Cardiovascular changes Flashcards
What happens to the heart as the uterus enlarges?
heart pushed up, aorta unfolds, heart rotated in L-upward displacement. Apex beat = more lateral
By how much does overall heart size increase in pregnancy
12% (increased myocardial mass [hypertrophy of smooth muscle L>R] and intracardiac volume)
What causes oedema and varicosities in the lower limbs in pregnancy?
enlarging uterus -> compression of IVC and iliac veins -> increased venous pressure in lower limbs (exacerbated by lying supine)
Explain supine hypotensive syndrome + prevalence
Lying supine exacerbates venous compression of the IVC and iliac veins -> fall in venous return, CO and subsequent BP
- in 10% of women -> nausea, dizziness, bradycardia and syncope = supine hypotensive syndrome
By how much does CO increase in pregnancy?
40-50% (4L/min at 10 weeks to 6L/min at 24 weeks)
Twin pregnancies increase a further 20% more than singletons
The max CO is reached by 20-24 weeks
What happens to CO during labour? How is this change mediated?
Increases by 15% in first stage and by 50% by second stage. At delivery increase in CO by 60-80% c.f. pre-pregnancy level due to relief of IVC obstruction and contraction of uterine blood -> systemic system.
- via contractions that increase venous return and activate sympathetic nervous system -> increase HR and BP (CO = SV X HR)
What happens to CO postpartum
Rapidly falls to pre-labour level by 1 hour postpartum
Slowly falling to non-pregnancy levels by 2 weeks PP
When are women with cardiovascular compromise at most risk of pulmonary oedema?
During second stage and the immediate postpartum
What happens to HR in pregnancy
Increases by 10-15bpm by 20 weeks due to progesterone driven hyperventilation (can be noticed as early as the luteal phase of the woman’s menstrual cycle)
What happens to SV in pregnancy?
Increases by 10-30% due to the arteriovenous shunt effect of uteroplacental circulation
- reaches peak by 12-24 weeks
What happens to mean arterial BP during pregnancy?
Falls by 6-19mmHg
What happens to systolic BP, diastolic BP and pulse pressure in pregnancy?
Diastolic BP falls more (8-15mmHg) than systolic BP (4-6mmHg) -> widened pulse pressure which represents the force that the heart generates each time it contracts
At what point in pregnancy does BP reach a nadir?
Fall in BP reaches a nadir in the second trimester (22-24 weeks) before returning towards non-pregnant levels by term
What happens to BP after birth
BP falls immediately following birth, then rises with a peak 3-6 days postpartum. Previously normotesnive women can become transiently hypertensive due to postnatal vasomotor instability
What happens to vascular resistance in pregnancy?
Decreases in first trimester
Nadir by 14 weeks (30% lower than pre-pregnancy)
- likely driven by hormonal changes -> enhancing local vasodilators e.g. nitric oxide, prostacycline and possibly adenosine.
Trends upwards towards term
