Lab 2 - Cardiac Cycle

Question 1

Explain the difference between electrical and mechanical events in the heart?

Answer 1

Electrical events = ECG (created by signals that control the timing of heartbeats for example the SA node, the AV node and the conduction pathway).

Mechanical events = the actual physical actions that pump blood due to pressure and flow changes (contraction/systole and relaxation/diastole).

(+ Vavular events = heart sounds)

Question 2

What mechanical event occurs at the start of ventricular diastole?

Answer 2

Ventricular diastole = ventricular filling

AV valve opens allowing for ventricular filling to begin

Question 3

What are the electrical and mechanical events that occur during ventricular diastole?

Answer 3

Electrical - phase of ventricular repolarisation (T wave on ECG) following systole to allow for the cardiac cells to reset to prepare for the next heart beat. After the T wave there is a prolonged period of no electrical activity as the heart relaxes.

Mechanical - Isovolumetiric ventricular relaxation then AV valve open allowing for passive ventricular filling and then in late diastole there is atrial contraction for the remaining 10% of CO to fill the ventricle to EDV.

Question 4

What happens to atrial and ventricular pressure during ventricular diastole?

Answer 4

Atrial Pressure - as blood fills the atria pressure rises. Once pressure becomes greater than ventricular pressure the AV valve opens causing blood to flow from atria to ventricle and atrial pressure drops. In late diastole the atria depolarised and pressure increases during contraction.

Ventricular Pressure - when the semilunar valves close the ventricles relax without change volume so pressure drops a lot. Once AV valve opens ventricular pressure remains low as the ventricles fill passively with blood. Pressure rises slightly due to the extra blood during atria contraction. Overall ventricular pressure is low.

Question 5

What mechanical event occurs at the start of ventricular systole (contraction)?

Answer 5

AV valves close so pressure increases in ventricles and cause the semilunar valves to open for ejection of blood.

Semilunar valves open - aortic valve and pulmonary valve - shunting blood from ventricles to either the lungs or to the body.

Question 6

What are the electrical and mechanical events that occur during ventricular systole?

Answer 6

Electrical events = ventricular depolarisation = QRS complex

Mechanical = AV valves close increasing pressure and preventing back flow. Isovolumetric contraction for a brief moment increasing pressure and then causing the semilunar valves to open and blood ejected into arteries.

Question 7

How does an increase in cardiac sympathetic nervous activity effect the electrical and mechanical events that occur during a cardiac cycle?

Answer 7

Electrical Events: It increases the heart rate by speeding up the firing rate of the SA node, reducing the time between action potentials. It also enhances conduction speed through the AV node.

Mechanical Events: It strengthens ventricular contraction (increased contractility), resulting in more forceful ejection of blood, and shortens the duration of systole. This leads to increased stroke volume and cardiac output.

Question 8

How does an increase in cardiac sympathetic nervous activity affect the relative amount of time spent in diastole and in systole?

Answer 8

They both shorten but diastole (time for heart to relax and fill) is shortened to a greater extend than systole.

Question 9

What is the thoracic cage?

Answer 9

Chest area from which each valve sound is best heard

Question 10

How do you work out Heart period?

Answer 10

Heart period is the time taken for one complete cardiac cycle.

It is measured from R-wave to R-wave.

Question 11

How do you work out duration of systolic period?

Answer 11

Systolic period is the time that the ventricles are contracting.

Measured from R-wave to the beginning of the second heart sound.

Question 12

How do you work out duration of diastolic period?

Answer 12

Diastolic period is the time that the heart is relaxing.

It is calculated by heart period - systolic period or from the beginning of the second heart sound to the peak of the following R wave.

Question 13

How do you work out duration of isovolumic contraction period (IVC)?

Answer 13

IVC is the time that the heart is contracting with all valves closed.

Measured from R wave to the beginning of the first carotid pulse wave.

Question 14

How do you work out duration of ejection period ?

Answer 14

Ejection period id the time that blood is leaving the ventricles

Calculated by systolic period - IVC period or from the beginning of the first carotid pulse wave to the beginning of the second heart sound

Question 15

How do you work out heart rate?

Answer 15

Heart rate is the number of beats per minute.

It is worked out by 60 divided by your heart period in SECONDS.

Question 16

Which cells in the heart determine heart rate/period of cardiac cycle?

Answer 16

Pacemaker cells - SA node

Question 17

How is the duration of the heart period affected by autonomic nervous input to the heart?

Answer 17

The rate of firing from the SA node is determined by the balance between the PSNS and SNS.

SNS increases the rate of firing therefore increasing HR whereas, PSNS decreases the rate of firing therefore decreases HR.

Question 18

Which mechanical and or electrical events are used to measure the systolic and diastolic period?

