CVS changes in pregnancy meet
- Maternal \(\uparrow\) metabolic demand
- Foetal metabolic demand
They begin by week 8 and peak in early 3rd trimester
Triggered by
- Oestrogen\(\to\)RAAS activation
- Progesterone\(\to\)vasodilation
- EPO\(\to\)erythropoiesis
Blood volume/composition
- Erythopoiesis \(\to \uparrow\) RBC volume
- RAAS \(\to \uparrow \uparrow\)plasma volume; \(\uparrow\)plasma vol > \(\uparrow\)RBC volume \(\to\) physiologic anaemia of pregnancy \(\to \downarrow\)viscosity
- Blood volume \(\uparrow\)50% by 3rd trimester \(\to \ \uparrow\)preload
- Albumin production constant \(\to\) diluted \(\to \ \downarrow\)colloid osmotic pressure \(\to\) oedema
HR
- Rises steadily, peaks at 15% increase
TPR
- Vasodilation + \(\downarrow\)viscosity + low resistance uterine circuit \(\to\) decrease 30%
CO \(\to \ \uparrow\) DO2 despite anaemia
- High preload, low TPR \(\therefore\)afterload, high heart rate \(\to \ \uparrow\)CO by ~50% at 3rd trimester
- 10% goes to uterus
- Increased renal perfusion to meet clearance demands
BP
- SBP and DBP slightly decrease
Anatomical effects of gravid uterus
- Heart shifted up \(\to\) left axis deviation
- Aortocaval compression \(\to\) \(\downarrow\) VR and CO \(\to\) VC and tachycardia; relieve by left tilt