16. Contractility and Cardiac Output Flashcards
What is the difference between positive and negative inotropy?
Positive increases the force of contraction
Negative inotropy decreases the force of contraction of the heart
(proportional to the amount of Calcium)
The cardiac muscle in the heart follows the same length-tension curve as skeletal muscle (smooth muscle does not!), what happens when pressure or volume in the LV increases?
Greater tension is generated
Afterload is the pressure required to cause ejection of blood. What is true regarding velocity of contraction and afterload?
As afterload increases, the velocity of contraction decreases
How do you calculate stroke volume?
SV= End diastolic volume (EDV)- end systolic volume (ESV)
How do you calculate cardiac output? (2 wAYS)
- CO = SV x HR
2. CO= [O2 consumed] / [O2artery]-[O2veins]
How do you calculate ejection fraction? (usually 55%)
EF= SV (EDV-ESV) / EDV
‘Volume of blood ejected by the ventricles depends on the volume present in the ventricles at the end of diastole’ is what relationship?
Frank-Starling relationship
How would a positive or negative inotropic effect change Cardiac output?
Postitive would increase cardiac output
Negative would decrease cardiac output
If you have increased preload (increased venous return, increased volume), what will occur to the pressure volume loop and CO?
Pressure volume loop will increase in width to accomadate high volume, cardiac output will increase since there is more stroke volume
If you have increased afterload (aortic pressure high), how does this change the pressure volume loop and cardiac output?
the loop will have an increased height due to increased pressure needed to eject and a lesser cardiac output (because decreased stroke volume)
Increased contractility via adrenergic stimulation would do what to CO and volume loop?
Would increase SV and CO, causing more blood to be ejected at a higher pressure
How does the sympathetic NS cause positive intropy effect to increase strength of muscle contraction?
Via B1 receptors, activate adenylyl cyclase, which phosphorylates sarcolemmal Ca+ channels and SR, releasing MORE Ca = higher muscle contraction = increased CO
How does the parasympathetic NS cause negative intropy (dec. contractility) in the atria only?
Via muscarinic receptor activation, which decreases inward Ca2+ and increases outward K+
An increase in heart rate can also increase contractility. What is the positive staircase effect/bowditch staircase?
Increased HR increases force of contraction in stepwise fashion as the intracellular Ca2+ increases (inc Ca2+ = increase in contractility strength)
an increase in heart rate can also increase contractility. What is postextrasystolic potentiation?
The beat that occurs after an extrasystolic beat has increased force of contraction because extra Ca2+ enter the cells during extrasystole
How do cardiac glycosides allow a positive inotropic effect, resulting in increased contractility?
They inhibit NaKATPase, so [Na] intracellular increases, leading to a decrease in Ca out/Na in exchanger, so [Ca] intracellularly increases
Cardiac work is comprised of volume work (cardiac output) and pressure work (aortic pressure) how is it calculated?
CO x aortic pressure
Pressure work is costlier than volume work. if pt has failing heart d/t aortic stenosisi or HTN –> REDUCE AFTERLOAD
The volume of blood ejected by cardiac output is equal to the volume it receives from?
venous return = CO @ equilibrium
as venous return increases, atrial pressure increases
As you decrease mean systemic pressure (MSP), the SV will be become?
Less
Enhanced cardiac function curve: inc. inotropy, inc. HR, ___ afterload
Depressed cardiac function curve: dec. inotropy, dec. HR, ____ afterload?
Enhanced: decreased afterload
Depressed: increased afterload
If you decrease volume, systemic pressure will decrease. As you increase vascular volume, systemic pressure will?
increase
If systemic vascular resistance decreases, your cardiac output increases and mean pressure will stay they same. If systemic vascular resisitance increases, your cardiac output decreases, and mean systemic pressure will?
stay the same
With a positive inotropic effect, what will occur to preload and CO?
CO will increse, preload will decrease
What will happen if blood volume is increased?
increased preload, increased CO and BP