Answer 18

Electrical:
Systolic = QRS complex
Diastolic = T wave

Mechanical:
Systolic - from closure of AV valves to the closure of the semilunar valves
Diastolic - from the closure of semilunar valves to the closure of AV valves (diastolic longer).

Question 19

What is rpm?

Answer 19

revolutions per minute - used for bpm

Question 20

What happens to D and S duration when heart rate increases during exercise and why?

Answer 20

Decrease in PSNS activity and an increase in SNS activity means that both D and S shorten but D shortens at a greater amount.

Question 21

What three places does the SNS act on / innervate?

Answer 21

The SA node
The conduction System
The myocardium

Question 22

What is pulsatile sound?

Answer 22

Pulsatile sound refers to a rhythmic sound that follows the pattern of a pulse or heartbeat. It is often characterized by a regular, rhythmic pulsation corresponding to the heartbeat.

Question 23

What does an increase in sympathetic nervous system activity cause on the SA node?

Answer 23

Increased pace/firing of action potenitals therefore reduction in heart period (increased heart rate)

Question 24

What does an increase in sympathetic nervous system activity cause on the conduction system?

Answer 24

increase in conduction velocity leading to better synchronised contraction

Question 25

What does an increase in sympathetic nervous system activity cause on the myocardium?

Answer 25

A reduction in duration of ventricular contraction (systolic period) with diastole shortening to a greater extent.

Question 26

How does sympathetic stimulation of the myocardium cause reduction in systolic period and diastolic period?

Answer 26

The SNS releases noradrenaline which binds to beta receptors which activates PKA which phosphorylates causing increased speed and strength of contraction and increase speed of relaxation.

Question 27

What proteins does PKA phosphorylate that causes increase speed and strength of contraction ?

Answer 27

LTCC and RyR2

Question 28

What proteins does PKA phosphorylate that causes increased speed of relaxation?

Answer 28

Phospholamban and Troponin I

Question 29

When we breath in is there an increase or decrease in HR?

Answer 29

Breath in = increase in HR
Breath out = decrease in HR

Question 30

What branch of the cardiac autonomic nervous system is most likely to be involved in the changes to heart rate over a breathing cycle?

Answer 30

PSNS - because PSNA is active at rest therefore resting HR is less than the SA nodes intrinsic rate of firing - therefore a withdraw of the PSNS is releasing the hand break and causes a very rapid change.

There is secondary impact from SNS but it is a comparatively slower response.

Question 31

What is respiratory sinus arrhythmia?

Answer 31

Respiratory sinus arrhythmia (RSA) is the natural variation in heart rate that occurs during the breathing cycle.

Essentially, your heart rate speeds up when you inhale and slows down when you exhale.

Question 32

What are lung stretch receptors stimulated by and what is the effect?

Answer 32

Inspiration - these decrease PSNS input to the heart during inspiration and cause increase HR during inspiration

Question 33

What are korotkoff sounds?

Answer 33

The sounds heard through a stethoscope when measuring blood pressure - created through turbulent/pulsatile blood flow by compressing the artery with blood pressure band.

Question 34

When do pulsatile sounds disappear?

Answer 34

When pressure of the inflated cuff falls below diastolic pressure as laminar flow is restored

Question 35

During exercise what percentage of ventricular filling is due to atrial contraction?

Answer 35

30-50%

Question 36

What occurred to Rob Waddell when preparing for the 2008 olympics?

Answer 36

Atrial fibrillation

Question 37

What is atrial fibrillation?

Answer 37

A condition which causes an irregular and often rapid heart rate.

Question 38

Why is atrial fibrillation a problem while exercising?

Answer 38

Atrial fibrillation (AFib) is problematic during exercise because it causes an irregular and often rapid heart rate, reducing the heart’s efficiency in pumping blood. This can lead to decreased oxygen delivery to muscles, fatigue, dizziness, shortness of breath, and an increased risk of stroke or other heart complications during physical activity.

Question 39

What wave is absent during atrial fibrillation?

Answer 39

P waves (because the atria is fibrillating)

Question 40

Are the QRS and T waves altered during atrial fibrillation?

Answer 40

They are fairly normal but irregular (the R-R interval is not consistent)

Question 41

How does atrial fibrillation cause a reduction in cardiac output?

Answer 41

Sinoatrial node is dysfunction therefore the slower Av node now acts as the pacemaker (sometimes irregular) and therefore decreased HR.

There is also no topping of ventricles by atria therefore lower EDV and decreased SV

Question 42

Why does Atrial fibrillation have a larger effect on cardiac output during exercise?

Answer 42

At rest atrial contribution to filling ventricle is small and not very important to maintain SV whereas during exercise atrial top up accounts for 30-50% of EDV therefore very important contribution to EDV and therefore SV. This is order to meet the increased metabolic requirements of exercise. For someone with atrial fibrillation they cannot increase they cardiac output enough to meet the increase metabolic needs of exercise.