Contractility and Cardiac Output Flashcards
Positive vs. negative inotropy
What is it in proportion to?
Positive: increased force of contraction.
Negative: decreased force of contraction.
The amount of Ca that is available to troponin on actin.
Length-tension relationship
Relates to the degree of myofilament overlap.
As pressure/volume increases, greater tension is generated.
Preload
End diastolic volume that is the greatest the ventricle can stretch prior to contraction (at the end of diastolly).
Afterload
Pressure required to eject blood (to open the aortic valve).
Should be nearly equal to the aortic/pulmonary pressure
Afterload and velocity
Increased afterload causes a decrease in velocity shortening.
Stroke volume
Volume of blood ejected by ventricle with each beat.
SV = EDV - ESV
Ejection fraction
Fraction of EDV ejected in each stroke volume.
Measure of efficiency and ocntractility.
EF% = SV/EDV
Cardiac output
Amount of blood ejected by ventricle each minute.
CO (Q) = SV x HR
Frank Starling relationship
Volume of blood ejected by the ventricle depends on the volume present in the ventricle at the end of diastolly.
CO must equal
Venous return
Ventricular pressure-volume loop
Point 1 to 2
Isovolmetric contraction
Pt 1 is end of diastole.
Ventricular pressure-volume loop
Point 2 to 3
Ventricular ejection
Pt 2 marks where ejection begins.
Ventricular pressure-volume loop
Point 3 to 4
Isovolumetric relaxation
End of systole, ventricles relax.
Pressure falls but volume is constant.
Pressure must reach the level where the semilunar valves open.
Ventricular pressure-volume loop
Point 4 to 1
Ventricula filling.
Increased preload
Increased venous return (more blood vol.).
Greater EDV.
Afterload and contractility are same.
Increased stroke vol.
Increased preload can cause
Aortic stenosis, HTN.
Greater pressure needed.
Reduced SV and EF%
Increased contractility
Adrenergic stimulation
Increased SV and EF%
Less blood left in heart.
Sympathetic effect on inotropy
Positive inotropic effect.
beta-AR activation
Forms of sympathetic activation (3):
Phosphorylation of sarcolemmal Ca2+ channels.
Phosphorylation of phospholamban (stimulatory)
Phosphorylation of troponin I (inhibitory)
Parasympathetic effect on inotropy
Negative inotropic effect in atria only.
Muscarinic receptor activation.
Forms of parasympathetic activation (2):
Decrease inward Ca2+ current during plateau.
ACh increases outward K+ current via K+-ACh channel
Positivie staircase effect
Myocardial tension increases with an increase in HR.
More Ca enters cells and is taken up into the SR.
Cardiac glycosides (5)
Used to treat HF. Inhibits Na/K ATPase Increases Na conc. Decreases cA EFFLUX Increases IC Ca. Positive inotropic effect.
Volume work
Pressure work
Minute work
Stroke work
CO
Aortic pressure
CO x aortic pressure
SV x aortic pressure (area within pressure-vol loop).
Cardiac function curve
Venous return increases
RA pressure increases
End diastolic vol and end diastolic fiber length increase (Frank-Starling).
