Physiology-Regulation of Cardiac Function Flashcards Preview

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Flashcards in Physiology-Regulation of Cardiac Function Deck (28)
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1
Q

What is the normal resting cardiac output? How do you calculate cardiac output?

A

5L/min. HR * SV where stroke volume = end diastolic volume - end systolic volume

2
Q

What is cardiac index? What is a normal level of cardiac index?

A

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

3
Q

How do you measure contractility?

A

Ejection fraction. (EDV-ESV) / EDV. This tells you how much blood is still there after systole. Note EDV-ESV = SV.

4
Q

What is contractility?

A

Power developed by the muscle for any given sarcomere length independent of preload and after load

5
Q

When is diastolic tension directly proportional to the rise in diastolic pressure? What is dP/dt?

A

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.

6
Q

What is stroke work?

A

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.

7
Q

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?

A

Exercise = volume work. Overcoming hypertension = pressure work.

8
Q

How do you determine cardiac efficiency?

A

Ratio of work output to total oxygen consumption

9
Q

What is the most important determinate of heart efficiency?

A

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.

10
Q

What energy is used to eject blood into circulation?

A

Kinetic energy of blood flow. This is only 1% of total work where external work is about 99%.

11
Q

What is represented by this phases of left ventricular pressure indicated by each arrow below?

A

Phase 1= ventricular filling. Phase 2 = isovolumetric contraction Phase 3 = Period of ejection Phase 4 = Isovolumetric relaxation

12
Q

Where does preload fall on this pressure-volume loop?

A

Preload is the end diastolic pressure at the end of end diastolic volume right before the heart begins to contract.

13
Q

Where does after load fall on this pressure-volume loop?

A

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.

14
Q

Where does contractility fall on this pressure-volume loop?

A

Contractility is equal to the pressure at the end of ejection.

15
Q

Where does heart rate fall on this pressure-volume loop?

A

The time to go around one pressure loop.

16
Q

How does cardiac function increase via mechanisms inherent to the cardiac muscle itself?

A

Frank-Starling mechanism (ventricular stroke volume increases as atrial pressure increases). SA node.

17
Q

What factors can affect the end diastolic volume?

A

Preload (filling pressure), filling time and compliance (stiffness) of ventricle

18
Q

What are some major factors that affect preload (effective filling pressure)?

A

*

19
Q

How could increased heart rate actually decrease end diastolic volume?

A

When the heart is beating to fast, the ventricles do not have time to completely fill.

20
Q

What are some factors that could compromise distensibility or compliance of the ventricles?

A

*

21
Q

How can you increase cardiac function via extrinsic factors to the heart?

A

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).

22
Q

What are the cardiac effects that come from vagal stimulation?

A

*

23
Q

How does systemic pressure relate to CO, relating to SV, relating to end systolic and diastolic volumes?

A

*

24
Q

How is stroke volume affected by only an increase in preload?

A

It increases end diastolic volume which will result in a greater stroke volume.

25
Q

How is stroke volume affected by only an increased after load?

A

It results in a larger end systolic volume and smaller SV.

26
Q

How is stroke volume affected by only an increase in contractility?

A

End systolic volume is decreased and SV increases.

27
Q

How is stroke volume affected by an increased after load when preload is variable?

A

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.     

28
Q

Why do heart failure patients end up with higher heart rates?

A

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.

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