Vascular, volume, and cardiac response to normal and hypertensive pregnancy.

Cardiovascular adaptations to the circulatory and volume changes of pregnancy have been studied in late normal and hypertensive pregnancy and postpartum. There has been evidence of a marked plasma volume expansion in normal pregnancy, blunted in preeclampsia; an increased capillary permeability during normal pregnancy; augmented left ventricular mass, which is increased in mild preeclampsia; and similar increases in peripheral venous distensibility during normal and preeclamptic pregnancy. In mild preeclampsia the enlarged ventricle has been shown to be capable of maintaining a normal cardiac output despite elevated afterload. The forearm vascular bed appears to play little part in these adjustments, because forearm venous distensibility has been shown to be higher during normal pregnancy than during postpartum; in hypertensive individuals there was no difference during pregnancy and postpartum. It is evident from this brief review that it is too early to draw clear-cut conclusions regarding the vascular, volume, and cardiac response to normal and hypertensive pregnancy. Research in this field, including two-dimensional echocardiography and plethysmography in larger homogeneous groups, will probably lead to a better understanding of the pathophysiological mechanism of pregnancy hypertension.