Cardiac Cycle

Question 1

Heart valve review.

Answer 1

The valve between atria and ventricle (AV valve) on the right side is called tricuspid (3 leaflets) whereas the left side valve is called mitral (normally 2 leaves).

The valves on the exit from the ventricles are the pulmonic valve on the right side and aortic valve on the left and both are semilunar

Question 2

When would AV valves be open?

Answer 2

when atrial pressure greater than ventricular P

Question 3

When would the aortic valve be open?

Answer 3

when left ventricle P is greater than aortic P

Question 4

What occurs during the P wave of the cardiac cycle.

Answer 4

atrial depolarization. It is not as large as the ventricular depolarization wave (QRS) because the mass of atria is much less than ventricular mass

Question 5

What part of the cardiac cycle diagram represent atrial depolarization?

Answer 5

The atrial repolarization wave is not seen, as it is buried under the QRS complex.

Question 6

What is the T wave?

Answer 6

The T wave represents ventricular repolarization. It is not as intense as the polarization wave because repolarization occurs more slowly than depolarization (recall that K channels operate more slowly than the fast sodium channel), that is, it is spread out over time.

Question 7

What happens following atrial contraction (after P wave)?

Answer 7

-mitral valve closes due to ventricular pressure increase from volume increase

NOTE: atrial systole, there is a slight increase in martial pressure too

Question 8

What happens as ventricular pressure exceeds atrial pressure and the mitral valve closes?

Answer 8

• Electrical activation of ventricle (QRS complex) leads to isovolumetric contraction during which ventricular pressure increases but there is no flow because both mitral and aortic valves are closed;
• as ventricular pressure exceed aortic pressure, the aortic valve opens

Question 9

What happens when the aortic valve opens?

Answer 9

• after aortic valve opens, both ventricular and aortic pressures continue to increase during rapid ejection period (corresponding to approx 40% of ventricular systole)

Question 10

What happens when ventricular systole ends due to repolarization of the ventricles?

Answer 10

Aortic pressure begins to exceed ventricular pressure, the aortic valve closes and the heart enters the period known as isovolumetric relaxation;

mitral valve does not open until atrial pressure exceeds ventricular pressure again.

Question 11

When is ascending aortic blood flow the highest?

Answer 11

peak towards end of rapid ejection phase;

note the retrograde flow for a fraction of a second, associated with aortic valve closure

Question 12

When is the first heart sound heard?

Answer 12

First heart sound occurs after closure of mitral and tricuspid valves; normally these valves close within 10 msec of each other and thus there is no split sound

low in frequency and prolonged

Question 13

When is the second heart sound heard?

Answer 13

the second heart sound originates from closure of aortic and pulmonic valves; it is shorter in duration and higher in frequency; second heart sound can be a split sound under physiological conditions involving deep breathing

Question 14

What is the S3 sound?

Answer 14

The S3 sound results from vibrations set in motion by the filling of ventricles during early diastole (right after S2) and is normally not heard in adults by stethoscope; if heard it may indicate cardiac disease associated with ventricular overload due to heart failure or valve problems; S3 is referred to as ventricular gallop.

Question 15

What is the S4 sound?

Answer 15

S4 is associated with atrial contraction and results from vibrations induced by a stiffened ventricle. It is sometimes referred to as atrial gallop.

associated with ventricle volume overload

Question 16

What is the eqn for work of the heart?

Answer 16

Pressure x Volume

Question 17

Are the ventricles typically completely empty following contraction?

Answer 17

No, the difference between the EDV and end systolic volume (ESV) is the SV. SV is usually around 80 ml. EDV usually around 130 ml and ESV is usually around 50 ml

Question 18

What will examining the cardiac cycle as a pressure/volume loop allow for determination of?

Answer 18

the effects of change in preload, after load, and contractility

Question 19

Describe portion A of the PV loop of the cardiac cycle.

Answer 19

A represents diastole where it begins with the after load from the previous contraction and pressure builds as ventricular volume increases- this is passive pressure (stiffer ventricles/more volume= greater pressure)

this takes us from the ESV to the EDV

Question 20

Describe portion B of the PV loop of the cardiac cycle.

Answer 20

at the end of A, the mitral valve closes and iso-volumetric contraction occurs in the ventricles leading to a large increase in pressure

Question 21

Describe portion C of the PV loop of the cardiac cycle.

Answer 21

at the end of B, the aortic valve opens and pressure increases due to contraction and eventually decreases as volume is lost to the aorta.. This brings us to the end of systole

Question 22

Describe portion D of the PV loop of the cardiac cycle.

