Cardiac Output (Part 2): Mechanical events and stroke volume

Question 1

Cardiac cycle

Answer 1

is about understanding how the pressure generated by the heart leads to the opening and closing of valves
Two sets of valves – AV valves which separate the top and bottom of the heart and the semilunar valve and aortic semillunar valves which separate the heart from the arteries.
Cardiac Cycle – understand how the pressure in the
4 compartments leads to the opening/closing of valves

divided into two phase
systole and diastole

Question 2

Systole

Answer 2

ventricular contraction and blood ejection

Question 3

Diastole

Answer 3

ventricular relaxation and blood filling

Question 4

What pressure and volume changes occur during the Cardiac Cycle?
left side of heart

Answer 4

Diastole
Ventricular filling

2 Systole
Isovolumetric Ventricular Contraction

3 Systole
Ventricular Ejection (rapid/reduced)

4 Diastole
Isovolumetric Ventricular Relaxation

1 Diastole
Ventricular filling (rapid/reduced)

Question 5

What are the heart sounds heard using a stethoscope?

Answer 5

1st sound – closure of the atrioventricular (AV) valves ‘lub’
- onset of systole (contraction)

2nd sound – closure of pulmonary and aortic valves ‘dub’
- onset of diastole (relaxation)

Question 6

Murmurs

Answer 6

change from laminar to turbulent flow

Question 7

Ventricular fibrillation

Answer 7

(heart attack)

Question 7

Damaged Valve

Answer 7

stenosis (noisey change in flow)

Question 7

Frank-Starling Mechanism

Answer 7

Ventricles contract with more force (i.e. stroke volume ↑) if it contains more blood (i.e. end-diastolic ventricular volume ↑)
Frank-Starling mechanism determined by length-tension relationship in the muscle i.e. the greater the stretch the more tensioned developed in the cardiac muscle
Frank-Starling mechanism maintains balance between right and left sides of the heart – stop accumulation of blood in the lungs (drowning!!!)
If ↑ venous return to right ventricle then ↑contraction
more blood to lungs
↑ venous return to left ventricle then ↑ contraction
↑ stroke volume
blood doesn’t accumulate in lungs

Question 8

Congestive Heart Failure

Answer 8

Congestive Heart Failure (CHF) is characterised by reduced Cardiac Output
Tiredness and shortness of breath
Fluid Retention to increase
cardiac output (venous return)
50% mortality in 5 years

Question 9

Chronic Left Ventricular Failure (most common)

Answer 9

Coronary artery disease leading to ischaemic heart disease and myocardial infarction (~ 65%) – systolic dysfunction

Hypertension (high blood pressure) (~ 10%) – diastolic dysfunction

Cardiomyopathy (viral infection, heavy drinking)

Getting old!!!

Question 10

Stroke volume

Answer 10

(ventricular ejection) is determined by the venous end-diastolic volume (pre-load), arterial (peripheral) resistance (after-load) and sympathetic stimulation.