Cardiovascular physiology and action potentials

Question 1

Describe what happens during the 5 phases of the cardiac action potential

Answer 1

Phase
0 Rapid Na influx (depolarisation)
1 Efflux of potassium (Early repolarisation)
2 Slow influx of calcium (Plateau)
3 Efflux of potassium (Final repolarisation)
4 Resting potential is restored by Na+/K+ ATPase

Question 2

How is a new cardiac action potential created?

Answer 2

slow entry of Na+ into the cell decreasing the potential difference until the threshold potential is reached, triggering a new action potential

Question 3

Where in the heart is conduction velocity fastest?

Answer 3

Ventricular conduction Purkinje fibres (2-4 m/sec)

Question 4

Where is conduction slowest in the heart?

Answer 4

AV node

Atrial conduction 1 m/sec
AV conduction 0.05 m/sec
Ventricular conduction Purkinje fibres (2-4 m/sec)

Question 5

How is the Left ventricular ejection fraction calculated?

Answer 5

LVEF = (stroke volume / end diastolic LV volume ) * 100%

Question 6

end diastolic LV volume - end systolic LV volume = ?

Answer 6

Stroke volume

Question 7

stroke volume x heart rate =?

Answer 7

cardiac output

Question 8

Systolic Pressure - Diastolic Pressure =?

Answer 8

pulse pressure

Question 9

Factors which increase Pulse Pressure

Answer 9

a less compliant aorta (advancing age)
increased stroke volume

Question 10

mean arterial pressure / cardiac output = ?

Answer 10

Systemic vascular resistance