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Unformatted text preview: Physiological effects of pregnancy Cardiovascular Cardiovascular Cardiac output • Rise in Cardiac Output (CO=HR x SV) by 40% (5l/min pre-pregnancy to 7l/min by 20 weeks GA • Mainly due to increased Stroke Volume (SV) of approx. 10-20 ml and maternal HR to 80-90bpm (↑15%) (as a result mom will complain she feels “palpitations’) Haemodynamics in Pregnancy • Blood Pressure (BP) will fall by in first trimester of pregnancy but rise again towards the end of term • This fall in BP is due to a decrease in total peripheral resistance (TPR) as a result of peripheral vasodilation (mom will complain she feels “hot”) • These changes are thought to present with a reduced diastolic BP and/or wider pulse pressure • The enlarging uterus and foetus may also compress the inferior vena cava and pelvic veins. This can decrease venous return to the heart causing hypotension (mom may complain of feeling “faint”) especially when lying flat (usually presents >24 weeks gestation). Therefore use of left lateral position or wedge/ tilt for women lying flat. • Increased venous pressure leads ID risk of varicose veins, haemorrhoids, leg oedema Vasodialation in Pregnancy • Mechanisms unclear • Vasoconstrictor levels e.g. of Angiotensin II increased but vasculature relatively resist to vasoconstrictors • ? Enhanced activity of vasodilators e.g. eicosnoids, kinins • ? Paracrine activities between endothelial cells and underlying smooth muscle cells e.g. by prostacyclin (Vasodialation (VD) ) thromboxane A2 (Vasoconstriction (VC) ) endothelins (VC) endothelium derived relaxing factors (such as Nitric Oxide) (VD) Many pregnancy problems and leading causes of maternal death are due to cardiovascular problems...
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- Fall '10
- Anthropology, varicose veins, Increased tidal volume