INTOLERANCE TO VOLUME EXPANSION - A THEORIZED MECHANISM FOR THE DEVELOPMENT OF PREECLAMPSIA

We present a theorized mechanism for the development of preeclampsia, suggesting that one important underlying pathophysiologic mechanism is intolerance to volume expansion. The stage is set for this intoleranc e by chronic volume constriction, which leads to a requirement for inc reased basal peripheral vasoconstrictor tone to maintain blood pressur e and allow for continued perfusion of the upright hominid head. In pr egnancy, volume expansion signaled by the placenta cannot be accommoda ted by the constricted vascular system. The inability of the normally adaptive endothelial vasodilatory mechanisms to overcome the chronic v asoconstrictor tone leads to endothelial damage, exacerbation of vasoc onstriction, and clinical hypertension. Disease resolution, characteri zed by diuresis, occurs with the elimination of the placenta-derived d rive to retain volume. The reason preeclampsia does not recur uniforml y with subsequent pregnancy is permanent restructuring of the maternal cardiovascular system with pregnancy that allows for greater plasma v olume expansion in future gestations. (Obstet Gynecol 1998;92:306-8. ( C) 1998 by The American College of Obstetricians and Gynecologists.).