Cardiac Output and Contractility Flashcards
Cardiac glycosides
Used to treat heart failure Inhibition of Na/K ATPase Increases Na concentration Decreases Ca efflux through Ca/Na exchanger Increase Ca intracellular Positive inotropic effect
Cardiac output equation
CO= Heart rate X Stroke volume
Positive inotropic effect on cardiac output and ventricular end diastolic volume/right atrial pressure
Increased cardiac output
Increased ventricular end diastolic volume and right atrial pressure
Preload
Amount of blood ready to be pumped - LV end diastolic volume
Wall tension in LV just before contraction is initiated
(fiber length at end of diastole)
Related to venous return
Frank-Starling relationship
Volume of blood ejected by the ventricle depends on the volume present in the ventricle at the end of diastole
Afterload
For LV, related to aortic pressure
It is the force opposing contraction, or the pressure required to eject blood (open aortic valve)
Velocity of fiber shortening decreases as afterload increases
Stroke volume
Volume of blood ejected by ventricle with each beat
Usually about 70mL
SV= EDV-ESV
Ejection fraction
Fraction of the EDV ejected in each stroke volume
Measure of efficiency and contractility
EF%= SV/EDV (usually about 55%, reduced in heart failure)
Cardiac output
Total volume of blood ejected by ventricle per minute
CO(Q)= SV x HR
Usually about 5L/min
Preload/afterload effect on CO
Increased preload will increase CO and contractility
Increased afterload will decrease CO, heart must increase contractility or HR to overcome
Effect of heart rate on contractility
Increased HR (positive chronotropic effect) increases contractility (positive inotropic effect) -Positive staircase effect - more calcium enters cells and taken up into SR Post-extrasystolic potentiation (arrhythmia, extra beat)
