The Cardiac Cycle - L4

Question 1

What is the cardiac cycle?

Answer 1

All the events associated with the flow of blood through the heart during a single complete heartbeat

Question 2

How long is the cardiac cycle is the heart rate is 65bpm?

Answer 2

approx 0.92 sec

Question 3

What is 1 heart beat divided into?

Answer 3

2 Sequential phases: systole and diastole

Question 4

What is systole?

Answer 4

Period of cardiac contraction and emptying
Often an implied time of ejection, despite period of isovolumetric contraction

Question 5

What does systole vary on? What is it at 65bpm and 200bpm?

Answer 5

The length varies depending on what the heart rate: 0.3 sec @ 65bpm, 0.16 sec @ 200bpm

Question 6

What happens at a higher heart rate to systole? What happens to calcium?

Answer 6

Myocardium contracts & repolarises faster at high HR (increased Calcium return to SR)

Question 7

Systole is often an implied time of x?, despite x?

Answer 7

Often an implied time of ejection, despite period of isovolumetric contraction

Question 8

What is diastole?

Answer 8

Period of cardiac relaxation
Often an implied time of refilling, despite period of isovolumetric relaxation

Question 9

What does diastole vary with? @65bpm?@200bpm?

Answer 9

The length varies with varying heart rate
0.62sec @65bpm; 0.14sec @200bpm

Question 10

Action of valves control?

Answer 10

Cardiac cycle

Question 11

When do the AV valves open - the bicuspid/tricuspid valves??

Answer 11

open when pressure in atria is greater then those in the ventricles
when pressure gets greater in ventricles than in atria then the AV valves close

Question 12

When do the semilunar valves open and close?

Answer 12

semilunar valves open when pressure in ventricles is greater then the pressure in the arteries and the semilunar valves close when the pressure in the arteries is greater then the pressure in the ventricles

Question 13

Mechanical phases of cardiac cycle step:

Answer 13

1. Late diastole: both sets of chambers are relaxed and
   ventricles fill passively.
2. Atrial systole: atrial contraction forces a small amount of additional blood into ventricles.
3. Isovolumic ventricular contraction: first phase of
   ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. 0.05 sec
4. Ventricular ejection: as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves
   open and blood is ejected.
5. Isovolumic ventricular relaxation: as ventricles relax, pressure in ventricles falls, blood flows back into cups of semilunar valves and snaps them closed.

Question 14

What does cardiac cycle begin and end with?

Answer 14

Begins with a ventricular diastole and ends with a ventricular diastole

Question 15

Heart sounds - what is S1:”lub”?
What is S2: “dup”?

Answer 15

S1 – “lub” (AV valve closure)
S2 – “dup” (semilunar valve closure)

Question 16

With diastole it is often an implied time of x, despite x?

Answer 16

Often an implied time of refilling, despite period of isovolumetric relaxation

Question 17

The sequence of events which may overlap are?

Answer 17

Atrial diastole -> ventricular diastole -> atrial systole -> ventricular systole

Question 18

What is the action of the valves?

Answer 18

They open passively due to pressure gradients

Question 19

EDV?

Answer 19

End diastolic volume = volume of blood in ventricle at end of diastole
130mL

Question 20

ESV?

Answer 20

End systolic volume = volume of blood in ventricle at end of systole
70mL

Question 21

SV?

Answer 21

Stroke volume = volume of blood ejected from ventricle in each cycle

SV = EDV-ESV
SV = 130-70 = 60mL in this case

Question 22

What is the ejection fraction?

Answer 22

% EDV ejected with each stroke: ranges from 50-75%

Question 23

What is ejection fraction useful for?

Answer 23

A good index of ventricular function

Question 24

Wiggers’ Diagram main events: 6

Answer 24

1. Atrial systole
2. Isovolumic ventricular contraction
3. Ventricular systole
4. Early ventricular diastole
5. Late ventricular systole
6. Atrial systole again

1,2,3 make up QRS complex
4,5 cardiac cycle

Question 25

cardiac cycle - one complete heartbeat

Answer 25

STEP 1 OF CARDIAC CYCLE both atria and ventricles are filling passively: overlap atria are passively filling from pulmonary veins from the lungs with oxygenated lungs and passively filling from the systemic return from the superior and inferior vena cava into right atria here, the AV valves are open as pressure is greater in atria then ventricles and blood fills ventricles ventricles are filling passively

Question 26

STEP 2 OF CARDIAC CYCLE: MECHANICAL PHASES

Answer 26

Atria have a systolic contraction to complete ventricular refilling to force remaining blood in through valves and then the valves close AV valves close

Question 27

STEP 3

Answer 27

When AV valves close, just before we have the ventricular contraction where we have ejection of stroke volume that is when we have the period of the isovulimic ventricular contraction: AV closed here as pressure in ventricles is greater then what is in atria. The ventricles are depolarising and they are getting ready to contract , the pressure is building, starting to contract but not forcefully enough to open semi lunar valves All the valves are closed at this point - no blood entering or leaving The volume remains the same but pressure is increasing, it is contracting. Lasts 0.05 of a second

Question 28

STEP 4 of cardiac cycle - mechanical phase

Answer 28

Systole has began, Ventricles are contracting, and now fully depolarised Ventricular ejection occurs - ventricular pressure rises and exceeds the pressure in aorta and pulmonary artery, semi lunar valves open and blood leaves heart through these ventricles. The stroke volume occurs

Question 29

Step 5 of cardiac cycle - mechanical phase?

Answer 29

Isovolumic ventricular relaxation Ventricles has been ejected and now ventricles stop contracting and pressure reduces in ventricles and pressure within aorta and pulmonary arteries increases and causes closing of semi lunar valves. All the valves in heart are closed When ventricles contract only 1/2 of blood is ejected, so some volume of blood left in ventricles The volume is same but pressure is reducing Ventricles are repolarising and getting ready to refill and begin the whole cycle again

Question 30

1. P wave? 2. QRS? 3. ST? 4. T wave? 5. TP?

Answer 30

1. Atria depolarising, threshold has been reached 2. Atria contracting and sending blood into ventricles and ventricles getting ready to contract and depolarises 3. Ventricles are contracting and ejecting its contents 4. Repolarisation of ventricle 5. Ventricular diastolic, they are refilling

Question 31

Isovolumic ventricular contraction happens at end of?

Answer 31

Isovolumic ventricular contraction happens at end atrial systole just before ventricular starts to do complete ventricle contraction

Question 32

What is the dicrotic notch?

Answer 32

The end of systole and the beginning of diastole in these arteries.

Question 33

EXAM Q - write about wiggers diagram, talk your way through each step: ECG, mechanical phase of cardiac cycle etc