Cardiac Output & Contractility Flashcards
Define preload.
amt. of blood ready to be pumped
L ventricle end-diastolic volume
Define venous pressure
pressure in the vena cava
can be used to estimate atrial pressure
Why is ventricular end-diastolic pressure the most accurate estimate of preload?
it takes into account the amt of blood AND the muscle fiber length at the end of diastole
Define afterload.
-pressure against which the heart must work to eject blood during systole
What happens to afterload if arterial pressure increases?
afterload increases
What happens to cardiac output (in the immediate time) as preload increases and as preload decreases?
- cardiac output increases as preload increases
- cardiac output decreases as preload decreases
What happens to cardiac output (in the immediate time) as afterload increases and as afterload decreases?
- cardiac output decreases as afterload increases
- cardiac output increases as afterload decreases
What happens to cardiac output (in the immediate time) as contractility increases and as contractility decreases?
- cardiac output increases as contractility increases
- cardiac output decreases as contractility decreases
What is the positive staircase effect?
- as heartbeats get closer together, less calcium is removed from the cell b/w beats
- thus, contractility increases d/t extra calcium being taken up in the sarcoplasmic reticulum
What is the equation for stroke volume?
SV = EDV - ESV
end-diastolic volume minus end-systolic volume
What is a normal approximate stroke volume in a healthy adult?
70mL
What is the equation for cardiac output?
HR x SV
heart rate multiplied by stroke volume
What is a normal approximate cardiac output in a healthy adult?
5 L/min
What is the equation for ejection fraction?
EF = SV/EDV
stroke volume divided by end-diastolic volume
What is a normal approximate ejection fraction in a healthy adult?
55%
What does it mean it something has a positive inotropic effect?
contractility is increased
What type of receptors affect cardiac contractility when receiving sympathetic input?
beta-1
What is the sympathetic influence on calcium channels in the sarcoplasmic reticulum?
phosphorylated
activated to release calcium
What is the sympathetic influence on troponin I?
phosphorylation
-reveals binding sites to allow for muscle ctx
What type of receptor affects cardiac contractility when receiving parasympathetic input?
muscarinic
True or False: the ventricles receive parasympathetic input
False
During what phase of the action potential does parasympathetic input have the most influence?
phase 4
What are the ionic effects of parasympathetic input?
- decreases calcium entering the cell during the phase 2 plateau
- increases K+ leaving the cell
On a pressure-volume loop diagram, what does point 1 represent and what cardiac activity happens after reaching point 1?
end-diastolic volume
–isovolumetric ctx
On a pressure-volume loop diagram, what does point 2 represent and what cardiac activity happens after reaching point 2?
aortic valve opens
–ventricular ejection
At what part of the pressure-volume loop does the ventricular pressure reach its maximum?
b/w pts 2 and 3
On a pressure-volume loop, what does point 3 represent and what cardiac activity happens after reaching point 3?
aortic valve closes
–isovolumetric relaxation
On a pressure-volume loop, what does point 4 represent and what cardiac activity happens after reaching point 4?
tricuspid valve opens
–ventricular filling
What is represented by the width of the pressure-volume loop?
stroke volume
What is represented by the area within the pressure-volume loop?
stroke work
How is the pressure-volume loop affected when afterload changes?
- afterload increase
- -loop gets taller
- afterload decrease
- -loop gets shorter
How is the pressure-volume loop affected when the preload changes?
- preload increase
- -loop gets wider
- preload decrease
- -loop gets narrower
How is the pressure-volume loop affected when the contractility changes?
- increased contractility
- -gets taller and wider (on the left)
- decreased contractility
- -gets shorter and narrower on the left
What is stroke work?
work done by the L ventricle to eject blood during one cardiac cycle
What is the equation for cardiac output in regards to oxygen (Fick Principle)?
CO = O2 consumption / ([O2pv] - [O2pa])
What is the effect on cardiac output of blood returning to the heart with an abnormally low level of oxygen?
it takes more oxygen to re-oxygenate the blood and thus decreases cardiac output according to the Fick principle
What happens to cardiac output as right atrial pressure iincreases?
cardiac output increases up to a certain point and then reaches a plateau
What happens to venous return as right atrial pressure increases?
venous return decreases
With a positive inotropic effect, what happens (in the immediate time) to cardiac output and venous return?
cardiac output increases
venous return increases
With a positive inotropic effect, what happens (in the immediate time) to right atrial pressure so that cardiac output and venous return stay in equilibrium?
right atrial pressure decreases
With a negative inotropic effect, what happens (in the immediate time) to cardiac output and venous return?
cardiac output decreases
venous return decreases
With a negative inotropic effect, what happens (in the immediate time) to right atrial pressure so that cardiac output and venous return stay in equilibrium?
right atrial pressure increases
What happens to cardiac output and venous return when total peripheral resistance changes?
as TPR increases, CO and venous return decrease
as TPR decreases, CO and venous return increase
What happens to cardiac output and venous return (in the immediate time) when blood volume increases?
cardiac output increases
venous return increases
What happens to right atrial pressure when blood volume increases, so that equilibrium b/w cardiac output and venous return is maintained?
right atrial pressure decreases
What happens to right atrial pressure when blood volume decreases, so that equilibrium is maintained b/w cardiac output and venous return?
right atrial pressure increases
