Cardiology I Flashcards
1
Q
What is stroke volume?
A
the amount of blood ejected w/ each heartbeat
2
Q
What is cardiac output?
A
CO = SV X HR
- aka cardiac performance
3
Q
What are the determinants of cardiac output?
A
HR, preload, afterload, & contractility
4
Q
How does HR influence CO?
A
- the sinus node is a pacemaker
- rate can be increased as demand increases (sinus node rate is sp dependent; will increase w/ adrenergic or sympathetic stimulation)
- w/ an increase in rate (to an upper limit) CO will increase
- w/ sustained elevations in HR, myocardial oxygen demand will increase
5
Q
How does preload influence CO?
A
- the force of cardiac contraction is dependent upon the level at which it is stretched prior to contraction (end diastolic volume)
- based on Frank Starling Mechanism
- once the stretch exceeds a certain level, cardiac output falls (fibers are pulled too far apart)
6
Q
What is the Frank Starling Law?
A
the stroke volume of the heart increases in response to an increase in the volume of blood in the ventricles before contraction (the END DIASTOLIC VOLUME), when all other factors remain constant
7
Q
What determines afterload?
A
- determined by the resistance to ejection
- resistance is determined by impedance & systemic vascular resistance
- impedance is usually a minor factor in animals & is determined by proximal aortic stiffness
- main determinant is systemic vascular resistance
8
Q
How does afterload influence CO?
A
- increases in afterload lead to a drop in CO
- afterload is increased by increased chamber size
- afterload is decreased by increasing wall thickness (normal response in failing hearts)
9
Q
What is the formula for BP?
A
BP = SVR x CO
10
Q
How does contractility influence CO?
A
- The intrinsic ability of the heart to contract independent of preload
- can be altered through outside factors (catecholamines increase contractility; beta blockers decrease; few drugs are available to increase contractility that are safe & easy to use during failure
11
Q
A
