Session 2 ILOs - The heart as a pump and control of cardiac output

Question 1

Describe the basic anatomy of the heart naming all valves, chambers and major blood vessels

Answer 1

2 atria and 2 ventricles, left and right (top and bottom respectively)
Left ventricle wall thicker than right

Major blood vessels:

• Aorta (posterior)
• Pulmonary artery (anterior)
• Inferior and superior vena cava (2)
• Pulmonary veins (4)

Question 2

List the 7 phases of the cardiac cycle stating the valve positions and blood flow for each phase (left side as example)

Answer 2

1. Atrial contraction
   - Atrial kick (only moves 10% of blood, rest is passive)
   - Bicuspid valve is open
2. Isovolumetric contraction (because all valves closed)
   - Ventricle pressure exceeds atrial pressure
   - Bicuspid valve closes
   - 1st heart sound ‘lub’
3. Rapid ejection
   - Ventricular pressure exceeds the aortic pressure
   - Aortic valve opens
4. Reduced ejection
   - Less of a gradient, ejection reduces
5. Isovolumetric relaxation (because all valves closed)
   - Ventricle pressure falls below aortic pressure
   - Aortic valve closes
   - 2nd heart sound ‘dub’
6. Rapid filling
   - Ventricle pressure falls below atrial pressure
   - Mitral valve opens
   - Passive flow of blood into ventricles from atria
7. Reduced filling
   - Less of a gradient, ventricle filling reduces (90% full by the end of filling)

Question 3

Define stroke volume and give typical values

Answer 3

Stroke volume: volume of blood pumped out of the left ventricle of the heart during each systolic cardiac contraction

Typical value: Resting is 70mL/beat = 5L/min

Question 4

Give the relative timings of systole and diastole at rest and understand how this changes with exercise

Answer 4

Systole duration: 0.35 seconds
Diastole duration: 0.55 seconds
Total duration of contraction (0.9 seconds)

Diastole lasts for 2/3 of the cycle and systole for 1/3.

There is a bit of a reduction in the duration of systole with increasing heart rate, but the biggest change is in the duration of diastole.

Question 5

Explain the origin of the 1st and 2nd heart sounds in relation to the cardiac cycle

Answer 5

1st sound ‘lub’
- Closing of the mitral and tricuspid valves

2nd sound ‘dub’
- Closing of the aortic and pulmonary artery valves

Question 6

Explain how mitral valve disease can affect the function of the heart and the heart sounds

Answer 6

Mitral valve disease:

1. Stenosis = snap as valve opens, diastolic rumble
   - Caused by rheumatic fever (almost all cases)

• Less blood can get through the valve so….
• Increases LA pressure = pulmonary hypertension/oedema and dyspnea - leads to RV hypertrophy
• And LA dilation = atrial fibrillation and thrombus formation OR oesophagus compression and dysphagia

2. Regurgitation = holosystolic murmur
   - Damage to papillary muscle, left sided heart failure (leading to LV dilation and valve stretching) or rheumatic fever

• Blood flows back into LA
• Increases preload as more blood enters LV = LV hypertrophy

Question 7

Explain how aortic valve disease can affect the function of the heart and the heart sounds

Answer 7

Aortic valve disease - 2 disease states:

1. Stenosis = crescendo-decrescendo murmur
   - Caused by calcification/stenosis, congenital or from rheumatic fever (autoimmune destruction)

• Less blood can get through the valve so….
• Increases LV pressure = LV hypertrophy
• And left sided heart failure = syncope or angina

2. Regurgitation = early decrescendo diastolic murmur
   - Caused by aortic root dilation or valvular damage (again, rheumatic fever)

• Blood flows back into LV during diastole
• Increases SV so systolic pressure increases and diastolic pressure decreases
• Bounding pulse and LV hypertrophy

Question 8

Define the terms Systole and Diastole

Answer 8

Systole: period of contraction of the heart
Diastole: period of relaxation of the heart

Question 9

Define cardiac output and explain how it is controlled

Answer 9

Cardiac output is defined as the amount of blood the heart pumps in 1 minute (in L/min)
Cardiac output is defined as SV x HR

CO is controlled by:

1. How hard the heart contracts (determined by EDV and contractility)
2. How hard it is to eject blood (aortic impedance)

Question 10

Define preload, afterload and contractility

Answer 10

Preload – Amount the ventricles are stretched (filled) in diastole – related to the end diastolic volume or central venous pressure
Afterload – The load the heart must eject blood against (roughly equivalent to aortic pressure)
Contractility - the force of contraction for a given fibre length

Question 11

Explain the Frank-Starling Law of the heart

Answer 11

Frank-Starling Law of the heart = the more the heart fills, the harder it contracts (up to a limit)

(The harder the heart contracts, the bigger the stroke volume. An increase in venous pressure will fill the heart more)