction by creating a more favorable overlap of thin and thick filaments
What are the two determinants of preload?
- filling time (heart rate)
- rate of venous return (venous tone, blood volume)
Starling’s law is best represented by a plot of what?
stroke volume v. EDV
According to Starling’s law, changes in venous return or filling time will affect stroke volume by altering ____.
end diastolic volume
Shifts along a single Starling curve are the result of what?
changes in preload due to changes in venous return or filling time
At a given EDV, decreased afterload results in what change in stroke volume?
it will increase the stroke volume
What might be a cause of change in afterload that shifts the Starling curve up or down?
changes in systemic arterial pressure
An increase in systemic arterial pressure will have what affect on a Starling curve?
it will shift the whole Starling curve downward
What are two major determinants of afterload?
- change in TPR due to changes in arteriolar tone
- aortic stenosis
Aortic stenosis is seen as what change of a Starling curve?
aortic valve stenosis leads to hypertrophy and an increased force, increasing the peak pressure in the ventricle, increasing afterload and shifting the Starling curve downward
An increase in inotropic state will have what effect on a Starling curve?
increased inotropic state will shift the curve upward
A beta blocker will have what effect on a starling curve?
it will decrease the inotropic state and shift the curve downward
What is the effect of cardiac glycosides on the inotropic state?
they inhibit Na/K pump, increasing intracellular sodium levels, activating the Na/Ca exchanger, increasing intracellular calcium levels, increasing inotropic state
What are some things that would increase inotropy?
sympathetic firing, a beta agonist, cardiac glycosides
WWhat are some things that would decrease inotropy?
- decreased sympathetic nerve firing to heart
- a beta antagonist
- a calcium blocker
- heart failuer
On a typical Starling curve, an increase in inotropic state can’t be differentiated from a change in what other factor?
afterload
In order to differentiate a change in afterload from a change in inotropic state, what modification must be made to a Starling curve?
EDV must be plotted against stroke work instead of against stroke volume
What is stroke work?
an estimate of stroke volume times MAP
Plotting stroke work against EDV, makes the Starling curve independent of what variable?
afterload
What is the Starling reserve?
the maximal increase in stroke volume that can be achieved by increasing EDV
What is the Inotropic reserve?
the maximal increase in stroke volume that can be achieved by increasing inotropic state
What is the total cardiac reserve?
the sum of the inotropic and starling reserves
