Effects of Acute Plasma Volume Expansion on Maternal Renal and Central Hemodynamics and Atrial Natriuretic Peptide Concentrations in Normal and Preeclamptic Pregnancies

Abstract

Objective: To evaluate the maternal renal hemodynamic response to acute plasma volume expansion in normal and hypertensive pregnancies, and relate it to changes in central hemodynamics and plasma atrial natriuretic peptide (ANP) concentrations.Methods: Seven women with pregnancy-induced hypertension (PIH)/ preeclampsia and 10 healthy pregnant controls in the last trimester were studied. Renal Doppler and echocardiographic investigations were performed, and maternal venous blood was sampled for determination of ANP concentrations before and after 30 min infusion of a crystalloid solution (15 mL/kg).Results: Baseline renal artery pulsatility index (PI) did not differ between the normal group (1.10 ± 0.13, mean and SD) and the PIH/preeclampsia group (1.12 ± 0.08). After volume expansion PI increased (P < 0.01) to 1.43 ± 0.23 in the normal group, but it remained unchanged in the PIH/preeclampsia group. After volume expansion, both normal and PIH/preeclamptic women showed an increase in cardiac output and stroke volume, and a decrease in total systemic resistance, while blood pressure and heart rate remained fairly unchanged. Baseline plasma concentrations of ANP before volume expansion in the normal (4.1 ± 1.3 pmol/L) and the PIH/preeclamptic (6.1 ± 3.9 pmol/L) groups did not differ significantly. Following volume expansion, concentrations of ANP increased (P < 0.05) in both groups to 6.3 ± 3.2 pmol/L and to 9.9 ± 6.1 pmol/ L, respectively. In the normal group there was a positive linear relationship between increased ANP concentrations and changes in PI (r = 0.68, P < 0.05).Conclusions: Despite similar changes in central hemodynamics and increases in plasma ANP in the two groups during volume expansion, renal vascular resistance, as estimated by renal artery pulsatility index, increased only in healthy pregnant women and not in patients with PIH/preeclampsia.