What is the normal resting cardiac output? How do you calculate cardiac output?
5L/min. HR * SV where stroke volume = end diastolic volume - end systolic volume
What is cardiac index? What is a normal level of cardiac index?
Cardiac output/body surface area. It is the cardiac output adjusted for patient side. A normal level for a 70 kg human = 2.9/L/min/m^2
How do you measure contractility?
Ejection fraction. (EDV-ESV) / EDV. This tells you how much blood is still there after systole. Note EDV-ESV = SV.
What is contractility?
Power developed by the muscle for any given sarcomere length independent of preload and after load
When is diastolic tension directly proportional to the rise in diastolic pressure? What is dP/dt?
During the isovolumentric contraction phase. Volume, radius and wall thickness are all constant at this point. dP/dt is the rate of rise pressure. Note the slope is highest during isovolumetric contraction.
What is stroke work?
The amount of energy the heart converts to work during a single cardiac cycle. This will be demonstrated by pressure under a pressure/ volume curve.
What are the two types of external work? What kind of work is required to help you while exercising? What kind of work is required to overcome hypertension?
Exercise = volume work. Overcoming hypertension = pressure work.
How do you determine cardiac efficiency?
Ratio of work output to total oxygen consumption
What is the most important determinate of heart efficiency?
Wall tension. This determines the amount of oxygen consumption. The radius of a dilated ventricle in heart failure is much greater than normal and efficiency is decreased.
What energy is used to eject blood into circulation?
Kinetic energy of blood flow. This is only 1% of total work where external work is about 99%.
What is represented by this phases of left ventricular pressure indicated by each arrow below?
Phase 1= ventricular filling. Phase 2 = isovolumetric contraction Phase 3 = Period of ejection Phase 4 = Isovolumetric relaxation
Where does preload fall on this pressure-volume loop?
Preload is the end diastolic pressure at the end of end diastolic volume right before the heart begins to contract.
Where does after load fall on this pressure-volume loop?
After load is the force in the ventricle as the heart begins to contract and through contraction. Note the after load falls off as blood is ejected.
Where does contractility fall on this pressure-volume loop?
Contractility is equal to the pressure at the end of ejection.
Where does heart rate fall on this pressure-volume loop?
The time to go around one pressure loop.
How does cardiac function increase via mechanisms inherent to the cardiac muscle itself?
Frank-Starling mechanism (ventricular stroke volume increases as atrial pressure increases). SA node.
What factors can affect the end diastolic volume?
Preload (filling pressure), filling time and compliance (stiffness) of ventricle
What are some major factors that affect preload (effective filling pressure)?
How could increased heart rate actually decrease end diastolic volume?
When the heart is beating to fast, the ventricles do not have time to completely fill.
What are some factors that could compromise distensibility or compliance of the ventricles?
How can you increase cardiac function via extrinsic factors to the heart?
Sympathetic (NE binding to beta receptors to release cAMP and increases in heart rate and contractility). Parasympathetic (ACh binding to muscarinic receptors and inhibits adenylyl cyclase to decrease cAMP).
What are the cardiac effects that come from vagal stimulation?
How does systemic pressure relate to CO, relating to SV, relating to end systolic and diastolic volumes?
How is stroke volume affected by only an increase in preload?
It increases end diastolic volume which will result in a greater stroke volume.
How is stroke volume affected by only an increased after load?
It results in a larger end systolic volume and smaller SV.
How is stroke volume affected by only an increase in contractility?
End systolic volume is decreased and SV increases.
How is stroke volume affected by an increased after load when preload is variable?
The first contraction results in a larger end systolic volume and a smaller stroke volume on the first beat. Now preload has increased, venous return will add blood and increase the end diastolic volume and stroke volume increases.
Why do heart failure patients end up with higher heart rates?
They have lower stroke volume and since extra blood cannot be expelled, the only way it can increase cardiac output is by increasing heart rate.