Cardiovascular physiology

Question 1

Draw Pacemaker action potential

Answer 1

Phase 0: baseline drift, -40mV. Slow Ca influx

Phase 3: Ca close, K open

Phase 4: hyperpolarisation

Question 2

Draw cardiac myocyte action potential

Answer 2

Phase 0: rapid depolarisation: Na influx

Phase 1: Na close K open

Phase 2: Plateau: L-type Ca channels. Absolute refractory period

Phase 3: L-type Ca channels close and K opens. Relative refractory period

Phase 4: Na/K: 3Na out 2K in

Question 3

Draw cardiac cycle: Art/CVP/Pressure

Answer 3

Heart sounds: S1: systole (mitral and tricuspid closure) corresponds with QRS, S2 diastole (Aortic and pulmonary valve close) corresponds with IVC

Question 4

Calculate MAP

Answer 4

MAP = SBP + (2DBP) / 3

Question 5

Calculate Perfusion Pressure

Answer 5

Max pressure of blood perfusing coronary arteries

CPP = ADP - LVEDP

(ADP = aortic diastolic pressure, LVEDP = LV end diastolic pressure)

Question 6

Coronary blood flow

Answer 6

CBF = CPP / CVR

Question 7

Central venous pressure

Answer 7

hydrostatic pressure generated by the blood in the great veins

Surrogate of right atrial pressure:

a: atrial contraction
c: bulging tricuspid valve into right atrium during ventricular contraction
v: atrial filling against closed tricuspid valve. giant v waves caused bt tricuspid incompetence
y: passive ventricular filling after opening tricuspid valve

Question 8

Draw pulmonary wedge pressure

Answer 8

RA: Identical to CVP. Normal P 0-5mmHg

RV: Oscillates between 0-5 mmHg and 20-25 mmHg

PA: Catheter moves in PA, the diastolic pressure will increase owing to presence of pulmonary valve, same as RV systolic pressure. Diastolic pressure rises to 10-15mmHg

PCWP: lower than PA diastolic pressure. Similar to CVP trace. Normal value is 6-12 mmHg. Values vary with resp cycle. Read at end of expiration. In spontaneously vent patients highest reading mechanically ventilated patients it will be lowest.

PCWP around 45cm

Question 9

Frank Starlin relationship:

What is cardiac output

What is stroke volume

What is preload

What is afterload

What is contractility

What is the Frank-Starling law: (normal, inotropy, failure)

Answer 9

Cardiac output:

CO = SV x HR

Stroke volume:

Volume of blood ejected from the left ventricle with every contraction

Preload:

initial length of cardiac nuscle fibre before contraction begins

Afterload:

tension generated in cardiac muscle fibres before shortening occurs

Contractility:

Instrinsic ability of cardiac muscle fibres to do work with a given preload and afterload