Physiological Changes & Pharmadynamics in Pregnancy
During normal pregnancy, major cardiac adaptation is required.[9,10] The physiological changes in pregnancy are necessary to adapt to the needs of the growing fetus and placenta. With respect to the cardiovascular system, pregnancy represents an extensive stress test in which the boundaries of maternal cardiac adaptation is tested. There is an increase in plasma volume by up to 45% above nonpregnant values, which begins by the mid-first trimester and peaks at the late-second trimester.[11,12] As a result, there is a mild increase in maternal left and right ventricular volumes, which is accompanied by an important increase of cardiac output by 30–50%, beginning from early pregnancy and being maintained throughout pregnancy. Figure 1 shows the hemodynamic changes during pregnancy. Moreover, this increase in intra- and extra-vascular volume creates a larger volume of distribution for drugs administrated during pregnancy, and nonpregnant dosing regimens may give subtherapeutic concentrations. The increased blood volume and cardiac output of pregnancy would led to severe hypertension; however, the hormone progesterone contributes to vasodilatation. This vasodilatation results in a decrease in systemic blood pressure. The drop in blood pressure may have disproportionate effects on perfusion in different vascular beds, which may be of direct relevance to uterine and choriodecidual perfusion in the placental bed. The mechanism of vasodilatation is disputed, but may depend on a variety of endothelinium-derived hyperpolarizing factor channels. Cardiac drugs intercepting and augmenting these mechanisms may have an effect on the vasculature. These physiological changes can unmask latent cardiac disease and/or the new onset of cardiac complications during pregnancy or peripartum.
Hemodynamic changes in the normal pregnancy.
CO: Cardiac output; Hb: Haemoglobin concentration; HR: Heart rate; SV: Stroke volume; TPVR: Total peripheral vascular resistance.
Reproduced with permission from .
Future Cardiol. 2015;11(1):89-100. © 2015 Future Medicine Ltd.