Mechanical Events Of The Cardiac Cycle

Question 1

Summarise the events in phase 1 diastole

Answer 1

1. Blood flow into the ventricle due to sufficient vena cava pressure
2. Ventricle not contracting so lower pressure than aorta
3. Backflow into the ventricles prevented by semilunar valves

Question 2

Summarise the events of phase 2 systole

Answer 2

1. Systole characterised by ventricle contraction
2. Ventricle pressure higher than atrial pressure thus the AV valves shut

Question 3

Summarise phase 3 systole

Answer 3

1. Characterised by the emptying of the ventricles and the subsequent fall in pressure
2. Semilunar valves shut and the diastole begin

Question 4

Explain the different types of aortic pressures

Answer 4

Lowest pressure in the aorta is called the diastolic pressure occurring during the diastole
Highest pressure in the aorta is called the systolic pressure occurring during the systole
Dicrotic notches are slight increases in pressure when semilunar valves shut

Question 5

What is pulse pressure and how to calculate it

Answer 5

1. Pulse pressure is the difference between systolic pressure and diastolic pressure
2. PP = SP - DP

Question 6

What is mean arterial pressure and how to calculate

Answer 6

1. MAP is the average pressure in the aorta during cardiac cycle

MAP

Question 7

Stroke volume

Answer 7

End diastolic volume is the volume of blood in the ventricle at end of diastole

End systolic volume is the volume of blood in the ventricle just after ejection

Stroke volume = EDV - ESV

During exercise stroke volume increases since more blood is pumped out

Question 8

Ejection fraction

Answer 8

Ejection fraction reflects the ratio of blood ejected in a beat to the total volume of blood in ventricle prior to ejection

EF = SV/EDV x 100 (%)

Question 9

Heart sounds explained

Answer 9

1. Blood flow is silent
2. Apart from when valves shutting causes momentary turbulent blood flow
3. Creating the lub dub sounds

Question 10

Explain the practical uses and limitations of the ECG

Answer 10

Measures how well the heart propagates electrical signals via measuring current over time

How it works: P wave = atrial contraction, QRS = ventricular contraction, T wave = ventricular repolarisation (ions)

PR segment reflects AV node to ventricle delay
ST segment reflects ventricle cycle
RR interval determines heart rate.

Limitation: does not indicate the mechanical health of the heart e.g. tissue damage not shown

Can pick up tachycardia - rapid hr, arrhythmia - abnormal rhythm, fibrillation - chaotic strengths/rhythms, heart block, heart attack