Answer 22

pressure drops drastically during isovolumetric relaxation and the cycle resets as the moral valve opens again

Question 23

What is the Frank-Starling relationship?

Answer 23

ventricular contractility (end systolic pressure volume relationship=ESPVR) is regulated by left ventricular volume at the end of diastole.

end diastolic pressure volume relationship=EDPVR

Question 24

What is preload?

Answer 24

the EDV and pressure before ventricles contract at the end of diastole

Question 25

What is after load?

Answer 25

ventricular pressure needed to open the aortic valve (volume is still EDV at this point). it is equivalent to diastolic aortic pressure

Question 26

What does systolic pressure mean?

Answer 26

the peak pressure in the AORTA, not the ventricle (the peak ventricle pressure is called the ventricular systolic pressure)

Question 27

What is diastolic pressure?

Answer 27

minimum pressure in the AORTA at the end of diastole, not the ventricle

Question 28

What is the effect of preload on pressure/volume relationship?

Answer 28

increased preload= increased SV

Question 29

What is contractility?

Answer 29

Strength of ventricular contraction independent of preload or afterload. Also known as inotropy.

Question 30

What is ejection fraction?

Answer 30

The fraction of end diastolic volume ejected by the ventricle during systole. It can be calculated as stroke volume divided by end diastolic volume. Normal values range from 55% to 75%.

Question 31

What is cardiac output?

Answer 31

Volume of blood ejected by ventricle in one minute. Can be calculated as stroke volume multiplied by heart rate.

Question 32

What is stroke volume?

Answer 32

Volume of blood ejected by ventricle during systole. Can be calculated as end diastolic volume minus end systolic volume

Question 33

What three factors change pressure/volume curves?

Answer 33

• preload (EDV, EDP)
• afterload
• contractility

Question 34

What happens if preload increases (and contractility and after load remain the same)?

Answer 34

Thus, based on the Frank-Starling mechanism, we find that stroke volume is increased, peak systolic pressure is increased (greater SV/stiffness= greater systolic pressure) but end systolic volume remains the same. Because arterial pressure equals stroke volume times heart rate times total peripheral resistance, this will increase arterial pressure, assuming that heart rate and resistance are also held constant.

Because arterial pressure equals stroke volume times heart rate times total peripheral resistance, this will increase arterial pressure, assuming that heart rate and resistance are also held constant.

Question 35

How does after load affect shortening velocity?

Answer 35

There is a reciprocal relationship between these variables. That is, the greater the force generated, the smaller the shortening velocity. This relationship explains why greater afterload (the pressure against which the ventricle must pump) results in decreased ventricular contraction velocity and therefore in a reduced stroke volume since the heart will therefore pump at a lower contraction velocity.

Question 36

End effect of increasing after load without changing preload or contractility?

Answer 36

This causes decreased shortening velocity, and therefore increased ESV and thus decreased stroke volume (because it needs more pressure to get there and maintain the pumping effect).

Question 37

How can increase after load occur?

Answer 37

afterload increase can occur if we increase aortic pressure (afterload) by, for example, increasing TPR (recall that aortic pressure equals product of cardiac output and TPR).

Question 38

What is the effect of increasing contractility while keeping preload and after load constant?

Answer 38

Increasing cardiac contractility (aka inotropy or end systolic pressure volume relationship) without altering preload or afterload. As can be seen, this event decreases end systolic volume and increases stroke volume and therefore peak systolic pressure.

This represents intrinsic activation of the heart, most frequently under the influence of increased sympathetic activity.

Question 39

What compensatory changes occur after increasing preload?

Answer 39

An increase in preload (EDV) causes an increase in stroke volume and therefore an increase in afterload (recall that stroke volume determines cardiac output from the formula: cardiac output equals stroke volume times heart rate and cardiac output determines arterial pressure from the formula: arterial pressure equals cardiac output times TPR). Increased afterload therefore causes a small increase in ESV.

Question 40

What compensatory changes occur after increasing afterload?

Answer 40

A primary increase in afterload (by for example an increase of TPR) causes a reduction in stroke volume and an increase in end systolic volume. This in turn causes an increase in end diastolic volume because the increase in end systolic volume gets added to the incoming venous return. The increase in end diastolic volume recovers part of the decreased stroke volume originally resulting from increased afterload (i.e. compensation)

Question 41

What compensatory changes occur after increasing contractility?

Answer 41

A primary increase in contractility (caused by increased sympathetic activity) will cause a primary decrease in end systolic volume and thus an increase stroke volume and therefore cause a secondary increase in afterload. Moreover, there will be secondarily decreased end diastolic volume due to the decreased end systolic volume. Afterload will increase due to increased stroke volume.