Cardiovascular physiology

Question 1

Blood pressure is directly proportional to

Answer 1

Systemic vascular resistance and cardiac output

Question 2

Cardiac output =

Answer 2

Stroke volume x heart rate

Question 3

Normal BP trend in pregnancy

Answer 3

Before the increase in CO can adequately compensate for the fall in SVR, BP begins to decrease in early pregnancy.
Continues to decrease in second trimester until the nadir in SBP and DBP is reached by about 22-24/40.
From then on, there is a steady rise to pre-pregnancy levels until term

Question 4

Normal BP trend postpartum

Answer 4

BP falls immediately after delivery, although tends to rise subsequently reaching a peak 3-6 days postpartum. Normotensive women may become transiently hypertensive following delivery ? related to return of normal vascular tone and a period of vasomotor instability while normal, and non-pregnant vasoregulation is re-established

Question 5

Intrapartum haemodynamic changes

Answer 5

15% increase in CO in first stage, 50% in second stage. UA –> autotransfusion 300-500ml of blood back into circulation. Sympathetic response to pain / anxiety further elevate HR and BP

Question 6

Postpartum haemodynamic changes

Answer 6

Immediate rise in CO after delivery (relief of IVC obstruction, contraction of uterus empties blood into circulation) - 60-80% increase. Rapid decline to prelabour values ~1h post delivery. CO back to pre-pregnancy values at ~2/52 PP.

Question 7

Normal cardiovascular examination findings in pregnancy

Answer 7

Bounding / collapsing pulse
Ejection systolic murmur (90%)
Loud first heart sound
Third heart sound
Relative sinus tachycardia
Ectopic beats
Peripheral oedema

Question 8

Normal ECG findings in pregnancy

Answer 8

Atrial and ventricular ectopics
Q-wave (small) and inverted T wave in lead III
ST segment depression and T wave inversion inferior and lateral leads
QRS axis leftward shift