Cardiac Cycle

Question 1

What is the difference between systole and diastole?

Answer 1

Systole= contraction
Diastole= relaxation

Question 2

What are the stages of the cardiac cycle?

Answer 2

Flow into atria (inflow leads to pressure rise)
Opening of A-V valves
Atrial Systole
Ventricular Systole
Ventricular diastole

Question 3

What causes the 1st heart sound?

Answer 3

Closing of AV valves (Lub)

Question 4

What causes the 2nd heart sound?

Answer 4

Closing of the semilunar valves (Dub)

Question 5

What causes the 3rd heart sound?

Answer 5

Early diastole of young and trained athletes. Normally absent after middle age. Sounds like “Kentu…cky”.
Termed the ventricular gallop.
Re-emergence in later life indicates abnormality (heart failure)

Question 6

What causes the 4th heart sound?

Answer 6

Caused by turbulent blood flow, due to stiffening of walls of left ventricle
Occurs prior to 1st heart sound
Atrial gallop

Question 7

What is the Summation gallop?

Answer 7

Tachycardia, 3+4 indistinguishable

Question 8

What is the function of the elastic arterial tree?

Answer 8

Stores pressure energy

Helps maintain pressure in arterial system during diastole (pressure drops only about one third from systolic BP)

Question 9

What are the major points of the cardiac cycle?

Answer 9

1. Chambers do not empty completely
2. Stroke volume= volume of blood pumped by each ventricle per beat (75ml) may double during exercise
3. Ejection fraction= % volume pumped out =55-60% (80% exercise)- in heart failure may be 20%
4. Systemic arterial pressure remains high throughout cycle due to elasticity of the vessel walls and peripheral resistance

Question 10

What is cardiac output?

Answer 10

Volume of blood pumped per minutes by each ventricle
-CO = HR x SV
At rest= 5L/min
Exercise >25L/min as HR increases 2-3 fold and stroke volume increases 2 fold

Question 11

How does heart rate affect cardiac output?

Answer 11

Normally increased HR associated with increased CO
If filling time decreased then SV decreased
Venous return determines cardiac output

Question 12

What is Stroke volume dependent on?

Answer 12

Contractility (force of contraction)= adrenaline, increased force
End diastolic volume (volume of blood in ventricle at end of diastole)
-Force is stronger the more muscle fibres are stretched (within limits): Frank-Starling Mechanism/ Starling’s Law of Heart
-Stroke volume proportional to diastolic filling

Question 13

What is the Frank-Starling Mechanism?

Answer 13

-Also known as the Preload (end diastolic volume)
Important in;
-Ensuring the heart can deal with wide variations in venous return
-Balancing the outputs of the 2 sides of the heart

Question 14

What is afterload?

Answer 14

Peripheral resistance
-Resistance to blood flow away from the heart- altered by dilation or constriction of blood vessels (mainly pre-capillary resistance arteries)
CO = Blood pressure/ peripheral resistance

Question 15

How does peripheral resistance affect cardiac output?

Answer 15

Normally small changes of peripheral resistance have little effect on cardiac output (physiological range)

• Expect increase to decrease stroke volume so decrease CO
• Decreased SV= increased end systolic volume so increased SV (Frank-Starling mechanism) so CO does not increase much